No rear breaks.

[Tangis 10]

Hi.

 

Sorry if my english is bad, but I'm not from an English speaking country.

 

I had two Corrado's back in the 90's, so when this project G60 showed up in the right colors (Black with beige leather), I just had to get it. This weekend I changed the breaks. Lines, calipers, pads and discs. But when it came to bleeding the breaks I ran into a problem. There is no fluid going to the back.

 

My bet would be the master cylinder, but I figured I'd check online if anybody have any experience with this. The break system in the Corrado was fairly complicated for its time, so maybe it has some safety features that I don't know about that disconnects the fluid from a circuit if it leaks badly or something like that? I loosened the rear break line directly on the master cylinder, but the break pedal was still hard and no fluid comming out.

 

There is no battery in the car, so IF it has a safety feature like mentioned it might be something electronic? Anybody knows? Or should I just get a new master cylinder?

[paddy26 3]

Does it still have the brake bias valve on the rear axle?

You should check that it is open when you are bleeding the brakes.

 

Edit: just re-read you post and see that there is no fluid when you open the pipe at the master cylinder.

Sounds like the master cylinder :(

 

\Paddy

Edited October 1, 2013 by paddy26

[Tangis 10]

Hi Paddy, thank you for your reply.

 

Yes, by the “method of elimination” I first opened a line on a caliper, then the input on the brake bias valve, then on the “T-splitter” right before the valve, and finally on the master cylinder. Still the pedal does not go to the floor and no fluid is coming out. So I’m afraid you’re right, must be the master cylinder.

[Tangis 10]

Hi Paddy, thank you for your reply.

 

Yes, by the “method of elimination” I first opened a line on a caliper, then the input on the brake bias valve, then on the “T-splitter” right before the valve, and finally on the master cylinder. Still the pedal does not go to the floor and no fluid is coming out. So I’m afraid you’re right, must be the master cylinder.

[Dox 22]

If you have front brakes it can't be the master cylinder. Is the car jacked up on stands? If so the load compensator will reduce the pressure to the rear brakes. You need to replicate the rear suspension under load of passengers to fully open the compensator valve.

[Dox 22]

What happens if you open one of the lines before the compensator? Does fluid come out?

[Tangis 10]

Since my last post I have tried a few things, but the result is the same, no brake fluid going to the rear.

 

AS mentioned in my first post, we traced the problem all the way to the master cylinder. We did this by first opening the line at the caliper, then before the compensator and then on the master cylinder. No fluid came out any of those places, and the brake pedal stayed “hard”.

 

That led us to believe the problem was the master cylinder itself, so I got a “new” refurbished one. A couple of weekends ago the old one went out and the new one in, but the result is the same, no fluid comes out of the master cylinder for the rear…

 

Talked to the shop I got the new master cylinder from, and they said the G60 cylinders are pretty complicated and it had to be “something electronic” that did not work.

 

To be 100% sure, and since I have other G60’s with the same cylinder, we checked the master cylinder on one of the other cars. It worked perfectly with fluid going to the rear and everything. So earlier today we removed the cylinder that we know works perfectly over to the Corrado, and the result is the same as before… No fluid going to the rear.

 

This leads me to believe that the brake shop is right, that it has to be “something electronic” in the corrado that does not work.

 

Anybody have any idea at all what might be the problem? Everything that has to do with brakes is now new in the corrado, master cylinder, lines, hoses, calipers, pads and discs. But still no rear brakes.

[VW_OwneR_85 1]

you put in new brake lines, copper? , make sure fluid can pass through them, a flared joint might not be finished properly causing a blocked pipe????

[buttles 0]

And your English is better than most from this English speaking country!

[Tangis 10]

you put in new brake lines, copper? , make sure fluid can pass through them, a flared joint might not be finished properly causing a blocked pipe????

 

Put in new brake lines, yes, and tested them with air. The flow is good all the way from the master cylinder to the caliper. The problem is that there is no fluid comming out of the rear output on the master cylinder when it is installed in this car. Works good in the other car. A very strange problem...

[Tangis 10]

And your English is better than most from this English speaking country!

 

Thank you :-)

[vw rule 19]

Hello there,

 

if your G60 is fitted with ABS then you need to have the engine running. This is due to the valve / valves being closed inside the ABS unit, which is in the engine bay.

 

When the engine is off the pressure in the brake lines will drop over time,

and more so if vehicle has been left for a few days or a week.

 

Once the engine starts up the ABS goes through a 10 to 30 second or so check, one of which is checking pressure in the braking system.

 

Basically the valve / valves in the ABS unit open up slightly

but not fully, so allowing the fluid to pass through to all area's in question.

 

Plus on the master cylinder normally you only have 2 brake pipes connected into it, one is the feed to ABS unit, & the second is the return from ABS unit to master cylinder, this is so you have all round circulation but only when the engine is running.

These valves only open up fully when the ABS system has to kick in to stop the wheels from skidding under very heavy braking,

assisted by the ABS pump,

which pumps fluid very rapidly to all four brake calipers, which in turn prevents the wheels like I say from locking up / skidding.

 

Also the Brake pedal will feel hard when the engine is off as you won't have any vacuum assistance,

you obtain this through the brake servo which has a diaphragm inside it, the master cylinder is bolted to the front of the brake servo, and passes through the inner center diaphragm and connects to brake pedal.

Once engine has started up the brake pedal should feel alot softer as the vacuum will be obtained from the inlet manifold,

from every suction stroke of the engines pistons.

 

When you bleed the brakes NEVER NEVER press the padal flat to the floor,

or you'll damage the seals inside the master cylinder,

(seals will flip the other way, or could let brake fluid pass and become weakened)

Only press the brake pedal down half way, just like with normal braking, this way the inner piston in the master cylinder will move to the same place every time, and so won't be pushed any fervor than it should be.

 

All seals in the braking system i.e master cylinder, calipers, brake compensator axle valve, ABS unit, all have to be air tight and must be dry no brake fluid on them.

 

Some people rebuild calipers and coat the rubber seals with brake fluid, THIS IS 100% WRONG.

The brake fluid is only ever in contact with the inner side of the seal, it never touches the front or outer side of the seal, not unless the seal is old and warn out due to friction / heat damage.

New caliper rubber seals or any seals in the braking system must be fitted in dry, with only the proper silicone grease being used.

This grease is orange or red in colour. This grease helps to keep the piston or the handbrake inner gear lubricated, plus it helps to stop the seals from swelling coursed by high temps, friction or from brake fluid it's self.

 

Have you ever looked at a caliper piston, when you pump the brake padal softly a few times, and the piston comes out a little it is always dry, you shouldn't see any brake fluid on it, if you do then the inner rubber seal is warn, meaning it's letting brake fluid past it, WHICH IS HIGHLY DANGEROUS.

 

NEVER NEVER strip and rebuild brake calipers or master cylinder yourself, unless you 100% understand and KNOW what you are doing,

because if anything fails on the braking system that you've touched, then you'll be solely responsible for any error.

 

 

Remember that on the Corrado if ABS is fitted,

when you're bleeding the brakes fluid will only just drip out of the bleed nipples or not at all,

when the engine is switched off.

 

When the engine is running you'll have both,

the vacuum assistance and the hydraulic pressure with in the braking system.

 

 

Hope this helps.

 

Si

[Tangis 10]

Thank you very much vw rule!

 

Now I have a few more ideas that we can try.

 

We did try a bit with the engine running, but maybe not long enough.

 

I notice you write that the fluid will only drip out the bleed nipples or not at all when the engine is of. I guess that means there is something wrong with the ABS unit if the flow does not increase after the ABS is done with it's check?

 

I'll try some more with the engine running.

 

And thank you again!

[Tempest 0]

Just to possibly ask the obvious: Is your G60 a left-hand or right-hand drive car? All left-hand drive cars have the so-calle Mk02 system, where you do not have a brake servo rather than a pump-driven system which pumps up brake fluid to approx. 150 bar and stores it in a pressure accumulator to then assist braking. When bleeding the rear brakes on these systems, you need to turn the ignition key - not start the engine - so that the brake system pump starts, then open one of the rear caliper bleed nipples and press the brake compensator located near the rear axle beam. The brake system pump does all the work, pumping the fluid through the bleed nipple. Do not run the pump for more than 120 seconds, otherwise let it cool down before you activate the pump again.

 

If your G60 is a right-hand drive car follow vw rules advice.

 

Tempest