82 911SC brake issues

[trojwl]

Greetings all

I recently did a total brake job on my 82 911SC. I did it all. The vacuum booster was leak-free so it was not addressed. I replaced the master cylinder (all parts were name-brand items from Bosch, Wagner, Raybestos, Centric, etc.). I replaced the rubber hydraulic hoses at each wheel. Brand new calipers. Brand new rotors. New hardware. And, of course, new pads (Centric #13037002). Basically, a brand-new braking system.
Pedal travel is spot on. However it feels like the pads never “grip” the rotors. It takes a lot of extra effort to stop in the last three percent of pedal travel. I have done some “breaking in” with hard controlled stops at speed. No improvement whatsoever.
The system has been power bled twice.
I can feel when pads make contact with the rotors, but then it feels like the pads are just skimming over the rotor. It takes a strong foot to come to a quick stop. It’s hard to get that “biting feel”.
I am looking for ideas/suggestions. I am using premium daily-driver Centric pads. I would use a more aggressive pad if that would help. New rotors are not that expensive.

Thanks

[Flojo]

sounds like either:
a) pads don't harmonize with rotors (happens)
b) booster not working
c) wrong master cylinder

lets's ignore a) and b)… what part numer MC did you replace with?

cos' if you took the turbo one (2.3) on your stock SC (1.9) you'll need quite some leg to brake (just like the early cars)

and last, maybe your bleeding (even twice or thrice) went wrong and there's still air inside.

Bill will sure chime in.

[trojwl]

The master cylinder is Centric p/n 13037002.

Also how much vacuum does booster need to operate? Check valve works perfectly. Feels like there is adequate vacuum for a booster. There is decent vacuum present but I've never measured.

Second power-bleeding was by a master mechanic.

I'm leaning now towards wrong part number.

Thx
Warren

[sugarwood]

What is that awesome color ?

[trojwl]

It's called "Rosewood" on the window sticker. It doesn't look like Rosewood on the color charts. My guess is that is was a custom FACTORY paint job as it doesn't appear on any of the color charts. They needed a name for the paint for the window sticker and I guess they simply chose Rosewood. I don't know if this color even has a name.
Car has never been repainted. No evidence anywhere. Even the leather inserts between the body panels look totally unmolested.
I go to local automotive paint store and simply get color-matched touch-up paint.

[Travis Neff]

Try doing the pad bedding procedure from the PMB website.

https://www.pmbperformance.com/bedin.html

[aigel]

Ugh ... too many things changed at once!

It is either friction or a pressure issue.

Friction:
- Any combo pad / rotor should have decent friction
- UNLESS you got them lubricated accidentially?

Pressure
- You have the system bled and there is no dampening feeling from air in the lines
- Your foot works
- There are 4 calipers, chances that they are all not working well is slim
- That leaves the master cylinder as suspect #1

That said, what is the mechanism of the MC not delivering pressure? I don't know of such a failure. Usually the pedal sinks if it bleeds by ...

I'll be curious to hear what others think and how this is resolved. It may just be "throwing parts at it" in a reasonable order at this point in time ...

Good Luck,

George

[trojwl]

Good article. Will give it a try.
Hopefully I don't get pulled over.

[trojwl]

The guy at Centric said part number for my master cylinder is same for all 1982 models.
However there is a second part number listed on Rock Auto for a 1982 "Turbo look" 911. I have no idea what this means. The guy at Centric made no mention of this. As you can see in pic, mine does indeed have a "turbo look". But it is not a turbo engine. I think there may be something internal like different bore size, etc. Why they would use a different unit for a "turbo look' doesn't make a lot of sense.
Hoping to find answer in forums.

[aigel]

Originally Posted by trojwl

The guy at Centric said part number for my master cylinder is same for all 1982 models.
However there is a second part number listed on Rock Auto for a 1982 "Turbo look" 911. I have no idea what this means. The guy at Centric made no mention of this. As you can see in pic, mine does indeed have a "turbo look". But it is not a turbo engine. I think there may be something internal like different bore size, etc. Why they would use a different unit for a "turbo look' doesn't make a lot of sense.
Hoping to find answer in forums.

The factory "turbo look" M491 had everything but the engine from what the 930 turbo had, flares, and most importantly turbo brakes. These are much more beefy than the brakes on the normally aspirated models. So, that's where that different part number comes from.

Cheers,

George

[jbs3]

This happened to me once on a Jaguar i was working on and drove me crazy. It turned out that there is a special procedure to specifically bleed a new master cylinder that i had not done. Your symptons are exactly what i was experiencing. Bleeding the master cylinder fixed the problem. Hope it helps.

[trojwl]

The Centric-verified part number was for all 911 models - including turbo-engine models (930's). Even makes less sense now why "turbo'look" requires different MC (assuming it does).

I'm not buying anything until I am one percent sure.

I'm doing the break-in procedure first (consecutive "panic" stops).

I've done 911 pad/caliper/rotor replacement more than a few times so this is all indeed very perplexing to me.

[trojwl]

Also, I believe having system power-bled twice should have taken care any air in the MC. Second time was at the shop.

[jbs3]

I went back and checked my notes. It is called “bench bleeding” and it is sometimes needed because sometimes an air bubble will lodge in the far end of the cylinder beyond all the connections. When there is air beyond the brake line connections, no amount of regular bleeding will get it out. Search on “bench bleeding”

[trojwl]

Good idea, Sounds quite feasible.
Will check it out.

thx

[James Brown]

what brand are the hoses, any changes to the hard lines?

[2jmotorsports]

I wonder if the vacuum assist is working. The big hose/tube running from the brake booster through the center tunnel to the left side of the CIS assembly. If nothing else works might be worth a smoke test to check for vacuum leaks.

[Travis Neff]

Factory turbo look cars were only in 1987 & 1988 I believe. You have the standard brakes on the back and would need the standard master cylinder.

Try bedding your pads using the PMB procedure, your caliper seals may also need to be broken in a bit, which the bedding procedure should get everything in harmony.

If that doesn't work I would try the bench bleed of the MC as suggested. I have heard of a way to do this while the MC is in the car, get two short hard lines and put them into our output ports of the MC & bend them so they dump back into the fluid reservoir and pump away (of course you would need to disconnect your existing output lines to put these short lines in). I have never tried this method.

[Walt Fricke]

For the SCs, the stock MC has a 20.64mm bore, and a 7" booster. The turbo of that era had a 23.81mm MC bore, and an 8" booster.
The larger MC was, I believe, to deal with larger bore caliper pistons. The larger booster was to increase the pressure the vacuum system applied to the rod that pushes on the piston in the MC.

But you have an SC turbo look. If you got the larger MC you have less hydraulic advantage boosting your pedal pressure if you have the regular SC calipers.

If you have a solid pedal, air in the system isn't your problem.

If you have a turbo MC and stock 3.2 calipers, you will need more pedal force for the same clamping force by the pads on the rotors. If you have a smaller booster (the pie plate large thing so prominent there at the rear of the trunk where the MC is), more pedal pressure needed.

The Centric guy is wrong about every thing being the same. To hell with Centric part numbers - what is the Porsche part number? Or at least the Porsche number Centric thinks is equivalent?

But if your vacuum booster isn't working, you'll also get the feel you have. I'd suppose you could simply disconnect the vacuum line at the booster, and plug the line, leaving the inlet on the booster open. Drive, and see if it feels like the bad normal. If it is worse, probably not a booster/vacuum problem.

[trojwl]

I've had the car for twenty years. I've done more than a few pad and caliper changeouts over the years with excellent results.

Car has always had decent brakes. I'm now certain that I have correct master cylinder. Centric has probably sold literally thousands of these units. To totally discount what the agent told me is silly. The is a special application on a 38 year old car. And technically the second part number that he did not mention might be listed under "930" and not "911".

In the Rock Auto site, the second part number is for "turbo-look" models (whatever that means). In my conversation with Centric tech support, I also got the same dimensional info for both units.
Obviously the second part number is for the 930 turbo.
I'm left with the pads. Literally all parts are brand name and brand new - including the rubber hoses.
Next course of action is a little more rigorous break-in process or more aggressive pads..