Master cylinder og pedal cluster?

[AndreasK]

77 911S. My brake pedal doesn't return properly. After braking they drag slightly (right rear caliper) and i have to pull the pedal back. Then they release and all is fine. Pedal feel is good and firm. Removed florbord and lubricated bushings, and it seemed somewhat better and almost seemed to return fully by it self. But the return of the pedal seemed somewhat sticky. Lubrication improvements only lasted about an hour, then it was back to weak return and brakes draging.

Do I rebuilt the cluster 1st or change the master cylinder. Or both when I´m already in there?

[spoke]

I don't think the brake pedal assembly is actually attached to the MC plunger. It kinda just sits in front of the plunger. Therefore, it seems that the MC should be ok.

I had a similar situation with my '71 914 where the brake pedal would stick. Turns out it was the bushings at the base of the pedal assembly. I was able to get it freed up by using some Silicroil and regular lubrication oil.

[GH85Carrera]

Often the original plastic bushings swell from the brake fluid leaking from the master cylinder.

The pedal cluster is not really attached to the MC. A rod just pushes into the MS from the pedal. It is a challenge to get your head in in there and disconnect the cables, and then unbolt the pedal cluster. Pull it out, and check the bushings. It is a pain to get the cluster apart, and rebuilt. There are places that do it as a service. It comes back all plated and pretty.

If the MC is leaking, it will happen again, so check carefully for leaks.

[AndreasK]

Thanks guys. I did get my head in there and I dont think there are leaks. Ordered new, brass, bushings. I'll make it a weekend project. Good to have it out of the way anyway😁

[lsf911]

I just experienced this problem on my 68. The brake pedal didn't return to full out position unless manually pulled out. I replaced the master cylinder and it fixed the problem. The master cylinder piston wasn't completely moving back causing the brake pedal to do the same. Not sure if yours is the same but am interested in hearing your story afterwards.

[Walt Fricke]

The springs in MCs are not strong, and certainly are not intended as a brake pedal return. There is a spring in the pedal cluster for just that purpose.

Replacing the bushings isn't that big a job. It helps to have on hand a new roll pin, because to get the clutch pedal arm off you have to drive the old one out. I think a twisted coil one from a hardware store might be better than the stock Porsche one in terms of longevity.

[AndreasK]

Cluster is out. Brake pedal does not return at all by the spring it self. Aparently the only return was the MC pushing it back. Bushings are sticky and the spring seems as springy as sphagetti. Got new bronse bushings and a new spring. Feels good to clean up, what must be the nastiest aerea of my car😁 No sign of rust or brake fluid leaks.

[AndreasK]

Did I get the wrong spring? Somewhat larger than the one on there. And quite roomy around the shaft. Mine is a 77s with the brake booster.

[Walt Fricke]

While having a spring, especially like this one, lose rate is a mechanical improbability (a spring's rate is determined by its length, wire width, and modulus of elasticity, and those don't change, I'd just put the new one in since you have it. Don't overthink this.

[AndreasK]

Originally Posted by Walt Fricke

While having a spring, especially like this one, lose rate is a mechanical improbability (a spring's rate is determined by its length, wire width, and modulus of elasticity, and those don't change, I'd just put the new one in since you have it. Don't overthink this.

Your probably right. I dont think the reason for my brake pedal not to return was due to the spring. It seems fine. But the bushings and shafts where pretty corroded and dry. Lots of resistance in there. But as long as the new spring fits, I think it will be fine and the better choice. Il try to asseble it as soon as my new paint is dry😀

[AndreasK]

Cluster back in the car, working nicely! Everything smooth an nice, much better pedal feel than before. Bonus point. My clutch was poorly adjusted before. Had do push it ALL the way in for it to release properly. Let it out a couple mm and it started engaging. With new bushings its perfectly adjusted. Very happy, looking forward to a long summer of driving

Feels really good to have the filthiest part of my car all nice and clean. Found no rust under the cluster




And my baby back on the road

[john walker's workshop]

2nd pic back, notice the horizontal part of the clutch pedal arm is twisted. Poor design and usually due to the clutch assembly and/or cable being old and stiff to operate at some time. Causes the pedal to be lower than normal.

[AndreasK]

Originally Posted by john walker's workshop

2nd pic back, notice the horizontal part of the clutch pedal arm is twisted. Poor design and usually due to the clutch assembly and/or cable being old and stiff to operate at some time. Causes the pedal to be lower than normal.

I've noticed them being slightly offline. Their not as bad as they seem in the pic, when in the car. Not a problem when driving. Dont think I'll reassemble to fix it😁

[john walker's workshop]

They're pretty easy to bend back. Just pull on it. If the clutch assembly isn't too old and stiff and the pedal action is easy, it shouldn't rebend.

[AndreasK]

Originally Posted by john walker's workshop

They're pretty easy to bend back. Just pull on it. If the clutch assembly isn't too old and stiff and the pedal action is easy, it shouldn't rebend.

Nice, thanks!