No Brakes on '87

[Arcking]

I'm having trouble with the brakes on my '87 pickup - not a 4Runner, but I believe it has a similar brake system. The brake pedal goes ALL the way to the floor, with very little resistance. After rigorous pumping of the pedal, some resistance can be felt, but the truck still doesn't slow noticeably.

When bleeding the front brakes, only fluid exits (no air). I haven't been able to bleed the back left brake due to a rusted bleed screw, but the back right brake seems to endlessly bleed a substantial amount of air. I have not been able to bleed the LSPV due to an issue with the bolt for allows for bleeding. You can feel all four brakes working to some extent when the truck is up on jack stands. As another note, after pumping the brakes the fluid in the reserve appears aerated.

Does anyone have any ideas as to the cause? Why do the front brakes not provide any stopping force? Is there a chance that this is due to not being able to bleed the back left or LSPV? Could the LSPV be bad? Any chance there'd be a hole in the line (return line) that wouldn't be leaking?

 

[DC runner]

You probably have a combination of bad master cylinder and a leak in the line.

If you have a leak in the line, the Master Cylinder can still usually build up pressure until you run out of fluid. Once managed to get my truck home with a rusted out rear brake line by purchasing several bottles of brake fluid and going very, very slow. Using engine braking to coast down. If I had to brake more than a few times, it would squirt out...

So. My point. Even with a huge gaping hole in your rear brake line; a functioning master cylinder can usually build up pressure to get the front brakes to stop. You seem to have 0 ability to build pressure. My guess, your master cylinder is shot. Gaskets gone.. any number of reasons; and have no pressure to stop the truck.

 

[Arcking]

Replaced the MC, both wheel cylinders, and lines from the cab back. Removed the LSPV as well. Still can't get all the wheels to lock up on gravel, though the right side will (especially right front) without having to pump the brakes. Any ideas? Have straight fluid from all 4 bleeders.

 

[SV_Dude]

Do you have any fluid loss when you pump your brakes? Also, in what order did you bleed your brakes? The proper order for bleeding the system is to start with the longest hydraulic line and work around the vehicle to the shortest line, and then do the LSPV last. So in this case, the order is: driver's rear wheel, passenger rear wheel, passenger front, driver's front, LSPV.


Some good reading for you:
Care and Bleeding of Your Brake System

 

[Hyde802]

.. I haven't been able to bleed the back left brake due to a rusted bleed screw, but the back right brake seems to endlessly bleed a substantial amount of air. I have not been able to bleed the LSPV due to an issue with the bolt for allows for bleeding.

I think you need to bleed these and get back to us.

I would recommend getting rid of the LVSP all together and get a manual valve to replace it.

 

[Arcking]

I think you need to bleed these and get back to us.

I would recommend getting rid of the LVSP all together and get a manual valve to replace it.

I think you must have missed my previous post - I've replaced both rear wheel cylinders (which includes the bleed screws), as well as removed the LSPV all together.

I haven't noticed any fluid loss when pumping the brakes. Bleed order was driver rear, passenger rear, passenger front, driver front.

 

[SV_Dude]

It still sounds like you have a lot of air in your system...

Have you ruled out your brake booster? Usually your symptoms do not indicate a brake booster though.

 

[Arcking]

It still sounds like you have a lot of air in your system...

Have you ruled out your brake booster? Usually your symptoms do not indicate a brake booster though.

How do I know when I've bleed the system 'enough'? I stopped bleeding each wheel when only fluid was released. Any chance one of the front calipers could be causing the problem?

I have not reviewed the brake booster - what would I do to check it?

 

[SV_Dude]

Since you replaced the MC, you probably had air in the MC area of the brake system. I would bleed the brakes enough to get a good amount of fluid out of each brake. Basically enough fluid to flush the lines. If you use a clear tube and attach it to the bleeder and a clean bottle then you can reuse your fluid so you're not wasting a bunch of it.

To test your booster do the following:

With the truck off, pump your brakes until you feel the brake pedal get firm. Keep pressure on the brake pedal and turn the 4runner on. If the brake booster is working then your pedal should almost sink to the floor.

 

[ToyoTech]

did you bench bleed the MC before install. that should help alot. like SV dude said. without bench bleed the MC you tend to have really small air bubbles at the MC

 

[Arcking]

As far as I can tell the booster seems to be fine. I did bench bleed the MC before installing it.

I'm going to bleed the system again in a week or so. Is there anything special I should keep in mind to ensure I get rid of any air present in the MC area? Do I need to be tapping on the MC while I'm bleeding, or anything like that?

How do I know that the brake pedal is adjusted correctly (travel-wise)? Do I risk destroying the MC if I adjust it incorrectly?