oy, brakes. (1 Viewer)

[bryancostanich]

hi all,

i have a '72 FJ55. i did the rear disc brake conversion, put the '84 monte carlo calipers and pads on, did a front axle swap with a '78 FJ55 with disc brakes, replaced my brake booster, master cylinder ('78 version), and most of my brake lines and hoses.

put it all together, bled it, tightened things up some more, tested it out.

it stops better than before, but i can't get the brakes to lock up, and i have to double-pump still for effective braking. on the second pump the pedal goes half way down and is solid, but the brakes still aren't great.

any ideas? bleed more? or am i just expecting too much? 4 wheel disc brakes with a brand new booster and master cylinder should be able to lock the wheels no?

 

[mooker82]

Did you take out the residual valve? Install a proportioning valve?

 

[vk7ybi]

Should be able to lock wheels. I suggest more bleeding. Make sure the calipers on the rear are on the proper sides, and that the bleed valve is at the top.

I've found that the best bleeding results on my 40 can be had with the gravity method.. What I do is remove the bleeder valve completely from the caliper, remove the reservoir caps and let gravity pull the fluid down.. Assistance can be provided by reinstalling the cap and pressing on the breather cap on the cap so that it forms a seal with the cap, then pressing the cap down creating positive pressure in the reservoir.. I usually run about 1/4 reservoir volume of fluid through the line to make sure its all flushed and clean.. reinstall the bleeder valve with fliud still draining.. Start with the caliper farthest from the master and work back to the shortest. With this method and 4 wheel discs, a 1 1/8" master the brakes start working right at the top of the pedal and pedal travel before lockup is probably an inch or so.. I need a smaller master.

 

[KLF]

I'm no expert on 40/55's, but I'll toss this out there to consider...

What size is your master cylinder? I think you need a 1" with 4-wheel disc brakes. Made a HUGE difference when I installed RDB on my pickup, I also went with the Monte Carlo calipers.

 

[bryancostanich]

Yup, installed a proportioning valve, removed the residual valve, installed a 2lb residual valve for the rears. valves are on top. i installed speedbleeders too.

I'll bleed the system some more. seems like i bled the s*** out of it, but i'll give it another go.

-b

 

[LRS30]

Does anybody have the link for the rear disc brake up-grade, and a parts list break down.. I would love to do this with mine..Thank's

 

[Poser]

Does anybody have the link for the rear disc brake up-grade, and a parts list break down.. I would love to do this with mine..Thank's

Frequently Asked Questions list stuck at the top of the 40 section topics.

 

[bryancostanich]

just to be clear, on the brake cylinder i put in, there was no residual valve.

 

[2fpower]

I posted this a couple hours ago, but did not show up.... user error?

Here is a hillbilly back woods method I have used with great results. As we know air wants to rise in hydraulic fluid enviornment, however we try to push it down and out the cylinders. Try this. Start with the furthest from the master, and pull the caliper off the rotor, take out the pads and put a c clamp on it that will allow for about 3/4 of movement. have someone pump the brakes. You may want to put a towel under the master now. Hold the capiper in your hand with the brake line at the top. Crank the c clamp down, effectively forcing brake fluid back up through the system. You should be able to see bubbles coming out of the master. Do it a couple times per wheel. Then reassemble caliper. Do each wheel like this.

Good luck

 

[bryancostanich]

I bled it again, got rid of the double pump issue, but i still can't lock them. it does respond super well now, i'd say maybe half inch down on the pedal and i start to feel it. i suspect i'm still leaking a little pressure somewhere, so when i get some time i'm going to go look through it again.

one thing i noticed though, after a little bit of moderate braking, my front rotors were hot to the touch. not sure what that's about, perhaps they're retaining pressure or something. kind of weird, since there isn't a residual valve on that front set.

 

[bsmith123]

discs

Ive seen a fair few writeups on brakes dragging and locking up after a couple pumps that came down to the adjustment on the rod out of the MC


But you may want to consider a metering valve, A metering valve makes sure that the back brakes get pressure before the front
as opposed to just a proportioning valve that sends less pressure to the rear. Both work together to make the brakes work better. A metering valve will also reduce work load on the front discs


Also is your MC a disc/disc, disc/drum, or drum/drum MC? Drums take more flow/less pressure than discs.

 

[PhilC64]

I have a similar setup as Bryan except that I am using a 92 4Runner MC. Am I making a wrong assumption that I do not have to use a proportioning valve with my 4 wheel disc set up?

I finished my brakes tonight and used a ghetto fab pressure bleeder. bleeder I've used it on 2 FJ40's and a couple of times on my 62. Works like a charm.

 

[bryancostanich]

i thought it was a disc/disc. but fxxx, it may not be. it's a master from a '78, and i was told that it would be a good match for what i want to do (disc/disc) - but that year had discs up front, not rear. there was no residual check valve that i saw in there. maybe i missed it. blech.

you know, the thing is, even if it were a disc/drum master cylinder, i should still be able to at least lock up the front brakes, no?

 

[fj404life]

New rotors/pads take some time to seat in...also could you have contaminated the pads during install? Just tossing ideas out.

 

[bryancostanich]

they're super clean. i got pictures to prove it. hahhaha

 

[bryancostanich]

i documented my install in my build-up thread: https://forum.ih8mud.com/40-55-series-tech/269434-72-fj-55-buildup.html

 

[bsmith123]

brakes

Maybe some one who has used a MC for disc/drum will pipe up on how it worked. I dont know that it would necessarily cause a prob I just know they are different. my pref though would be to use the whole system together as designed-disc/disc

good call on the contam maybe a spray down with the brake cleaner and make sure they are not glazed. I used to rough em up a little with sandpaper before install

 

[bsmith123]

proport valve

Am I making a wrong assumption that I do not have to use a proportioning valve with my 4 wheel disc set up?

Phil

Use of the proportioning valve does not change with type of brakes---that is the residual valve. Residual valves keep pressure on the seals on rear discs or keep the pistons from retracting too far on drums. Usually 2lbs pressure for discs and 10 lbs for drums


The proportioning valve gives more pressure to the front brakes than the rear because there is more weight on the front and you can apply more braking force. Without it you will get less than optimum braking force on the front

A metering valve gives rear brakes pressure first then front

so you could have all 3 valves in a disc/disc combo or a combination valve combining metering, proportioning, and the differential pressure switch that gives the low fluid light


Sorry I am not familiar with your particular set up just brakes in general

 

[bryancostanich]

i talked to marf over at SOR today, he took a look at my setup, said it looked like i did everything right, but that what is likely happening is my booster isn't giving enough assist, and that i should put on a booster from a '93 or newer landcruiser (first year they had 4 wheel disc brakes).

@bsmith123 - oh, and i think drum brakes are 6lbs residual pressure, not 10lbs, no?

 

[jtoro]

Are you sure the callipers are correctly aligned on the disk? Take a look at the surface of the pads, they should show contact on ALL their surface. You should also check on the soft line from the chassis to the rear axle, if it was not changed, you might have a problem there, they wear and loose their strength, allowing part of the pressure to dissipate thus loosing braking power.