Master Cylinder Residual Valve

[FJROSS]

I replaced the existing O.E.M. master in my 70FJ40 with a new one. I've tried everything to resolve the 2 pump pedal. I even picked up a O.E.M. master rebuild kit. From what I've read, the front brakes have a 2 pound residual valve and the rears have a 6 pound. If I look close there are number cast into the top of the plastic valves. the rebuild kit has a #1 and #2. I believe the ones that came with the new O.E.M. were #6 and #14. Does the smaller # go to the front brakes and the larger to the rear? I'm just trying to solve the brake pedal issue. They have been bleed and adjusted several times, new shoes, cut drums ect.. ect.. ect... I may decide to go to rear disc eventually and have read that you can remove this valve and try using the O.E.M. proportioning valve thats mounted to the master or replace it with an ajustable depending on the load. Downey offers a inline 2# inline valve, does the adjustable proportioning valve do the same job? Thanks Dave

 

[mr_manny]

Not familiar with Downey's valve...I thought 2-lb valves are for disc brakes, and 10-lb are for drums.

I'm running a 4whl-disc supra master, which I added front and rear 2-lb in-line residual pressure valves to (running 4wh discs).
My brakes would slowly lock-up after a few miles of driving, so I removed the guts from the in-line valves before identifying my booster-rod adjustment problem.

https://forum.ih8mud.com/40-55-series-tech/112525-help-newbie-brake-problem.html

you might have too much play in yours...also did you bench bleed your replacement master?

 

[FJROSS]

Thanks for the reply mr_manny. I also srarted out with the same gradual brake lock up problem with my stock disc/drum set up that led to replacing most of the brake system. I believe that 31 years of not changing the fluid turned the fluid to thick muddy mess, this may have stopped the pressure from neutralizing and causing the lock up. My brakes would release after about a half hour. Yes I bench blead and also pressure blead. As for as the booster rod lenght, I used a soft piece of plumbers putty and checked the distance between the master and the booster rod that was adjusted to 3/32 to 1/16". The only other thing is that I was about a half inch short of the F.S.M. on the pedal height adjustment. The pedal is adjusted all the way up to the point where the rubber on the brake pedal is hitting the brake switch mount so there's no more adjustment for a longer pedal throw. Thanks Dave

 

[Mr. Toad]

Re: 2 Pumps:

Check these two things: Drum brake cylinders not adjusted far enough out, or a MC that has the wrong bore size. The latter is more common that you might think.

Did you have the 2-pump problem before the MC switch?

 

[Pin_Head]

If you need more than 1 pump, the drum brakes need adjusting (tighter). End of story.

 

[rusty_tlc]

If you need more than 1 pump, the drum brakes need adjusting (tighter). End of story.

Exactly, this cures it every time.

 

[FJROSS]

Re: 2 Pumps:

Check these two things: Drum brake cylinders not adjusted far enough out, or a MC that has the wrong bore size. The latter is more common that you might think.

Did you have the 2-pump problem before the MC switch?

No, brake pedal was hard but I had the lock up problem after driving awhile. Master was replaced with the same stock O.E.M. unit (available from Toyota) that was on the truck. Brake drums have been adjusted numberous times. The last time they were adjusted I made sure that the cylinders were equally adjusted outwards till I couldn't turn the tire by hand and then backed off 2 clicks. Brakes were applied a few times to make sure they were centered than readjusted. As per my first post, I even rebuilt my 1 week old master to rule out it was'nt faulty with the factory rebuild kit. Is there any possibilty that the residual valves in the new master and rebuild kit is not keeping enough pressure to the rear drums to only need 1 pump for a hard pedal? The numbers that are cast into the original plastic valves does not match the valves in the replacement master or the parts that came in the rebuild kit. I don't know the numbers off the top of my head but I believe that the small number cast into the plastic valve was in the front brake line so thats the way I reinstalled the rebuild kit, with the smaller of the (2) numbers to the front. Thanks Dave

 

[Mr. Toad]

Interesting.

Can't offer anything more except to check to see if the new and old MCs have the bore size stamped in them. E.g. 7/8", 1", etc. Compare them.

See this post. Smaller bore = more pedal travel.

 

[65swb45]

No, brake pedal was hard but I had the lock up problem after driving awhile......Thanks Dave

This is a CLASSIC sign that the pushrod that actuates the master cylinder has not been properly adjusted. It provides a little too much engagement, or more accurately, does not provide full disengagement. Brakes gradually end up engaging themselves.

Loosen the pushrod.

Hint: you will need a measuring devise to set the correct length for the rod.

Best

Mark A.

 

[Pin_Head]

Is there any possibilty that the residual valves in the new master and rebuild kit is not keeping enough pressure to the rear drums to only need 1 pump for a hard pedal?

No.

Did you adjust both wheel cylinders on each wheel?

It is hard to imagine what could cause this besides brake adjustment. If your new master had a much lower volume than the old one I guess it could need two pumps.

 

[Fast Eddy]

I had the lock up problem after driving awhile. Master was replaced with the same stock O.E.M. unit (available from Toyota) that was on the truck.

...

Is there any possibilty that the residual valves in the new master and rebuild kit is not keeping enough pressure to the rear drums to only need 1 pump for a hard pedal?

I had "the lock up problem" until I removed the residual valve from the front brake circuit.

I assume you're using the stock residual valve? Have you fully cleaned it out? Otterav said his was full of old gunk and his brakes worked great after it was properly cleaned out.

 

[lostmarbles]

Well here's my 2c worth FJROSS.

Not changing the fluid for 31 years means there would have been crud everywhere!

But if you're sure the "residual valve" chambers are free from crud - I'd forget about the residual valves. (That area is a favoured place for crud to accumulate.)

Here's a picture of my residual valves :


There's a factory-installed hole that ensures mine can NEVER do the job claimed of them. (Yours are probably flatter white thingies but they probably work/don't-work the same.)

Edit May 2010 .... My understanding now is that a Residual Valves DOES maintain residual pressure within the brake lines it feeds but only while the return springs are pushing the wheel-cylinder-pistons back after a brake application has finished. (The purpose of this temporary "residual pressure" is to help keep the seal lips securely pressed against the cylinder walls while the pistons are moving and thereby help avoid fluid leakage.)

The job of stopping the linings from being pulled too far off the drums (by the return springs) is performed by the ADJUSTORS and not the residual valves. (So the residual valves don't "help limit wheel-piston-travel" because the adjustors already do that.)

I suggest you play with varying the length of the pushrod between the booster and master (again) PROVIDED YOU ARE SURE YOU HAVE NO CRUD IN THE SYSTEM.

Oh - and the only other thing. My brake lines after the master travel UPWARDS (as they are routed along the firewall) before dropping DOWNWARDS. This "loop" tends to trap air unless I power/reverse flush those lines. (Just something else to be aware of.)

Hope this helps.

 

[Pin_Head]

Also check for a "ballooning" rubber break line. These things can cause crazy problems.

 

[FJROSS]

First I would like t thank all of you for your help. I hope I can answer some of the replies to help eliminate some of the problems. The entire brake system was flushed with solvent except for the master, the proportioning valve that mounts to the mc and the front calipers. A quart of fresh fluid was rinsed thru the lines to remove any solvent. All (4) hoses were replaced with new O.E.M. as well as a new Toyota master with the same 7/8"bore as the one removed. Dual stage booster was replaced with a NEW mini truck booster. The booster to pedal rod needed to be cut approx. 1/4" and the booster to master rod was adjusted by measuring and double checked with a pc of soft putty for a clearance of 3/32 to 1/16". Rear wheel cyclinders were replaced with ccot units. Master was bench blead and then all lines were manually pump blead, only to find the 2 pump pedal. I thought I still had air in the system so I pressure blead through the master and even broke the hard lines at the frame and hose points to see if I could remove any trapped air. After reading some past post I came to the conclusion that if there was air in the system that the pedal would always be soft and not get hard on the second pump. For $28.00 I thought I would also rule out the possibilty of fluid getting past the seals of a faulty brand new master and installed the factory rebuild kit. I also read repeated post about improper brake adjustment. I adjusted the brakes several time all the way out till they could no further move and than backed off two clicks, drove the truck to center the shoes in the drums and readjusted to have the same problem. I even adjusted all 4 cylinders out till they couldn't be moved and tried the brakes like this to eliminate the possibility of any excessive throw that would give me the second pedal pump, still same problem. If disc/drum master have 2 pound residual valves for the fronts and 10 pound for the rears, are the white bakolite residual valves responsible for these pressures. If so. neither the Haynes or FSM never mention any specifics on the placement of these valves in the rebuild section. The Toyota rebuild kit has no instruction or mention either. The original master had a #1 cast into the front valve and a #2 into the rear valve. The new O.E.M. master had a #13 in the front and #14 in the rear if I remember. So when rebuilding the new master I put the reidual valve of lesser value to the front disc and higher # to the rear. You would think if there is a differance (2 pounds front disc and 10 pound rear drums) that it would be specified in the FSM. Do you think Toyota could be producing these masters with all disc residual valves? I was almost thinking of installing the 31 year old rear residual valve back into the new master. Does the proportioning valve that mounts to the master have anything to do with this and for that fact what the **** does it do? If this was bad, could this cause a problem Today I even visually inspected the front calipers by compressing the calipers and seeing that the pistons are moving. I appreciate all the help and this has now become a quest before odering the rear discs. Thanks Again Dave

 

[lostmarbles]

Heck. With all your "brake work experience" Dave, you must know a darn site more than me about this.

Perhaps all I can give you is moral support really. But I'll spew out a few more words........................... cos I'm always verbose.

The way I see it, regardless of what the "residual valves" and "proportioning valve" are supposed to do, provided they are full of fluid - how can they absorb "one-complete-pedal-movement's-volume-of-fluid" and thereby stop your brakes from being applied on the first pump? Surely they can't!

Which means - If you haven't got trapped air - You're back to questioning what's happening with every brake piston in your system. There must be one there that is travelling far more than necessary.

(Unless you have a brake line bulging out like a balloon which is a possibility that Pin_Head suggested.)

Your mission - To seek and destroy the culprit piston (Well. Maybe not "destroy" but it doesn't sound as good without that "destroy" bit.)

PS. It might be time for "desperate measures". Perhaps you could try isolating different wheels to see if the problem disappears. Say - Using vicegrips to "gently" clamp various hoses (but obviously you must be careful not to damage the hoses. And I probably shouldn't even be suggesting this.)

 

[Pin_Head]

Do you have the wheel cylinders installed so that the bleeders are at the top?

I still think it is an adjustment problem. You can have a lot of air in the line and the pedal will be spongy, but it won't pump up like this where you get a firm pedal on the second pump. Are you sure that both adjusters are tightened so that they can't turn any more and the wheel is locked tight? You can lock it with only one shoe, leaving the other cylinder unadjusted.

Sorry if this is pedantic.

 

[FJROSS]

Do you have the wheel cylinders installed so that the bleeders are at the top?

I still think it is an adjustment problem. You can have a lot of air in the line and the pedal will be spongy, but it won't pump up like this where you get a firm pedal on the second pump. Are you sure that both adjusters are tightened so that they can't turn any more and the wheel is locked tight? You can lock it with only one shoe, leaving the other cylinder unadjusted.

Sorry if this is pedantic.

I layed out the wheel cyclinder as per the #s on the ccot boxes and there site. Since the the brake line tappings and bleeder tapping are in the center, is there a top and bottom for the bleeder? This is what I found this morning. My FMS says to tighten the shoes you turn the adjusters from the center of the wheel out to the rim. Mine is the opposite, to tighten I need to turn the adjusters torward the center of the axle.

 

[Pin_Head]

Yes, there is a top and bottom hole. I don't know what you mean by the "taps are in the center". Pictures might help.The bleeder is always at the very top because bubbles rise.

It sounds strange that you would have to turn them the opposite way that the manual says. Maybe you flopped them L to R? As long as you have tightened both adjusters so that the drum can't turn and the adjuster cant turn any more either, that is as tight as it gets. If you still have to double pump, something else is wrong.

 

[1969 FJ40]

I believe I read that you said that the drum had been cut. I assume you mean turned to clean up the surface. I am curious to know if it is possible one or both of the drums were turn past the maximum allowable diameter. My suggestion is to measure the inside diameter of the turned drums. I do believe that this situation of extra diameter would require more fluid to push the wheel cylinders and shoes out far enough to come in contact with a larger than spec drum diameter. I have known this to happen once. This Dia. spec should be in the factory service manual.

-Gordon

 

[lostmarbles]

I layed out the wheel cyclinder as per the #s on the ccot boxes and there site. Since the the brake line tappings and bleeder tapping are in the center, is there a top and bottom for the bleeder? This is what I found this morning. My FMS says to tighten the shoes you turn the adjusters from the center of the wheel out to the rim. Mine is the opposite, to tighten I need to turn the adjusters torward the center of the axle.

I'm working my way down these new posts so I haven't yet read any after this point Dave. But I'd like to say at this point that moving an "adjustment-wheel-notch" towards the centre of the wheel (on all adjustors) is the correct way to "tighten the shoes" (take up the wear by adjustment).

That is the way my vehicle is, and my vehicle is definitiely untouched (in that respect) from the way it left the factory.

So what you have is CORRECT as far as I'm concerned.