S3 OTS Brakes

[Paul Buckley]

My S3 braking system was professionally mechanically 're-commissioned' three years ago with recon servos, new vacuum tank, new master cylinder, lines, pads etc.

Just recently, after a week or so not used, on the first brake application it seems that the rear brakes operate seconds before the front brakes come in, or it may be that the power servo cuts in after a couple of seconds of brake application.
Also, sometimes the front brakes drag for a few seconds after brake release.
The brakes squeal embarrassingly loudly when hot, and occasionally continue to do so for a second or so after brake release, which is how I know.

Your cumulative thoughts would be appreciated.

[jagwit]

new master cylinder

There it is. Refit the old one and report back.

[sideways60]

I Have Just Removed my Front Calipers and Discs , Good working order , Make me an Offer before they go on Ebay next Week . regs Russ

[Paul Buckley]

Thanks Phillip.

So you think that the problem lies in the master cylinder?
Could you enlarge on that for me?
I thought the problem might be the transfer valve, but I am not sure how it works.

Russ, I don’t know if your offer of slave cylinders and discs was meant for me.
However, my slave cylinders were refurbished, and the discs were new, less than 1000 mls ago.
Thanks anyway.

[Paul Buckley]

Thanks Phillip.

So you think that the problem lies in the master cylinder?
Could you enlarge on that for me?
I thought the problem might be the transfer valve, but I am not sure how it works.

Russ, I don’t know if your offer of calipers and discs was meant for me.
However, my calipers were refurbished, and the discs were new, less than 1000 mls ago.
Thanks anyway.

[jagwit]

So you think that the problem lies in the master cylinder?
Could you enlarge on that for me?

Yep. I have found the quality of aftermarket parts to be most disappointing. The master cyl on the E is actually a rather complicated bit of kit. I believe the quality of manufacture of the new "equivalents" is not the same (or better) than original, causing the issues you are having. Specifically I recon the problem lies with that pin and plate in the nose of the master cyl. Exactly what/how, I'm not sure yet.

So, if your original master cyl is still ok, put that back in, if only to see if you have the same issues.

[Barry]

I think you will find the first place to look is the small reaction valve piston and regrease. Attached is a very useful tip sent to me by Eagle. I had the same problem.
Best
Barry

[Barry]

Sorry, see attached explanation.

[Paul Buckley]

Phillip.
Thank you for that. It would seem that you are right, but I’ll do what Barry suggests first.

Barry.
Sorry, I wrote ‘transfer valve’ when it should have been ‘reaction valve!’

Yes, I kind of suspected that the problem was with that valve.
Thank you for the ‘Eagle’ tip, very useful and seemingly easy to solve.
At the mom I am in the Isle of Man but as soon as I return I will have a go at cleaning that piston and I will post the result.

If it works as it did for you, It will save me having to change the master cylinder.
Can’t be bad ......

All the best to you both

[mgcjag]

Hi Paul....before pressing the brake pedal with the valve disassembled cover the end of the cylinder with a rag to catch the small piston......it can fly out with some force when you press the pedal and very easily disappear across the garage....Steve

[Barry]

That was the advise given to me too. If you read the caption on the photo it says you need two people, one at each end!

[Paul Buckley]

Phillip and Barry, thanks for the warning

[jagwit]

On my ex-OTS the symptoms were as follows:
1) Problems only started after a continuous drive of 30 min or more;
2) Free play on brake pedal would gradually diminish as the drive went on;
3) A delay arose between releasing the brake pedal and actual brake release;
4) Then one could feel the brakes (not sure if front or rear or both) binding and this became more as the drive continued and eventually would force me to stop for an extended period of time to allow "whatever" to cool down.

Sold the car like that (declaring the issue to the buyer).

Its only after others reported similar findings and their solutions to the problem that I realised my problem was also related to the new master cyl I had fitted to the car. Odd thing was that the problem did not manifest immediately after fitting it. It was only some time later that this started happening.