Brakes - sanity check please (1 Viewer)

[Code Red]

OK, here's the situation.

Problem is a "sinking pedal" on my brakes. (i.e. I can pump it up to a hard pedal, but then it slowly loses pressure and sinks to the floor.)

1990 FJ62.
LSPV has been bypassed.
Sinking pedal last week.
fluid on outside of drum on driver's side rear.
E-brake still tight, but suddenly not holding.


This is my daily driver, and I didn't have time to wait for the weekend. I took it to a local shop and had them tear into the rear brakes. I suspected the wheel cylinder let go on the driver's side.

The fluid was coming from an axle seal. The shop told me there was no leaking fluid from the wheel cylinders.

In an abundance of caution, and because I wanted to eliminate one possibility, I told them to go ahead and do wheel cylinders while they were in there. The gear oil from the axle meant I was replacing shoes any way, so I went ahead and told them to go backing-plate out in the rear - i.e. new wheel cylinders, hardware kit, shoes, and drums (1 was too far gone to turn).

They did all of that, and the parking brake works again, but the sinking pedal is worse, and they couldn't bleed it enough to get me a consistently hard pedal.

I brought it home anyway, and bypassed the LSPV, thinking that this was a potential bleeding problem. That definitely improved the braking performance when they are engaging, but the sinking pedal is still there, and they only grab temporarily, then the pedal sinks almost to the floor. The front brakes (I think) are still functioning normally.

There is a slight (1 drop every five minutes of pumping and bleeding) weep on one side of the union I installed when I bypassed the LSPV. Perhaps an issue with the double flare. I am not worried about that. I can fix it, and I don't think it's losing fluid fast enough to be the cause of the sinking pedal. I have watched it from underneath while my wife rode the pedal to the floor and didn't see anything come out. No air coming from any of the bleeder valves. (went around three times, ran 2.5 quarts of new brake fluid through it. I am bleeding through a clear tube so I can watch for air. I am not getting any. I think I have it completely bled. No other visible leaks. But the pedal still sinks. It is currently undrivable.

I think its got to be the master cylinder, but would appreciate any other opinions/possibilities before I tear into it again.

Thanks!

 

[Spook50]

You've got a blown out wheel cylinder I'm still betting. Curious what brand the shop used. Do your rear brakes with new cylinders and fix the flare on the LSPV bypass. You'll have to bleed everything again so be sure you have a helper.

 

[Code Red]

Thanks Spook50!

Why do you think its the wheel cylinder rather than the master?

The wheel cylinders are new, Toyota, parts. ( I wasn't worried about the shoes, hardware kits, or drums, but I paid extra (and waited a couple days) to get OEM wheel cylinders). That doesn't guarantee that I didn't get a bad one. But I would have expected to get fluid coming out of the drums by this point if one of them was leaking that badly. The pedal will go all the way down in about 2-4 seconds, and has done so dozens (if not hundreds) of times since the new wheel cylinders were installed. If all of that fluid has been coming out of a bad wheel cylinder, then it should be visible by now, no? That said, it won't hurt to check. I'll pull the drums off and see if I can find any fluid on the inside.

 

[cruisermatt]

Sounds like MC

 

[orion]

Sounds like MC

x2

Bench bleed the new one REAL good before putting it on the truck.

- Brian

 

[Code Red]

Thanks guys. I'll pull the drums off just to make sure before I get started, but I just ordered a MC.

In the past I have always bench bled them using the little plastic tubes and fitting that come with the replacement MC. I am assuming the ASIN/ADVICS ones come with those as well.

 

[Spook50]

Thanks Spook50!

Why do you think its the wheel cylinder rather than the master?

The wheel cylinders are new, Toyota, parts. ( I wasn't worried about the shoes, hardware kits, or drums, but I paid extra (and waited a couple days) to get OEM wheel cylinders). That doesn't guarantee that I didn't get a bad one. But I would have expected to get fluid coming out of the drums by this point if one of them was leaking that badly. The pedal will go all the way down in about 2-4 seconds, and has done so dozens (if not hundreds) of times since the new wheel cylinders were installed. If all of that fluid has been coming out of a bad wheel cylinder, then it should be visible by now, no? That said, it won't hurt to check. I'll pull the drums off and see if I can find any fluid on the inside.

The more I think of it, the more I'm leaning towards @cruisermatt's suggestion of MC. Once there's enough pressure behind it, a seal is likely giving out. Were it cylinders like I first suggested, there wouldn't be an opportunity to build up pressure at all. That's what happened when one of mine went out many years ago.

 

[Godwin]

Once replaced a bad MC that if you hit the pedal hard the brakes would work well with a firm pedal. Roll up to a stop and give the brakes a more gentle push and the pedal would sink to the floor.

Just remembered that I've experienced this type of MC failure twice.

 

[YooperCruiser]

A sinking pedal is a classic symptom of a master cylinder that is bypassing

 

[Chris Cahill]

Master cylinder. Be sure to buy a good quality, new master cylinder, bench bleed before installing and then re-bleed the brakes. it's a pretty easy job. The new ones I have purchased in the past don't come with a cap so you will need to re-use the old cap.

 

[Code Red]

Thanks guys. MC on the way. Hope to install on Saturday. I'll post an update when its in.

 

[Code Red]

New MC installed. Pretty easy 2-3 banana job. No more sinking pedal. Back in service as daily driver.

I broke the die on the double flare tool, I'll have to get that next weekend, but it's not weeping like it was. I don't believe it things fixing themselves. So I'll probably go ahead and re-flare it anyway.

Start to finish, including bleeding the brakes, in about an hour. (10-15 minutes to bleed the new M/C, 5-10 minutes to remove the old and install the new. 20 minutes to bleed brakes. 20 minutes of head scratching and crawling around looking for leaks. Speed bleeders are great when doing that by yourself.

To answer my own last question, the ADVICS (new distributor for Aisin?) master cylinder did NOT come with the fittings and tubing for bench bleeding. I went to O-Reilly's for that and bought the $12 kit off the shelf. They also had a Dorman kit for $11 that only had one fitting per size (you need one for each port) and black tubing instead of clear. For an extra buck you get everything you need. Shame it's not included with the MC though.

 

[cruisermatt]

Bench bleeding MC’s is a waste of time anyways, so no worries there

 

[Godwin]

Bench bleeding MC’s is a waste of time anyways, so no worries there

I agree with this. Bolt it up, fill reservoir with fluid, have someone apply brake pressure, crack open the lines at the MC and go from there.

 

[cruisermatt]

Yep, never understood it, you have to bleed the lines at the calipers anyways, why make a big mess on your work bench too

 

[4runner2FJ60]

On harder braking is it normal for the 60 to pull to the right some? I have replaced everything brake wise and converted to the 4runner front calipers. She stops very well.

 

[2mbb]

pulling one way or the other is not what brakes are designed to do.

 

[Gretsch]

Yep, never understood it, you have to bleed the lines at the calipers anyways, why make a big mess on your work bench too

I never have understood it either. See folks talk about it all the time, but seems normal bleeding gets it done. Whats the thought process on the bench bleed idea? Whats it supposed to do that normal bleeding doesn't?

 

[cruisermatt]

I never have understood it either. See folks talk about it all the time, but seems normal bleeding gets it done. Whats the thought process on the bench bleed idea? Whats it supposed to do that normal bleeding doesn't?

It might seem crazy but…sometimes… people just repeat stuff they heard for decades without thinking about it

 

[cheezypoof]

I never have understood it either. See folks talk about it all the time, but seems normal bleeding gets it done. Whats the thought process on the bench bleed idea? Whats it supposed to do that normal bleeding doesn't?

The only thing I read that makes sense is the MC sits at a slight angle when installed in the truck and you might not get all the air out when bleeding. Who knows, but bench bleeding is easy and I didn't find it too much of a mess.