Coupe Brake Vaccum Servo Upgrade

[MikeyB571]

I need some help really badly, please if anyone can help it will be much appreciated.

I have an Audi Coupe and have installed a Vacuum assists brake servo as it used to have the Hydraulic assist. I got a upgrade kit from 034 Motorsport.

The cars been off the road for a while as I have just put a 2.8 30v ACK engine in it.

So I took it to MOT today and it failed because he said the servo was not working. The problem is that you can clearly see that the servo is working. If you turn the engine off and pump the brakes, after a few pumps the pedal goes hard. However the test that MOT testers are supposed to use is to pump the brakes with the engine off and then start the engine while holding pressure on the pedal. When the engine starts the pedal should go down and that proves the servo is working.

However when holding alot of pressure it doesn't go down, if I hold less pressure it does go down or if I release the pressure abit it then comes in.

I'm really stumped here and would appreciate any suggestions as to what might be wrong, I can only assume that the servo valve is mis-adjusted but I don't know how to adjust it.

[johne]

Go somewhere else for your MOT

John

[MikeyB571]

Go somewhere else for your MOT

John

I think that is my only option, been working on it now for the last two days and there is definitely no leaks. It must be just a design issue.

Brakes are working perfectly so it's safe.

[siV6Qcoupe]

Hi,

I've done the same conversion, 2.8 30v and use a vacuum servo. My car has passed the MOT with the vacuum servo, the test you speak of sounds like when the servo has completely been discharged of vacuum it is then tested on it's ability to instantly regain vacuum once the engine has been started to enable power assistance to the brakes.
The only time I couldn't press the pedal down was when I took the servo apart and incorrectly assembled it. Do you have the one-way valve the correct way around only letting air to be drawn out of the servo? Have you checked the linkage at the brake pedal is not hindered in any way? strange problem.

[MikeyB571]

Thanks, at least I know it can work. Where did you get the servo from, I got the upgrade kit from 034 motorsport. I am now concerned that the master cylinder is not compatible with my the servo.

I still haven't got my engine properly tuned as I put an aftermarket ecu on it. What did you do with engine management, initially I was gonna put an A4 loom in and gave up on that idea. I have also been considering the PES, it looks awesome.

[Pirvu Eugen]

I had installed in my coupe with 3B engine the vacuum assisted servo without problems. The only thing i added in plus...was an vacuum acumulator...pretty big...
But worked perfect for me.
Hope you solve the problem!

[siV6Qcoupe]

Thanks, at least I know it can work. Where did you get the servo from, I got the upgrade kit from 034 motorsport. I am now concerned that the master cylinder is not compatible with my the servo.

I still haven't got my engine properly tuned as I put an aftermarket ecu on it. What did you do with engine management, initially I was gonna put an A4 loom in and gave up on that idea. I have also been considering the PES, it looks awesome.

I just picked up a servo from eBay that looked like it would fit. I had some initial problems and had to shorten the piston rod of the master cylinder used on my v6 coupe. I later bought an Audi 80 vacuum servo and it fitted perfectly without modifying the master cylinder. I would be aware that the U.S. left hand drive coupes use a different master cylinder if I remember.

As for engine management I used a U.S. 30v ECU as these do not use an immobiliser. I then spliced the coupe's v6 engine loom into the connections at the 30v ECU, there are a few new looms to the extra sensors to be made but everything can be made to work.

[zer matt_c]

Go somewhere else for your MOT

John

It wont make an ounce of difference as the D.O.T. runs an mot database so the new test station will know where its been and what its failed on.

[MikeyB571]

I just picked up a servo from eBay that looked like it would fit. I had some initial problems and had to shorten the piston rod of the master cylinder used on my v6 coupe. I later bought an Audi 80 vacuum servo and it fitted perfectly without modifying the master cylinder. I would be aware that the U.S. left hand drive coupes use a different master cylinder if I remember.

As for engine management I used a U.S. 30v ECU as these do not use an immobiliser. I then spliced the coupe's v6 engine loom into the connections at the 30v ECU, there are a few new looms to the extra sensors to be made but everything can be made to work.

Thanks,

I'm just making up a spacer now and see if that does the trick, it should have the same effect as shortening the rod.

As for ECU, I have the same idea kind-of and failed miserably. The ECU and wiring loom I have was using CAM BUS and the immobiliser. So in the end I started from scratch with the wiring loom and got myself a Solaris S6 ECU. Had lots of missions with the flywheel and crank sensor, then the idle control. But I have finally got over these problems now. Ready to be mapped on the rolling road once I get an MOT.

[MikeyB571]

I just picked up a servo from eBay that looked like it would fit. I had some initial problems and had to shorten the piston rod of the master cylinder used on my v6 coupe. I later bought an Audi 80 vacuum servo and it fitted perfectly without modifying the master cylinder. I would be aware that the U.S. left hand drive coupes use a different master cylinder if I remember.

As for engine management I used a U.S. 30v ECU as these do not use an immobiliser. I then spliced the coupe's v6 engine loom into the connections at the 30v ECU, there are a few new looms to the extra sensors to be made but everything can be made to work.

I just tried using a spacer about 5mm, and it made no difference at all. I have just bought a new servo from ebay off an audi 80 and will see if that works.

Thanks for the advice.

[MikeyB571]

Got this sorted now, replaced the servo with a Audi 80 secondhand one and it's all good.

[Rusty]

Never heard of this test on an MOT... how strange!