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Irritating '89 Ranger brake issue


Shran

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I need some opinions on what is going on here. The scenario is that I have D35 and 8.8 swapped my '89 Ranger and the brakes are just spongy as hell when the engine is running - pedal feels good with the engine off.

New parts include front calipers, hoses, everything in the rear including wheel cylinders, and master cylinder. I have tried two different boosters with no improvement (one known good, and the original.)

I am getting clean fluid and a good flow at all 4 wheels and have bled everything a dozen times - the brakes just go away when I start the truck.

I have also tried adjusting the booster pushrod. This resulted in better brakes but still slightly spongy, and after a couple miles they got hot and locked up. I obviously went too far with the pushrod so I dialed it back in way below the minimum length and then back out to the .980" spec, and the pedal essentially hits the floor now when I start the truck.

Any ideas? Is it worth bypassing the RABS deal on the frame just to rule it out? Seems like I wouldn't be getting any fluid out of the rear if that was a problem. I am not a dummy with brakes and have done a million brake jobs over the years but this one is stumping me.
 


Denisefwd93

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Seems to me, you pretty much answered your own question, as you're no slouch around brakes you know what the answer is with the rabs.

my experience with boosted brakes is there's always a little sponginess because the booster does so much of the work, but I could be wrong on that
I need some opinions on what is going on here. The scenario is that I have D35 and 8.8 swapped my '89 Ranger and the brakes are just spongy as hell when the engine is running - pedal feels good with the engine off.

New parts include front calipers, hoses, everything in the rear including wheel cylinders, and master cylinder. I have tried two different boosters with no improvement (one known good, and the original.)

I am getting clean fluid and a good flow at all 4 wheels and have bled everything a dozen times - the brakes just go away when I start the truck.

I have also tried adjusting the booster pushrod. This resulted in better brakes but still slightly spongy, and after a couple miles they got hot and locked up. I obviously went too far with the pushrod so I dialed it back in way below the minimum length and then back out to the .980" spec, and the pedal essentially hits the floor now when I start the truck.

Any ideas? Is it worth bypassing the RABS deal on the frame just to rule it out? Seems like I wouldn't be getting any fluid out of the rear if that was a problem. I am not a dummy with brakes and have done a million brake jobs over the years but this one is stumping me.
 

Shran

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I just read another thread on Explorer Forum about essentially the same issue. Ended up being the rear soft hose expanding. I have not replaced that yet, for $16 I will try that first.

I agree, there is always a little vs manual brakes, but this is way extreme. My other Rangers and Explorers have fairly firm brakes, this one is just awful.
 

Denisefwd93

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Well if you look at the construction of the rabs valve you will see it's designed the Trap air
I just read another thread on Explorer Forum about essentially the same issue. Ended up being the rear soft hose expanding. I have not replaced that yet, for $16 I will try that first.

I agree, there is always a little vs manual brakes, but this is way extreme. My other Rangers and Explorers have fairly firm brakes, this one is just awful.
 

IIBRONCOS

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I would toss the RABS valve for sure. I did on my 1988 B2
 

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Easy way to tell if it's the valve is to disconnect the line from the input side (from the master) and cap it off somehow (screw it to an old fitting from something that has the other end soldered or welded closed). If the spongy pedal remains, it's not the valve or anything beyond it. If the pedal firms, then further investigating of not just the valve, but also beyond is warranted (you'll know whatever it is isn't the front brakes).

FWIW, my RABS has always worked fine, and has kept me from swapping ends on wet streets at least a time or two. I wouldn't just get rid of it unless it's found to be bad.
 

Shran

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Thanks for the suggestions. I'll mess around with it a bit more and report back.

I don't mind keeping the RABS valve if it's not bad, I'm not sure how functional it is though. I may have it unplugged - this is the truck I did a 4.0 swap on with a '94 Explorer harness and all of the Explorer ABS parts were left out. It also sat in a field for quite a few years so I keep uncovering more things that suffered from field rot.

Speaking of RABS on these trucks, I can't remember ever feeling it kick in. Maybe it just has never worked in anything I own, I know what 4 wheel ABS feels like and certainly have never felt that in an old Ranger.
 

4x4junkie

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Generally you can feel the RABS pulsating in the brake pedal.
On many occasions it has kicked in on my Ranger when humidity makes the rear brake shoes grabby.
On my BII w/rear discs I've very rarely felt it kick in, but a hard-enough stop will still do it.

Is your 8.8" disc brake? Another thought that came to mind, I've seen before where the rear calipers were put on the wrong sides... This would put the bleeder screws at the bottom rather than the top (preventing proper bleeding). Something else to check for anyway.

Edit:
N/M, I see you mentioned wheel cylinders, must be drums.
 
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Shran

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Yeah, drums in the rear. I did check the new calipers on the front for correct side-side orientation though! :D
 

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If the RABS valve bypass doesn't yield any results different results then make sure you have the proper master cylinder. I'm not sure on the rangers but some vehicles have a different size bore inside of them which would allow more or less fluid to be pushed to the brakes. With a smaller bore master on a system that needs a lager bore this would be a common symptom. Just some food for thought because you did an axle swap.
 

Shran

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I would agree 100% on that IF I had a disc brake swap or something like that... but the front calipers are the same, and the wheel cylinders are very close in size (7/8 bore on the 8.8 vs either 3/4 or 13/16 bore on the 7.5.) Very little difference in fluid volume. Master cylinder is correct for the application, it crossed my mind to use an Explorer master cylinder but the brake line fittings are different and the bore size is the same - 15/16", I think they just changed to metric fittings after '89.

My '86 Ranger with a D44 solid axle and 8.8 disc brake rear has incredibly good brakes in the front and virtually none in the rear. Obvious proportioning problem that I have never fixed but I am still using the factory master cylinder.
 

Shran

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It is fixed.

I replaced the rear brake hose, eliminated the ABS valve with a nipple, and found that the passenger side rear brake adjuster had come apart inside the drum (no idea how that happened.)

I had my kid help me bleed the brakes and it stops great now. I don't know which piece was actually the problem, maybe all three, but anyway all is well.
 

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