At wits end....please help please!

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Jul 20, 2006 | 12:45 AM

crg

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At wits end....please help please!

I have searched old threads and tried that advice and still no joy. 91 F-350 4X4 7.3L with little or no rear brakes and spongy pedal. I have had very poor braking for years and have installed new vacuum pump, booster, master cylinder twice in a row, brake lines, hoses, wheel cylinders and calipers.I just replaced my semi metalic pads after wearing out in 12000 miles and noticed that when resetting the calipers to take up the clearance, the pedal went clunk to the floor as if the rear brakes are doing nothing. Now the last thing I could think of was the RABS valve which an old thread claimed to cause a similiar problem. I removed and bypassed it today only to still have a pedal that takes about 10 seconds to go to the floor if I hold pressure on it with the engine running.
I am getting ready for the family vaction and really don't want to go out with poor brakes again. Any suggestions?
Thanks!!!

Jul 20, 2006 | 01:50 AM

parrisw

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From: Victoria BC, Canada

I think on those there is some sort of brake valve on the left frame rail at the front just in front of the drivers door, check that, some times they leak internally causing this problem, it may even have bleeders on it, to bleed it out.

Will

Jul 20, 2006 | 11:52 AM

andym

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From: Bonita Springs FL

Quote:

Originally Posted by crg

I removed and bypassed it today only to still have a pedal that takes about 10 seconds to go to the floor if I hold pressure on it with the engine running.

There's the key statement right there. You have a bad master cylinder. Where are you getting your master cylinders from? If you're getting them from autozone or one of the cheap parts stores, you get what you pay for. Spend a couple more bucks and get a Ford master cylinder and make sure you install it the right way and you'll be fine.

Jul 20, 2006 | 05:50 PM

crg

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The update is as follows. After driving it today without the RABS valve, I have what seem like alot more rear brakes. After stopping by the local major brake shop and getting the foreman to step on my pedal, he says it's normal to go slowly to the floor if you push hard and hold. I did a panic stop to test today and I stopped fast enough to axle hop the rear duals but no sign of fronts locking. Now I have a very heavy flatdeck so no RABS shouldn't be a concern so I was going to run without it.
Has anyone else removed this valve and not been able to lock the front?
Thanks again guys!

Jul 20, 2006 | 05:58 PM

andym

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Joined: Mar 2002

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From: Bonita Springs FL

Quote:

Originally Posted by crg

After stopping by the local major brake shop and getting the foreman to step on my pedal, he says it's normal to go slowly to the floor if you push hard and hold.

I have no idea why he would tell you that, but I can absolutely guarantee you that he's wrong. The pedal should NEVER sink no matter how hard you press on it.

Jul 20, 2006 | 09:50 PM

Boss429F150

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i agree. the seals inside your master cyl. are bad. if you're driving and your pedal starts to sink, if you hit your pedal hard a couple times i bet you'd have your good pedal back for a couple sec. before it started to sink again. If your pedal was supposed to sink to the floor then going down a hill with your foot on the brakes the whole way your pedal would drop then you're outta luck.

Last edited by Boss429F150; Jul 20, 2006 at 09:51 PM. Reason: spelling

Jul 20, 2006 | 11:03 PM

parrisw

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From: Victoria BC, Canada

Is it going right to the floor like pedal hitting the firewall??? or just really low, Lots of fords, diesel's in paticular have low feeling pedals, but when you drive it it stops with little effort.

Also installing new aftermarkey Master cylinders, when you bleed it, bench bleed it first, put it in a vise push in the cyl with a screwdriver, otherwise sometimes you will never get all the air out. Also the most important thing about aftermarket master's, do not push the cylinder all the way in until it bottoms out, this is critical, cause the way they build them they drill out the line holes after they honed the bore on some brands, leaving burrs inside, this can cut the seals causing a faulty new master.

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Jul 20, 2006 | 11:47 PM

crg

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It would be great if someone else could try this: With the engine idleing, push very hard on the pedal and hold. Does it slowly go down over ten seconds to the floor or very close to it? Keep in mind if I do that kind of pressure while I'm driving, I am axle hopping the rear duals and everything is sliding off the seat (now that the RABS valve is removed). Normal braking including sitting at a light on a hill, does NOT sink to the floor. Also keep in mind that if the seals are shot in the master, it is very unlikely the fluid returns to the reservoir and I have no leaks or fluid lose into the booster.
After driving this today, I am willing to agree with the people posting the RABS solution a couple of years ago that this has given me proper rear brakes again. As I have a 2000# flatdeck, I am basically never unloaded to worry about rear lockup with moderate braking. As I am 12300# loaded with my camper on this long wheelbase, I think I want a bias on the rear brakes too.
My remaining questions are am I likely to have too much rear braking and is this pedal sinking really normal?