Brake Bias (1 Viewer)

[emac]

77 FJ40 front disc rear drum all new brakes, lines, wheel cylinders, booster, master, etc. Great pedal, good brakes except under hard braking. I am getting too much rear lock up. I backed off the rear shoes way more than the 4-5 turns the WSM suggests and they still lock up. Pedal starting to suffer, so that was too far. Tire pressure is about 26F 28R, running 235/85/16 tires. Owners manual calls for 22F 26R, but I haven't tried that low. Suspension/alignment is fine.

I am thinking the brake proportioning valve is bad. Has anyone tried this one from @Racer65? I like the way it fits without modifying the lines.

Adjustable Brake Proportioning Valve for Toyota Brake Lines - Fits FJ40

Or any other suggestions are appreciated.

Just thought I would ask, because rear lock up is dangerous in a vehicle like the FJ40. Thanks guys!

 

[JohnnyC]

Does the master have the residual valve still in it for the rear drums?

Front rotors new? Or cut? Rotors clean with no oils on it?

Rear drums new or cut?

 

[emac]

hmmm. Thanks JohnnyC, I never thought about the residual valve. My master is aftermarket. Maybe I should check the front line for a residual valve. As I understand the drums need the residual valve and the discs do not, correct? My rotors and drums are turned.

 

[emac]

Did some more reading I think I am going to remove the proportioning valve, take it apart and clean it. If that doesnt do it, then move on to an adjustable one. When I overhauled my brakes that valve was pretty nasty, and I just cleaned it out without taking it apart.

 

[ginmtb]

Here is @Racer65's proportioning valve installed on mine:

 

[emac]

I took apart the old corroded proportioning valve cleaned it real well, adjusting rear pads, bled the system and i still get rear lock up. Not as bad, but worse than I feel safe with. Especially since my son drives it.

I am going to order the adjustable valve and give it a try.

 

[JohnnyC]

Residual valves?

Also... is this a rebuild? Is there weight in the back? Or is the rear of the cruiser bare ?

 

[emac]

I didn't mess with the residual valves, since that seemed more important when doing drum to disc conversions. It is pretty much all rebuilt. no weight in the rear. It does have a small lift and new springs. I think the adjustable valve will do the trick. What are you thinking JohnnyC?

 

[JohnnyC]

I am thinking you need weight in the back... this IS a big reason for the rears locking up before the front

I am thinking you need to make sure there is no residual valve in front sys and you in fact have one in the rear ... when you had it all apart would have been a great time to in bolt quick and check

 

[emac]

I agree, but 99% of the time I don't have weight in the rear. I think the valve will allow me to adjust for how I use it. I feel it would be safer to have a little more stopping distance than rear lockup.

I had a close call several weeks ago with a dog, I hit the brakes hard, rears locked up and it started to swap ends. I let off and barely missed the dog but saved the rig. Dog ran right under the front bumper headed for a cat across the road. I was going about 45mph downhill on a back road. I typically don't brake too much for animals, unless I am certain it is safe to do so. I am a pretty experienced driver, so it wasn't too scary, but I worry about more inexperienced drivers, like my son!

 

[emac]

Well, the brake bias saga continues. I bought an adjustable proportioning valve from City racer. Installed, bled and no help. No matter where I adjust it, I dont seem to get much of a change. I checked the master for residual valves and they did not have anything in them. All four corners are getting pressure and bleed fine. I dont know why the proportioning valve isnt doing anything, unless the front just arent getting good pressure? Pedal is good, rears just lock up fast, almost like they are the only ones working. If I go in reverse and cram the brakes the front will almost lock up, so they are working. Maybe it has to do with the winch on the front? But, I really would have expected the adjustable valve to come close to no pressure at the rear, leaving the front to do the work.

I am thinking it is with the master cylinder. It is an aftermarket Cardone unit. I think I got what I paid for. It was cheap, around $50. I checked my brake lines to make sure rear went to rear and front to front! It still doesnt make a lot of sense. I hate throwing parts at a problem, but the master is a possible junk part. Thoughts?

 

[76 PTO]

Mine stops on a dime but the rears have too much bias even with Racers valve all the way closed. Maybe 2 proportioning valves in line?
Mine is very close just need a little less in the rear.

 

[emac]

Mine stops on a dime but the rears have too much bias even with Racers valve all the way closed. Maybe 2 proportioning valves in line?
Mine is very close just need a little less in the rear.

I went ahead and ordered a new Master. Aisin. Once I do that, I have to call it done as i cant think of anything else to try, except maybe some rear ballast!

 

[bikersmurf]

FYI, rear drum brakes will always lock before discs. Front Disc brakes won't lock under normal circumstances.

That said, poor brake bias can make it way worse.

I'd look for a shop with a skid pad to give you some before and after data to sort out the extent of the problem.

I'd also recomend 'soft' organic front pads and stay away from hard long wearing pads that'll never wear. My first set of $20 pads lasted 95k miles.

 

[nogo]

Fj 40/42

Drum/drum master cylinder size is 25.40mm, rear wheel cylinder size is 22.22mm.

Disc/ drum master cylinder size is 22.22mm, rear wheel cylinder size is 25.40mm.

You might want to check you have the right combination.
The bore size should be stamped/embossed on the master cylinder.

 

[emac]

Fj 40/42

Drum/drum master cylinder size is 25.40mm, rear wheel cylinder size is 22.22mm.

Disc/ drum master cylinder size is 22.22mm, rear wheel cylinder size is 25.40mm.

You might want to check you have the right combination.
The bore size should be stamped/embossed on the master cylinder.

Thanks for the info. That may end up being very helpful. I think my rears are 7/8. Why do places sell rear wheel cylinder kits for 1971-80. That would mean they are the same for all years??

 

[nogo]

Thanks for the info. That may end up being very helpful. I think my rears are 7/8. Why do places sell rear wheel cylinder kits for 1971-80. That would mean they are the same for all years??

Lots of different size wheel cylinders across the range of models, ie: the LWB pickup with disc/drum runs 28.57mm rear wheel cylinders, this size cylinder would decrease the reaction time of the rears even further.