Hard brake pedal and smoking brakes

[absunbeam]

Took the Mk2 out for a trip around the block, noticed that when I let off the gas it was braking on its own. Pedal was hard, nursed it back to garage and noticed smoke coming from both front calipers and did not want to move. Let it set for 15 min and the pedal had movement again. Any clue what is to blame the booster or the master? Guessing something is not releasing pressure.

 

[alpine_64]

My first thought was a front brake hose collapsed internally.. but its unlikely that hit both wheels at the same time... but hey...sunbeams ...

The booster sticking is most likely.. bypass the booster as a quick test.

 

[bernd_st]

Sounds as if your booster is stuck. Pretty common specifically if you still use the Girling brake booster...

 

[puff4]

As Bernd noted, I almost guarantee that what you have is a booster failure. If it was newly rebuilt, chances are the seal around the outside of the vacuum piston wasn’t trimmed properly and as a result, it’s sticking badly. if it hasn’t been recently rebuilt, then it’s possible the main piston is sticking in the bore because the seals are shot. But yeah, it’s almost definitely the booster.

 

[alpine_64]

As Bernd noted, I almost guarantee that what you have is a booster failure. If it was newly rebuilt, chances are the seal around the outside of the vacuum piston wasn’t trimmed properly and as a result, it’s sticking badly. if it hasn’t been recently rebuilt, then it’s possible the main piston is sticking in the bore because the seals are shot. But yeah, it’s almost definitely the booster.

Id suggest the leather seal or the wrong grease.. comon issues with the rebuilds causing piston to stick

 

[bernd_st]

Got a hot hint from the UK Tiger boys earlier: The orginal leather seal should be boiled out in 100° C hot water before being reused ( there is no replacement anyway). Unfortunately the leather swells when being exposed to brake fluid. This will almost certainly make the piston stick sooner or later whatever you do with grease, centering, etc. Didn't try it yet, but makes a lot of sense to me - given the many failures after Girling rebuilds...

 

[puff4]

I seem to recall that my booster had a neoprene seal, and there was a Tiger Tom tip about trimming it down that I followed. I did the job 25 years ago, so… ¯\_(ツ)_/¯

 

[alpine_64]

I seem to recall that my booster had a neoprene seal, and there was a Tiger Tom tip about trimming it down that I followed. I did the job 25 years ago, so… ¯\_(ツ)_/¯

What booster kevin? Lockheed?

All The Girlings i know have thr leather swal and used a special red grease iirc....

The combo of swollen seals and wrong grease after rebuilds would lead to sticking brakes or inconsistent and grabbing pressure.

Often not much better than when the original leather seals had caused locking brakes.

 

[puff4]

I’m remembering better now. There was a thick neoprene foam o-ring that goes under the leather seal… and that keeps it sprung against the drum, yes? That was the one TT said to cut down prior to installation. The reasoning was that the foam seal was too thick, and caused seizure of the piston.

 

[puff4]

Here… I found this reference… note the last part of it.

 

[bernd_st]

We also experimented with the foam rope seal, cutting it into two halves/ using only half, etc. Still piston got stuck.

Amazingly, just found a source for a new leather seal:

Girling Mk2a 5,1/2″ Remote Servo New Vacuum Piston & Leather Seal - Stage1 Motorsport

Replacement 5,1/2' mk2a Girling remote servo leather vacuum seal and new pistion 100% correct replacement for the old warn out parts and copied from a NOS Girling seal and rod This listing is for a new seal & rod only NOT the servo!!! POST PLEASE READ!! Post is set at £14.99 uk and £35.00...

stage1.org.uk

Not too pricey, but need to see the quality..,

 

[absunbeam]

The booster was freshened up about 10 yrs ago. Picked up some Servo rebuild kits and will check out the condition of the seal. Thanks for all the tips will get into it in April.

 

[sunalp]

While I think the booster is most likely your problem, you can by pass it to make sure before
you take it apart. On an Alpine it's pretty easy to do, not sure on a MkII if it is.

 

[absunbeam]

I did that on my Mk1 to dummy it up. Doug Jennings Sr has always stated that you don’t need a booster and work well without it.I do recall a couple of United's ago some one had made up some lines to bypass the booster for those who had them lock up on the tour. it is a good idea to carry a line JIC!

 

[alpine_64]

I did that on my Mk1 to dummy it up. Doug Jennings Sr has always stated that you don’t need a booster and work well without it.I do recall a couple of United's ago some one had made up some lines to bypass the booster for those who had them lock up on the tour. it is a good idea to carry a line JIC!

C.A.T sell a bypass line

 

[puff4]

I decided to run without a booster many years ago, and apart from a somewhat harder pedal, it all works fine. I made up a line using two unions and a coiled bit of brake line. I coiled it to allow it to expand and contract a bit.