hptechnician

All, I have an 85 4Runner w/ SFA. I replaced the master cylinder, both rear wheel cylinders and the brake lines from the rear wheels to the block on the rear axle. I CAN NOT get the back brakes bled. The front is brakes are good.

I have tried everything to purge the air from the rear. I disassembled the load sensing valve, carefully cleaned (basically rebuilt it) and reinstalled it (the jets at the bottom were clogged with crud). I have bench bled the master cylinder and then installed it only to get air in the system again. I have even bench bled the master cylinder on the truck too. The entire line from the master cylinder to the rear (top line straight off the master cylinder) has air. I even used a vacuum pump on the rear trying to pull the air out while the master cylinder pushed fluid in... no dice.

I noticed the master cylinder is sitting with it's front up in the air - not level. Could this have something to do with it? Does anyone have any other ideas on how to solve my problem? This is all I need to fix to get it drivable!

aalan

Try this.
Get a clear plastic glass or container and fill it with brake fluid. Loosen the bleed valve on one of the rear cylinders. Place a small clear hose over the bleed valve, it must be small enough not to allow air around it. Place the other end of the hose in the container of brake fluid. Have someone pump the brakes while you look and see if air is blowing out of the hose, it should be. Then when you let off the brakes it will suck fluid back in. If you cant get any air blowing through that line you have a problem elsewhere.
Chances are you are just airlocked somewhere, kinda like a fuel line with the Carb.
Hope this helps.
Let us know. We'll be watching!

hellfire

thanks this will be helpful

brownbagg

its the lspv on the rear axle, they always give problems bleeding brakes

4Crawler

iTrader: (3)

Are the bleeder valves on the rear brakes clogged? I recently ran into one clogged rear and one clogged front bleeder on my '85. Pulled out the bleeder and used a wire to run down the opening and clear out the crud that plugged it up. Then used a solvent rinse bottle to flush out the inside. After that I had no problem bleeding the brakes. I use a vacuum setup, but recently replaced the hand pump with an electric vacuum pump, that really works well.

johnnyjay

I had the same problem when I did mine. I got a brake booster off of an 89 which was bigger than my original 85 and rebuilt both axles. So I had no fluid at all for about a week. I tried everything but what worked for me was asking my wife to pump the brakes and crack the lines. Over and Over again. It took about 5 times but I got it done and it now stops on a dime. If I could only get it to speed up as fast as it stops I will be set. Try the old fashion way.

desertcamper67

So if you've tried the pump and hold method with no luck try this: Have your helper push down on the pedal AFTER you open one or both rear bleeders on your new wheel cylinders. Once the pedal is all the way down, close the bleeder(s) then your helpers foot can come off the pedal. Once the pedal is all the way up top again open the bleeder(s) then have him push the pedal back down. It doesn't have to be fast or hard just ride it all the way down. Repeat this but check the master cylinder fluid level after about 3 tries.
This has worked so many times for me with an uncooperative bubble. This way the fluid and bubble(s) only travel one way. Out the back.
I hope this works for you. Good luck.

Oh yeah, did you pinch off the rubber line going to the steel line on the axle when you did the cylinders? And if so did you remove the tool? Sounds silly but I've seen home mechanics do this stuff. Why did the steel lines need to be replaced? Are your other steel lines okay?

hptechnician

OK so I have pretty good brakes now. I replaced the rear diff. and in doing so I had to pull the rear axles. That required me to remove the rear lines. Since they were rusted, I just cut / replaced them. When I went to bleed the lines, I snapped a bleeder on the wheel cylinder off.

I also replaced the master cylinder. It was leaking bad around the bottom of the reservoir. I replaced it with a rebuilt one from the local parts store.

What I finally did to get brakes was bleed the master cylinder as directed in the documentation that came with it. Then I used a vacuum bleeding kit from Advanced Auto Parts (around $60). I connected the vacuum to the rear line right before the load valve thing. On the other end of the line I connected a clear plastic hose and stuck it in a new bottle of fluid. I used the vacuum to pump fluid into the line.

I basically rebuilt the load sensing valve. I dismantled it and cleaned everything with carb cleaner. The little jets at the bottom were all plugged.

I still had to do some "pump and hold" on the brake pedal once I connected all the lines back up, but I seem to have pretty good breaks now. If anyone wants more detailed description, let me know.

aalan

Yeah. I would like to know what the load sensing valve is. I have not messed with mine, but when I first hit the brakes on a cold start they will nearly go to the floor until they get pumped up. After that everything is fine.

DoveGray85

The Motive Products power bleeder works well. It's about 70 bucks, well worth it to avoid a lot of aggravation. It will also save your master cylinder from being damaged from all the pedal pumping.

kasko

Not sure if your breaks are better yet. I was having kinda the same issue. I replaced almost EVERYTHING with new and still next to no brakes. I started to use an old brake caliper to bleed every fitting on the rear breaks starting at the "T" on the rear axle looking for possible air leaks. (You can have a leak that lets air in but shows no sign of a fluid leak) I worked my way up to the 90 degree fitting by the right front tire. It ended up being that fitting was bad, which was the one thing I did not replace new. It was letting air in but showing no fluid leaks. Replaced it and have wonderful breaks now. hope this helps