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Can't get front brakes to fully bleed


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My new set of pads and rotors are being particularly recalcitrant, spent nearly 2 hours trying to bleed and still not quite right. I did rebuild the calipers with new seals and pistons and it was fairly clean inside. A touch of grease and the new stuff was in with no issues and no leaks. I had never rebuilt calipers before, is that maybe at fault?

 

 Went through a big bottle of brake fluid. Did a gravity bleed, had someone help me power bleed (both using a version of Mopar1973Mans pickle jar), tried bedding the new pads and rotors. Went several more rounds after the new fluid hit and bubbles were gone. Still can push the pedal to the floor without too much fuss and the rears will even lock up, the front just aren't doing their part. They are working, I can hear the tires scrub and the slight smell of warm brakes as well as being warm to the touch. They certainly do not appear to be dragging. I even wiped down the rotors and pads with brake cleaner (again) after the 2nd time I came back from trying them out just to be sure. There was a little pad residue but nothing else, no change. Pedal feels plenty firm.

 

Ideas? Keep bleeding? They certainly worked fine before I started working on the front end.

Edited by That Guy
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 The brake master cylinder may have gone bad, had that happen to me just last week on a customers car.  I replaced front brake pads, rear brake pad and rear rotors.  I went to pump up the system before road testing and the peddle went to the floor; replaced the master and all was good.

 

Another time a customer said his brake peddle went to the floor.   After fooling with this car for a while and talking to the customer he confessed that he took the caliper apart to rebuild to rebuild them.  I replaced the front calipers and all was good.

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I also replaced the master, but that was about 2 months ago. Not saying it can't be bad, but it seems unlikely as it was working fine prior.

 

I should also say, I can push it to the floor, but it takes considerable effort and the rears lock up about 3/4 of the way down. Normal braking the truck seems fine, I just feel it should be able to lock the fronts. The brakes start applying at about 1/2" of travel, which is normal. The fronts are definitely working, just not how they should.

 

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I've gone from dry to fully load on my truck just using the mayo jar. I've rebuilt my calipers left the lines open drained the system. Now hook up all calipers and bleed. Front are independent from the ABS pump. So if you can squeeze the pedal to the floor you've got air in the system.

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How are the rubber brake hoses, are any of them ballooning under pressure?  If not, clamp off the rubber brake lines and see if the peddle still goes to the floor.  If it does then a bad master..    If it doesn't then release one side only at a time and repeat to find if it's a bad caliper.  

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Let me make sure I understand your problem correctly, you said the pedal feels fine it just isn't stopping like you think it should or like it used to?  If the pedal dont go to the floor or there is no pedal fade while braking then its probably not air in the system.  If they worked prior to the brake work but not after then I would be suspect of what was done during the brake work.  Maybe one of the calipers is hanging up.  Does the truck go to one side or the other when braking?

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The pedal feels fine initially. By the time you are half way down, it starts to feel sluggish, the rears are on the verge of locking up. Pressed further, no additional breaking, rears are locked. going to the floor changes nothing. Just stab the pedal (panic brake) rears lock, fronts keep rolling. Both would be performed on relatively cool brakes (80-90*F) and there is no fade. 

 

It isn't stopping like it used to, or like it should. Would previously lock all 4 at about 3/4 pedal travel. RWAL isn't working and explains the rears locking. It seems like currently, the rears are doing all the heavy lifting. 

 

Truck does not have any brake steer at all. 

 

I checked piston extension using air before they were back on the truck. The slides and the 2 rubbing areas fore and aft (tracks?) have a touch of grease and anti seize respectively, and move as freely as new pads/rotors will allow. I won't deny some unknown fault of mine there, but I'm not seeing anything different than I've done in the past, other than rebuilding calipers. I have rebuild hydraulic cylinders, surely a square seal and a dust boot cant be that complicated. 

 

As IBM said, I'm beginning to suspect the original rubber lines. I'm pretty sure I have a new set on my parts shelf somewhere. Was going see if they are stretching the next time I have available (wednesday) and go from there. If they are stretching because the lines were moved outside their normal limits (hung from the control arms) then I'll replace and reconvein once some progress is made. If not that, I'll look at further bleeding, then pull it back apart and check it out again. 

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If the master cylinder drained while having the brakes apart, you could just have air in the master cylinder. You may need to bench bleed the MC or if it's level when mounted in the truck, bleed the lines where they attach to the MC and then again at the wheels. 

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When bleeding you want to push the pedal all the way almost to the floor with engine off. I do most bleeding by myself with a one way check valve bleeder on the end of the clear tube, but also in the jar. When most air is gone  (not seeing much in the clear tubing) I have my wife help with further bleeding the old fashioned way (open and shutting the valve) because I could still see small amounts of air returning up the clear tube everytime she helped when the pedal came back up. You need to start with the passenger side first then the drivers side, but you have to push the pedal all the way down almost to the floor when bleeding. I generally don't let the resovior go less than half full. With each pedal pump the fliud should go down about 1/8th of an inch each time. 

 

I just did my fronts last sunday with one new caliper and pads..... it took about a half a bottle.

 

To check for air in the system while driving, pump the brake pedal several times, if there is air in the system the pedal will come back up like normal for just a split second, but then go back down.

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27 minutes ago, JAG1 said:

I just did my fronts last sunday with one new caliper and pads..... it took about a half a bottle.

 

Just to do a flush job on my truck I use up to if not more than a half gallon to 3/4 of gallon. The reservoir on my truck holds a full quart just about on its own. If the calipers are empty and compressed back in then you have to fill all the voids again with fluid. If the calipers are compressed in again then the old fluid is forced out and you start filling with new fluid. 

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  • 2 weeks later...

Years ago I used a piece of clear hose about 10 feet long and ran from each bleeder to the master cylinder and just kept pumping away. In my case the porportioning valve was stuck. I took it apart and put it back together but then it leaked so I bought a new one.

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On 12/11/2020 at 6:52 AM, Great work! said:

In my case the porportioning valve was stuck.

 

This was caused by not doing fluid flushes every 30k miles. As brake fluid ages the fluid takes on moisture. It's a hygroscopic fluid which means it will absorb moisture from the air. As the moisture is absorbed over time the boiling point of the fluid is reduced so brake fade happens sooner, and the moisture starts to rot the rubber lines and seals on top of oxidizing the metals inside all the brake system. Like you the proportioning valve had failed because of corrosion of the metals. 

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