Carrera Brake upgrade questions

[cali74]

So I've been reading posts about brake upgrades and the pieces involved. I have a couple issues though that I hoped y'all could help clarify and point me in the right direction on. Thanks in advance :-)

I'm upgrading a '74 911 to 3.5" spaced bilstein struts and aluminum front crossmember. I have those bits, along with the rest of the front suspension bolted up, but not all tightened down (except for the a-arm related bolts as I had to work forever to get the polybronze to spin freely when torqued down).

I also have a set of carrera brakes (non-boosted setup)-- front and rear calipers, rotors, and master cylinder. I have an adjustable tilton biasing valve on order as I don't have the stock valve.

First Problem: with the crossmember in place the new master cylinder won't fit into place. Measuring the MC and the distance from the tub to the crossmember it appears to be about the same length -- begging the question will it fit at all??

Should I remove the front crossmember to fit this MC, or should I go with another MC? The feed line entry on the new MC is different from the old one, and looks like it gets in the way of the tie rod boots - does this issue require angled feed line fittings on the MC (one or both?)?

If I should switch to a different MC than the stock carrera one - which should I use? The car's previous MC doesn't garner my trust so I would buy a new one even if that was the proper size for the new calipers.

Speaking of feed lines - they are very expensive from pelican for the silly plastic lines. What size line can I use to replace the expensive plastic sections and can I run 2 continuous pieces from the resevoir to the adapter bits on the MC?

I also want to change out all my hard brake lines except the one through the tunnel. This seems like a good time because I can plumb in the tilton valve somewhere convenient while I'm at it. I've read in some posts about using SS line everywhere instead of hard lines. That seems like it would be easier as I wouldn't need to buy a flare tool and struggle with the tube bending. Thoughts on this issue like replacement frequency or total cost vs. a flare tool and hardware?

Additionally, I took the stock '74 front hubs off the stock '74 rotors last night, but haven't checked the new carrera rotors for fit. Is there anything I should expect with this process (like needing longer mounting bolts and if so what size, or front wheel hub and bearings not fitting the turbo struts at all)?

There's plenty of other murphy's law problems that have come up, but I think that's most of the brake specific issues. Thanks!

[Bill Verburg]

also have a set of carrera brakes (non-boosted setup)-- front and rear calipers, rotors, and master cylinder. I have an adjustable tilton biasing valve on order as I don't have the stock valve.

There are 2 different sets of Carrera brakes(not counting the 964 up models which are also Carreras. )
early Carrera '73-77
late Carrera '84-89

The early Carrera used 282x20 & 290x20 mm rotors & either S or A front calipers w/ M rear calipers

Late Carrera used 24 mm thick rotors and wide versions of the A and M calipers, the wide M's also had bigger pistons and needed a fairly aggressive 33 bar p/v.

My updated brake data page is bing moved to here, check it out for fuller details.

So the 1^st issue is which set of Carrera brakes do you have?

the 2^nd issue is that only the late Carrera brakes want or need a p/v.

If you have late Carrera fronts then the p/v can still be avoided by leaving the stock M rears w/ the late Carrera fronts.

First Problem: with the crossmember in place the new master cylinder won't fit into place. Measuring the MC and the distance from the tub to the crossmember it appears to be about the same length -- begging the question will it fit at all??

The aluminum x member actually gives the m/c more room. The the stock 19.05mm non boosted 911 m/c you started w/ is fine unless of course it has deteriorated over the years, in which case replace w/ the same. There is an ATE 23.8 mm m/c which is longer and just barely fits w/ the aluminum x member, you should not be using that m/c w/ any of the versions of Carrera brakes.

I would use the stock feeds.

Stock '74 hubs are fine w/ any of the Carrera calipers and rotors

[cali74]

Thanks for all the info Bill! ...

1st issue: I have the late carrera brakes

2nd issue: I'd like to not use the old brakes at all, which means I'll need the proportioning valve. Does the tilton knob unit provide enough "proportioning" (restriction?) to replace the stock unit, and if so will it still be in an adjustment range so that with different tire/weight setups I can get the brake lockup dialed in properly?

Master Cylinder:

I read here about master cylider sizing saying that:

Originally posted by Bill Verburg
...When the caliper slave cylider is increased(keeping the master constant) it moves bias to the front. Keeping the slave constant but incresing m/c size has the opposite effect.

again assuming equal diameter rotors f/r, and the caliper piston s mentioned you are front biased ~2:1, on a 911 you would want to reduce this to ~ 1.6:1. I'm unsure as to what you might need on a 914.

To reduce the front bias you will want a sligthly larger front m/c.

Pedal feel is the combination of many factors, some like mount stiffness are out of your control, the main thing you can control is slave to master ratio.

Bigger m/c reduce total hyd. ratio gving less brake torque for a given amount of leg. Unbosted ratio of ~32:1 is close to the limit and I would certainly want a boost at that level

Another good info link I found was here. Though I'm not sure I want to go so far as calculating everything with a set of assumed coefficients....but that might be me being too lazy in which case I'll understand if you say to go do that (as an EE it sounds more appealing to go work on the now-thick pile of papers constituting my new wire harness design :-) ).

You mention that the stock 19.05 MC is what I should use. Would going with the carrera MC make the leg effort greater for a given stop? I definately would like to not need to squat press the brake pedal all the time :-) At the same time, would going with the 19.05 MC and the tilton valve offer a good combination?

Thanks again so much! This is a great learning process, hopefully others enjoy it too.


Anybody reading have any thoughts on this other thread???

[JP911]

I'm with Bill on the MC. No need to change to anything larger. I installed the 23mm with my 930 brakes and I've second-guessed that decision (one school of thought says to stick with the 19mm). It takes alot of "leg" to get those stoppers stoppin.

IMO, messing with the proportioning valve is going to be a pain in the a$$ for very little gain. I would rebuild your current rears, get new lines, pads, and rotors, and skip the Tilton valve.

[Bill Verburg]

ok late Carrera all around
the tilton will be fine, if this is a track car mount it where you can get at it easily, the factory ran the rear lines up out of the center tunnel by the drivers side


for a street car mount it out of the way.

Master cylinder sizing is a balancing act between pedal feel, moving a large enough volume of fluid and leg force needed to generate adequate line pressures.

Carrera and 911 sized caliper pistons want ~19-21mm m/c pistons, the bigger the m/c the better the feel but the more leg is needed so power assist becomes more desirable. If you go too big then line pressures suffer especialy w/o boost.

[Bill Verburg]

Originally posted by JP911
I'm with Bill on the MC. No need to change to anything larger. I installed the 23mm with my 930 brakes and I've second-guessed that decision (one school of thought says to stick with the 19mm). It takes alot of "leg" to get those stoppers stoppin.

IMO, messing with the proportioning valve is going to be a pain in the a$$ for very little gain. I would rebuild your current rears, get new lines, pads, and rotors, and skip the Tilton valve.

So my post above.

The 930 calipers need 20.5-25mm m/c yes, you can get away w/ the 20.6mm SC/Carrera m/c but pedal feel suffers, the brakes get touchey, especially w/ boost. 23.8mm is very nicely sized but needs more leg than many like. Boost is the solution you can use either the 7" or 8" vacuum can to fine tune, the 8 gives you more boost the 7 less.

[cali74]

Nice picture :-) Thanks again for the help - I think I'll try putting the P/V in the smuggler's box and probably get a new 19mm MC...

Since the stock feed lines are toast and they are $180 for two plastic tubes, do you happen to know the size of the line needed in order to make new ones? The image on pelican for the '74 feed lines shows the metal ends on the feed lines which seems incorrect.

My brake system had a few inches of braided hose from the resevoir fittings (2), then two plastic lines that fit inside the braided hose and go down to the master cylinder, where the plastic line fits over 2 barbed fittings that are in the rubber grommets. Other posts suggest making extensions for this system, but I haven't found the diameter listed in the posts that would successfully fit the resevoir tips and the MC attached bits. Pelican sells "999-181-021-50-M107" which is supposed to replace the braided section going from resevoir to feed lines. Can I just use longer lengths of this line to go all the way to the M/C, or would I need a slightly smaller diameter line at the M/C end and have to mate the two somehow?

oh, and for repetition from other posts sake...as I understand it the hard lines are Edit: 3/16" with 10x1.00mm ISO bubble flare ends. Do I have that right?

thanks,
matt

[Bill Verburg]

do you happen to know the size of the line needed in order to make new ones?

Not offhand

Can I just use longer lengths of this line to go all the way to the M/C, or would I need a slightly smaller diameter line at the M/C end and have to mate the two somehow?

Sure, it's not a pressure line, you just need whatever is impervious to brake fluid and fits over the fittings at the ends.

the hard lines are 3/16", ~4.6mm, 10x1.0 fittings, bubble flare,