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Rear Brakes Not Working


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Hey everyone,

 

I have a question about the rear brake system on my 91 Pathfinder.

 

I just installed new parking brake cables, new wheel cylinders, new drums, and new shoes.

 

When testing the rear brakes they would not lock up while I had the rear raised and the vehicle running in gear. I thought I might have a problem in the master cylinder or proportioning valve. I'm pretty sure this truck has ABS however. There is a speed sensor on the rear axle, and wiring going into the proportioning valve on the frame rail.

 

Will the rear brakes not lock up if the front wheels aren't moving? Do all four wheels need to be in rotation for the rear brakes to lock up?

 

It has a high pedal and seams to stop fast, but I guess I could be driving around with only front brakes. Although I find this hard to believe.

 

Thanks in advance for any help you can offer! :beer:

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That, or when you bled the brakes when you had it all reassembled, did you also bleed the ABS unit on the mid/inside passenger frame rail? There is a standard bleed nipple on it. I recommend making sure the shoes are properly adjusted (hand brake should tell you this), then bleed the passenger rear, drivers rear and the ABS unit. I have found that I needed to gravity bleed the system to get good results, but the usual 2 person method will suffice to see if you are in the ball park.

 

Yes, you can be driving around on your front brakes only. It is 2/3-3/4 of your stopping power...

 

B

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I did bleed all those components. The e brake could use some adjusting, but it grabs the rear wheels and will hold the truck at a standstill when it's in gear(A/T). However I still don't understand about the rear wheels rotating while in gear on jackstands. If I apply the brakes the rear wheels won't stop rotating. Is this because of the ABS?

 

It can't be an adjustment. The shoes are adjusted all the way out where they are lightly touching the drums. With the drums off hitting the brake opens the shoes way out and will almost push the wheel cylinder out of the hole. If they move that far out, and the pedal is high, I don't think adjusting a few thousandths of an inch will change anything.

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I did bleed all those components. The e brake could use some adjusting, but it grabs the rear wheels and will hold the truck at a standstill when it's in gear(A/T). However I still don't understand about the rear wheels rotating while in gear on jackstands. If I apply the brakes the rear wheels won't stop rotating. Is this because of the ABS?

 

It can't be an adjustment. The shoes are adjusted all the way out where they are lightly touching the drums. With the drums off hitting the brake opens the shoes way out and will almost push the wheel cylinder out of the hole. If they move that far out, and the pedal is high, I don't think adjusting a few thousandths of an inch will change anything.

 

 

Did you check the adjustment after trying to stop the wheels while on stands? Could have possibly had the shoes not 100% in place and even if you had them adjusted to the point of touching before, after settling they are way out of adj.(I've seen it), You hitting the gas with the brake amd making it power over the brakes? Shoes on correctly? Bleed in the correct sequence and have solid fluid? Is your master cylinder good? Did you run the system dry on brake fluid at all?Just trying to cover some basics...

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Did you check the adjustment after trying to stop the wheels while on stands? Yes, many times to be sure.

 

Could have possibly had the shoes not 100% in place and even if you had them adjusted to the point of touching before, after settling they are way out of adj.(I've seen it) Yes, they were pumped out checked/adjusted many times.

You hitting the gas with the brake amd making it power over the brakes? No, I was only trying the brakes wheel the wheels were coasting, or under idle. Both times they continued to roll over.

 

Shoes on correctly? Yes definitely. They only go on one way, and the entire assembly is installed with new parts.

 

Bleed in the correct sequence and have solid fluid? I believe so, Proportioning valve, Right RR, Left RR.

 

Is your master cylinder good? I'm not entirely sure. It pumps fluid to the back, and will pump the wheel cylinder out of it's casting. But maybe that's possible without providing enough pressure to tighten the rear brakes.

Did you run the system dry on brake fluid at all? Not at all

Just trying to cover some basics...

 

I appreciate the responses guys, and thanks for writing them! Hopefully I'll get to the bottom of this soon.

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It's purely technical, but...

Bleed in the correct sequence and have solid fluid? I believe so, Proportioning valve, Right RR, Left RR.

The proper sequence is farthest for the master cylinder first, working closer. Ie, RR, LR, ABS unit. Not saying that is the fix, just saying...

 

Is it possible that you have a bubble in the soft line? I have only seen this once or twice, but it acts similarly. You step on the brake and a section of flex line balloons and almost no hydraulic pressure gets to the actuating cylinder. It's a long shot, but it sounds like you have covered most everything else.

 

B

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When you adjust the rear brakes, the wheel must be on. It's usually best to do this both wheels up in the air. Not the safest but works best to make sure both sides are equal.

Spin the wheel and adjust the brakes so that the wheel will make about one rotation with medium like force.

Check adjustment with the e-brake as well. So that it comes on after the first few clicks. it shouldn't have to be reefed all the way to the top.

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Is it possible that you have a bubble in the soft line? I have only seen this once or twice, but it acts similarly. You step on the brake and a section of flex line balloons and almost no hydraulic pressure gets to the actuating cylinder. It's a long shot, but it sounds like you have covered most everything else.

 

B

 

:goodpost: Something that is rarely thought of, and rarely an issue, but I have seen it happen.

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