Dana 44 Disc/Drum Can't Get Any Pressure (1 Viewer)

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Aug 3, 2015
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NORTHERN CALIFORNIA
Hi All,

I'm new to this site (and a new, first time FJ 40 owner, so please forgive me if this topic has been covered. I can't find any threads that solve the issue I'm having). You guys are so helpful with all the information I've read about other issues while I"m trying to resurrect it! Thanks for all your postings.

I bought my first FJ40 about 1.5 months ago. The previous owner gutted the wiring (engine wiring and all), swapped in Dana 44's from a Jeep Wagoneer, and let it sit for 4 years in his yard. It's got a Chevy 350, with SM465 tranny and stock transfer case. The Dana 44's have stock disc's in the front, and drums in the rear. The PO also installed a Wagoneer proportioning valve (think it's actually a stock or boneyard find, as it's somewhat rusty). I've got the wiring done (don't let EZ wiring fool you - it's not THAT easy), the engine running strong, and got all the brake lines made and installed. With the axle swap, at the same time, PO swapped in a power brake booster and master cylinder from a 1985 FJ60. Once I connected everything up, I figured out the master was shot so I replaced it with a new one. I could only get very little pressure with the new MC, but enough to actually stop it pretty well so headed out to my tire shop to get new tires and wheels put on (35x12.5 BFG KM2 MT's on Flat Black Pro Comp Rockcrawler wheels - I'm dying to get this thing back tomorrow). On the way, my front calipers bound up and I had to pull over (smoking brakes, the hole deal). I had it towed to the shop, and they de-pressurized once they cooled. The shop can't get any pressure on the peddle at this point. I've worked on these brakes for about 1 full week before driving it, and am somewhat at a loss as I don't have good knowledge of a pieced together system like this. My shop can keep working on them, but at this point I'm gonna pick it up and put the money into new brake parts. Anyone have any ideas what could be going on?

Couple other questions I have:

1. Can I replace the proportioning valve a Chevy valve? They look identical to a Wagoneer, with the same line size connectors, but are more readily available (can get one off Amazon tomorrow and have it by Saturday). Also, do they need to be bled? I'm wondering if that is part of the problem.
2. Will the '85 master/power booster work with this application? I'm not sure it's pushing enough volume to pressurize the brakes, and it seems like the push rod engages the master cylinder piston slightly when it's mounted (I've adjusted the piston depth at the master and brake pedal arm but it still sticks out slightly too far). Should I go back to a stock FJ40 MC? I'm getting a lot of fluid from all 4 wheels when I bleed them.
3. I don't know anything about brake boosters - could the booster have a leak somewhere, and be putting suction on the MC causing it to lock up the brakes? It seems weird that it starts binding up as I'm driving (and the engine is running, pulling suction on the booster the hole time). I did notice the peddle was getting firmer before I stopped driving it when the brakes bound up (BTW, it was the front discs only - nothing, not even any heat at the rear drums).
4. If I go back to a stock, manual FJ40 MC, will it work with disc/drums?

Sorry to be so long winded. Thanks for any help you can give me!
 
Who knows! PO did it before I purchased it....
 
You may just want to pick up an adjustable proportioning valve on a jimmy rigged system like that, gives you adjust ability. When you changed the master did you do a thorough bleed on the system. A bad booster may result in a firm pedal.

I am a big fan of stock, not sure if the master will work with the brakes though.
 
Where are you pulling the vacuum off the engine??? Have you checked the brake booster check valve? 2x on adjustable Wilwood proportioning valve.
 
Put a vac guage on the mc and see what it is might not be enuff or you have a leak in the system somewhere or its pulling from the wrong spot
 
Thanks for the feedback everyone. I'll look into an adjustable valve, a leak, and inspect the check valve on the booster. I did bench bleed the master before installation, and bled the heck out of the lines. I'm pulling vac from the carb.
 
If your pedal is constantly pulling down, or "self-applying" you have a booster issue. I had this problem AFTER putting in a Toyota factory rebuild kits years ago. Took apart the actual valve portion of the booster and found flashing cover a port giving a "false" signal. Not saying that is your problem per se, just that if the booster is always applying assist then there is an issue with it.

Now as far as the pressure issue, or lack there of actually, perhaps the caliper seals were damaged when over heated? It sounds like you have possibly two or more issues at play here. I would start with the hydraulic side first. Assess the caliper condition and check for leaks. Bench bleed the master cylinder first, then bleed the entire brake system properly, ie. back to front, furthest point first, etc. Push in all new fluid and expel all the air. This is a must, I believe.

You can check the booster while you have the cylinder off to bench bleed. Attach the vacuum hose and start the motor. If the pedal moves at all or you hear any air leaks around the push rod attached to your pedal, your booster has failed. If after you re-install you MC and bleed your system and you do not get any assist its probably failed. With mis-matched components like that, you'll need to verify both push rods are properly adjusted as well. There should be a rod for the pedal and a rod inside for the master cylinder. As far as how to determine if your proportional valve good or not, can't help you too much there. I would agree with others here who have suggested an adjustable model.
 

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