Brake lockup

[djnolan]

The left rear brake locked up on my 87S. The car had been sitting for a few months. When I started driving it, something didn't feel right. There was some wheel hop going on. My local mechanic put it up on the lift and diagnosed a seized disk brake. He loosened it up and lubed it with some spray grease which made it feel normal again. Guess it needs a thorough brake rebuild.

[944 Ecology]

Look for swollen rubber brake lines...

[djnolan]

George,

I did the caliper piston seals and brake hoses on the front way back. I guess it is time for the rear.

Thanks!

[Monkey Wrench]

mine sat so long that Ill need to go over the whole system. I'm considering using dot 5.

I feel it makes sense if you are not using the car as a daily driver and dont really want to bleed the brakes every 2 years. some probably just use their cars in fair weather and put them away .

I don't think it make sense if you are doing a lot of hard driving and pushing your brakes to the limit. Its not for racing.

If you do not bleed a hydraulic system, and instead use dot 3 or 4 as recommended, the brake fluid takes on water from the air and the fluid's boiling point becomes lower over time.

many are afraid to do the switch after hearing that the fluid has a lower boil point. so they use the regular dot 3 or 4 , fine but then they also fail to bleed the brakes on a regular basis. After about two years time, they are operating with fluid with a lower boil point than if they chose silicone. dot 5 - the fluid has now become a mixture of brake fluid and water. - next the pistons seize up. the pistons rust. the system again requires a rebuid.

because of the labor involved I think this is a very common issue, many just will not bleed every two years. hey its not a very fun job , and nothing is broiken so we tend to put it off. - human nature.. Often the sytem is not touched for several years until they encounter an issue.

the fluids are incompativle so I think it makes the most sense to consider the switchover after considering the car's intended usage pattern and preferably when the system is being rebuilt anyway.

the advantage is then your brake parts don't rust out and seize up because dot 5 won't ever absorb water into the braking system.

there is ia quick fix for those of us who are a bit lazy, just use a turkey baster ,( but don't return it to the kitchen ;-)
suck the fluid out of the reservoir and refill, it does circulate somewhat during use, so it will have some effect, althoucgh not as thorough as "proper bleeding". Easy to do that on a fairly frequent basis. ( during each oil change? ) Only takes a minute. just don't step on the pedal if you empty the reservoir. then keep using dot 3 or 4. you cna still do a proper bleeding every 2 years but if you fail to, It likely helps.


this is a link to a volvo amazon website but its about the fliuid.. It makes some good points if you are considering a dot 5 changeover.
the 944 shares the fluid with the clutch but the clutch will work fine on dot 5 and there is no chance of boiling a clutch cylinder anyway.

when Ive used it I did a complete brake rebuild, it worked fine over the past 20 years. no bleeding , no seizing no issues.

Now if you just drain and refiull and flush without replacing rubber, Im not sure if that's ok or not.. dot 5 is not compatible with 3 or 4.

3 and 4 are compatible with each other.
4 seems a bit more expensive , 5 is even more expensive.

https://sw-em.com/Amazoning%20with%20Silicon%20Brake%20Fluid.htm

[924RACR]

Yeah, I'm not a fan of the DOT5 TBH - because of the fact that it doesn't absorb water... really becomes a question of how well you purge the system, because if there does get to be any water in the system, the system will work fine BUT any water can collect and corrode the pipes from the inside!!

Whereas DOT4 or 3, while yes they'll absorb the water, that means it's in suspension rather than concentrated, and so doesn't have the ability to corrode out from the inside.

Yes, of course there's the issues with changing it, contamination etc... but those are really only an issue for track use, which we of course mitigate by changing it. IMO a normal DOT3 is perfectly fine for a car that's not hitting the track, especially our cars which have loads of brake. If you are having issues with stock 944 brakes on the street, time to look more closely at the pad selection/condition and calipers and rotors maybe - really can't see boiling the fluid, even with a decent amount of water in it, if you're driving in any way which would remotely allow you to keep your license!!

Do what you will, of course - your car and your money - but I do counsel against DOT5 usage for this reason.

[Monkey Wrench]

Its interesting that you would think that water would be a problem if using silicone fluid.
have you seen cases where this is in fact an issue?
I have not.

it is often used in collector vehicles becuase of the issue of water absorption by dot 4 and 5. basically the fluid doesn't need to be changed on a regular basis , only when serviced for other reasons, but I suppose you can still bleed it if one felt that water infiltration could be an issue. Ive had it in my old volvo or 20 years without any issue and that was dome wiht a full rebuild so no chances of dot 3 04 4 contamination.

but it might be interesting to give it a bleed next summer, and just see what comes out.

the changeover can be problematic, if the sytem still contains dot 3 or 4

there's some on wikipedia.
https://en.wikipedia.org/wiki/Brake_fluid

I did note wikipedia says it should not be used on any car with antilock brakes. due to frothing issues when antilock brakes are activated. I actually never owned a car that new ;-)

it does have this ( below) which reflects your comments. the changeover does require that all the old brake fluid is removed as any old fluid likely contains moisture.

"Brake fluids with different DOT ratings can not always be mixed. DOT 5 should not be mixed with any of the others as mixing of glycol with silicone fluid may cause corrosion because of trapped moisture. "

in my case I need to rebuild the system so I do not see this as such an issue but there is a point in that it does require that all the old fluid is completely removed.

Silicone the standard fluid for US military equipment.
it doesn't eat paint so some with collector vehicles use it becaue they don't want those issues.

- used in harsh climates, but that point doesn't apply so often to our sports cars.

I feel it makes sense for collectable cars which are used on an occasional basis. soome here have classic cars which thye use occasionally for pleasure use and tend to see a pattern of longer periods of storage.

one factor as I see it is that on some collector cars the brake parts can be difficult to find thus expansive to replace so it's a way of protecting those expensive brake parts and increasing their longevity.

[Monkey Wrench]

"Whereas DOT4 or 3, while yes they'll absorb the water, that means it's in suspension rather than concentrated, and so doesn't have the ability to corrode out from the inside."

IF the system is bled on a regular basis , I do agree. Then it won't rust out the brake parts.

that said, I have seen MANY cases where wheel cylinders and callipers running dot 3 or 4 are full of rust and need to be replaced because of that.
ive never see a brake line rust out from the inside, it sounds possible , even perhaps catastrophic !
I have never seen a hard brake line rust issue actually ocurr in my lifetime of tinkering with old cars. in my personal experience I have seen lots of stuck pistons, lots of failed seals.
I've never had a flex line burst either, but It's n doubt good practice to replace them in an aged car, to avoid that possibility.

[924RACR]

Yeah, agree with all your points... definitely a lot safer using DOT5 as you point out with an all-new system build.

I have had a flex line pop, actually only a few weeks back on track at 120mph in my racecar... not a big deal, TBH, but not great either! I agree also regarding plenty of old cars sitting and rusting with DOT3... kinda almost all our cars, as we got 'em...

[Monkey Wrench]

I did blow up soen flex lines last summmer , I was heating the fiitngs wiht a torch, I simply could not undo them without using some heat.

so the hose was affected by the hot fitting and once the fluid boiled it blew the line out fro the fitting. I didn;t care much. I was changing them anyway. I wondered if the pressure would cause an issue but no evidence of that.

best if you can get one end of the line undone befre using heat I suppose. opening the bleeder nipple seemed to have little effect. maybe the gas pessure comes up too suddenty for the nipple to evacuate it.

sometimes what Ive done is just sit in the car and give the brakes a harder than normal push, figuring it wokd at least pressure test the system,, perhaps bad practice. It could perhaps cause damage to seals?

in my old volvo I went ahead and made stainless steel pistons, I made enough for a spare set of callipers. took some time but I figured ok now they wil not rust. problem is they are cast iron with chtrome and the chrome starts to flake due to rust.

seems like the pistons aren't so expensive that this is actually practical , I had some fun making new ones and din't spend any money. they worked fine.

a think I realized was that the calipers themselves dint really suffer from wear, thye have no moving parts, they only guide the piston and the seal makes the seal not the bore..

f the posrsch has floating callipers there will be a pin and bushing. I have a volvo 740 and it had an issue where the calliper casting hole wore out, so good to lube those pins during brake inspections.

a couple of the callipers I was set to rebuld last summer , well they must have been aftermarket ones. normally the boot seal fits ino a groove and then when the piston is insetted it is locked in place by the groove which cant; exit the bore.

well some of the had this different fit. I think some rebuild factory rebored the first 3-4mm of the hole and then used a type of boot seal that incorporates an L shaped metal ring. it ooked like thiose were pressed into the bore on a hydraulic press.

this prevented me from being able to rebuild them because of this practice. I could not extract the L shaped rings and I don't think the boot seal had a groove like it should due to them beinng rebored to fit the ( new style) pressed in seal.

I think the rebuilder basically fixed them fine but they could no longer be rebuilt. I likely could have removed the steel rings if I persisted , but I had no access to a new boot seal that incorporated an L shaped metal ring.

I htink the rebuild "factory" had these special boot seals with the L shaped rings inbedded into the seal. they probably had a boring jig on a milling machine to make the right size hole..
so this prcactice worked on in their rebuid shop but not so good in my back yard when the boot seals ruptured. there was no "pocket" for the boot seal to be retained as it was originally.

for the original post. I gues she can replace the seals and pistons and probably that would work ok.

I spoke to a mechanic who said hed just polish the old rusted pistons up oh his wire wheel, slap some brake parts grease on them and not worry about a bit of missing chrome. a sloppy practice but It probably fixed the car for a few years. saved the s=cost of buying rebuilt callipers.

nicer just to change the boot seals piston seals and the pistons, Id do that.

I tried soaking the callipers in mutriatic acid, ( 1-3 with water) got them clean of all paint and rust, then neutralized them (baking soda) painted them.

a better way I think :
Id use a plastic tub and some washing soda and connect to a battery ( ikeep a charger on the battery)
and you need an expendable iron electrode, any good sized chunk of scrap iron wil do.

Ill pull it out of the bath a few tines and scrub it down , clean the bucket , put fresh. let it go more. I use a rag and baking soda to clean the black stuff off. this removes all the rust nicely.

remove the rust and paint that way.. the muriatic acid is very nasty stuff, terrible fumes. I consider it too dangerous t play with.. It did work but I prefer to use electrolysis now.. Ill plan to treat my porsche callipers that way. make them look noce again.

bit more work but less expensive than buying rebuilt callipers. buying rebuilt callipers is faster One wouldn't wanto pay shop rates for all that work..

at home on a tighter budget, in my own sweet time, rebuilding them makes sense for me.

the outcome of havung rebuilt callipers is probably similar, I might load up a bit more paint than a rebuilder does. maybe paint then red or a color, if you like the look of it.

I dont think you need "engine paint" a spray bomb of enamal, rustoleum maybe. good enough. I never saw them get hot enough to bubble my enamal paint off.

I got some "brake parts assemby lube". it's like a thick greasy oil that is brake fluid compatible.
you can just use brake fluid , thats fine, I figure the specail lube might be good if you don't use them and they sit around a while.


in the volvo girling callipers I htik the castin can actullly split and there may be some criush washers, not sure if there is any reason to split them apart.

somethign to note if your callipers are made in one piece, or perhaps made in two sections and then joined together. I think making them in two pieces was necessary for the construction of some callipers because the piston hole(s) that is bored is then blocked by the parts that retain the pads. the mill needed a straight shot to bore that piston hole initially.

some of the clalipers are of different construction from others obviously..

volvos used bendix, ATE and girling all in fairly close years. I like the non floating girling ones best. they have oposing pistons.

I think having them float might have saved cost but then the calliper can have looseness and resonation between the two opposing sides. they saved cost on the additional bores and pistons. you have what you have.

some may put volvo 240 callipeers on a 944. I've heard that can be done sucessfullly, I dont know if there are any required mods.

I think the 16 valve ones or maybe post 85 944 may have had differnent front callipsrs.. mine is the earlier style. likely they needed bigger brakes with an extra 100 HP.. mine was only 150 HP or so. - a "square dash early 85 "

were the rear callipers the same all the way through 944 production?

[924RACR]

Shouldn't be any issue to massively hammer the brake pedal while parked; if that causes an issue, better you found it while parked! As long as you're not bending the brake pedal or firewall (the later of which can in fact be a issue on these cars, well known hence the available brace/weld kit), all good.

I test ABS systems all the time (day job, at Bosch) - and you'd probably be surprised at the amount of force we regularly put through those systems. We'll readily generate line pressures approaching 200bar; normal locking pressure are around 80-100bar, vehicle-dependent, and normal driving operation without encountering ABS activation (at least on dry pavement) tends to be in the 30-60 bar range.

Calipers should definitely be lubed as appropriate points, like slider pins - preferably with brake grease, which can handle the temps. I have a pot of synthetic brake grease, feels like it's probably a lifetime supply... LOL

Piston material selection also wants to take into account thermal conductivity, as well as corrosion resistance. That's why a lot of modern cars use phenolic pistons... but of course they're not as strong, so you get to replace the whole damn caliper quickly. Hot tip: don't buy a Ford! Then again, they're far from the only ones - GM does a lot of that too, as does FCA...

I do like the idea of the home-brew electrolysis bath...

[wwdwgs]

Scott, since you work with ABS', can you tell me, is there a way to activate ABS "valves" without out a scan tool in order to bleed the brake systems after Master Cyl. was replaced? This is for Hondas, not Porsches. I was thinking about tapping into the wires and, carefully following a wiring diagram, energize valve by valve to bleed the brakes.

[924RACR]

No, sorry, you definitely would need to use a bleed sequence - CAN messages, these days, or other such diag messages - to make it happen.

The wires you're thinking of are actually circuit paths, and even if you were able to get to them you'd stand a good chance of frying the coils just by feeding them voltage... not to mention multiple valves need to be actuated, in proper sequence...

[wwdwgs]

Understood!

[Monkey Wrench]

what sort of maximum hydrauic pressure ( PSI or bar) would our (non abs) 944's be seeing?

and thank you that was some great info !

[924RACR]

Just depends on how hard you push on the pedal! Being as how the driver is the only source of pressure in that system...

But you can for sure generate over 100bar in the system, with serious pedal effort.

[Monkey Wrench]

100 bar seems extreme, much higher than I anticipated. .

just trying to approach it with round numbers, if the piston in the master cylinder is 1 inch in surface area and the driver stomping thre pedal hard as he can might put 200 pounds of presure on it, well it is a lever so maybe it can exert 4x? the pressure than at the foot, that would be 800 lbs of hydraulic pressure.

in reality it is a bit more complex because it is a double piston, if it was a square inch but the ( joining) rod is part of that so that makes it effectively smaller.. ( subtract the surface area of the joinitng rod from the piston that is in between) the one on the end, there is no rod involved.

. smaller piston more hydraulic pressure. also the foot pressure is split between two separate hydraulic syutems. they also may not have an exactly equally proportional hydraulic pressure.

I think I could work out the math from the piston's effective square inches and the length of the lever but it gets a bit more complex figuring in the area of the two pistons and not really knowing exactly what that is.

the hydraulic math is not so hard..

https://www.calculatorsoup.com/calculators/physics/pressure.php

the other way would be to connect a pressure gauge but Ive nevr actually considered doing that.

Im suprised at how high you say it may be but I think it was perhaps my interpretation that the hydraulic pressure was way lower than 100 Bar or that would be 1450 PSI

I do work on hydraulics, aside from cars and it is not at all unusual to see hydraulic pressures much higher in machinery.

interesting stuff. with your job it sounds like you (924RACR) are all over this stuff with a bit more specific experience in car braking systems..

employing antilock systems, I do not know much about that. I assume it is amplifying the pressure but also breaking it into segments of time intervals while monotoring feedback from an encoder on the wheel.. i assume those pulsations woould reach some pretty high peaks.

blowing line at 120MPH sounds exciting ! pretty that must be some pretty extreme braking !

interesting stuff to think about.. , thank you.

[924RACR]

Video is here, for your amusement...
https://www.youtube.com/watch?v=y9DGSPf56es

Naturally, the failure is just before the end of the video... this is the whole race from the start.

Regarding ABS function... pure ABS only (as fitted to the 944s, for example) only reduces pressure from what's applied at the master cylinder, or allows it back in to each wheel.

To raise pressure above MC, there are many functions, including TCS and ESC (stability control), panic brake assist etc... but that also requires additional hardware beyond basic ABS.

But yes, those pressure numbers are correct.

FWIW, note that the video above actually has front brake pressure logged, and shown in bar; my normal full-decel apply is around 60 bar (with no booster, mind you)... and you can tell when the line blows (while at 1.5g decel, roughly, pretty well on max decel) as the brake pressure drops then recovers, because of the loss of resistance from the failed circuit plus extra brake pedal travel...