Gang,  We need some help.

1995 16v 4dr Sidekick
(had rear ABS, not using diff sensor anymore, haven't disconnected anything except the rear sensor, haven't unplugged any fuses or any connections under the hood)

We are using Toyota Land Cruiser FJ80 axles
4 piston fronts, single piston rear disc brakes.

We've been experiencing a problem with our brakes, that we need some help with.

Symptom(s)

Brake fade after bumps;
When driving over washboards or other rough surfaces the brake system seems to have a bunch of air in it.  IE needs pumping to bring up to pressure to be able to brake effectively.  Meaning the front brakes don't appear to be working at all and the rears are weak.  They can almost be locked up after mashing the pedal on the floor hard, but still nothing from the fronts.  Unless of course I pump the crap out of them, then normal brakes.
(rear brakes seem to work better than front)

Brake fade after water crossing;
Just after having driven through a creek crossing, (could be related to sympton number 1) the brakes need pumping to bring up to pressure.  (again, like air in the lines)  The rears work better then the fronts.

Brake pedal modulation when going over bumps (percieved when only going downhill);
I've noticed that when going over washboards, or other rough surfaces while going down hill.  Slightly applying pressure to the brake pedal (riding the brakes), I can 'feel' the brake pedal modulate under my foot with the bumps.  AND it feels like the brakes work 'better' when they are modulating.  (actually getting 'brake-like' action)  Kinda feels like a modern ABS system on the pedal, where the pedal pushes back against your foot.  However, I think that its because the rear tires bounce off of the ground and lock up slightly.  (very strange feeling)

Street driving,
Unpredictable pedal behavior.
Sometimes the brake pedal feels perfectly like it should, firm and solid.  All wheels can be nearly locked up.  Other times the pedal seems to hit the floor and needs to be pumped to get pressure.  Most often the rears can be locked up and feel like only they are doing the braking.



We've replaced the booster and master cylinder

And have bled the system THOROUGHLY.
Several quarts with the 3 pump then bleed method, starting with the farthest away brake and moving closer to the master cylinder finishing up with the wierd device next to the master cylinder.  (4 doors are different than 2 doors and have some secondary device inline with the brake system with a bleeder cock on it.)  Maybe related to ABS system?

Not ever having serviced quad pistion calipers, is there anything special that anybody can think of?

Maybe the elusive proportioning valve isn't working properly, or maybe it is?  Maybe it needs to be removed/replaced/re-engineered?
(don't know where/what the proportioning valve might be, nor how it may affect my issue.)

Overall, it feels like at times there is air in the system.  The symptoms requiring the pumping seems to be totally random. 

Sometimes the brakes are tight, just fine, right there, even  after long periods of no braking, no pumping was needed.  Just like normal.

Sometimes, the brakes need to be pumped between 1 and 6 times to get good braking power.  Then let off the pedal, drive 2 seconds and then they may need to be pumped again to get the brakes working.

Overall the rears seem to be working MUCH better than the fronts.  They can almost ALWAYS be locked up, even though the pedal is RIGHT near the floorboards.
The fronts however won't lock until I pump the every loving heck out of it a bunch of times and then REALLY lay into the pedal, then, only then may I get a squeak of the tires from the front.

Anybody got any ideas ?

Maybe there is still some air in the lines?  (unbelieveably?)

We are not experiencing any leaks.  No additional fluid has been needed.  All of the pads and rotors are in good shape.  (I haven't rebuilt the calipers yet, but getting close)

Any help, advice, comments you can provide would be greatly appreciated.

Thanks,
~Nate & Heather

I would be interested to see if the ABS sytem
is getting involved even tho the sensor in the
rear is still disconnected, I would look into the
way the ABS is supposed to work, and if "pulling
the plug" on it would have any negative affects,
as in not working properly under normal non lockup
braking action.

Have you thought about replacing the ABS Suzuki
Master Cylinder with the Toyota one from the truck
the axles came off of ?  or just an earlier MC from
a non ABS 4 door (tho I think the MC is the same
between the 2 door and 4 door) just some ramblings
of a mad man

Ohh and make sure the fluid follower is in the resivour
so air doesn't get in the lines during rough rides

Wild

I always heard that the disc caliper has to have residue pressure to maintain the pad on the rotor. The drum situation doesn't as there are springs/arms which pull the shoes off the drum. There is some type of valve in the master's output where the line connects. It's suppose to keep the residue pressure intack. I don't think the proportioning valve does this. The proportioning valve works the pressures between the front and rear lines. Sort of like the 'H' pipe in an exhaust.

Actually, I always thought you were supposed to bleed the brakes from the master cylinder-outward, starting with the closest bleeder valve and ending with the furthest away...

Actually, I always thought you were supposed to bleed the brakes from the master cylinder-outward, starting with the closest bleeder valve and ending with the furthest away...

i was watchin horse power tv ( i think it was that one, it was on the power block this morning) and im pretty sure they said to bleed the brake the furthest away form the mast cylinder

I think your master cylinder is not pushing enough fluid to run those big breaks.  I think Wild is on the right track in that you may need to replace your master with one from A Toyota.  It takes a lot more fluid Volume to move calipers (dual piston especially) than it does to move wheel cylinders that is probably why your rears are kindove working.  The air in the lines feeling is usually caused by a bad master.  I know you said you changed it but that's generally what I've seen be the culprit of what your describing.  That extra unit with the bleeder you were describing is the ABS pump for the rear.  I have one on my 2 door also and I am planning on eliminating it.  If your not using it Id say plumb around it It may be restricting some fluid flow.  (Don't know but it sounds good)  I just don't think a stock master has a large enough piston to push the fluid your system needs.

Thanks for the feedback so far guys.  I really appreciate you taking the time to reading that huge post above and then spending time to provide input.  I know you could be doing other things like working on your own rigs.  So I'm very greateful.

The master cylinder I used to replace our 'failed' one was a used cylinder from another 4 door with ABS.  We left it mated to the brake booster and swapped both together.  Maybe I should try a re-manufactured cylinder from a local parts store, as it does feel like a faulty master cylinder.

I'll also try to remove the ABS column on the inner fender from the system to see if that helps.  (good advice)

It may be true that the 4 piston Toyota calipers are too much volumn for the master cylinder to handle.  Does anybody have any experience with swapping other makes of master cylinders/boosters into Sidekicks to know if any other bolt patterns, or pedal throws match?

It would be neato to think that there is a magic upgrade or even simple upgrade out there.  However I can redrill holes in the firewall and fabricate linkage to the pedal.

Ohh and make sure the fluid follower is in the resivour
so air doesn't get in the lines during rough rides

Darin, I haven't looked that closely at any brake reservoir  to know what a 'fluid follower' is.  Is it like an anti-float, or a ball that falls down when fluid is gone to keep air out?
(I will dig into our old one tonight)

I always heard that the disc caliper has to have residue pressure to maintain the pad on the rotor. The drum situation doesn't as there are springs/arms which pull the shoes off the drum. There is some type of valve in the master's output where the line connects. It's suppose to keep the residue pressure intack

This might make some sense.  During normal street driving the brakes behave ~80% of the time.  They maintain good pressure.  However, go over a speed bump, a dip in the road or potholes and you're back to pumping again, at least until the next set of bumps.  Maybe a valve in this master cylinder is damaged too.

The proportioning valve works the pressures between the front and rear lines. Sort of like the 'H' pipe in an exhaust.

Does anybody have any real experience with the proportioning valve on Sidekicks?  Could it be that I'm getting WAY more pressure to the backs than the fronts?
Could I operate without it and just put 50-50% pressure on all of the calipers?

Actually, I always thought you were supposed to bleed the brakes from the master cylinder-outward, starting with the closest bleeder valve and ending with the furthest away...

This is the link I found on bleeding brakes, and is the method I used.

http://www.stoptech.com/whitepapers/howtobleedbrakesright.htm

Again thanks for your help guys, if any body has any experience with upgrading master cylinders has any advice they'd like to give, I'm very open to listening.  If anybody has any other comments on my situation I'd like to hear it.  I'd like to be able to stop like normal again.

~Nate

I think it might help out your situation if you put in an adjustable proportioning valve.  If your going to remove the ABS your going to have to replumb anyway.  The chances that your stock one is giving you the bias front to rear is real slim.  In addition to that I'd start looking for a master from a donor car with 4-wheel disks.  It shouldn't be to hard to make an adapter plate to mount the master to your existing booster if you cant find one to bolt right on.  The best way I can describe what I think is causing you problems is your trying to inflate a tire (Big Disc Breaks) with a bicycle pump (master), it can be done it just takes a lot of pumping.  When I put the 4door breaks on my rig I found that the master seems to only let a certain amount of fluid back in after you release the breaks, that would account for your good pedal sometimes when your hitting bumps you may be releasing the check valve allowing the breaks to release more requiring the breaks to be pumped back up.  

Just my thoughts at least thats where I'd start.

Patrick

I've just had another thought.
I've increased the length of the rubber lines substantially.

The front lines I've gone from the stock rubber lines to 30" rubber lines.
The rear line, I've gone from the stock line to 30" rubber line.

Do rubber lines ballon and consume volume?

Would it be beneficial upgrade to braded steel lines to possibly reduce line balloning?  (I understand that steel braded lines are not US DOT approved.  Is this true?

Rubber lines do swell but not to much when there new.  I've never heard of steel being illegal why would all the lift kit manufacturers include them in there kits if they were.  IMO steel is better and it won't hurt to swap them.

Oh yea that reminds me if you want to cut down on the flexible lines you can run a hard line down to your spring put a short flexible line in to jump onto the spring and back to hardline for the rest.  I did that on my scout and it worked great.

when I had my toyota with discs all around I had a similar problem. The calipers are solid mounted due to the 4 pistons. I had a combination of slightly warped rotors and worn rear wheel bearings allowing some slop.

When I would go wheelin or lots of corners the axles/spindles would walk side to side and push the pistons in. I would have to pump the brakes to get solid pedal feel. I installed a 2lb. residual valve to the rear and it solved my problem.

when I had my toyota with discs all around I had a similar problem. The calipers are solid mounted due to the 4 pistons. I had a combination of slightly warped rotors and worn rear wheel bearings allowing some slop.

When I would go wheelin or lots of corners the axles/spindles would walk side to side and push the pistons in. I would have to pump the brakes to get solid pedal feel. I installed a 2lb. residual valve to the rear and it solved my problem.

I'm thinking something similar, you're getting some extra movement when wheeling and its pushing the pads back. It sounds very similar to what used to happen on some early Ducattis with floating discs, over the bumps the discs rattled about more and pushed the pistons out so there was no braking initially. Try pulling and pushing at the tyre with it jacked up, can you move the wheel in and out, there may be some movement in the bearing housing or you may have some play in the bearings. Are the rotors running absolutely true and square to the calipers?
You do need more fluid to move the pistons in the calipers, I have found this with my rear disc conversion. The residual valve is supposed to help but they are really designed for hot rods and sports cars that have their master cylinder lower than their calipers, they prevent the fluid from being syphoned out. You can also get them for drum braked cars but they require an even higher line pressure (10lbs)

Im thinking that the modulation I feel on the bumps might be caused the rubber hoses flexing with the bumps and changing the ballooning characteristics of the lines?

I say this because the brake caliper mounts are stock for the axles.  These aren't home made or custom build caliper mounts.  They are direct pulled from a stock Land Cruiser.

It could be that the bearings aren't tightened down enough and have some slop.  I'll definately double-check this also!

Keep em coming.

~Nate

So to summarize some potential easy solutions.

Go braded lines, reduce line ballooning.

Double check bearings/warped rotors/pads for rotor slop. Basically pushing pistons back into calipers.  (I think I'm good here, but can check again easily)

Remove ABS components from system.  (replumb lines as necessary)

Check fluid follower in reservior.

More involved solutions;
Upgrade master cylinder
Upgrade master cylinder/booster
Install adjustable proportioning valve.
Install residual valve to keep line pressure up.
I've also heard about swapping front and rear lines at the master cylinder.
I've also read that Jeep and Ford MC's might fit on Sidekick boosters.

More advice is very much wanted!