help setting up booster delete and retain ABS

[e30_302]

Wilwood says you can get full line pressure with the knob turned all the way out, but I don't believe it. Maybe it's my imagination but my car stops better without it. UUC front kit, stock rear, Fox Mustang master (21mm), and I still want more rear brake bias.

[TobyB]

The proportioning valve can only reduce rear brake pressure- if your front calipers are
bigger than stock hydraulically, then you'll have increased front brake, not rear.

The stock early ABS leaves the (pretty close to ideal) 70/30 split, then adds abs on
top of it. It has a valve in the rear line, but it doesn't SEEM to be a proportioning
valve, more a 'delay' valve to keep the rears from getting pressure before the fronts..

The later ABS uses that funky split (22/17?) master cylinder. I initially thought they
ran the 17mm to the back to add extra rear brake that the ABS then modulated out
when you braked hard, but it's been too long since I took it apart.

As to bench bleeding, that's a Chevy thing- they love it. Sometimes a bubble gets stuck
in the master, and it's a bear to get out, but usually you can pop off the offending
line, let it bleed into a bottle, then reattach successfully. I have a cut- off piece of
brake line and tubing that works pretty well for that. I've used it twice- once on the 2002,
once on an RX7.

The other thing generically I've found- hit it with a hammer. As in, tap the calipers a
few times, and re- bleed. Sometimes that helps with the smaller air bubbles that love
to stick to the castings and not float up to the top.
Also, go out and romp on it. Heat and vibration will help float air out, and the pressure
will seat the pads and get mechanical spring out of things. It's a little contradictory,
as you'd like good brakes BEFORE you go, but it often works.

hth

t

[FredK]

It does sounds like there's still air in the system, unless your front BBK total piston area is something insanely large.

Do you know what size pistons you have in the Wilwoods?

[Sh3rpak!ng]

Initially, I suspect the proportioning valve. in theory, you don't need it with ABS. Altho
I see why you'd want it... but it could be messing with the valving in the ABS.

And then, looking at how the ABS pump is so low, I wonder if maybe air's getting trapped
in your (very pretty) brake lines somewhere.

Beyond that, yes, a 22mm master will shorten your travel, but give you an even harder pedal.

...aaaand that's about all I know.

t

Thanks. Wouldn't I need the prop valve to help balance the front/rear brakes? Especially now that the fronts are much more powerful than they were before? I mean, even originally the car has a fixed prop valve. Also these abs units are in several models with different braking requirements...

And regarding ABS placement, yes it's lower than before, but it was always lower than the reservoir/MC even as original. Same with most of the lines if you compare, I didn't drastically change the geometry I don't think

Someone pointed out that the MC should be bench bled before installation and before bleeding the calipers. I didn't do that, actually never heard of it, and even the paperwork that came with the new MC didn't say anything about it. After further reading, kinda sounds like that's an important step. Do you think that could cause the issue? Still trapping air in the MC somewhere?

Try taking the prop valve out. You're cutting rear pressure and don't really need to. Helped me at least.

With the valve fully open (it is currently) there is no pressure reduction. And won't I need the prop valve to help balance front/rear bias with the bbk?

[e30_302]

Try taking the prop valve out. You're cutting rear pressure and don't really need to. Helped me at least.

[TobyB]

Initially, I suspect the proportioning valve. in theory, you don't need it with ABS. Altho
I see why you'd want it... but it could be messing with the valving in the ABS.

And then, looking at how the ABS pump is so low, I wonder if maybe air's getting trapped
in your (very pretty) brake lines somewhere.

Beyond that, yes, a 22mm master will shorten your travel, but give you an even harder pedal.

...aaaand that's about all I know.

t

[Sh3rpak!ng]

I am on the tail end of a months long project repairing accident damage, turning my engine bay into a throne for the motor to sit inside of, and totally rebuilding the brake system.

I am using the massive single MC booster delete, a 19/19mm MC from an older VW, retaining ABS (albeit relocated), a rear proportioning valve, front wilwood 4 piston calipers with BP-20 pads and vw corrado discs, rear oem calipers and stoptech street pads (subject to change).

I have installed everything, bled the system 4 times now, managed to jump the relays/solenoids in the ABS unit to cycle it as I bleed (to clear out any remaining air?), and I have a mooshy pedal. The pedal isn't hard at all, it gets progressively harder to press the further I push it until it's nearly at the end of it's travel. At that point I'm pressing very hard and the car slows, but I can't lock up the brakes at all, and I'm really stomping on them. One thought I had was perhaps the MC I chose isn't appropriate for the front calipers. I will be picking up a 22/22mm MC from a vw corrado to try out tonight. If this doesn't improve things, I'll bypass the ABS to see if it's got air in it that I haven't been able to purge.

Does anyone have input on this topic given my described situation? What setups (MCs, calipers, pads) have others run successfully?



Here are some pictures of my system currently.

Overview:




MC, prop valve, and lines running to the ABS:




Detail of the prop valve:




ABS relocation under the driver side fender, directly in front of the wheel:







Lastly, this car's purpose is autox, DEs, weekend canyon carving fun and event/show attendance