I'm at my absolute wits end- Fading Brake pedal despite best efforts (1 Viewer)

[musthave]

Ok well the deal is with the one you hook to a compressor is it pulls a good vacuum, and while its doing it you can then go pump the pedal which moves fluid and pistons and helping do dislodge any stubborn air bubbles. Make sense? Just hooking up vacuum doesn't get some of the real stubborn air out. You will go through like a quart of brake fluid doing this tops. If you do this and it still has a sinking pedal then let me know-their are more diagnostic steps you can take. If the abs unit has a special bleeding procedure you will have to look that up as some do have their own procedure. Doing such a procedure in your scenario might be a good idea.

In the morning, I want to jack up the back end really high. Use the compressor vacuum and bleed each cylinder for a good 15 minutes. In between each, bleed the LSPV. Meantime, look up how to bleed the ABS unit, if anyone knows the correct procedure for this, let me know.

When my brakes worked poorly and I did EVERYTHING new (not all OEM) the last thing I did that helped a lot was: In the snow I got ABS to kick a few times then did it while sliding right into my garage. Then bled. I did get air out. AND this was after it was on a VAC for approx. 10 min. per caliper at my buddy's shop (and after I put like a gallon through the system!!

AND two yrs later.... My brakes still don't feel great. Also my ABS is INOP right now with no effect to braking.

That sucks that you don't have good brakes, I can relate.

I got up to 40, on pavement, slammed on the brakes with both feet, but I don't think the ABS kicked in. Perhaps I need to try it on gravel. No snow here, which is just another problem... How else do you get the ABS to kick in?

 

[Chester]

Vacuum at 20 or so inches Hg. at the bleeder seems to keep plenty of suction on the system, but is there better method to deliver fluid pressure towards the cylinder? And is that what you're trying to accomplish in order to get the air to move out?

 

[D'Animal]

One way to see if the booster is bad is to let the rig idle. Step on the brake pedal and see if the idle changes. If it does, you have a bad brake booster.

Or it is an electrical gremlin having a party with the hydraulic gremlin and they both decided they don't like you.

 

[jkilcullen]

Running vs not running will help with a more productive bleed. with it running you are getting the power assist to force more fluid at a higher pressure out of the bleeder faster, thus moving stubborn air pockets toward the bleeder. if my previous tips don't do it for you try to remove the bleeder completely then smash the brake as if making an emergency stop then have a friend install bleeder before releasing. proceed to bleed normally a couple times at that same bleeder immediately following. start with lspv, then rear passenger, then lspv, then rear driver, lspv again, front pass, front driver. (yes lspv is that fxxxed up of a system that after looking over the diagram I feel that its necessary to do it that much.

edit keep the ass end in the air for all of that madness to help it along

 

[jkilcullen]

I have bled a zillion vehicles and some have been very stubborn. For the very stubborn ones I have developed a easy method that works well for me. First question though-do you have an air compressor? Second you need a vacuum bleeder like the one from harbor freight for like 30 bucks that you hook the air too. If you have those things, then hook it up. As you crack each bleeder with it hooked up, leave the bleeder open and pulling fluid and then get in the vehicle and pump the pedal for like 20 seconds. Do this for each wheel. This has always worked. If you don't have this style bleeder you can't do it. They are worth the money as you can use them for various things. With this method you don't even have to bench bleed the master if you don't want too if its new.

This is also an excellent approach and easy to do alone, I broke my vacuum bleeder a while ago and should probably have bought one while I was fighting with my cruiser over this past summer

 

[Pin_Head]

Sounds like you got air in the ABS system. If you have enough pedal to stop rapidly, it is time to activate the ABS valve and pump by locking up the wheels on a low traction surface, like gravel, dirt or snow.

 

[Qball]

Didn't read through the entire thread but have you tried to activate your abs a bunch of time to get the fluids out of the abs unit? It helped me after kicking in abs a dozen times or so.

 

[Chester]

Sounds like you got air in the ABS system. If you have enough pedal to stop rapidly, it is time to activate the ABS valve and pump by locking up the wheels on a low traction surface, like gravel, dirt or snow.

This sounds like it's the most likely culprit, nearly every other possibility comes up short. It sounds like gravel or dirt road would work well for causing the ABS to cycle, but they paved paradise around here years ago, wet aspalt might be all there is. Can it be triggered via sensors?

 

[Timpanogos Slim]

My nightmare didn't end until i replaced the booster. But i should have known the booster was bad by the way that i needed all of my leg strength to keep the truck from rolling.

 

[Yota truck nut]

thanks for the tips guys. I have a spongy pedal as well. I am going to try some of these tips

 

[Pin_Head]

It sounds like gravel or dirt road would work well for causing the ABS to cycle, but they paved paradise around here years ago, wet aspalt might be all there is. Can it be triggered via sensors?

The ABS can be triggered with a special service tool, but most people don't have access to one. You could pay the dealer to bleed them or if you live in urban Florida, you could do donuts on the golf course fairway after dark.

 

[Qball]

One way is to put either left or right 2 tires on road surface and 2 tires on dirt shoulder, the traction difference helps to trigger the abs easier.

 

[1FZj80]

If it gets air back in it, then it must be leaking somewhere. That is a different situation.

A failed abs valve/seal does not required air in the system to get a spongy pedal or the feel of brake fade (even if it is not actually happening).

The abs actuator includes solenoid valves, a pump and a reservoir to modulate line pressure to prevent lock-up. If the solenoid valves, pump check valves or other system seals fail, pressure in the system may be leaked through the actuator resulting in a long pedal and poor braking.

If everything else in the system has be checked, the abs actuator may be the culprit :-(

 

[scrowley]

Is there an easy way to bypass the abs unit temporarily to see if abs unit is junk? My pedal still is not the best. I've replaced/done everything possible. It was a few month ordeal trying to get a good enough pedal. that was a fee yrs ago now.

 

[izzyandsue]

Musthave, sent you a PM, let me know.

 

[Trux]

I had a similar issue on a Nissan truck. The brake lines were bulging, but you couldn't see the lines were bad. Pieces of the rubber brake line also clogged the steel brake lines a bit.

Make sure your using the correct brake fluid, some types don't work with certain makes.

Have you adjusted the Rod that activates the master cylinder since you put the new on? If so, sounds like your rubber brake lines are old or didn't like the fluid used.

The other guy on this post who replaced his with steel lines had it work. To me, this sounds like your problem. I would get extended steel lines , but first check that rod is pushing the master cylinder in far enough

 

[Trux]

If you accidentally spilled certain fluids on your lines this can make them balloon and not have pressure

 

[Dave 2000]

I noted you said bleeding and getting a good pedal is easy....it is only a couple of days later that there is a problem right? If that is the case then you ARE bleeding all the air out and getting a good pedal, so air is slowly working it's way back in, the result a long pedal. And yes you can get air in and NOT fluid out if for example you have a porous pipe somewhere. Also of note, have you checked the wheel bearings all round?

regards

Dave

 

[musthave]

My nightmare didn't end until i replaced the booster. But i should have known the booster was bad by the way that i needed all of my leg strength to keep the truck from rolling.

I "think" the booster is good, when taking it out of the picture, have hard brake pedal, but still fades the same. Inline, I get easier pedal, but still fades the same.

The ABS can be triggered with a special service tool, but most people don't have access to one. You could pay the dealer to bleed them or if you live in urban Florida, you could do donuts on the golf course fairway after dark.

One way is to put either left or right 2 tires on road surface and 2 tires on dirt shoulder, the traction difference helps to trigger the abs easier.

I got up to 60 on wet grass and on gravel about 5 times this morning, stopped fast, ABS worked fine. Pedal to the floor though.

A failed abs valve/seal does not required air in the system to get a spongy pedal or the feel of brake fade (even if it is not actually happening).
The abs actuator includes solenoid valves, a pump and a reservoir to modulate line pressure to prevent lock-up. If the solenoid valves, pump check valves or other system seals fail, pressure in the system may be leaked through the actuator resulting in a long pedal and poor braking.
If everything else in the system has be checked, the abs actuator may be the culprit :-(

I'm hoping that it's not the ABS actuator, may get a preliminary price from @beno though. Another bank breaker.

 

[Pin_Head]

And yes you can get air in and NOT fluid out if for example you have a porous pipe somewhere.

No. I'm throwing the MT (Mierda de el Toro) flag on this one.

I got up to 60 on wet grass and on gravel about 5 times this morning, stopped fast, ABS worked fine. Pedal to the floor though.
.

Now bleed the brakes again and you should be done.