vacuum booster. fixable?

[red89diesel]

So, I've (very) gradually been fixing a number of brake problems with my 89 NA diesel jetta.  Replaced the wheel cylinders, one caliper (because of a broken bleeder valve, that eventually got a broken easy-out tool stuck inside of it.....), all the lines, and now the master cylinder.

The whole job started because my master cylinder was leaking a lot of fluid into my vacuum booster, causing my brakes to seize up after driving for a few minutes.  After installing the new MC the first time, I noticed that there was a small amount of fluid coming out between the MC and the booster.  I assumed that it was probably just the small amount of fluid that I hadn't managed to turkey-baster out of the booster when I had the MC off, and decided to take the MC back off and try to clean out the booster a little better.

Now (and this wasn't a problem before), the sort of bullet-shaped piece inside the booster that fits inside and applies pressure to the master cylinder is detached from the rings that would hold it in place in the booster.  Do y'all think I need a new booster, or could I just fit that piece back into those rings and put it all back together again?  

Nothing looks bent or broken or anything inside the booster; it looks like the piece just worked its way out of place when I was pulling the MC off the second time.  I just don't want to put it all back together again only to find out that I do in fact need to replace the booster......

Thanks in advance,
Constance

[bajacalal]

I know this is an old post but nobody ever replied.

I thought if your master cylinder leaks fluid into the booster you need a new/rebuilt booster. It eats the rubber diaphragm parts inside the booster. When I used to work at a parts store we would not offer a warranty on a booster if you could see brake fluid had got in it and we would sell boosters with the master cylinder already attached for this reason.

[red89diesel]

Hey, Thanks for your reply.  I ended up replacing the booster.  I put a new master cylinder on first, and then decided to replace the booster.  I think the old booster may have damaged my new master cylinder (I think the non-adjustable booster pushrod was too long).  So, now I think I might need another new master cylinder (Agh!), since there's a very small amount of fluid on the inside of the new booster now (just on the metal coil spring, not on the rubber diaphragm).

Do you know how to adjust the vacuum booster pushrod properly?  The one on my new booster is adjustable, and seems improperly adjusted, but I'm not sure how to tell if it's right without a lot of trial and error.

Thanks again!
-Constance

[bajacalal]

First, do you have the relevant manual for your car? It would help.

Ok, replacing the m/c is a pain in the @$$. Buy a good quality m/c, you don't want to keep doing this. I have done a number of them on different cars. I always have problems trying to get all the air out of the cylinder. Any little bubble of air is going to cause a soft master cylinder. First bench bleed it real good like the instructions that come with the m/c say. I still usually have to bleed all the brakes a lot to get all the air out. A pressure or suction device (I use the suction tool) meant for bleeding brakes with only 1 person really speeds up the process and it still seems to take forever.

As for adjusting it, I have not seen an 1989 VW but there is usually an acorn shaped nut on the end of the pushrod that can be turned for adjustment. Check the free play at the pedal and adjust accordingly. Usually you don't have to disconnect the brake line tubing, just separate the m/c enough from the booster to turn the nut. I will look at my manual when I dig it out to be sure. In the past I measured the protrusion of the pushrod on the old booster and set the new one to match and it was fine with that except for once I think.

[red89diesel]

Thanks.  I do have a manual.  The manual says that the pushrod should not need adjusting, and doesn't describe how to adjust the pushrod if it does need adjusting.  My guess is that the factory part that came with the car wasn't adjustable.  And, I do know how to adjust the pushrod, just not what length I should adjust it to.  I returned my old vacuum booster the the shop I bought the new/rebuilt one from as a core, so I don't have it now to compare....I will remember that next time, although I'm not sure that the old one had a pushrod that was of the proper length in the first place.

Thanks for your help!

[bajacalal]

You are correct... Now I feel dumb because my 2 VW manuals do not discuss this adjustment.

I would think a good rule of thumb is that the brake pedal should have just enough free play that you can push the pedal just enough to turn the brake lights on before you start to lightly activate the brakes.

What problem are you having with it and why do you think the adjustment is bad? If the pedal feels too soft and the brakes don't work well this is usually air in the lines. When you replace a m/c the air is not always easy to bleed out. If the pedal is hard but only at the bottom of its stroke (on cars with drum brakes) you usually have rear shoes that are riding too far from the drum.

[red89diesel]

Hm.... well, there is definitely air still in the lines. The reason I think it's too long is that I'm working under the impression that a properly adjusted pushrod will produce some sort of minor eruption of the brake fluid in the reservoir when the pedal is depressed about 1/2".  I wasn't getting anything when I pushed in the pedal, and then, I turned the pushrod in a lot and there's still no sign of movement in the brake fluid reservoir.

The main reason I think I need to replace my new MC with a new MC is that it seems to be leaking a very small amount of fluid into the booster already.  I was thinking that maybe this could've been caused by the pushrod being too long before I adjusted it and messing with the seals in the MC.  Do you know if that could be the case?  I'm not really sure what causes a MC to leak - I just know you can't fix it once it starts happening, and if it is being caused by my booster pushrod, I don't want to mess up another MC while testing different pushrod lengths out.

[bajacalal]

If you don't see brake movement in the brake fluid when you pushed the pedal, I suppose it could just be way the VW master cylinder is constructed that doesn't allow you to see it. Can you tell the liquid inside the booster is indeed coming from the master cylinder and not just condensation or something leftover from the factory?

I don't know how you drew this conclusion that the pushrod was too long. If the pushrod was poking out and was depressing the master cylinder way down when you installed it then yes, but now you may have retracted it too far so it is not pushing the master cylinder when it is supposed to. 1/2" is not much and from my experience that is usually the amount of free movement you get before pushing the master cylinder.

I think the leak would be more likely a defective master cylinder. Avoid Chinese crap autoparts. I don't see how it could start leaking from the long pushrod, it would bottom out but I don't think it should leak unless you were forceful with it. I guess it could leak if you pushed the master cylinder a lot without the brake fluid to lubricate it. I have also seen master cylinders fail after you bleed the brakes. This is caused by pushing the pedal past its normal range of motion, which damages the seals if there is corrosion in the master cylinder past the normal range of motion. This usually happens on old master cylinders or where the car sat for a long time without being driven allowing corrosion to build up.

Also I think you should try to get all the air out of the lines before attempting to make brake adjustments. The brakes will never operate correctly with air in the lines.

[Zulfiqar]

When I replaced my honda hackjob MC and booster to the original VW parts I ran into rebuilding them first then installing them, being a RHD mk2 it is a very ROYAL pain in the a** job to put in, remove inlet manifold etc...

anyway

you should have just about 1.5 or 2 mm preload of that finger into the MC when you attach it, not more and if you are leaking fluid into the booster - your O ring living at the edge of the MC along with the holding bush is leaking or is installed incorrectly.. -