How to know if the brake servo is working or has failed?

Hi there again.

First, a big thanks to everyone for all the advice so far about the various issues i have had, i bought a non runner 1978 scirocco a few months back not really knowing anything about these cars and you guys have really set me straight. I'm up and running now so MOT is the next target, thanks to all those who have taken the time to answer my noob questions.

Today i bled the brakes on my standard 1978 scirocco. As the fluid was really discoloured, i was hoping this would improve braking performance quite a bit.

There is a bit of an improvement but it's not what i had hoped for so now i am wondering if the brake servo needs replacing?

As i haven't any experience of what the brakes should be like, (normally i ride motorcycles and my only other reference is my 2009 Passat) I'm having difficultly deciding if the braking is as designed for a 42 year old car and i don't really want to shell out for a servo if that won't make any difference.

Is there some way to test the servo itself?

Also, if it has failed, is there an aftermarket part? I saw some secondhand ones on fleabay from a caddy for 60 odd quid but i prefer new if i can get it.

Many thanks for any tips

David

After some more searching online i found the following info (in case someone else would like to know)

(Courtesy of pagid.com)

To test for correct servo action, follow the instructions below:  

Test 1 Pump the brake pedal with the engine off until it becomes stiff and doesn't travel.   

Test 2 Press the pedal with some pressure, start the engine and the pedal should travel as the vacuum should increase.   

Test 3 Disconnect the vacuum pipe. Connect to gauge to check for vacuum with engine running (min of 0.5 bar negative pressure). If there's low or no vacuum, check the pipe, connections and pump (if it's a diesel vehicle) and replace as required.  

I hope this is useful

I saw also during my search some posts recommending a golf mk2 master cylinder and servo conversion for improved braking.

Can someone confirm that if buy a mk2 master cylinder and servo together, will they bolt straight on?

Since i anyway likely need to buy a servo i might go for that if it fits straight in

Thanks for any help

David

Hi David

Regarding replacing the servo, there’s a full how to in the technical section, it walks you through a full upgrade on the servo / master cylinder, plus a list of all the parts required.

good luck.

Cheers

Thanks

OK, I had a good search around the forum and found all kinds of posts about fitting a mk2 gti 16v servo and master cylinder as a replacement.

Although it looks like a good conversion, I think I am just going to try first replacing the standard servo.

I had a look at it and I found this printed on the servo:



I suppose that is the oem part for my 78 Scirocco, I had a look around for a replacement using the part number 172 78 4 S but nothing appeared, so I am wondering what that brand name is? (maybe that can help my search)

Thanks for any tips.

David

Before fitting bigger servo etc and spending time on money swopping the servo check what's fitted to the car.
My 1978 Mk1 has the older style brake calipers with the small square pads, what's fitted to your car?
What brake hoses are fitted, braided or rubber hoses?

I did find it a pain to bleed out all the air when I rebuilt my brakes.

The brakes on a standard Mk1 Scirocco with the small pads are not great but you should be able to lock up the front wheels if you press hard enough.
They will feel rubbish if comparing them to a 2009 Passat with ABS all Mk1 Golf and Mk1, Mk2 Scirocco suffer from the servo being the wrong side of the car with lots of linkages which can wear or have been dismantled and re assembled and not set up.

What happens if you have the engine running and press the brake pedal and hold it on hard, does the pedal slowly drop to the floor?

Oh just spotted you are in Belgium so I guess your car is left hand drive…

Later VWII type calipers with the bigger pads are a direct swop, the VWII calipers is fitted to VAG cars up to 2000 ish so plenty about.

Early small pads you probably have fitted to your car.

https://www.ebay.co.uk/itm/VW-MK1-golf-1-5d-front-original-full-brake-set-calipers-and-carriers/163886290912?hash=item26286257e0:g:YWMAAOSwDCFdkmoy

Later VWII calipers you want, you will need carriers etc..

https://www.ebay.co.uk/itm/MK1-GOLF-GTI-239mm-front-brake-calipers-carriers-Genuine-VW-AUDI-refurbished/184208749955?hash=item2ae3b27583:g:3rwAAOSwY5pegh81

https://www.ebay.co.uk/itm/VW-GOLF-MK1-MK2-SCIROCCO-CABRIOLET-CADDY-FRONT-BRAKE-CALIPER-HOUSING-PAIR-A555/192487688239?hash=item2cd129082f:g:4LgAAOSwTvFasRJ1


Or you can go bigger discs with different calipers again but a servo upgrade is a good idea at this point…

Make sure that your vacuum pipe isn't cracked or holed and that you don't have a issue on the grommet that the check valve goes in to the servo…. could be a simple fix, as when my Diesel Vacuum pump broke taking out the vacuum to the booster…

Thanks a lot for the suggestions.

Briano1234 said

Make sure that your vacuum pipe isn't cracked or holed and that you don't have a issue on the grommet that the check valve goes in to the servo…. could be a simple fix, as when my Diesel Vacuum pump broke taking out the vacuum to the booster…

The pipework looks together, I can't see the grommit you refer to?




What do you think?

There is a kind of daisy chain of parts on that pipe, all of which might leak on that hose, maybe I should get a new pipe and clamp it all with new clamps, but what are those other plastic parts? could they also be causing an issue?

My current thinking is that the servo has corroded through and so needs to be replaced, Ideally I would also replace the mc at the same time.

Maybe I can blast and paint the master cylinder if it is a very expensive item or hard to find.

I am a little nervous as I still have not manage to find a replacement part for the servo part number shown in the last photo (172 78 4 S) and I am not really sure where to look next.

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here are some more images for general info, in case it speaks to anyone here:











Thanks for any suggestions or info.

David