Spongy Brake Pedal

[JCook5003]

So guys, I'm completely on my last nerve with my brakes. I have an 84 Toyota truck which has a swapped in 20R and 5 speed.

I recently rebuilt the back IFS axle brakes with Land Cruiser wheel cylinders and all new hardware and pads. The fronts are stock solid axle calipers.

Now the problem.....I've bled the brakes a ton at the calipers and wheel cylinders and the LSPV. The pedal is still super spongy, it will grab great near the floor but literally has no pedal pressure or feel.

Ideas or suggestions?

 

[JCook5003]

One more thing....truck does have a 1" bore master cylinder already installed by the PO.

 

[flash02]

So are the back brakes now disks? Is the master cylinder new?

Bleeding toyota brake systems with that effing load sensing proportional control valve can be a....pain in the ass. The FSM will give you very specific procedures to beed the system, I've fought with my brakes time and time again and have finally gotten my brakes to work well, still I feel like I shod have a better pedal feel.

 

[JCook5003]

Rears are still drums. Master Cylinder isn't new but is only about 2 years old but the truck did sit for a year without running.

 

[coryc85]

I have the same setup as you, the LC wheel cylinders in the back, a 1" bore master, and I have the V6 IFS calipers up front. Does your e-brake work? If your rear shoes are grabbing with the ebrake, then the rears should be properly adjusted. My adjusters were frozen up and the ebrake didn't really hold. If they are not frozen, the shoes still may not be out far enough, you may have to pull the ebrake a bunch of times to get the adjusters to turn enough clicks. If that is all good and your ebrake grabs just fine, then I'd say you've got an air pocket in there.

 

[KLF]

If you pump the brake pedal, does it get firmer? This can indicate excessive bearing runout in the front wheels, or the rear shoes need to be adjusted. Ya, check that the e-brake is keeping the rear shoes adjusted. Do you use your e-brake?

 

[flash02]

Okay, some more ideas....you really need to make sure the rear brakes are adjusted, if they are not then that could be the cause if the spongey pedal. I really think a lot of these issues, min too, are due to the LSPCV, I feel that it allows the back brakes to pull too far from the drums. I've heard about people removing the Toyota LSPCV and installing a an adjustable proportional control valve which also has a residual vale.

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[JCook5003]

So to answer a few questions. I dont have a rear e brake anymore, I run an All Pro T-Case E Brake. It seems like I'm hearing about the back brakes not being adjusted a lot, how can I confirm they are adjusted correctly/adjust them?

The truck doesnt get driven yet, it's in the final stages of being built up.........does that matter.

Typically on first pump the brake goes all the way to the floor and will still grab hard enough to lock the tires in gravel right against the floorboard. If I pump it up say ten or so times I get what feels like a normal pedal as long as I hold it in. As soon as I release the brake pedal it goes back to almost the floor and needs pumping up again.

I've bled the crap out of them, it's hard for me to imagine there being air in the system still......I guess it is possible, I used the bleed sequence over on Pirate in the FAQ and it matches the one in my factory manual.

I'm literally going nuts over these brakes. I just want to drive the darn thing.

 

[KLF]

OK, then I am relatively sure your rear brakes are out of adjustment. And, since you don't use the factory e-brake anymore, there is no way for them to automatically adjust as the shoes wear. So, you'll be manually adjusting them occasionally. Each time you yank on the factory e-brake, it sets the adjustment.

My advice? If you can afford it, and since you're already taken care of the hard part (e-brake), phone up Sky Manufacturing and order up the brackets and parts to convert over to rear discs. I did, much easier to work on. Monte Carlo calipers are surprisingly cheap, like $15 each loaded, from NAPA.

 

[JCook5003]

My advice? If you can afford it, and since you're already taken care of the hard part (e-brake), phone up Sky Manufacturing and order up the brackets and parts to convert over to rear discs. I did, much easier to work on. Monte Carlo calipers are surprisingly cheap, like $15 each loaded, from NAPA.

Yeah I've been pricing all the odds and ends, like you said the hardest and most expensive part of the swap is already done. I might as well just go ahead and run the disks, honestly I'm tired of messing with it. That might be the least painful.

Did you remove the LSPV at the same time? Did you swap in a manual proportioning valve and residual valve? Those two things I know nothing about but know lots of people are doing it. Advice/Opinions?

 

[KLF]

I still have my LSPV, but it's going away when I put the truck back together. I have a Wilwood manual valve that will be under the hood, and I'm gonna try a residual valve, see how it works out. Some need it, some don't.

 

[snobdds]

How have you eliminated the master cylinder as being good?

 

[JCook5003]

Yeah the Master Cylinder was new as of two years ago........I cant imagine it's bad.....

 

[snobdds]

Yeah the Master Cylinder was new as of two years ago........I cant imagine it's bad.....

That's not a very good way of eliminating the source of most spongy break pedal problems. You could adjust and bleed and bleed, when it's the MC the entire time. Internal leaks are hard to diagnosis and are more often than not the problem...

 

[JCook5003]

That's not a very good way of eliminating the source of most spongy break pedal problems. You could adjust and bleed and bleed, when it's the MC the entire time. Internal leaks are hard to diagnosis and are more often than not the problem...

Well is there a way to check it other than just replacing it?

I know the brake shoes are probably not adjusted correctly, I never adjusted them when I installed then and I no longer have an e brake to adjust them automatically....

 

[snobdds]

Push your brake pedel in....does it hold steady for as long as your foot is on it (engine running & don't pump)?

 

[JCook5003]

No. It gradually fades until it sinks to the floor. If I pump it up to good pedal it will hold that pedal though until I release it.

 

[snobdds]

Sounds like your master cylinder is bad, or at least won't hold pressure. The bad thing is that could also be an air pocket in the line somewhere and needs more bleeding.

With the price of new Master cylinder being relatively cheap, I would get a new Aisin MC. For hydraulics I like to stick with Aisin, which is the OEM supplier.

Then Bench bleed the MC then connect the lines and do a full bleed on the system a few times...

 

[KLF]

Do the free stuff first: adjust the rear brakes. Check runout on the front wheels/rotors. Do a proper bleed (LR, RR, RF, LF, LSPV), see if it helps. If not, then pull the MC, take a look at the piston/cups/bore. It's a pretty simple system.

 

[JCook5003]

Do the free stuff first: adjust the rear brakes. Check runout on the front wheels/rotors. Do a proper bleed (LR, RR, RF, LF, LSPV), see if it helps. If not, then pull the MC, take a look at the piston/cups/bore. It's a pretty simple system.

No need to adjust those rears.....I just ordered the disk brake kit from Sky, I found the calipers for $14 each locally and the rotors for $22, I can turn them myself on the lathe to the bigger bore.

After that I guess I'll take a look at the MC if it doesnt solve the problem.

KLF, could you post a link to the proportioning valve you used and the residual you are looking at?