brake conversiomn, 944 to volvo callipers?

[Monkey Wrench]

Ive owned quite a few volvos..
a comment was made about possibly converting my 944 to girling callipers from a volvo 240.. some of this ( below) is a little off topic but it didn;t fit the original thread so I just started a new thread.

I just did the brakes on my 88 740, new pads rotors callipers, rubber lines.
bought a rebuild kit for the front callipers but the boot cover for the piston on one was pressed in with a metal flange. I guess maybe rebuilders bore the clinder and then press in the seal.
one did have a groove and I found I needed to seat the boot in the groove and then push in the piston, then since the piston never leaves it locks the protective rubber boot in place.

the seals in the kit needed a groove to fit into so I could not rebuold one, since it had this pressed in seal.. so I replaced it for a rebuilt calliper,

I bought slotted front discs with some coating,, and paid a bit more, but they were still real junk !
there is a grease seal near the backing plate/ spindle I had to shim the hole as it was oversize so the seal wouldnt stay in. ok i cut a strip ofalunimum and got past that.. on one side I removed the bearing race, it has bearings and a castle nut, after about 1988 volvo went to a hub with captive bearing and the disc drops over the wheel studs. older ones like mine have the bearings and castillated nut and the disk has bearing races.

that makes changing discs easier but it also presents a problem where any dirt between the mating parts causes the disk to have runout, with the bearings and disc combined there is no chance of that happeneing , because the disk runs on its bearing. although its more expensive ot change the discs I think this si superior as it elliminates that possibility of runout

I didnt do this but what one can do if the disk drops over the wheel studs, is put a dial indicator on the disk, record the runout, then bolt the disc on in a different orientation , you have 5 choices. you can then pick the orientation with the least amount of runout.
volvos often have a bolt it holds the disk in place until the wheel is tightened. pin and a hole in the mag to locate it. I usually just chuck the pin but i guess the idea is to retain balance.

on one side ( front of my 740) I just put it in, on the other side , I thought well I should ptrobably remove these chinese races , I dont trust the metallurgy..

There was a lot of dirt behind indicating how dirty the factory wasat the point of assembly.

when I went to press in new races that I got with the good quality US made bearings, well they were not a press fit, the callipoer bore was too large, it fit, I put some red locktite but the race could start spinning and it should not. maybe heat can break the locktite but the greas ewould burn at hat point. so I dont think it will heat to the point of the locktitre failing..

when I got to the grease caps, same thing they fit so loose there was nothign to hold them in, I put some sheet metal shims and used some of that aluminum heat duct tape to try to stop my grease caps from falling out.

very sloppy machining on these new offshore callipers !

I would have sent them back to the rock place but I had them a year or so in waiting.

the hardest part was getting the rubber flex liines undone from the solid lines , I had to apply a torch and even though I had the nipple open when the hose got hot it basically exploded the line out if its fitting, I didn;t care about the line I had new ones, but maybe it made a shock through the system. next time Ill remove the hose from the calliper entirely if I need to heat the brake line fittings. that would be smarter.

when doine and bled a few times, the light was on indicating unbalance, it has a spool that shifts and it shoud stay centered so it doen;t turn on the dash idiot light. I took it apart and dropped a little oring, I found two smaller ones that sort of fit, it went down into the frame somewhwere ..
anyway that worked I got it centered and it cant; really leak as it has end caps on that spool. of course I had to bleed again.

- I learned that after about 88 Volvo used a brake fluid level warning light, and stopped installing this spool that detects if the system has unequal brake fluid pressure between the two sides..
does a porsche have one? it seems like a nice upgrade to instal a fluif level warning light or audible alarm. especially in my old 66 with single circuit system. Im wondring if I can buy just the float or a cap with the float or somethign so I could have a fluid level warnign light in my single circuit volvo 122S

since the porsche has only one reservoir that mught be easy or maybe it has one already?

in the 944 it seems that if the fluid does run low what will happen is the clutch will fail first so that is sort of a warning, a arning lamp migh be an extra , maybe worth adidng if it s not there?

I thought I'd just replace the rear rotors and put new pads but one was too stuck so I replaced both rear callipers with rebuilt ones. I also put new discs.

now i have it working but the master seems to leak down, I know that driving an old master cylinder to its limits when bleeding , can blow seals as the piston isn't "used to "going down to the bottom of its bore so there could be dirt and that can blow the master cylinder piston seal .

well although I did buy a new vacuum bleeder, it still happened.. now the car wants to drift ahead at the traffic lights unless I am careful to keep pressure on as th epedal sinks slowly.

I had bought and replaced the master last summer, it came with a bottle , it leaked, I bought a new master with the reservoir at the time but it was the bottle , it had a bad seam weld in the plastic so I lost all the fluid from both sides .. I fixed it by ordering another master with the reservoir. so I still have a new master cylinder onhand.

so if you replace a plastic brake fluid bottle and its not OEM, its a thing to watch for, that was dangerous. anyway now the master cylinde is bypassing ( not leaking eternally) Ill replace the master cylinder and re-bleed it .

My 88 740 has single piston callipers, I don't like them.

now my 66 volvo , it has girling callipers on front drums at back, thoise are better callipers, as well the volvo 240 also uses girling callipers also very good. my 1989 240 has rear discs. those things have good brake systems.

in my 1966 122 I made new pistons myself out of stainless steel so they won't rust and I also changed the fluid type for the clutch and master to silicone fluid, this is beacue I park it a whole lot more than drive it. its no good for racing or hard driving but its good for collecot rcars that are stored, I have zero issues using silicone fluoid in the hydraulic clutch, you can't boil a clutch.. the only way to convert a porsche would be to separate the reservoirs or change both to silicone, since people are likely to drive a 944 hard , well you dont wan to boil your brakes and silicone fluid does have a slightly lower boil point.

the interesting thing that learned was that if your car has dot 3 or 4 and you have not bled it to remove water for two years , then the boiling point of your fluid is LOWER than it would be with silicone fluid. obviously the humidity level has some beraring on how long it takes to suck water out of the air and disperse it into your brake fluid. so the time duration will perhaps differ on that.

I did make my own spare set of pistons for my 122S callipers, so ihave a spare set thats all rebuilt but I don't know if those callipoers might fit the porsche or if maybe I need 240 girling callipers.. It does sound like its worth knowing more.

I bought my porsche with the brakes all stuck so I plan to go into that I just didnt want all my other cars to be down so im trying my best to put all these little fires out.

with murphys law in play of course my 88 ford van with stright six blew a waterpump, gushed, towed home.. while I had my 740 all apart.

I did relace that waterpump 10 years ago for reliability. Anyway I just got done replacing its waterpump and so that's all fine. im upgrading my van to two batteries, with a battery isolator just so on cold days I have a backup or I may use it a bit like an RV. Ill rig up a button and a relay so it can enguage my spare battery to start if needed.
the isolator works by allowint the second battery to charge but only whant the car is running and then the voltage is higher. if oarked I can only drain the spare batttery if Im using it for accessories. It has a wheelchair lift so it made sense to have aspare battery for that. Ill connect the headlights because then I dont put myself in a no start situation if I do leave them on


I ordered a battery box on the rock place, it was too small , my mistake , oh well ordered a second, it came with no lid so I ordered a third again I get a battery box with no lid, the rock place removed the charge so now I seem to be collecting battery boxes.. Its ok I can use them for other stuff.

I bought only the hoses and the seal kits for my 944 thinking I'll see if I can just replace the seals and hoses and pads but Ill see.. maybe it will need new pistons. they do seem really stuck. this is one of the first things I think i should takle.

with all these old cars I seem to be in a constant batle to keep fixing any failures and I plan to take my time with the 944 , it keeps getting slid aside to keep the workhorses running. my 944 has a decent body, it will need a lot of basic maintenance from being parked so long but Im optomistic that it wil be a really cool and pretty reliable car.

Im attracted to the notion of changing the callipers over , I guess to the 240 girling ones. I am interested to learn more.

[Monkey Wrench]

if I recall right my 1966 122s has two smaller pistons on one side and one larger one opposing. ( with double the surface area) the 240 is likely similar but Im a little grey on that. it is not a floating calliper with just one piston.

I am assuming that the 944 (Mine is early 85) might have a similar weak point where the pin that the calliper slides upon gets wear in the bore of the cast iron calliper.

in my 740 it has an issue of going oval, if this is an issue, the hole could potentially be re-bushed or reamed and a larger diameter pin turned to fit. from wht i saw the rebuilders may fail to adress this potential issue when rebuilding callipers.

im wondering if since the 944 has floating callipers are others seeing a problem with rattling due to worn bores or slide pins?

pads, I wasnt; sure I just put semi metallic, they seem to work ok so far. I did not detect thumping on my 740 so maybe they are true enough to work. whats your favorite choice for pads? some make a lot of diust, some wear the discs fast. soem have squeal issues. Im not sure whats best these days.

the brake vacuum bleeder kit I got was also a cheapo, I oreded it on amazon , same day delivery, its pretty cheaply made. is there a somewhat decent brand to look for?

some convert a pressurized bottle used for speading fertilizer etc to the cap to pressurize the master, I guess also feeding more fluid so you don't need to remove it to refill the bottle. you can buy the pressure type bleeders as a kit.

I know the reservoir on a volvo just pushes over the master cylinder, similar with the 944 so it seems that the pressure might blow the bottle right off, I guess you can tie wrap it down.
do you prefer vacuum or using pressure for bleeding , or finding a helper? or maybe just a bit of hose into a bottle wiht some fluid. I figured a check valve on that hose might help a little. usually Ill find a helper but I do think there is some advantage to not driving the piston right to the bottom of the master cylinder. if its a new cylinder thats a non issue if it's old I thinkit can cause the master cylinder to bypass as the seals pick up any rusty gunk from the walls of the bore.

I think I can honestly say I've been trying not to break the budget by trying to use some offshore parts and what Ive been seeing is some real junk.. its hit and miss but obviously only using strictly Porsche OEM parts is expensive. overall Ive saved a bit on parts, its not a question which I'd prefer. I do not think offshore parts are a good solution for every part, some is ok.
I think there are some judgement calls involved.

[Jfrahm]

I can't make out what you are trying to fix. A brake fluid leak at the master?

Make some improvement to the calipers? The 944 system is great for the street and far far easier to just sort out vs. engineering a change/upgrade.

You should have a low brake fluid warning, part of the brake (!) under the clock?

---
Brake Warning Light
The warning light comes on when the ignition is turned on and must go out when the engine is started. If it does not come on when you turn on the ignition, have the fault rectified without delay to ensure that the light can perform its monitoring and warning function reliably.
If the warning light comes on during a journey, it indicates that either the brake fluid level is too low or, if accompanied by usually long brake pedal travel, one of the two brake circuits has failed. In such a case your stopping distances will also be increased.
Pull to the side of the road and carefully test the brakes a few times. If you feel safe and confident enough, drive slowly to the nearest authorized dealer and allow for the change in braking efficiency.
Do not drive any longer than absolutely necessary with a faulty brake system.
---

[Monkey Wrench]

long post , sorry to cause confusion.

I need to have a look at my 944 brakes, ill probably change the seals in the stock callipers. in another thread it was suggested that I might consider using girling callipers from a volvo 240
which are a better design, the porsche as I understand it has a floating calliper. I assume 2 pitons as it needs ot have 2 hydraulic circuts

evidently some others have upgraded to these girling callipers quite sucessfully.

in the post above I pointed out how I had issues of the sliding single piston callipers used in my volvo 740.

in this era Volvos used ATE , Girling and Bendix calipers in various configurations. Volvo didn,t make callipers, did porsche?

are others seeing wear in the sliding pin or it's bore in the casting? I noted that this was an issue with the 740 I have, the symptom was the car rattled, but if there was any braking , it shut up.

this was becuase of wear in that sliding pin and the bore in the calliper. The pin is replacable, the hole goes egg shaped, at least if its not being greased. the problem could perhaps contribute to brake squeal.

with the girling callipers used on a volvo 240 there is no sliding, the only moving parts are the pistons and the pads, this is because they used opposing pistons.

I like the non sliding callipers a lot better, I think it is a better design. so Im wondering if I have a simple bolt on choice or if this is a serious mod.

If I were to for example just order new callipers, would I have a choice to just order rebuilt Girling 240 ones? that soulds like a nice option to me.

at this point I dont have much invested in the porsche but I will spend time on it's brakes.


im not sure if anything needs to be redrilled or modified, or if they can just bolt in.

two bolts and the calliper comes off. there are some factors such as the distance between the bolts and the offset from that surface to the disk surface. also the piston area and pad surfce are all relative to pad pressue and the mechanical addvantage of hydraulics.. one would also not want the system to be able to run out of fluid.

Im not sure whats involved, maybe they can just bolt on?

what triggers the porsche warnig system? I do not htink my early 85 has electrical indicators or ABS

it may have a low level float sensor int he reservoir, it may have a switch that detects unequal hydraulic pressure. perhaps there is a switch for if the pedal goes low or something similar.
the above seems to be writen in the contaxt of a user manual but it doesnt; indicate what the sensors refer to, or by what means they are triggered. thanks for including it, it is helpful.

[Jfrahm]

Volvo 240 caliper thread on RL:
https://rennlist.com/forums/924-931-944-951-968-forum/962450-write-up-budget-4-piston-calipers-for-944-na.html

Google search based link:
https://www.google.com/search?q=962450-write-up-budget-4-piston-calipers-for-944-na

Re: the warning light, if you don't see the (!) light with Key On Engine Off then that should get repaired. It should light for either low fluid or an out-of-position proportioning valve.

[wwdwgs]

MW, Porsche didn't manuf. the brake calipers then (at least for 924/944's street cars).
since you have acces to 240/44 calipers, you can measure pistons' area, pads' area, mounting holes distance, offset and if the calipers clear the wheel. Also, I think, the rubber hose is dofferent in length.

Jfrahm, thanks for the links.

[Monkey Wrench]

I think Ill start with the rear, I can pull one apart , drop it in a bucket of water and washings soda, hook it to a battery, that seems to do a great job of rust and paint removal. it doesnt remove any of the metal , just the rust.

I just had a hunk of metal I had used it as my expendable electrode so it had gathered about as much rust as possible then left it out in the rain all winter. I decided I wanted that hunk as it was a good size for a project.

for the first day I left it and had my polarity reversed , all that did was create more rust lol, but then I reversed the electrodes and it came all clean..

the process does leave a black residue, Usually Ill give it a scrub, Im wondering if there is an easy way to remove the black coating. a rag with baking soda and elbow grease works but maybe there is a way to dissolve it or something?

at one point I went and got some pickling paste from an industrial supplier. tried that. its an acid used for rust removal but its a very strong acid, it seemed to just rust things more.. I'd made some braised parts and so they were blacked from the process. I dropped a few anodized washers in it, it generated heat and fumes. Yea dont do that. its a very harsh chemical.

I tried dropping parts in muriatic acid , it does work but that removes base metal too and it eats aluminum for breakfast. the fumes of the stuff are completely horrible. I thin it does provide a good hook for paint. Id neutralize the parts with baing soda and then warm them do drive out moisture then paint while still warm, the rust will appear very quickly after being in acid, same as sandblasting.

I do use the rust converter someties, it works pretty well if you are not super fussy it will slow the rrust and prep for paint.

acids can remove rust but I much prefer the electrolysis method, then no real harsh chemicals and a box of washing soda and water is cheap. any scrap iron is ok for the expendable electrode. it will attract all the rust from the item being stripped. I Don't use stainless, it may give off poisonous fumes. I see it recomended sometimes..

people who do powdercoating might have some tricks.. rusty pistons are probably not worth trying to save, not if you can get them for 30 bucks or so. I think a a hydraulics shop can rechrome and resize them if its somethign rare. Thise guys are experts with the right equipment and chrome baths

made my own pistons from stainless for my 122S it worked well but thats quite an undertaking. I felt it it solved the issue of the chrome flaking off the pistons. I assume it was just cheaper for the factory to make them from cast iron and chrome them. maybe the cast and stainless have differnt expansion rates ? I never noted any resulting issues. probably someone with a CNC lathe could make them a lot more efficiantly.

Ill see whan I get to the fronts if I have some spare 240 fromt callipers , then a side by side comparison with them apart would be good. Im not set on making changes but I'm curious about how practical this is. I assume it is no harder and no more expensive to buy either caplliper as a rebuilt unit.

I brought a used disk in to try tutning it on the lathe at work , it has a large enough capacity, it seemed to work ok but I didnt have the provisions set up to quickly mount them on the races between centers.. replacing rotors seems cheaper and more common these days than turnign them but with some, the metal quality may not be as good as the OEM ones. One can't tell by looking at them especially online so maybe 'the brand' is the only way to determine if they are of good quality.. Maybe there is some benefit in having OEM ones turned.

I think the quality of the cast iron varies between different foundaries. from what Ive seen castings made in Germany and Sweden were very good quality and the offshore ones, probably produce a lesser quality cast iron.. in a picture on the web you really cant tell the difference.

as an example, old Record bench vices made in england were very good quality, Ive seen ones that were beat upon for 50 years and stood up. , they moved to india and now they are junk by comparison. Likewise I think decent brake parts need to originate from foundaries that care about the porosity and metalurgy I htink a lot fo decent castings were made in the midwest but things changed. those foundaries migrated. that has a lot to do with why certain countries had a good reputation over others.

one can turn a crappy casting so it is true and precision but I think one of the secrets to keeping them from warping and glazing unevenly relates to the quality control back at the original steel foundary.

[wwdwgs]

MW,
have you every tried to listen to the identical metal parts by striking them with, let's say, a hammer? Different sound - may mean different density. I think.
The new pistons (for Volvo 240 calipers) are about 6-7 USD a piece (2 for rears, 4 for fronts) from some suppliers.
The 240/244 calipers with ABS are easier to adapt on 924/944's.

[Monkey Wrench]

when I put a calliper int he lath it sure did have a ring to it, it was quite loud.
maybe if one had a few they could make comparisons, hang them on a wire and give them each a little whack..

thre tapping with a hammer method is often recomended when talking about grindstones. a lot of manuals will suggest that to detect a crack, which deadens the ring, wiht the idea to not explode a fractured grindstone in your face.

I think Id been under the impression that brake discs usually vivbrate due to warpage, which yes it can, but Im seeing evidence that as importantly , the surface actually gets glazed, uneven and so as the disc goes around it has a better grab"on some segments. resurfacing helps get through that glaze.. I sometimes use sandpaper and oilstones and do the best I can with my free elbow grease, but it s hard ot remve enough.


I keep thinking along th elines of making a brake pad made of diamond grit. I have a whole bunck of lengths about 1/'2 inc square.. My screwball theory is that one could install one pad made of this industrial diampond , then drive it maybe on jackstands if its the back and grind them in place then replace the pads.

I sometimes find it suprising if I look at a tire and spin it how much it may be out and not go even noticed, they are often not very true.

its possible to true the tires up by grinding them right ther on a car youd loose rubber and make a mess but it would probably run smoother.





Ive wonderd how when a car is parked in the same spot and then used, wll maybe having rusty patch in some local areas is really bad.

I went on to wonder if there is some substance that would protect rotors when parked for extended periods,, well we wouldn't use grease, It might be somethign that could burn up or wear off easily without harming the braking or clog the pads up.. my mimd draws a blank.

i woud think that a porous casting would have a more deaad thunk than a decent one..

at one point I worked for Heidelberg german priinting pressses, those things use excellent castings very high precision, and Ive worked on machiens made in japan where they put super thick sideframes and you could see how porous the casting was. Heideberg has their own foundary in Germany. printing presses are very heavy and very prescision so they do not want the castings to move after the machine is built.

probably you can studythe grain structure and ther is differnt types of cast, grey cast, etc. Im not too knowledgambe about it , on cheap castings they are porous, where you can often see it is where they fracture. cast iron is brittle so if you hit it it can break, but definitely the steel used is important. maybe thats the difference between cast iron and cast steel.

some foundaries bury castings and leave them a period of time to normalize before turning to size. they might if they are making lathe beds and such.

I think if youare lookiing at a machinery purchase, one can fairly ask, where is the foundary? can I see it on google earth? Point is , if they say its "north american made" but if they import the castings from overseas, its hard to show you the foundary.

[wwdwgs]

A read about 240 to 944 brake caliper conversion a bit more and was impressed that Volvo had/has dual braking systems (for the front only?). This would mean that even two working pistons should provide fair braking, in the event of other two pistons failure.

[Monkey Wrench]

yes both the 240 and 740 have two circuit systems that allow both front brakes and one rear brake to work even when the other circuit leaks.

It just so happens that I rebuilt the brakes on my 88 740, I replaced all the (6) rubber lines, callipers diskc and rotors then the master cylinder started to slowly creep down at traffic lights. I know this is caused by a seal, it is "bypassing" within the master cylinder.

I had a new one on hand , and an older one from a 740 so I figured Id just swap the pistons and seals so thye would at least be new.

upon disassembly and comparison between the 340 and 740 master cylinder, It turned out that I actually had a new one for the 240 not the 740 so I couldn't use its parts to effect a repair.

the 240 master cylinder was cast iron , the one from the 740 was alunumin both have dual pistons and a somewhat separated reservoir.

the master looks similar but one of the ports is on the other side.

I attempted to take the new one apart and see if I might be able to swap the internal parts. the parts are very similar, but the bores are different. its the rubber seals that are worn but they had a different OD.

SO..
I ordered a kit with the pistons seals and rubber parts ( all the internals) for the 740 so the project is in wait. when it arrives Ill try swapping the pistons with new seals and the springs, its all in a kit.

It would be possible to compoare the master cylinder of the 240 to the porsch 944 if the piston size differs it means the car has a different hydraulic ratio.

the pedal is effectively a lever but it won't change.

I think if you start playing around with the displacement or area of the cylinder that affects things. the larger the piston on the master is the lower the pressure will be and the more fluid it can move per inch of stoke.

you can figure that out by measureing but the rod's area needs to be subtracted. another way would be to make careuful measurements by measuring how muvh fluid it can move in its full stroke, althought he master should never be able to complete a full stroke in reality, its important that they are compatible , we have basically two factors, one is the area of the pistons and the mechanical gain, the others is the physics of the system , basically redesigning it and not considering the volume of fluid necessary upon a failure, could make it run out of fluid

as discs wear the fluid is replaced by lowering the fluid level and this happens slowly and on a constant basis over time so that wear doesnt; get subtraced from the fluid used in one stroke. it slowly makes the reservoir go down over time and the calliper pistons slowly move outward toward the discs.

If its an older vehicle with drum brakes, this is a different situation beacause :

Since the shoes return upon each use, the system needs the fluid capacity to prevent running out even when drum brakes are worn out and not being adjusted.

As brake adjustment loosenes up, the pistons need more fluid until the shoes are readjusted, some vehicles have an auto adjusting mechnism, not all do.

in my 122S, which has manually adjusted drums at the rear, my pedal is a bit low and I believe this is due to the rear brakes just needing to be readjusted. the pistons in the wheel clinders are moving further than they would need to on each stroke ,
If properly adjusted , less fluid is needed. ( for each use)

if you do a lot of bleeding and if you use a helper to step on the pedal, then you give the master cylinder a workout. sometimes after doing other brake service work the problem I am having ocurrs.

they sympton is that If I sit in the car and press the brake pedal, of my 740 , then the pedal slowly sinks. it has no air or external leak, I believe what is happening here is the fluid is leaking past its seal in the master cylinder.

the kit is only around 30 bucks for my 740 , the entire clinder can be as high as a couple hundred. I'll give the kit a try.

to "recondition" it I just need to remove the cylinder remove the clip and the whole works come out, careful it is spring loaded so can fly apart. as long as the bore is ok and not pitted, it shoudl work.

I happened to have a spare that I had removed from a working vehicle so I can try to rebuild that one, so I don't meed to put the car down until I have a rebuilt one in hand. I could not swap the internal parts.

I dropped the good piston and related parts from a 240 master into a 740 master and the fit ws really loose. the 240 had a smaller ID so that won't work and it also proves they are not the same diameter as one another.

Volvo used various configurations of brakes, in 88 they also had antilock systems, I guess it was a time when it was being introduced. I dont know what year the 944 went to antilock brakes but im sure my early 85 was made prior to that.

likely such changes happened within a year or two as competing makers evolved with technology in a somewhat parallel manor.

I think a disadvantage of this possible switchover of 240 callipers to the 944 system 944 is that it could change the hydraulic pressure or perhaps the amount of fluid needed per stroke.


another factor that came to light is that inside the master cylinder there is a little "wall' it effectively separates the two sides of the reservior in such a way that a leak can only drain one half once the fluid reaches a somewhat low point it becomes captive to that siude of the system to prevent th emaster cylinders bottle from depleating.

its basically holding a little reserve of fluid. the 740 and 240 have different bottles. they may also have a different amount left in that little reserve..

if that little "wall " is a higher it means more fluid is retained in the bottle AFTER one side ( potentially) leaks out

if that little separated section of reserve were to be used up that would mean a brake failure as air would then get into the not failed side of the master cylinder.

in order to have a systme where one side can leak and still have 2 front brakes it is necessary forr the master cylinder to be able to support this sytem of habing two lines and two pistons and two sides of the master cylinder bottle.

I can see a situation where a guy thinks he can do all this , and it works, he is successful and has brakes that work , but he has perhaps changed a bit of engineering like the above example.

part of it is hydraulic pressure or pedal pressure , the other is the amoiunt of fluid, another factror is that as the pad size differs, an increase in pad size, reduces the PSI of the actual pad at any given hydraulic pressure. more area of pad may also change the braking force. that amount of fluid left inthe reserve is a factor.

so we have several factors at play here..

The 're-plumbing' is farly straightforward. if the 944 has two brake systems to each front calliper, if not a manifold of some sort would be needed,and as well a separated baster cylinder.

the spool that detects a imbalance tiurns on a warning lampin a volvo 740 or 240 is actaully also the plumbing junction so possibly one of those could be incorporated. versions past about 88 have a low fluid warnign lamp instead of this switch that detects a pressure differential. the manifold in a slightly newer volvo probably has no switched spool. that switch turns on a warngi light on the dash it is not inorporated intot he ECU or that sort of electonic logic. it only grounds the wire turnign on the warning lamp when the spool shifts. the spool shofts as it detects an imbalance of hydraulic fluid between the two somewhat independant hydraulic systems.

to sum up, I think Id be a bit afraid that changing the callipers may affect these other important design and engineered points and I do not feel so comfy that I think im in a spot where I can make very well asessed engineering decisions .

there is actually a lot of engineering involved in this sort of switchover that may not be obvious at first glance.

perhaps if the callipers are swapped and if also used manifold and use the master cylinder from the car that matches where the callipers came from. it would be more complete.

if there is only one piston ( only one hose) on each front calliper a leak in the system would then cause the steering to pull severely with only one calliper left working. with a failed system that has both front callipers strill working it would stop quite normally by comparison.

I once stripped a fitting so being a bit stuck , I crimped off a line in my car while I went to get parts, I made the trip but if I used the brakes the car would pretty much nose dive right off the road, it seriously affected the safety. it pulled and it was not just a little. it was severe.
if one of the backs was missing it would be less severe. the fronts do the majority of the work.