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Old 09-06-2016, 03:06 PM
Telly Telly is offline
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Default 87 FJ60 Brake Fail Question

I've got an odd one...the brakes on my 87 FJ60 start failing on rough gravel roads only. I have to "pump them up" for them to work properly. The strange thing is the brakes work work fine with normal highway/town driving. I'm thinking two possibilities, air in my brake lines or failing master cylinder. Again, weird about only occurring on rough roads. Anyone have a possible explanation? I'm not driving the truck until I figure this out.
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Old 09-06-2016, 04:30 PM
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loose front wheel bearings causing the rotors to push the pads back into the calipers?
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Old 09-06-2016, 05:33 PM
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Do they always return to normal?

Have you had you rear drums apart lately? Maybe binding up and the rough roads let them loosen up a bit?
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Old 09-06-2016, 06:15 PM
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Haven't thought about the brakes themselves. Both front and rear brakes were completely rebuilt last summer (by me) and I replaced all the soft brake lines with braided SS. When I apply the brake (on rough road), it feels like there is no vacuum in the master cylinder, similar to manual brake set-up. It still brakes but not near as efficiently. A couple quick pumps cures the problem which is kinda scary. Hate to throw good money after bad but I wonder if changing the MS would be a good idea as a PM measure...the rig has a ton of miles.
Another thought, maybe I'm loosing vacuum at the engine/MS connection during the rough ride? I'll check it out tonight along with a potential loose front wheel bearings.
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Old 09-06-2016, 06:21 PM
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One more bit of info, I installed a 5.3ls motor last year and the brakes have always worked great since the swap. I'm guessing the vacuum in the ls is not the problem but I'll confirm.

Edit: I'm at work right now (not working) and it dawned on me that I don't think it has a vacuum connection.
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Old 09-06-2016, 10:19 PM
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If you did an LS swap the check valve on the vac line to the booster needs to be there. Did you install one? is it still working properly? One from an olds works it was part of a service campaign (yikes) and fits inline.


I can look up the PN if you need it. That might be your jam but you might give the front wheels a wiggle anyways.
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Old 09-07-2016, 10:59 AM
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check valve I did:

http://forum.ih8mud.com/threads/new-...8#post-8495867
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Old 09-07-2016, 12:10 PM
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I did some more reading and it looks like the 60's are supposed to have a check valve in the booster. maybe mine was never good necessitating the addition of a new one (I didn't realize it had one) and maybe yours is going bad?

I dont have my truck today or i'd look
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Old 09-07-2016, 06:41 PM
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Marco,
Great info. I don't have a check valve in the vac line. I'll do some reading on your Mud post. I did give the both front wheels a wiggle last night and I was surprised that my drivers wheel has some play. I'm going to check preload this weekend and I'll report back.
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