saggy brake issue

ds1919 · Aug 11, 2010

oops I meant Soggy brake issue:

86 Bronco II 4x4

Replaced- master cylinder,front calipers,front brake lines, rotors and pads, rear wheel cylinders, rear shoes, turned drums.

A while back I replaced my front pads. Before I did this, everything was fine, and the braking system was top notch. After the pads, it was saggy. So I thought it was the rear stuff, and I replaced everything back there. Then I replaced the master cylinder. I have bled these brakes over and over, step by step according to my manual. They just dont work like they did before. The brake pedal feels like it goes all the way to the floor, or the master cylinder pistons are pushed all the way in, make sense?

I have not done two things that I can think of: replacing the brake booster, and adjusting the rear brakes.

Would either of these have an effect on how well the brakes work?
I feel that the brake booster just makes it easier to press the pedal down, but overall braking should still work if this part is malfunctioning?

Would adjusting the rear shoes possibly fix this?

martin · Aug 12, 2010

The first thing is to adjust the rear brakes. Long pedal travel is just one thing that unadjusted rear brakes can cause.

ds1919 · Aug 12, 2010

welp, I adjusted the rear brakes, and even tho the E-brake works better, it has not changed my soggy brakes...

I think I'm gonna try to find a power bleeder somewhere...

igiveup · Aug 12, 2010

Hello

Try gravity bleeding the brakes. I have done this with my B2, Stang and T-Bird and it works good. Just don't let it go dry other wise you start all over again.

igiveup

ds1919 · Aug 12, 2010

thought about doing that but was worried that air would creep in from the bleeders.

I'm going to try to play it safe and find a complete set of speed bleeders.
My concern is that there may be an air bubble somewhere in the line(s), I hope this method will remove any possible bubbles.

adsm08 · Aug 12, 2010

Well you can rule out the booster. You were absolutely right about its function being to make it easier to push in the pedal.... sorta. It also allows you to apply thousands of pounds of pressure to the brakes. The pedal being easier to push is a side effect.

Did you bench bleed the new master and are you sure you don't have a leak somewhere?

ds1919 · Aug 12, 2010

yes I bench bled the MS before I installed it, but I've always wondered if I did not do it correctly. if there is a chance that an air bubble is trapped in there, what would be the best way to remove it?

I just bought a set of 4 Russells Speed Bleeders on ebay, should be here in a few days. Would those work to remove any and all trapped air? Or do I need to take it into a shop that has the mondo power bleeder to force all the air out?

I looked at all four corners, the MS, and all lines, no leaks. Also, this soggy brake saga has been ongoing for a few years (yeah I'm lazy, its not my daily driver), and the fluid has remained full.

thanks

bd2988 · Aug 14, 2010

Look at the brake booster check valve and grommet. That was my problem when my pedal went to the floor. Raybestos part #CV89000.

adsm08 · Aug 14, 2010

If you have the plastic reservoir you could get a vac pump and a big rubber cone and reverse vac bleed it.

ds1919 · Aug 14, 2010

bd2988 said:
Look at the brake booster check valve and grommet. That was my problem when my pedal went to the floor. Raybestos part #CV89000.

hmm, interesting. when you say that your pedal went to the floor, did you lose all braking?

Where is your check valve located?

Also I see you have a much newer ride, I am not sure if I even have a check valve, I have to go look at my manual...

I still have brakes and they do work even on very steep trails, but the pedal travels pretty much to the floor, but it does stop. No leaks, no fluid loss.

If you could describe in more detail what happened when you check valve broke, that would be great, thanks

bd2988 · Aug 14, 2010

ds1919 said:
hmm, interesting. when you say that your pedal went to the floor, did you lose all braking?

Where is your check valve located?

Also I see you have a much newer ride, I am not sure if I even have a check valve, I have to go look at my manual...

I still have brakes and they do work even on very steep trails, but the pedal travels pretty much to the floor, but it does stop. No leaks, no fluid loss.

If you could describe in more detail what happened when you check valve broke, that would be great, thanks

The check valve is on the brake power booster, there is a vacuum hose coming off of your intake that goes onto the brake booster, and right at the end that connects to the brake booster is your check valve, and the grommet which the check valve pushes into. The part is the same, I checked it on rock auto for your 86 and it is the same part number (for the 2.9l v6). It's only like 7 or 8 bucks. From 86 I'd assume that grommet is probably pretty dried out and cracked.

That's the same as my brake pedal was, it would occasionally work perfect, but other times (usually) it would go almost to the floor but still stop the truck. I'm not necessarily sure the check valve was bad, but the grommet it pushed into was cracked, and for the low price I just replaced the valve too (valve comes with the grommet).

The part only takes 5 mins to install, so probably worth a look. All you have to do is pull it out, take the check valve off the hose, pull the old grommet out. Put the new grommet in, put the new check valve on the end of the hose, and then push it in. Hey, for 8 bucks it's worth a shot.

ds1919 · Aug 15, 2010

Im headed down to the parts store, found the valve and grommet for $10 in town.

Will keep this thread updated, hopefully this will work. Sounds promising :icon_thumby:

greyghost · Aug 15, 2010

Let me throw this in the mix for what its worth.
My Haynes manual says about the booster:

"On 1983 through 1987 models, make sure the booster rubber reaction disc is properly installed if the master cylinder pushrod is removed or accidentally pulled out. A dislodged disc may cause excessive pedal travel and extreme operation sensitivity. The disc is black, compared to the silver colored valve plunger that will be exposed after the pushrod and front seal is removed. The booster is serviced as a unit and the entire unit must be replaced if the disc cannot be properly installed and aligned, or the disc cannot be located within the booster unit itself."

Ken

ds1919 · Aug 15, 2010

greyghost said:
Let me throw this in the mix for what its worth.
My Haynes manual says about the booster:

"On 1983 through 1987 models, make sure the booster rubber reaction disc is properly installed if the master cylinder pushrod is removed or accidentally pulled out. A dislodged disc may cause excessive pedal travel and extreme operation sensitivity. The disc is black, compared to the silver colored valve plunger that will be exposed after the pushrod and front seal is removed. The booster is serviced as a unit and the entire unit must be replaced if the disc cannot be properly installed and aligned, or the disc cannot be located within the booster unit itself."

Ken

yet another variable in this soggy equation - an yet quite a venerable one, I kinda dont think the check valve will fix it, because the grommet looked okay,and the old valve was working as it should. BUT, all my troubles started when I changed the front pads. Most likely from moving the caliper pistons back into their recessed positions to accomodate the newer thicker pads. Perhaps the disc broke?

Anyone have a pic of this disc? that way I know what to look for.

This may seem like a miniscule thread, but as this diagnosis/experimentation/testing continues, it turns out that there can be all sorts of factors leading to poor braking. Which of course, is more important beyond explanation...

So! a pic would be great, cause Im going to remove the MS tomorrow. Right now I'm going to test drive it down my very steep mining road to the river (and do some prospecting of course). I will know if the check valve works by hte time I get back up.....

hopefully and most lilkey, I'll be back with some color....haha :icon_cheers:

adsm08 · Aug 15, 2010

You didn't put the calipers on upside down did you? I've seen it before. Bleeders should be at the top.

saggy brake issue

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