Speeddemon944

Hi,

89' Turbo S w/ABS Big Blacks up front - stock rears. Crossdrilled rear - slotted floating fronts from VCI.

So I have been chasing this squishy brake issue for sometime now and need some help/ideas.

Things I have done -

New front Calipers
Stainless lines (Front/Rear)
Swapped ABS pump
New Master Cylinder
New fluid
Brake ducting

During bleeding I got a ton of this weird silicone looking stuff came out and we are talking quite a bit. I bled the S**t of the brakes and the silicone stuff is gone. It only cake out of the rears.

The brakes feel nice and hard with the car off. Once she is turned on then they seem to soften quite a bit.

The only thing left is new rear calipers but at $850 a piece from the dealer I think I want to rebuild them first. So with that in mind -

What am I missing?
Have any of you tried to rebuild the 4-piston rear calipers? if so, how well did or did it not work?
Rebuild kits from the dealer run $70 a side so about $300 - this includes the pistons. Is there a place to kit just the scraper ring and assorted O-rings?

TIA

cajuncroc

I had the same problem with my S2 racecar. I assume the master has been checked for leaks. I would also test the check valve on the booster. It should just pop out, and you should be able to suck, but not blow through it.

I finally had to re-adjust the brake bar that connects the brake pedal to the brake booster. It's very sensitive, a half turn-the back brakes would lock up, or a half turn the other way the pedal would have a lot of travel before the brakes would engage. The locking nut is 17mm (a crawfoot works best) and I think the bar itself is 7 or 8mm.

Speeddemon944

Thanks for the input. I will check both!

NM'87 951

I second the vacuum issue. Sounds like assist isn't working right.

Tiger03447

Well, with an '89 model car there are several items you might want to look at..#1 has the master cylinder been bled recently? Possibly air got into it when refilling with the new fluid. #2 could be bad flexible brake lines. might need new ones; old ones can go bad from age and you would never know it. #3. bad brake booster

Any signs of leakage back through the firewall or where the master bolts to the booster? Any fluid in the booster? Both might indicate a bad rear seal in the master..just some things to check over..thanks.

Speeddemon944

Quick Update -

1. Brake pedal rod checked - OK
2. Master cylinder was bled after I replaced it - I used both the motive pressure bleeder and then a human in the drivers seat. I cracked the lines going to the ABS pump and the individual lines going into the calipers I had my assistant pump the pedal until good solid streams came pouring out. Then I bled them via the bleed valves on all calipers.
3. In my OP I mentioned that the rubber lines had been replaced with stainless lines via Paragon.
4. No fluid in the booster

I still need to check the check valve. No leakage behind the firewall.

Any sure-fire way to check for firewall flex?

Oddjob

Has the car always had this problem/feel, or something has changed? How do the brakes feel on track? What fluid are you using?

This is odd. Color? What do you think was the source of this? Something left in one of the components that you swapped (ABS pump, MC)



Does the pedal push to the floor?

Speeddemon944

The previous owner (Dad) had been chasing this issue for awhile not sure exactly when it began. He was the one who swapped the ABS and front calipers. Fluid was Ate Super Blue - I flushed to Ate Type 200. On the track they are quite soft and get softer as the session goes on.

Ok, so regarding the silicone stuff...my best description of it is that is looks like...jizz I have gotten all of it out as far as I can tell.

No, the pedal does not go to the floor under any scenario.

I checked the check valve and it is good (via the blow/suck test) and when I pulled the check valve a bunch of air rushed into the booster so I know the booster is good as well.

My latest theory is this - The read calipers need a rebuild.

Reason - I have fluid come out of the top of the reservoir after track sessions due to heat (I am ASSuming). I think the rear calipers are not pulling the pistons back like they should and are causing the fluid to heat up. I have noticed some weirdness on the pad recently (almost like it is crumbling apart). So I have some rebuilt calipers on the way..

I have NEVER had brake heat issues with this car once I got the usual items done - ducting, floating rotors, fluid, SS lines, etc... I fact the brakes WERE so good on this car that I did the same things to my spec car and use Hawk DTC-60/70 in an attempt to replicate the "feel" and performance of the turbo's brakes. I did get really close too.

Thanks for your help and keep at it guys (and gals) it is helping!

mytrplseven

I wonder if the wrong type brake fluid was used at some point and caused the contamination of the system. You mentioned a silicone looking stuff in the lines.

kevin12973

I thought I heard when bleeding ABS it helps to take the car out on a gravel road and brake hard to engage the ABS to purge the air through the module? Maybe bull sh!? but thought it may spur discussion.