Need break help 89 FJ62 (1 Viewer)

[Barclay]

I have bled my breaks and feel that all of the air is removed from the lines along with all the old fluid. Problem is that I ahve a good firm break peddle when the engine is off but once I start the truck, the peddle gets soft and goes almost to the floor. does this mean that the booster is bad??

Thanks in advance.
David Barclay

 

[Kynot62]

Doing what you said it should go down slightly but not to the floor.

When you step on the pedal several times with the engine off there should be no change in what's called the pedal reserve (distance off the floor)

Other check is to let the engine run for one or two minutes, shut it off step on the pedal several times slowly, If the pedal goes down all the way at first but rises after the second and third times the booster is air tight

Last check is to step on the brake pedal with the engine running, stop the engine with the pedal depressed. If there is no change in the pedal reserve after 30 seconds the booster is airtight.

Thats all the checks in the FSM for the booster. When you bled the brakes did you also bleed the bypass valve by the back axle?

Sometimes it's a pain to get all the air out, could still have air in it.

Tony

 

[chitown40]

Many folks forget to bleed the LSPV above the rear axle. Make sure you do that.

 

[Barclay]

I think the LSPV has been removed from my truck. Even if there was air in that valve, would that effect the firmness of the pedal while truck was running verus not running??

David Barclay

 

[Kynot62]

Do the rear wheels lock up on a regular basis? If not the LSPV is still there. Look to the left of the rear diff at that rod attached to the housing, follow it up and it is hooked to the bypass valve. Would be odd that it's not there.

The pic shows where its at.

Tony

 

[Barclay]

Its not there previous owner did remove. The truck has disk breaks on the rear. As for locking up the rear, never has happened, the front will lock up.

David Barclay

 

[devo]

Check to see if the master cylinder is larger than the OEM. It should have at least a 1 inch MC, say off of a FJ80 or 75 series. Also if the rear brakes are the Eldorado calipers there is a good chance you can not push enough fluid to fill the caliper to get that firm sensation under foot. If the previous owner put rear disc on did he also replace the front OEM calipers with 4runner calipers? If so you can't use the stock MC and have to use the 1 inch MC.

I think if the brake booster is not working it should be hard to push the pedal due to lack of assist.

devo

 

[Kynot62]

I would find a good mechanic to look at the entire system. The previous owner has extensively modified things (ie the disc brakes and the removal of the proportion valve) and as such I would suggest you find someone to look things over.

Odd that the front will lock up but not the back. This in itself is a bit of a problem. There could be a proportion valve in the system that is not set correctly but that would require someone to have a good look and find it.

Posting your location (city and state) might make it easier to suggest a shop that may be able to help

Tony

 

[cruiser911]

Mine did this and i had to bleed the master cylinder and then rebleed off the brakes,

 

[Barclay]

Thanks for all of your help and ideas. I will take it to a shop and see what they have to say, and yes it has the larder MC. I stilll very confused as to why the brake peddle gets soft only after the engine is started?? By the way I am located in Russellville, Arkansas.

David Barclay

 

[devo]

I would suggest that the pedal gets soft because of the vacuum assist that you get from the brake booster.

disconnect the vacuum line from the booster while the engine is running and see if the pedal firms up.

devo

 

[mtb_rider]

I just got done fighting a very similar issue in my 62, and agree with the previous posts. The pedal softens up after you start the engine due to the vacuum assist. I just rebuilt my entire back brakes and did a full system flush (along with new front pads a little over a month ago) and after doing that work, had a softer pedal than I did before doing the brakes, no matter how much we bled them. I was at the point of replacing the MC. But then went back and bled the LSPV. Not only did I get a bunch of air out of it, but the fluid was still muddy brown after doing the flush. Bled until fluid was clean and solid, now my brakes feel great.

Where yours will get more complicated is that it's so heavily modded.