How can you test a 1994 mk3 Golf td brake servo or vacuum pump

[tsam19]

Put new brake pads/shoes all round & fresh brake fluid & bled correctly.

Replaced the servo pipe that connects from the brake servo to the vacuum pump as it was leaking due to a split pipe.

However I don't understand why the brake pedal is still spongy when applied during driving & I get the impression there are no brakes ?

The pedal travels quite near to the floor, any further & it would touch.

Having driven the same reg car (M) there is a vast difference in the feel of the brake pedals on both cars, that is as soon as you touch the pedal the brakes are apparent, but on mine the symptoms are above.

Basically having done all that work I would expect the brake pedal to be as tight as you would find in a new car or there abouts.

The only thing I can think of that may be causing the problem is the servo unit
itself ??

Or possibly the vacuum pump ??

Or the master cylinder ??

What is the purpose of both units - brake servo & vacuum pump & master
cylinder ??

If anyone can shed any light on the thread thats great.

[BobProperty]

You're not going to like me but either you haven't bled it properly (possibly due to some quirk of the brake system) or you've had the master cylinder go. Those would be my initial reactions to the symptoms you are describing.

[tsam19]

I've always used 2 people to do this job.

The way I bleed the brakes usually is to connect the brake bleed pipe to the brake caliper nipple & the other end submerged into a clean clear glass jar with enough brake fluid in it to cover the slit in the end of the pipe.

Pump the brake pedal slowly watching for air bubbles in the glass jar, then when they stop appearing if any.

Get the pedal man to press pedal down then raise the pedal slightly - sort of mid way position & keep it there until.

Then lock off nipple & move to the next brake nipple, one at an angle to the last one.

Then repeat.

If thats not right then I will have to find the correct way to do this job.

Alternatively if this is the correct procedure & it is the master cylinder at fault.

How would I know for sure that it is the MC & not the vacuum pump or servo ?

[STEWY L]

You're not going to like me but either you haven't bled it properly (possibly due to some quirk of the brake system) or you've had the master cylinder go. Those would be my initial reactions to the symptoms you are describing.

i must agree with the above post.
i assume the pads/discs were worn to bring about the affore mentioned all round replacement of all pads and discs, and that the current problem did not exist until this work was carried out?
it either hasn't been bled correctly mechanically,or the vag com hasn't been present,(i believe it is almost a must, but i'm only guessing on that side of things so could be miles away),
having typed all of that,originally, perhaps the pedal was on the floor,
and wrongly diagnosed as pads /discs?
these have been changed,but the real fault is still present,i.e. master cylinder?
if it was easy,the bills from garages would be less.
that's the bills we all strive to avoid?
regards,
stewy.

[quicksilver]

Hi you say you replaced pads and rear shoes if so and you have rear drum brakes have you adjusted the rears correctly before replacing the drums or are you just relying on the auto adjusters?

[BobProperty]

I've always used 2 people to do this job.

The way I bleed the brakes usually is to connect the brake bleed pipe to the brake caliper nipple & the other end submerged into a clean clear glass jar with enough brake fluid in it to cover the slit in the end of the pipe.

Pump the brake pedal slowly watching for air bubbles in the glass jar, then when they stop appearing if any.

Get the pedal man to press pedal down then raise the pedal slightly - sort of mid way position & keep it there until.

Then lock off nipple & move to the next brake nipple, one at an angle to the last one.

Then repeat.

If thats not right then I will have to find the correct way to do this job.

Alternatively if this is the correct procedure & it is the master cylinder at fault.

How would I know for sure that it is the MC & not the vacuum pump or servo ?

I'll answer the last question first. If the pedal goes to the floor, the brake hydraulics aren't right, the servo etc. are irrelevant.

How I would bleed a brake system*:
(Tube, jam jar etc. as your description.)
Starting with the furthest brake from the master cylinder, assistant presses brake pedal down slowly. Open valve, let old fluid and air out. As assistant presses pedal near to floor, close valve. Assistant lifts pedal slowly. Check fluid level. Repeat until only bubble free, clean, new fluid comes out of valve and brake pedal is "hard" when assistant presses it while valve is closed.
Repeat whole process round each brake in turn ending with closest to master cylinder.
Stand on brake pedal for some time to make sure it doesn't go down slowly. (If it does you've most likely not fully closed a valve. Otherwise, rejoice in the knowledge that you've probably discovered a leaking slave cylinder and you've also probably just got brake fluid all over a set of pads )
Road test alone.

(*With my luck I sometimes find that there is a one-way valve/split system/balance valve/something else in the pipework which means what I just did wasn't completely effective and you have to find some details out as to how to get round the situation for that model. )

[tsam19]

Having owned & driven the car for a few years now, having checked the brake pad/shoes condition on a regular basis.

I know when the brake pads/shoes need replacing.

I don't need & have never connected a 'Vag Com diagnostic device to the car for it to tell me the brakes need changing !

However if your saying that after all the work I've done I need to connect a vag com device to the car to reset whatever needs resetting in order for the brakes to work properly, I don't have one & I'm not paying a garage to connect one just to reset the cars computer.

I don't think its that technical after all its a 1994 MK3 Golf !


When I bought the car the brakes seemed ok, the pedal was never on the floor, otherwise I wouldn't have bought it

Now that the time has come to replace the these bits, which is normal over time due to usage etc.

I guess the pedal is still near to the floor as it was before & is still spongy when pressed when bringing the car to a stop.

In comparison with another car of the same age & mileage etc.

This braking system seems poor.

So maybe the problem was there all along ie the 'Master Cylinder' or similar is unserviceable causing the spongy soft feel instead of the solid platform you should feel under your foot when braking with new all round pads/shoes etc ?

[BobProperty]

Hi you say you replaced pads and rear shoes if so and you have rear drum brakes have you adjusted the rears correctly before replacing the drums or are you just relying on the auto adjusters?

Something in the back of my mind says that you can put some back brakes together wrongly such that they appear to go back together but the slave cylinder doesn't make contact correctly.

[tsam19]

For the back drum brakes I've always relied on the auto adjusters & have been advised by many mechanics that the front pads & discs will always wear out 1st before the back, due to 80% of the braking done by the front of the car & the remaining 20% at the back.

So initially you'd go through say 3 sets of front brakes before having to replace 1 set of rear.

The way the shoes sit in the rear drum is pretty straight forward.

The Haynes manual seems to explain the remove & refit procedure best it can, so I can only follow that advice really.

[quicksilver]

Hi the reason i asked if you adjusted the rear brakes before fitting the drums is that in my time i have had many brake problems caused by badly adjusted rear brakes causing the wheel cylinder pistons to travel too far when trying to bleed.
if you pump up the pedel do the brakes feel any better?