pulsing brake pedal after full drum brake job

[Pat]

Okay, first I had some noise coming from my back brakes on my 2002 Pathfinder, so I tried to get the drums off to look at the pads. The rust ridges were severe and both adjuster star wheels were totally seized. I ended up using a crowbar against the back plate to force them off, breaking hardware and both wheel cylinders in the process. I proceeded to rebuild the brakes with new pads, hardware, wheel cylinders, and hard lines on both sides. I grinded the rust ridge off the old drums and reinstalled them. bled just the back brakes and went for a drive.

Well the pedal had a severe pulsation when braking and felt very soft. My next step was new drums and a full system bleed of all 4 wheels. To my amazement These problems are persisting, even though everything back there is new. the soft pedal is a bit better but the pulsing is the same.

I looked at the backing plates and they appear even and unbent, but the way I was prying who knows, LOL
Could air in the system make the pedal pulse? I didn’t think so but I’m no expert. This was actually my first time ever doing a full drum rebuild.

Any thoughts or tips will be very appreciated, Thanks guys & girls.

Topic

[college man]

see if this helps.

http://www.ericthecarguy.com/faq/solving-brake-problems

[Pat]

Thanks, I’ve already looked at this. I feel like this is a sort of unique case.

[george gonzalez]

if you had to pry the drums off you might not only have bent the drums but also bent the spinny thing.

[Pat]

The hub seems pretty beefy to get bent by my noodle arms. But If it was, how could I check this?

[Bill]

I think most professionals have done what you had to do to remove rear drums at one time or another. It’s very strange to have the same problem after installing new drums but I have had the same problem happen myself.

Many brake drums today are made offshore and sometimes they just are not round. I suggest that you return them for another pair or a different brand or have them machined round. I think once you have the pulsation cured and the new brake shoes are seated in your brake pedal feel will firm up.

[Pat]

I’ve replaced the front rotors and pads and this cured my pulsation. But for the life of me I can’t get the pedal to firm up. I’ve bled each wheel again and again, but the pedal still goes right to the floor when the engine is running. I’m suspecting the master cylinder has failed. I really don’t want to resort to going to a garage. This is very frustrating.

[Lorrin Barth]

If the pedal is going to the floor and you can’t pump it up it is most likely the master cylinder. By the time you get done with this project you are going to be a brake expert.

Anyway, if you decide to change the master spend plenty of time bench bleeding. There probably will be instructions with the replacement part or look on youtube.

[Pat]

Thanks. I’ll report back with an outcome.

[Stephen Bowen]

How did you do the adjustment of the rear brake shoes? The rear brakes normally have a direct impact on your brake pedal height.

Two things I can think of. Rear brakes not correctly adjusted. In the past I’ve installed the shoes and new drums/turned drums. I run the adjuster up so I can hear the brake pads just touch the drums when spinning the axle. Same on the other side. I then hit the brake pedal a few times to ‘center’ the brake shoes, and then going through the access hole–adjust the star wheel until I have the shoes just sound like they are making light contact with the drums. (Not so tight it creates resistance, but so when you spin the axle you can hear a very faint rubbing) It takes a lot of practice to dial it in, and this is only my method for doing this. (some dial it in close—put it back together and then run things backwards/forwards for the star wheel adjuster to do the same thing automatically)

In regards to the master cylinder– Look under the master where it connects to the power brake booster. Brake fluid eats paint. If you see an area that looks like someone hit it with paint stripper just under the master–then it’s 100% shot.

Another trick is to loosen, do not remove the nuts retaining it to the booster. Pull it forward and check for brake fluid behind it. At times a bad master cylinder can dump brake fluid back into the booster so it won’t show up.

These are not fool proof checks…But they can give some hints/clues. Also there is the pedal bleed down test. I personally would double check the rear adjustment of the shoes, and then chase after master cylinder issues.

Another note on the master cylinder that often gets overlooked. If the pedal hits the floor due to a sudden leak— The cylinder uses a set of ‘rubber’ cups in a bore, set of springs and a rod…It’s quite the operation. However if one of the ports in the cylinders housing happens to ‘catch’ one of the ‘rubber cups’. (normally a defect in the machining process when built) It can put a nick in the cup and cause it to leak back. The fact the pedal hit the floor already might have done this.

These are just some suggestions and ideas. Without having the vehicle in front of me? Can’t tell what exactly is going on, or the details. So all this is generic things that can happen.

S-

[Stephen Bowen]

[quote=”barneyb” post=102688]If the pedal is going to the floor and you can’t pump it up it is most likely the master cylinder. By the time you get done with this project you are going to be a brake expert.

Anyway, if you decide to change the master spend plenty of time bench bleeding. There probably will be instructions with the replacement part or look on youtube.[/quote]

Barneyb nailed this! Anytime replacement of the master cylinder is done—this procedure needs to be exact and correct.

S-

[Pat]

Thank you very much for the detailed response, it is much appreciated. I will try more adjustments on the shoes as you suggested.

A couple more notes, when bleeding I was pressing the pedal down to the floor on every stroke. I did not know this was bad until I began researching this problem. Do you think I might have damaged the MC from this? Also the front left line bleeds out foamy fluid every time I bleed it. Could the caliper be letting air in?
The pedal does not get firmer when pumping it (engine running).

[Stephen Bowen]

[quote=”patriley” post=102742]Thank you very much for the detailed response, it is much appreciated. I will try more adjustments on the shoes as you suggested.

A couple more notes, when bleeding I was pressing the pedal down to the floor on every stroke. I did not know this was bad until I began researching this problem. Do you think I might have damaged the MC from this? Also the front left line bleeds out foamy fluid every time I bleed it. Could the caliper be letting air in?
The pedal does not get firmer when pumping it (engine running).[/quote]

Foamy fluid is air in the lines. I’d guess that’s a large part of the issue with the spongy pedal.

Oddly enough when bleeding brakes you need to have the pedal hit the floor. Pump the brakes several times. On the last ‘pump’ do not release the pedal, and have a helper (or yourself and the helper working the bleeders) open the bleeders until the pedal hits the floor.

That’s the catch-22. If you have even a tiny burr or nick in the M/C? It can and will damage the rubber cup.

One thing to try would be a vacuum pump with a brake bleeder adapter.

http://www.harborfreight.com/mityvac-vacuum-pump-39522.html

They have a cheaper one for $29 that does the same thing.

All you need to do? Is just remove the master cylinder cap and keep the master cylinder FULL while using the tool. The vacuum will draw the air/fluid out and once you have no bubbles or foam? Secure the bleeder screw, check for leaks…top off the fluid and see what happens.

Any air/foam looking fluid is a huge red flag for spongy brakes.

Sometimes even gravity bleeding can work. Top off the master…crack open the bleeder..and just let gravity do it’s thing. Keep the master full, and once you get clear clean fluid–shut the bleeder.

As for the question could the caliper allow air to get ‘in’? Unless you see a leak, it shouldn’t. (Air getting ‘in’ to the system…you’ll sure see fluid making an ‘exit’ as well)

Keep us posted!! This one is interesting.

S-

[EricTheCarGuy]

For starters, this for future reference.

Next, for someone who says they read through the Brake Problems article, you sure are asking a lot of questions that were covered there, including about the master cylinder, how to isolate a brake pulsation, how to resolve a spongy brake pedal, and the above video.

http://www.ericthecarguy.com/faq/solving-brake-problems

That said, it seems like you have things pretty much sorted. Keep us posted if things change.

[Pat]

Issue resolved. Another bleed at each wheel did the trick. 6th times the charm, I guess.

My apologies if I’ve asked too many questions and a huge thank you to everyone who has posted in this thread. You guys rock.

[Stephen Bowen]

Very glad you have it worked out. Sometimes it takes a lot of tries to get all the air out of a brake system. Even more so with all the complex ABS pumps and systems in place–Just ripe for a lot of places for air to collect.

Be safe!

S-

[Author]

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