Brake advice

[DJ911]

Had my car in the shop last week to have the brake upgrade done and install my the sport shocks. The car is sensational to drive... the upgraded suspension and stopping power is a great match for the 3.0 installed by the PO (Shane, let me know if you are ever in Adelaide and want a blast in the old girl).

There is however an unusual problem with the brakes and any suggestions would be appreciated. For background the upgrade was to second hand (low mileage) boxster calipers, new carrera rotors, new brake lines, left the original master cylinder. Hawk racing brake pads and racing brake fluid.

After a short drive yesterday the car started to pull left under braking. As it would happen the car was back at Poole's this morning on the hoist for another reason so while it was elevated he took a look at the brakes. Interestingly while applying light brake pressure it was the right that seemed to provide more resistance when turning the wheel, though bugger all in it. Took a look at the rotors and pads which seemed fairly normal, perhaps slightly inconsistent wear patern on the lefts and swapped pads left to right 'just in case'.

Because the torsion bars are tired and showed signs of sagging I asked Mark quickly checked the corner weights - perfect. Probably not necessary but wanted to eliminate this.

So back on the road for another test drive and braking was flawless and remained so for the next 5 kms, then quite abruptly started pulling to the left again.

This was not the case on my trip home from the office after the car sat for a few hours - no problem.

Now the Mark assures me the brakes were very thoroughly flushed to clear all the old fluid, so he feels that is an unlikely cause. Next planned step is to have the caliper pistonsblooked at / cleaned as it seems they may be sticking. Rebuilding a logical step after that. They are second hand and appeared to be in good condition but not sure what else to try.

Any suggestions/thoughts?

Cheers

[Fishcop]

You probably need to outline the actual symptoms...

[9er]

left..... it must pull to the left?

[DJ911]

You probably need to outline the actual symptoms...

Fat fingers... not the symptom but the reason for the incomplete post

[SIR70t]

Dirk , for sure , would love too.. I'm just honestly pleased you are adding (completing) the original idea....
We are but temporary custodians of these great cars...

And I would upgrade the master cylinder

[9er]

My guess would be some foreign matter in the fluid galleries of the caliper. Not sure if retaining the old master cylinder is a winner either(unless you have only fitted it recently)
As a coincidence, after a big drive day yesterday I felt the Carrera was pulling left slightly, so I pulled down the calipers today and they were pretty ordinary inside, with sludge and contaminants. This is despite thorough flushing when I fitted the new master cylinder 18 months back.

[Fishcop]

Sorry I was a bit quick

I think brake pistons also. There's nothing wrong with second hand and most of the time it'll just fine; but a brake rebuild is pretty cheap and will give you a solid baseline to work from and peace of mind. A dragging left calliper will pull and a right calliper that is failing leaves the left working - which will give you the left pull.

Have you got a pyrometer? Might be worth going for a drive on a quiet road and have a passenger take temperature readings on each side after coasting to a stop and also after braking to read where the heat is occurring.

[DJ911]

Chris,

So in your opinion would the foreign matter scenario explain the intermittent nature of the problem? Do you think that if the pistons were in need of repair the symptoms would be more consistent?

Thanks

[9er]

Dirk, yes I'm thinking maybe a blocked to partial blocked to open fluid passage situation depending on the foreign matter.
I dont know the Boxster calipers, but I would expect the pistons themselves to be fine and putting a seal kit through with the thorough clean out and maybe a light hone of the bore should do the trick.
For me the ATE grease(or I guess any specific caliper rebuild grease) helps make the job that bit easier.

[Jeff Eelkema]

Hoses

Dirk

I've seen hoses that start to crack up internally and little bits of rubber act as one valves which prevents a proper return of fluid back to the M/cyl and then an imbalance. This typically takes a few applications to start to show up which might account for the lack of pull on a short run after the car has sat and fluid has slowly balanced out.

If the hoses aren't new I would fit a pair, cheap start. In the process of fitting calipers etc the hoses would have been disturbed.

As an aside, I NEVER fit ANY S/H brake parts without first stripping, cleaning and fitting new seals. The calipers and pistons should be fine so it should only take around an hour a side plus a seal kit (this is in a proper W/shop with proper tools etc-home repairs are always much slower).

cheers

[9er]

Knowing you Dirk I'm sure you have done your research, but did you read this anywhere? " For 1969-76 cars with non-boosted brakes, we recommend an upgrade to Mercedes Benz master cylinder 002-430-9301-M4."

[DJ911]

Gents,

Thanks of all the useful feedback. Greatly appreciated.

Plan of action is to have the cylinders torn down / cleaned up and seals replaced if required.

Likely to move ahead with replacing the master cylinder as well (Chris, I did see that info on the MB unit - thanks). So then the upgrade would be complete - sorted callipers, new rotors, new lines, new master cylinder.

Cheers