Repeated brake bleeding

[Radish150]

I seem to be having some trouble getting ALL the air out of my brake system (67 all manual). The master and all the cyls are new so there are no leaks, so no new air should be getting IN, but I have taken it down to the monkeywrenchers to have them bleed the system now about 4 times now and each time it seems better but soon the pedal is sinking down a again and a pump or two will bring it up hard. I've had them pump it up hard and release the bleeder under pressure, as well as just open the bleeder, then press the brake pedal, close the valve, release pedal, repeat. The problem is starting to get on my nerves... any advice?

thanks

 

[fieldsken1]

put a tube from each bleeder into a bottle and open bleeder and leave open all night. the bottle so it wont make a mess anyway open bleeders and leave alone all night and they will gravetilly bleed. then see what happins in the am

 

[60fj25]

If you put a new master cylinder on you probably need to bench bleed it. Basically it's bleading the master before you try bleading the entire line.
here's one post, There are more. (I know it's a post about clutches but the pic is of a brake master)
https://forum.ih8mud.com/40-55-series-tech/156411-bench-bleed-clutch-master-cylinder.html
I don't know why you can't do that while the MC is still on the vehicle.
In this post, Pinhead said gravity bleeding should also work and I respect his knowledge. I didn't know about gravity bleeding when I tried and was not able to get a good pedal until I bench bled.

 

[Blue77FJ40]

To bench bleed the master while on the vehicle, take two pieces of brakeline to make some specialized tools! Measure, cut, and bend some brakeline pieces to fit where the system brakelines attach. One end will obviously have a flare, and the other end is just cut. Detach the system brakelines and have the tool brakelines go from where they attach on the master and loop them into their respective filler bowl, well below its surface level when filled. Once the brakeloops are in place, just keep pumping until there are no more bubbles. Then just reattach the system brakelines. Sorry, no pics, but my master bleeder loops look like the letter "J" if that helps.

 

[srgould41]

I recently rebuilt the brakes in my '71. New master and all new or rebuilt cylinders. I had a heck of a time bleeding too. I finally burped the upward facing cylinders by removing the puck, fill the cavity with fluid, rotate one side of the cup up to release air trapped under it, rotate it back down, clean out the fluid on top of the cup, put the puck back in (don't forget to block the lower puck so it won't fall out the bottom while you are working on the top). It was messy and a PITA and still didn't remove the need to pump up the brake pedal. Before this procedure I had a full pedal throw worth of travel and after burping the cylinders it was down to about an inch or so. Adjusting, readjusting, and more readjusting got each side even finally. That resolved the last bit of the pump up. I didn't think it could be that drastic. I swore there was still air in there.

Oh, and I never bench bled the master. Instead I loosened the brake lines at the master and bled fluid out there...

Do some searching, there are others who used this method successfully.

Steve

 

[Trollhole]

If you have the CCOT master that is your problem.

Asin is the only way.

 

[FJROSS]

I have a 77 FJ40 that I replaced the rear cylinders with CCOT's wheel cylinder and had the same problem. Stock wheel cylinders use a metal plate that seat up against the spring and a rubber seal. The CCOT cylinders use just a domed rubber seal that goes up against the spring which is where the air gets trapped. It took me over a week to figure this out and during that time I got so frustrated that I ordered the rear disc brake conversion. By the time the rear disc kit arrived, I figured out that there was air trapped in the cylinders. After burping the air out while the cylinders were in place, I had a rock hard pedal. No regrets on the disc conversion, one of the best upgrades I ever did. If you look up past threads by me (FJROSS) there's one called ( Brake problem finally solved) that describes the procedure.

I recently rebuilt the brakes in my '71. New master and all new or rebuilt cylinders. I had a heck of a time bleeding too. I finally burped the upward facing cylinders by removing the puck, fill the cavity with fluid, rotate one side of the cup up to release air trapped under it, rotate it back down, clean out the fluid on top of the cup, put the puck back in (don't forget to block the lower puck so it won't fall out the bottom while you are working on the top). It was messy and a PITA and still didn't remove the need to pump up the brake pedal. Before this procedure I had a full pedal throw worth of travel and after burping the cylinders it was down to about an inch or so. Adjusting, readjusting, and more readjusting got each side even finally. That resolved the last bit of the pump up. I didn't think it could be that drastic. I swore there was still air in there.

Oh, and I never bench bled the master. Instead I loosened the brake lines at the master and bled fluid out there...

Do some searching, there are others who used this method successfully.

Steve

 

[srgould41]

It was FJROSS's write up that I used to resolve my own issue. Thanks FJROSS!

I have a 77 FJ40 that I replaced the rear cylinders with CCOT's wheel cylinder and had the same problem. Stock wheel cylinders use a metal plate that seat up against the spring and a rubber seal. The CCOT cylinders use just a domed rubber seal that goes up against the spring which is where the air gets trapped. It took me over a week to figure this out and during that time I got so frustrated that I ordered the rear disc brake conversion. By the time the rear disc kit arrived, I figured out that there was air trapped in the cylinders. After burping the air out while the cylinders were in place, I had a rock hard pedal. No regrets on the disc conversion, one of the best upgrades I ever did. If you look up past threads by me (FJROSS) there's one called ( Brake problem finally solved) that describes the procedure.

 

[Radish150]

"Tiny bubbles.... in the line, make me giggle" Thats Don Ho you savages!

put a tube from each bleeder into a bottle and open bleeder and leave open all night. the bottle so it wont make a mess anyway open bleeders and leave alone all night and they will gravetilly bleed. then see what happins in the am

Hey, well this method sounds appealing for sure... but how much actual fluid will drain out with the air bubbles? Will I have to temporarily attatch a 50 gallon drum of brake fluid to the master so it wont drain dry in the night? Just off the top of my head that sounds like a way to drain all the fluid out of the system and replace it entirely with air . I trust though, that that is not the case.

Also, the looped brake for purging the master is nice... thanks.

 

[Radish150]

srgould41:

You did WHAT??? Just kidding, I hope it does not come to that. Letting them sit all night as per fieldsken is much more my style !

 

[fj404life]

I went through 2 aftermarket masters that gave me a double pump pedal and after a few days both started leaking inside the firewall. Finally gave in (got wise) and ordered an OEM. Good pedal and no leaks!

 

[fieldsken1]

Hey, well this method sounds appealing for sure... but how much actual fluid will drain out with the air bubbles? Will I have to temporarily attatch a 50 gallon drum of brake fluid to the master so it wont drain dry in the night? Just off the top of my head that sounds like a way to drain all the fluid out of the system and replace it entirely with air . I trust though, that that is not the case.

Also, the looped brake for purging the master is nice... thanks.

well if the bleeders are at top none or very little fluid will come out but the air will go to the top

 

[Trollhole]

Says it's for a 55. hmmm Wonder what the difference in the 40 and 55 brake master was back then. Especially for a single circuit.

ALL-FOREIGN CAR PARTS - Import & Domestic Car Parts, Import & Domestic Truck Parts, Brakes, Rotors, Distrubutors

 

[brider]

Firm pedal? try adjusting...

Before you do anymore bleeding, jack each wheel up and get VERY familiar with the Landcruiser drum-brake adjustment procedure. Since you didn't mention that you did the hardware swap yourself (or maybe I missed that), I'll bet that each of the (8) wheel cylinders were NOT properly adjusted, resulting in the familiar double-pump-then-hard (that's what SHE said!) syndrome.

Basically, if your pedal stays hard after pumping, that's an indication that the air is actully bled from the lines, but the required pump is opening the cylinders up to make pad contact. I just did this in my 55.

BTW, I got one of those fancy vacuum-tank bleeder setups where you "pump" the tank to a vacuum, open a valve, and the vacuum SUCKS the air/fluid thru the lines and out the bleeder. Reduced bleed time by 90%.

 

[Radish150]

Ok Brider thanks, will do.

 

[Texx]

I'll save you the research. Adjust each cylinder until it locks the wheel, not just drags. Back the adjuster off 3 clicks. Repeat 7 times. If your master is bled, start at the farthest wheel cylinder from the master, bleeding in order. It'll work, at least some. Drive it a few days, it'll get better. Worked for me, x20+ times.

 

[Pin_Head]

X3 on adjusting your brakes first. If the brakes aren't adjusted, it will always take two pumps to get a pedal.

 

[lostmarbles]

X3 on adjusting your brakes first. If the brakes aren't adjusted, it will always take two pumps to get a pedal.

And my experience with drums-all-round is that "correct adjustment" can be difficult to achieve with worn linings (even where those linings all exceed minimum-thickness specs).

I believe the outside-surface of the linings should ideally conform to the same radius/curvature as the drums that they "mate" with.

And linings that have done 170,000kms or so (probably a "lower mileage figure" in the case of a petrol-engined FJ40 where you have little engine-braking) are usually worn too much on their "leading edges".

...........My 2c



PS. In July 1996 @ 175,000kms, I replaced my ex-factory shoes/linings (which were all still well-above minimum specs). And this made a tremendous difference to my being able to get my brake pedal up high.