Brake pedal pulsing after changing rear brakes

My pedal gets softer after the first few stops which is when it starts pulsing. This morning I came to a complete stop at a stop light and the pedal felt like the correct level of firm and smooth. While sitting at the light the pedal sank to the floor and chattered the rest of the way to work. Does that sound like air in system?

 

OP do you have ABS on your truck?

The ABS system can get wonky and cause a pulsating pedal (even without the ABS light flashing).

Otherwise perhaps re-bleeding your brakes would be a good move, just to rule out any trapped air.

 

It does indeed have ABS. Would doing brake work cause it to get funky like that? I also recently replaced the load sensing valve thing.

 

Hard to say. Did you at all touch the ABS wheel speed sensors (located behind the backing plate on the rear axle assembly - one at each wheel)?

An easy way to rule in/out ABS involvement would be to remove the secondary ABS fuse from the fuse box, and drive around for a day or so. If your pulsating pedal goes away, you know it's an ABS issue (which then opens a whole 'nother can of worms). Be aware, this will cause an ABS light to illuminate on the dash, but the system will be disabled.

 

That's a really good idea. I'm planning on bleeding the brakes again tomorrow and will pull that fuse as well. Just throwing shit to see what sticks at this point. On the ABS thing, would it make sense to slow down smooth until a certain point in the pedal travel and then starting chattering?

 

When you did this brake work- LSPV and rear brakes- did you cap off the brake lines or do anything to prevent fluid loss? Particularly with ABS, it's important to minimize fluid loss to prevent air bubbles from getting into the ABS modulator. Outside of a Toyota SST there is not a great option to bleed the ABS system. It's kinda just go out to a dirt road and mash on the brakes a few times, return home, bleed the brakes, rinse and repeat.

That being said- you need to check off some simple things before pointing the finger at the ABS. What method are you using to bleed the brakes? Old fashioned way (one person pressing the pedal, while another open and closes the bleeder valves)? Are you using a pressure bleeder (Motiv or knock off)? A vacuum bleeder, etc... I will say that in my experience, that the Motiv pressure bleeder produces exceptional results, while the old fashioned method can be hit or miss.

You could have caused the master cylinder or brake booster to fail on such an old truck with all this brake work. So those are things to consider.

Generally- It's hard to suggest the right course of action here, cause you're describing multiple issues. Pedal pulsing / vibrations are generally caused by excessive runout on a rotor or drum. Pedal soft/firm is fluid/master cylinder/brake booster. ABS has it's own unique feel to it- and you can hear the pump modulating the brake fluid; it's pretty obvious when something is out of whack with the ABS. If you don't hear the ABS pump modulating the brake fluid, you can almost certainly cross that one off the rabbit hole you've opened up.

Oh- and this is all assuming you did the rear brake work right, and adjusted the shoes correctly. IMO (which some here disagree with), it's easy to over adjust the shoes so that they are making too much contact with the drum. If you've done that, you might be warping the new drums due to excessive shoe drag.

 

Good point, I do know the ABS sound as I do a lot of snow driving. We didn't take any fluid loss measures when swapping the LSPV, so maybe we fucked up there. I used a clear rubber hose on the bleeder valves to check for air bubbles, but maybe we didn't circulate the whole system. I'm praying I didn't do any master cylinder/booster damage as that seems like a project. Thanks for the input, I'll report back tomorrow.

Edit: after doing a quick Google search it sounds like a failing booster would result in fluid loss and poor braking. I haven't lost a drop of brake fluid and the braking has been fine, just feels like shit. I'm not ruling it out just thinking out loud

 

Sounds like you should start with a solid system bleed. I cannot recommend enough the Motiv bleeder AND a 3rd party adaptor (Motiv, themselves do not sell a Toytoa/Lexus adaptor, but they can be easily found in the jungle for reasonable prices). You load up the tank, pressurize it, and then go around with a bit of tube leading to a catch can, open the bleeder, and let it go until you see clear fluid without bubbles coming out. It's super easy to replace fluid in (almost) the entire system- still the same problem with the ABS here. It's so good that my friends who work on their cars come over to my place afterwards to re-bleed their systems when they do brake work.

 

Sweet, it looks like harbor freight sells a knockoff for $25. Obviously not the best but it's in stock near me. I'll lyk how it goes

 

If both the MC and brake booster fail, or rather if the MC fails it can leak fluid into the booster, causing it to eventually fail, and you'd never see a drop of fluid on the ground. Not saying you have this issue, but just something to be aware of.

 

Had a car that braked perfectly until it slowed to 30 mph. At 30 mph and below the ABS would engage. It was a cracked ABS ring which was not being picked up ABOVE 30 MPH. Below 30 and it detected a larger gap between the reluctor points and would come on...

Just sayin'...

 

OP, don't forget that this was the exact moment your trouble began. Pull your new drums off and have them turned at the machine shop. This is very common with new drums. Try pulling your emergency brake while driving down the street as a test. This will only activate your rear brakes and you will probably feel pulsing. Be careful doing this and don't lock up your rear brakes.

 

I did the rear brakes and LSPV together, so it could be either. I currently have the LSPV rod mounted in a way that sends most of the brake power to the front and have tried it in different positions, with the same results. I can feel the rears engaging to different degrees as I move the rod but the pulsating does not change. That being said if I can't figure this out this weekend i will have a shop look at the drums.

 

I'd at least try the emergency brake test. That would help you isolate the pulsing to front or rear brakes.

 

So I'm pretty confident it's air in the lines, I don't get the pulse when yanking the parking brake. Tried to bleed them again and there is a noticeable difference in the pedal now. I must've been not paying attention when bleeding it the first time because the bleed valves on the front calipers are fucked up. That being said I'm sure there's air in the system as I can't bleed the front end.

 

I just wanted to close out this thread if someone stumbles on it in the future. I finally got around to fixing my front calipers and properly bleeding the system and the problem is almost entirely gone. I'm thinking another bleed could do it. I had to pull the front driver caliper off the truck, clamp it to the workbench, get it red hot, and crank the bleeder valve off to replace it.

 

I'm following up on this thread a few months later. I have bled the brakes half a dozen times, and the pulsing persists. After each bleed, it chatters at a different point in the throw of the brake pedal. As of now, it chatters almost at the top of the throw and gets smoother as more pressure is applied. Before I bled the system last week, it continued to pulsate a bit farther into the compression of the pedal. Does anyone have any idea what this is? Am I bleeding my brakes incorrectly?

 

Could it be that thread I read in post #14?

lemme search……

 

https://www.tacomaworld.com/threads/rear-brakes-pulsating-after-replacement.716858/#post-29961063

 

I am becoming more convinced this could be the problem/solution. Powerstop sent me another set of drums a few months ago but still have the issue. They could be storing them all upright in their warehouse.