BJ40 brake mystery (1 Viewer)

[Rojo Viejo]

1980 BJ40 in Costa Rica. Front disc brake conversion by previous owner. What the heck is this hose coming off the rear brake line splitter? It appears to be just a piece of braided rubber hose about a foot long, held upright by a tie wrap with a solid plug clamped in the end. It looks somewhat factory original. What does it do? I have not seen it on any parts drawing or in any service manual. Could it have anything to do with me not being able to get the air bled out of the right rear (last in the chain / farthest from the master). I tried vacuum bleeding and suspected air was being pulled in around the bleeder threads. I sucked two bottles of fluid through, the fluid was clean but still lots of air - big bubbles. Today I used the two man method with an assistant, pushing a full bottle through with the same results - still lots of air. If air is leaking INTO the system, why is fluid NOT leaking out somewhere. Where is the air getting in? I have pulled all wheels and drums and inspected wheel cylinders and front caliper pistons. No fluid leaks. Moving on up the chain, both front brakes and the left rear (1st, 2nd and 3rd in line from the MC) bled successfully, no bubbles. The other problem is the brake pedal goes to the floor the first time you push gently. But if you stomp it hard or pump it up, the pedal is hard and holds / does not leak down. I installed a new master cylinder even though the old one wasn't leaking out the back seal. It didn't seem to make a difference. I guess it wouldn't be the first time someone got a new master cylinder that was bad. I bench bled the new MC, and bled it again when connecting the lines, then bled the wheels starting with the farthest from the MC (RR on mine). I never let the reservoir get low. Having the motor running doesn't seem to make any difference and the booster is getting and holding plenty of vacuum. I tried to rule out rear brake adjustment by expanding the shoes all the way out until the wheels were locked. Still have to pump the brakes up. I may be dealing with multiple unrelated issues. I am stumped.

 

[jim land]

maybe the diff breather

 

[Living in the Past]

maybe the diff breather

X2 That type of clamp would not hold brake fluid under pressure. Remove it and you will find a opening in to the housing. Reason is to prevent water from getting if the axle is under water.

 

[Rojo Viejo]

I would have never guessed that. Coming out of the brake splitter like that gives the impression it is connected to the brake system somehow. I see it now in the differential parts drawing - "rear axle breather hose". Thank you! (Still have brake problems tho..)

 

[bj40green]

Pumping the pedal means that you are compressing air. When you release the pedal the air expands and you're back at 0.
You can't compress brake fluid but you can compress air. So you still have air in your system.

Rudi

 

[Rojo Viejo]

Rudi - I agree, it must be air. But where is it coming from? Is it possible for me to run 5 or 6 x 12oz bottles of fluid through the MC and out the RR bleeder, never letting the MC get low, and there STILL be air in the system? Isn't this amount much greater than the total volume of the system? No air is coming out the other 3 wheels' bleeders. Should I continue to bleed and put fluid through it no matter how much it takes? I guess I have to, as long as air bubbles are still coming out. Am I bleeding in the correct order - furthest to nearest the MC? RR, LR, RF, LF. My brake line runs along the left (driver side) frame rail, then splits at the axle to right and left. One port on the MC feeds the fronts, the other feeds the rears.

 

[Stumpalama]

Bench bleed the MC before installing.

 

[Rojo Viejo]

Bench bleed the MC before installing.

I ran clear hoses from the 2 MC ports back into the full reservoir submerged in fluid, then pumped it until no more air bubbles. When I installed the MC, I started bleeding by cracking the fittings on the MC under pressure to let out any air bubbles that may have entered when I was connecting the lines. I tried vacuum bleeding the wheels, then 2 man bleeding. I haven't tried gravity bleeding. Does that really work?

 

[Rojo Viejo]

Pumping the pedal means that you are compressing air. When you release the pedal the air expands and you're back at 0.
You can't compress brake fluid but you can compress air. So you still have air in your system.

Rudi

Is the air I am bleeding out of the system all that there is, and it's just a matter of getting it all out? Or is there some way air can be entering the system without there being a visible fluid leak somewhere? (No air has entered the MC since initial filling and continued replenishing.)

 

[aljollano]

I had the same problem that you are having in my fj43. I ended up bleeding the system with a brake bleeder pump. Some where in the line there is a spot where air stays and is harder to get it out but that pump is a great tool to have.
A.J

 

[handcannon]

Do you know if the brake cylinders are stock or aftermarket? At the moment I can't say just where I read this, but I have read of others who have had problems bleeding all the air out of aftermarket cylinders. To alleviate this some have had to remove the rubber boot from the upper end of the cylinder, slightly lift/tip the piston to allow brake fluid to fill the last of the upper part of the cylinder, thus removing the last bit of air from the system.

Don

 

[bj40green]

Do you know if the brake cylinders are stock or aftermarket? At the moment I can't say just where I read this, but I have read of others who have had problems bleeding all the air out of aftermarket cylinders. To alleviate this some have had to remove the rubber boot from the upper end of the cylinder, slightly lift/tip the piston to allow brake fluid to fill the last of the upper part of the cylinder, thus removing the last bit of air from the system.

Don

This works only for one cylinder because the other one is up side down. Turn both (4x) fully out before bleeding.
I read two things in your story:
- It seems that you suck in air every time you release the brake pedal which is why you keep getting air bubbles every time.
- And / or an air bubble is moving forth and back which is causing the soft / pump pedal. This air bubble is probably in the MC area because the brake lines are too small to let and air bubble move back and forth.

I had a similar situation and went to a "Taller" who attached a pump cap held in place with a "tourniquet" on one of the reservoirs and pumped fresh brake fluid into the lines.

Rudi

 

[Rojo Viejo]

My rear cylinders were replaced last year. I'm pretty sure they're stock, and there was no problem bleeding the system after installing them.
I had a Motive Power Bleeder back in the US when my obsession was Porsche 928's. I sold it when I sold the 928's and moved to Costa Rica, thinking I would never need it again (since the cap was for Porsche 928). It was absolutely the easiest way to bleed brakes. I should be able to cobble together a "power bleeder" here using a small bug sprayer (or maybe my AC flush gun), some hose, an extra MC cap and a large hose clamp.
Rudi - I was careful to close the bleeders before my assistant ran out of peddle and released each time. And I kept the end of the bleeder hose submerged in fluid.

 

[DSRTRDR]

you still have air somewhere in the system - bleed the other brakes, too

 

[Stumpalama]

Notice any leaks? A cracked or swollen hose? could something be cross threaded/not fully seated?

 

[landcruiserrich]

Sounds like theres still air in your master cylinder. I like to use a syringe full of brake fluid and squirt it in through the outlets of the mc. Ive never had much luck doing the clear tubing recirculating method. If that doesnt work then i would try throwing your old mc back on.

 

[landcruiserrich]

Also when youre bleeding the wheel cylinders and calipers and getting someone to pump the brake pedal for you, make sure theyre using slow, complete strokes and pumping at least 5 times. Quickly pumping the pedal may not push the air bubbles all the way out and makes it harder to bleed.

 

[Rojo Viejo]

Wait a minute... I might be on to something here. Shouldn't the bleeders be at the top of the front calipers? It's possible the mechanic who rebuilt the calipers for me last year switched sides when he reinstalled them. If this is what's giving me problems, how was he able to get them bled and have a hard pedal? Maybe he "bench bled" the calipers before installing? I'm not getting any air when I bleed the fronts, but maybe there's a big bubble stuck at the tops?

 

[handcannon]

Yup! In order to bleed properly the bleeders MUST be at the highest point. Good eye!

Don

 

[Rojo Viejo]

I switched the front calipers. With the bleeders at the top, the brakes bled easily, quickly and completely. Now I have a rock hard brake pedal. I could have pushed a 55 gal. drum of fluid through the calipers with no bubbles and still have air in the system - trapped at the top of the calipers. I feel a little stupid with the problem right under my nose all along. Sometimes the obvious goes unnoticed. Pura vida!