Brake pedal soft and mushy after new pads installed... (3 Viewers)

[ashooter]

Just replaced the front brake pads on my 92 FJ80. When I used a screwdriver to pry the pistons back enough to remove the old pads, and install the new ones, some brake fluid overflowed out of the reservoir... I figured it was just reduced fluid capacity, since the old pads were just about gone and the new ones are about a half-inch thick.

After installing the new pads, the brake pedal is super soft and mushy, so I bled the brake lines, starting at right rear, then left rear, then right front, then left front... Topped off the reservoir under the hood between each brake bleed. Some air came out the front brakes, but not much (if any) out the back brakes.

Fired up the truck and brake pedal was still mushy/soft, so bled everything AGAIN - this time bleeding each brake until I had pretty new, clean fluid coming out. Again, there was more air that came out of the front brakes, but I bled the heck out of them until I was getting no air, and reasonably clean fluid coming out, and again topping off the reservoir between bleed sessions - probably topped of 3 or 4 times for each front brake before I had bled enough to be satisfied. Anyway, reservoir never got low enough to start sucking air into the system from the top.

Went through almost 2 Qts of brake fluid by the time all was done.... Fired up the truck, pedal is STILL soft/mushy. Definitely NOT safe to drive.

Any ideas what I've got going on?

Thanks

 

[jpoole]

Maybe your caliper pistons have some corrosion or gunk on them and pushing them back in has caused issues like seal damage. Similarly, if your master cylinder had been operating in the same range for a long time and this work caused it to travel into a new range the rubber seals/cups could have encountered roughness in the bore and could also be damaged now. I've encountered both of these issues, esp. with cars that aren't drive that much and could leave parts of the caliper pistons exposed for a long time or parts of the MC bore unused for a long time. Add in older fluid and the risk of issues like this only go up due to the water that the fluid will collect/store.

From your description the only change you made that would have impacted the hydraulic system for your brakes was pushing the pistons in. Did you take any other steps that could be related like opening a brake line anywhere in the system, etc.?

 

[Wompom]

Do 91-92s have an LSPV? If so bleed it...

 

[jpoole]

Agree on bleeding LSPV and possibly ABS pump too if you have them. How air got into the system and the pedal became soft is the question though as compressing caliper pistons shouldn't typically cause this unless there are issues.

 

[ashooter]

Do 91-92s have an LSPV? If so bleed it...

Yeah, I didn't think about the LSPV... Wouldn't bleeding all the way at the rear brakes suck any air in that part of the system back through/past the LSPV though?

No ABS pump... that I'm aware of.

 

[jpoole]

Wouldn't bleeding all the way at the rear brakes suck any air in that part of the system back through/past the LSPV though?

You need to use the bleeder port on the LSPV itself when bleeding these rigs. Even when that step is taken it can be hard to get a good bleed.

I personally use a pressure bleeder and also some brisk pedal strokes for each bleed step in the process. I also bleed lines on the abs, etc. because even though I've replaced all brake system components on my 80 besides the hard lines, ABS pump (and computer/wheel sensors to try for accuracy) I still suspect there's room for improvement.

 

[241lux]

the calipers will be rooted or one of them anyway ,air has got in somewhere its most likely dirt has got into the seal as you pushed the piston back. Weather the calipers are worth rebuilding is another story everything I take off most toyotas is flogged out not worth rebuilding maybe Im a lazy parts changer.

 

[jpoole]

what @241lux said. I wouldn't be worrying with bleeding at this point unless you are just trying to collect more info. I'd plan to rebuild or replace all calipers and the master cylinder too unless it's newer. You should be able to buy OE rebuild kits and OE pistons if you want to rebuild yourself. Replace any piston with visible issues. I have the part numbers for my '97 but I don't think they'll help you. It wasn't expensive to rebuild my calipers and replace with new mc (around $100 total I think) and going ahead and doing them should save you a lot of headaches and wasted time bleeding when there are other problems. Do not use non-OE rebuild kits, the rubber will likely not last long at all after exposure to brake fluid.

 

[ashooter]

So, to bleed the LSPV, I would need to go through the whole bleed process again, correct?...

Start at farthest bleed valve from the master cyl (right rear) and work my way forward, NOT skipping the LSPV this time....?

 

[ashooter]

jpoole wrote: what @241lux said....

Ugh... Hoping to avoid that whole new project, which will keep the truck out of service for a couple of more weeks waiting for parts, and doing the work.

 

[241lux]

does it have an electric component to the booster ?some Toyota's do and if the ignition isn't on its a pain to bleed, I haven't seen an 80's for a while.

 

[jpoole]

@ashooter Good luck! If that's the goal then trying a few more bleeds may be worth a try but I wouldn't be too optimistic if I were you and I'd start organizing the parts order. I'd also be gentle on the Master cylinder and not push it all the way through it's stroke while bleeding if you can avoid it.

If you aren't trying to minimize how much you spend you can possibly get calipers and MC from your local Napa fairly quickly, as in within a day or two. Napa used to the a good option for calipers in particular, and may still be. As long as there isn't anything weird with '92 brake parts you should be able to get OE parts from a number of online sources within a week or so.

 

[ashooter]

241lux - I don't think having the engine on would make much difference. I've bled the brakes in the past, and it worked fine with the engine off. Just have a helper pump-pump-pump, then hold (the brake pedal down) while I quickly loosen the bleeder valve and let some air/fluid out before the hydraulic pressure is gone. Then repeat... over and over.

 

[241lux]

no just the key on so the electric component is energised,

 

[jpoole]

Booster is vac driven so no need for key on for these unless there is something I've missed with the older or foreign market versions.

 

[landtank]

the LSPV is part of the front circuit and should be bled after the rears and before the fronts.

 

[ashooter]

Bled everything again, and there's no change in the brakes.

Feels pretty much the same as when I had a leaking brake line - pedal goes down, gradually loses firmness like it's losing pressure. Truck does slow down and stop, but very gradually (dangerously weak braking). There is NO fluid leaking anywhere, though. Just feels like it's losing pressure in the system, same as when I had the leaky brake line a few months ago.

I'm thinking I may have either damaged something (seal or boot) inside a caliper or inside the master cylinder when I pushed in the pistons in the calipers and fluid blew out under (or through) the cap on the reservoir.

Questions:

1) Any comments/advice related to the above?

2) Would it be worth a try to just replace the cap assembly on the reservoir?

3) If I just shotgun it and replace the whole master cylinder assembly and both front caliper assemblies ("brake cylinder" in the FSM), do I need to also replace the "booster" or do anything with that?

Thanks

 

[jpoole]

Sounds like an internal MC leak because you are losing pressure, with pedal fall, but have no leaks externally.

In this case it wouldn't be the shotgun approach to replace or rebuild front calipers and MC as there's good reason to believe both have issues. I'd definitely replace the rear calipers as well so that the system is all updated at the same time and the additional parts cost is not much higher, though the labor to replace them separately at a later date surely would be. I'd also closely inspect the LSPV for leaks (fluid can be captured in the rubber boot around the arm if there's a slow leak) and I'd replace it if it's leaking or consider replacing it if it's original/really old. Now is also the time to inspect your rubber hoses/lines. If they are cracking and are very old it's easier to replace them now than breaking the system down again to do them in a year or two.

I know that's a lot of parts to replace but the way that these issues came up indicates that you may have had older/contaminated fluid in the system for a while and/or the parts are at least pretty old. Given those possibilities updating the hydraulic/wear components in the brakes makes a lot of sense and is a high priority place to keep in good order even if you have to spend a few extra $$. I've been down this road many times with older autos and often have tried the minimal/cheap path of only replacing a few items. That only works if you know that the rest of the system is in good shape and/or recently replaced, otherwise when one item fails it's a decent indication that the other equivalent items are soon to go as well.

No need to touch the booster as it typically makes your pedal harder and brakes weaker when it starts to fail.

I wouldn't worry with the cap replacement. The OE equivalent Advics MC at least comes with a reservoir and cap already in place for a great price.

If you want to save money and have time rebuilding all with OE parts and a careful eye for your caliper piston and MC bore conditions is a great option. Otherwise buy the best new/rebuilt parts you can and plan to bleed the heck out of the system when it's all back together.

Plan to fully flush your brake fluid every two years moving forward. Brake fluid is designed to absorb water, which it does very well, and after a few years there is water trapped in the system that starts eating away at it. Corrosion forms on the surfaces that the seals ride on and that eats the seals, etc. Regular fluid flushes can extend the service life of brake parts a lot.

 

[ashooter]

Thanks jpoole! That correlates with some advice from an old mechanic I just ran into at the post offc a few minutes ago who used to have a shop. Described to him what my symptoms are and he said it sounded like I messed up a seal inside the master cyl when forcing fluid backward through the system pressing in the pistons in the calipers. Makes sense that what I'm feeling is pressure bleeding off as fluid runs around/through a bad seal inside the master cyl.

 

[ppc]

You never want to push fluid back into that master cylinder. The bleeder screw should be opened to allow the fluid out as the pistons are pushed back. Pushing the pistons back by prying them with a screwdriver can cause them to bind. You should remove the caliper and use something like a C-clamp centered on the piston to push it back equally. In addition to pushing old contaminated fluid back into the master cylinder it can also be pushed into the abs pump screwing up the sea!s located there.

Best practice to keep the brake fluid fresh is to fully flush the system each time any of the pads get replaced.