90 f350 brake pedal fade

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02-26-2014, 02:57 PM

bodmec

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90 f350 brake pedal fade

1990 7.3 diesel with vaccum booster
ok,new member,same old problem!! lol
Ok,,I have searched and read a whole lot,still none of the topics address my situation.
I have replaced: rear wheel cylinders,shoes,front calipers,front rubber lines-left and right, 4 diff master cylinders,,yes I bench bled each one,yes I used a pressure bleeder on the entire system,,yes I removed the spring from the rwal unit. and yes the rear shoes are adjusted properly. and there are no signs of leaking fluid anywhere...
Okay,while not running have a great pedal no fade and no need to pump them up,,but as soon as its started it feels like its blowing by the master cylinder,even after all that mess there is no change,, any suggestions?
thanjks,,this thing is killing me, btw the pedal fades to the floor
ps,, have also made block offs for the master cyl to isolate front from rear,,problem seems worse when rear is blocked and front is hooked up.

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02-26-2014, 06:18 PM

brokeasajoke

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Im fighting a weak pedal too. Bypassed the rabs and thought i had it. Was able to lock wheels going down driveway buy drove down road and went back to same to the floor pedal. Think im gonna change booster next. I have nothing left to change unless wheel cylinders letting air in.

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02-26-2014, 06:33 PM

airdale94

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Put your blockoffs on both ports and test. If it bleeds down the problem is in your master cylinder. Did you bleed the master cyl. on the vehicle also. Not sure on the Fords but on the GMs if you push the plunger in more than 1" when bench bleeding you can damage the master cyl. Did the instructions have any special steps.

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02-27-2014, 07:41 AM

bodmec

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Quote:

Originally Posted by airdale94

Yes block off ports on master cyl. and holds good. also block of one at a time. Front goes down a lot faster and further than the rear.
Yes bled master on truck to,,also pressure bled as well.

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02-27-2014, 07:51 AM

bodmec

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I thought about buying a Zero loss factor booster but when i block off the master cly. outlets the pedal holds great. I do not know how that could make any difference Has anyone had any luck with the Zero loss brake booster my case?? please read top of my start page...
P.S. this is a diesel with a vacuum brake booster THANKS, BODMEC

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02-27-2014, 09:00 AM

fordtruckman838

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If the pedal is fading to the floor when the rear is blocked off, it really sounds like you have a small pinhole in one of your steel lines leading to the front calipers. I fought with one for almost a month as it was nearly impossible to see where it was leaking. I finally found it by having my brother in law (it was his truck) hold the pedal down while I crawled under it. In this way I was able to see a very small stream of fluid spraying from the steel line. Where it was located it was not spraying on the frame just down onto the ground. This made it impossible to see otherwise.

Good luck

Bill

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02-27-2014, 10:45 AM

airdale94

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If your master holds with the blockoffs and leaks down with the fronts hooked up it has to be in the front brake system. A brake booster won't cause a low pedal, it only provides power (force) assist. Does your brake light come on? Those caliper pins have a up side and a down side. One edge side is wider than the other. If you look at the caliper and mounting bracket you can determine which edge goes where, caliper side or mount side. Have you tried rebleeding the fronts. Rap the calipers with a hammer to dislodge any trapped air bubbles. Have you verified both calipers are holding?

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02-27-2014, 04:14 PM

bodmec

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Quote:

Originally Posted by fordtruckman838

I have looked but haven't seen any wet spots,however I haven't looked my someone was holding pressure,I will check that thanks.

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02-27-2014, 04:21 PM

bodmec

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Quote:

Originally Posted by airdale94

Im with you on the booster,but I read somewhere some guy saying it fixed all his problems,,same as mine.

No brake light that I have seen yet
Caliper pin are correct,they have a tab that kinda acts like a lock when put in.
Have rebled the front with a pressure bleeder,did not tap calipers however,been turning wrenches 25 years and never had to do that but this case is weird.
Calipers appear to be holding but will check again to verify,,thanks.

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02-28-2014, 12:57 AM

airdale94

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Quote:

Originally Posted by bodmec

Caliper pin are correct,they have a tab that kinda acts like a lock when put in. Calipers appear to be holding but will check again to verify.

Those caliper pins yes have a stop on them but you can get them upside down. The caliper will be a little loose in the mount. When you push on them with no power assist they seem fine. If you have one or more upside and engine running (power assist) the extra force causes the loose caliper to "seat". Not saying that's for sure you're problem, but I've seen it bite more than one experienced mechanic. Top side of pin /\ bottom side of pin \ /.

Last edited by airdale94; 02-28-2014 at 01:01 AM. Reason: add

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03-04-2014, 05:13 PM

bodmec

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We checked every square in. of line slowly (no leaks). Also went back to pressure bleeding. Blocked off rear again and with lf/ft side blocked. Pressures bleed Rt side. (Pedal still fads. Blocked Rt/Ft bleed again. Pedal held. I did not replace the Rt/Ft steel line brake line until now. So I replaced it and Pressure bleed still had same problem, (pedal faded)
So I replaced the new Caliper with another new one. It was a remand Cal. Pressures bleed again. Still have a fading pedal on 1<sup>st</sup> push down then let off and push again holds better on 2<sup>nd</sup> push down will not go as far and will stop now. Still not as good as I would think it would be.
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03-04-2014, 06:27 PM

brokeasajoke

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Im still scratching my head

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03-04-2014, 06:28 PM

brokeasajoke

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Not hijacking your thread. I changed my booster and i gained a little. Mine was definetly bad. Pulled my pins greased and reinstalled they were in correctly. Bled left rear wheel cylinder and gained more. Seems it always has a little air in it or maybe its just in my head. Pedel dosent get hard after 2 pumps now.

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03-05-2014, 11:12 AM

bodmec

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Thank everyone has has replied to my post.... However I'm still looking for answers....

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03-05-2014, 12:37 PM

fordtruckman838

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I know you said you were pressure bleeding, were you using a system that reverse bled: ie pump the fluid in from the caliper? I know that reverse bleeding is so much easier and more effective than bleeding from the master down.

Is the caliper installed correctly, ie with the bleed screw on the top of the caliper? I had a friend install the calipers on the wrong sides of his pickup; this located the bleed screw on the bottom of the caliper. it was impossible to bleed the lines until they were switched.

Otherwise I am beginning to run out of ideas..

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