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Rebel526

Scratching my head- brake problems.....

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'87 Pathy, 3.0, 4x4

 

So, I thought my MC was going bad because I would have to pump the brake pedal to get brakes. Once pumped up (two or three pumps), the pedal felt normal, not spongy or soft. So, yesterday I swapped out the MC. Bench bled it first, of course. Then, bled the brakes, starting with the Passenger rear, then driver rear, passenger front and finally the driver front. Bleeding went normal and pedal felt fine. After cleaning up all the mess and putting everything away, started to drive....just to find the problem was still there, had to pump the pedal to get brakes.

 

I did not see any evidence of a leak anywhere, and again, once pumped up, the pedal does not sink or feel spongy.

 

I am at a total loss.....any ideas? Am I forgetting something or missing something?

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Either you still have air in the system or your brake booster maybe on the way out. Or your 'new' M/C is defective?

 

Try tapping each caliper with a plastic mallet or similar tool while your bleeding that corner. Sometimes air bubbles will attach themselves to the inside of the calipers and lines.

 

I usually buy a large container of brake fluid and 'power flush' the system when I bleed the brakes. To do this you simply 'crack open' the bleeder and have someone pump the pedal several times while adding fluid to the reservoir. You don't want to let the reservoir run empty or you'll have to do it all over again.

 

Once a fair amount of fresh fluid is present in the bleeder bottle. Close the bleeder and pump the pedal about 6 times and hold while slowly opening the bleeder. You'll usually see some bubbles escape. keep doing this until all you see is fluid with out bubbles and then move onto the next corner until they all have been done this way.

You should end up with a consistently firm pedal. If not then you have other problems. Such as a defective 'new' M/C.

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I suppose it's possible that the 'new' MC is bad, but it seems strange that it's doing the EXACT same thing the 'old' one did ('old' one is just just years old, not that it matters much).

 

I did 'power flush' the system after letting each bleeder gravity bleed till I was certain I had fresh fluid at each wheel. I feel 98% confident that there is no air in the system, but I guess I could be wrong there, too. If there was air in the system, wouldn't that make the pedal squishy?

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Not necessarily. A gravity bleed is not the same thing. The air still clings to the inside of the caliper piston and sometimes the walls of the brake lines. You may also have a caliper with a stuck piston preventing full travel while your bleeding. How old are the calipers?

 

These trucks are getting old and brakes are not lifelong components and they wear out just like everything else. Especially in the environment they work in.

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After the gravity bleed, there was a thorough 'regular' bleed, pressing the brake, cracking the bleeder, then closing the bleeder. Went through a large bottle of fluid in bleeding and flushing.

 

I have no idea how old the calipers are, that may be a good point....

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Do you have lots of pad left? If the pads are low on material the pedal will go way down like that. Also, disk or drums in the rear?

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Medium pads, drum on the rear

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Have you rebuilt the rear wheel cylinders lately? Or adjusted the shoes in the drums?

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^ Definitely check the drums. If they are way out of adjustment it will take quite a bit of pedal stroke to engage them.

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Do the Nissan rear drums adjust by driving in reverse and hitting the brakes like the old Chevys? I have discs but just wondering.....

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Just did the front brakes on mine, a '93 SE v6 4wd. No leaks, no brake issues at all other than pads worn down to indicators. Was going to replace pads and rotors. When I cracked open the bleed valves and began compressing the caliper pistons (twin piston calipers on mine), the fluid came out, but not from the open bleed valve. The fluid peed out of the piston seals. Never had that happen before ... not that suddenly. I've seen a caliper that had been leaking for some time weep fluid when compressing - these blew completely out and had to be replaced as well. Found out the factory calipers use plastic pistons. Bingo. Most new and reman use metal pistons. What disgruntled Nissan engineer decided to do that!? Plastic caliper pistons...

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I'll be revisiting the issue in the next few days. Had to wait for weather and time off from work to align, LOL

 

Been driving my Pathy for two years after rescuing it from sitting for 5 years with a blown motor. When I originally went through the brake system, I only found one bad wheel cylinder on the drivers side rear. All other brake parts are at least 7 years old. I guess I've been lucky I got 2 years out of everything, considering the shape everything was in when I bought it.

 

Hopefully I can get it up on a lift at a friends' work in the next few days and pull all the wheels and get a good look at each brake setup.

 

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Do the Nissan rear drums adjust by driving in reverse and hitting the brakes like the old Chevys? I have discs but just wondering.....

 

If everything is working properly, yes.

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In the manual it says the ebrake adjusts the drums.

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After replacement of the OLD brake pads and shoes, was having the same thing happen to my 95. So I went the cheating way out....while having the alignment done, had shop power bleed/ adjust. For $60 the brakes are tight and reactive, plus my ebrake is nice and tight, holds the truck now. All you might need is to have it bled under pressure?

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Hmmm... That's what I was trying to tell you all along. You could invest in a Mighty Vac system. The one made by Speed Motive and never have to go to a shop again. Plus you can do all types of foreign and domestic brake systems. It's a one man job that way too.

 

Money well spent IMHO.

Glad you go it fixed. Many people forget that brake fluid absorbs moisture as soon as the seal on the bottle is broken. All of the trapped moisture in your brakes system corrodes every thing and eventually will ruin the cylinder bore's of both the calipers and wheel cylinders make life rather unpleasant when you really need to stop!

 

Do a complete fluid flush and bleed at least every 2 years no matter how many miles you drive. It's like sex...do it at least twice a year whether you need too or not ! Lol. ; )))

 

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Got it up on a lift yesterday and pulled all the wheels and checked brakes all the way around. No leaks anywhere. Nothing obvious wrong. Adjusted rear brakes (didn't really need it, but figured what the heck (Only took two clicks of the adjuster on each side). Went ahead and re-bled the brakes. Also, while up in the air, yanked rear springs and slipped in the JGC springs I had acquired.

 

After getting it back on the ground, I was happy to discover the brakes felt normal again...I can only guess that there was some wayward air in the system somewhere....Unfortunately, I am not seeing any lift from the JGC coils springs....So....the hunt continues....

 

Thanks to all for the replied and ideas!

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