Rear disc proportioning issue, insite please (1 Viewer)

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Feb 14, 2007
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Houston Tx
So the rear monte carlo disc brake conversion has been mounted on the rear of the 77' 40. Removed the stock proportioning valve. Installed the 2lb residual valveright after the master cylinder and before the wilwood adjustable proportioning valve. With the prop valve adjusted all othe way out, the rear brakes still lock up before the fronts. I feel that I need to decrease the proportioning between the front and rear but am having trouble getting that worked out. Anyone have any thoughts on this.
 
Put the stock valve back in.... you need the original valve AND the adjustable.


Mark...
 
Now why is the stock prop valve needed in conjunction with the new? I was under the impression that the new prop valve would replace the old. Is it creating an add restriction in the line or what....I am a bit perplexed.
 
The oem valve reduces the pressure to the rear brakes... because drums need less pressure to work...... the oversize calipers in the GM conversion overpower the front breaks in this setup... neither the OEM or the aftermarket valve reduces the pressure enough to make up for this.
You need both valves to reduce the pressure enough.


simply how it is done :)


Mark...
 
Why did you install the residual valve? Everything I read said to remove the stock residual and proportioning valves and install an adjustable unit.
 
There is your problem. I believe as you CLOSE the valve, less fluid travels to the rear. Right now, you are allowing max fluid to the rear.

As for the rest of the comments, I ran my FJ40 without residual valve in stock master, NO aftermarket 2lb valve, and a summit prop valve with no problems.:meh: Must have hit a good streak:cool:

That's what I have right now for my configuration, and things seem to be adjusted pretty well. I do believe that adjusting the valve open cuts the braking power to the back though. (will double check)

jC
 
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Why did you install the residual valve? Everything I read said to remove the stock residual and proportioning valves and install an adjustable unit.


I doubt you will find anything writtenurging removal of the OEM proportioning valve. if so.. it is wrong.


The OEM residual valve needs to go... but an aftermarket. in line 2 pound valve gives a firmer pedal and is a nice addition.


Mark...
 
I doubt you will find anything writtenurging removal of the OEM proportioning valve. if so.. it is wrong.


The OEM residual valve needs to go... but an aftermarket. in line 2 pound valve gives a firmer pedal and is a nice addition.


Mark...

I have been following this becasue I am about to implement a rear disc conversion myself. let me get this straight - For a '77 FJ40, OEM configuration features a OEM proportioning valve AND an OEM 2lb residiual valve for the rear brakes?

I was under the impression that there was ONLY a 2lb residual valve in the OEM configuration.

Where does the OEM proportioning valve reside? Pics please. :beer::beer::beer:

Without hijacking this thread, may I ask if the above statement is also true for a 1979 FJ40?:confused:


Thanks,
Chris
 
Chris, I can't answer for all the information and mis-information above, but I can tell you how we've been doing it for about 10 light years:
(1) We instruct you to remove the factory 6lb. residual valve from the master cylinder. We instruct you to install our 2lb. residual valve down stream from the proportioning valve. If you leave in the 6lb. residual valve, your rear brakes would always be slightly applied all the time. Disc brake pads need only 2lbs. to keep them up at the rotors, 6lbs. is already squeezing!!!
(2) We instruct you to remove any OEM proportioning valve because they are not adjustable. We instruct you to install our adjustable prop valve slightly down stream from the master cylinder (near booster area), then go directly into the residual valve, then directly into rear brake line.
(3) After home install and home bleeding, we instruct you to go directly to a professional brake shop and get "power blead" and have the prop valve professionally adjusted on gauges.

A zillion guys are now going to tell you they didn't do what we recommend and that their brakes work just fine. Good for them, but we have to provide instructions that keep us from dealing with your widow and her attorney.
 
Proportioning valve is circled in red.
image.jpg
 
Chris, I can't answer for all the information and mis-information above, but I can tell you how we've been doing it for about 10 light years:
(1) We instruct you to remove the factory 6lb. residual valve from the master cylinder. We instruct you to install our 2lb. residual valve down stream from the proportioning valve. If you leave in the 6lb. residual valve, your rear brakes would always be slightly applied all the time. Disc brake pads need only 2lbs. to keep them up at the rotors, 6lbs. is already squeezing!!!
(2) We instruct you to remove any OEM proportioning valve because they are not adjustable. We instruct you to install our adjustable prop valve slightly down stream from the master cylinder (near booster area), then go directly into the residual valve, then directly into rear brake line.
(3) After home install and home bleeding, we instruct you to go directly to a professional brake shop and get "power blead" and have the prop valve professionally adjusted on gauges.

A zillion guys are now going to tell you they didn't do what we recommend and that their brakes work just fine. Good for them, but we have to provide instructions that keep us from dealing with your widow and her attorney.

Excellent. I think I found what they were calling the OEM proportioning valve. it bolts just underneath the booster. And you're right; from what I can see, it does not look adjustable. Thanks a bunch. My wife and kiddo thank you too.

-Chris
OEM proportioning valve.jpg
 
Arrogant attitude is fine and well... but if you follow the advise to remove the factory proportioning valve...then expect the same result that all the guys who follow this advice get... tail ends that look up too soon.

Yes Chris, the OEM valve is not adjustable... the OEM residual valve is in the MC. It is a 6 pound valve. A residual valve and a proportioning valve are two different beasts with two different tasks. The OEM system has both of course.


Mark...
 
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I doubt you will find anything writtenurging removal of the OEM proportioning valve. if so.. it is wrong.


The OEM residual valve needs to go... but an aftermarket. in line 2 pound valve gives a firmer pedal and is a nice addition.


Mark...

Where are you positioning the aftermarket 2lb residual valve? Close to the rear brakes, or close to the master cylinder? I have seen pics showing it positioned close to the rear brakes, but I can't see how it makes a difference. The OEM is like you said, IN the master cylinder, so position must be a matter of convenience in terms of splicing it into the lines...?

Here's another thought that has probably already been discussed. Is the OEM residual valve used to manage the OEM front discs compatible for use in the rear brakes? In other words, get an additional 2lb OEM residual valve and just swap it with the current 6lb vavle used in the master cylinder? I recognize that the newer Monte Carlo brakes are likely to more powerful than the stock OEM front calipers...so swapping in the OEM 2lb residual valve (assuming its possible) would get you properly designed in terms of residual pressure, but you still have a a rear disc bias.

But is sounds like what you are saying Mark is that the OEM proportioning valve (unadjustable as it is) is needed to counteract the bias of the Monte Carlo calipers IN ADDITION TO the aftermarket adjustable proportioning valve. Are they that much more powerful?

So given the specs I have read thus far on the Wilwood proportioning valves, they provide for up to a 60% damping effect(i.e. effectively a reduction of master cylinder output). So that would indicate to me that the Monte Carlo calipers are on the order of twice as powerful as the OEM calipers...assuming the OEM proportioning valve provides at least a 10% damping effect all by itself. This is based partly on your comment that either of the proportioning valves by itself it not enough to dampen the rear calipers relative the front calipers.

Do you have pics of your setup? I really want to do my homework on this, as it is probably the most critical system of my rig.

Step hills, no brakes = BAD.



Thanks for everyone's help.
-Chris
 
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Chris, I can't answer for all the information and mis-information above, but I can tell you how we've been doing it for about 10 light years:
(1) We instruct you to remove the factory 6lb. residual valve from the master cylinder. We instruct you to install our 2lb. residual valve down stream from the proportioning valve. If you leave in the 6lb. residual valve, your rear brakes would always be slightly applied all the time. Disc brake pads need only 2lbs. to keep them up at the rotors, 6lbs. is already squeezing!!!
(2) We instruct you to remove any OEM proportioning valve because they are not adjustable. We instruct you to install our adjustable prop valve slightly down stream from the master cylinder (near booster area), then go directly into the residual valve, then directly into rear brake line.
(3) After home install and home bleeding, we instruct you to go directly to a professional brake shop and get "power blead" and have the prop valve professionally adjusted on gauges.

A zillion guys are now going to tell you they didn't do what we recommend and that their brakes work just fine. Good for them, but we have to provide instructions that keep us from dealing with your widow and her attorney.

Jim,

I have the Monte Carlo disk brakes in the rear and 79-85 mini truck disk parts in the front. I also have your big bore master cylinder and adjustable proportioning valve. I have found that even with the proportioning valve adjusted to max limit, the rears will lock up before the fronts on a gravel road.

At Moab last week, going over ledges and super steep descents, it felt like the rears were doing all the work. At times the rears were locked up while the fronts were still turning, even with me standing on the brakes with both feet.

Questions: With the MC I have do I still need to add the 2lb residual valve? If so, do I add one to both the front & rear?

The pads look good on the fronts, is there anything I can do to improve the braking power on the fronts? Could there be something wrong with the front calipers that I'm not getting good clamping pressure? I don't see any leaks. Are there any calipers I can convert to that are an upgrade over the stock units?
 
Jim,

I have the Monte Carlo disk brakes in the rear and 79-85 mini truck disk parts in the front. I also have your big bore master cylinder and adjustable proportioning valve. I have found that even with the proportioning valve adjusted to max limit, the rears will lock up before the fronts on a gravel road.

At Moab last week, going over ledges and super steep descents, it felt like the rears were doing all the work. At times the rears were locked up while the fronts were still turning, even with me standing on the brakes with both feet.

Questions: With the MC I have do I still need to add the 2lb residual valve? If so, do I add one to both the front & rear?

The pads look good on the fronts, is there anything I can do to improve the braking power on the fronts? Could there be something wrong with the front calipers that I'm not getting good clamping pressure? I don't see any leaks. Are there any calipers I can convert to that are an upgrade over the stock units?

4Runner calipers will offer a significant increase in "clamping pressure" over the mini calipers, although I don't know how they compare to the Monte Carlo calipers. I think that 60 calipers have larger pistons also (but I'm not 100% sure of that).
 
Are the 4runner calipers a direct bolt-on replacement? Do you know what year 4runner I should ask for when I go to the junkyard?
 
Where are you positioning the aftermarket 2lb residual valve? Close to the rear brakes, or close to the master cylinder? I have seen pics showing it positioned close to the rear brakes, but I can't see how it makes a difference. The OEM is like you said, IN the master cylinder, so position must be a matter of convenience in terms of splicing it into the lines...?

Here's another thought that has probably already been discussed. Is the OEM residual valve used to manage the OEM front discs compatible for use in the rear brakes? In other words, get an additional 2lb OEM residual valve and just swap it with the current 6lb vavle used in the master cylinder? I recognize that the newer Monte Carlo brakes are likely to more powerful than the stock OEM front calipers...so swapping in the OEM 2lb residual valve (assuming its possible) would get you properly designed in terms of residual pressure, but you still have a a rear disc bias.

But is sounds like what you are saying Mark is that the OEM proportioning valve (unadjustable as it is) is needed to counteract the bias of the Monte Carlo calipers IN ADDITION TO the aftermarket adjustable proportioning valve. Are they that much more powerful?

So given the specs I have read thus far on the Wilwood proportioning valves, they provide for up to a 60% damping effect(i.e. effectively a reduction of master cylinder output). So that would indicate to me that the Monte Carlo calipers are on the order of twice as powerful as the OEM calipers...assuming the OEM proportioning valve provides at least a 10% damping effect all by itself. This is based partly on your comment that either of the proportioning valves by itself it not enough to dampen the rear calipers relative the front calipers.

Do you have pics of your setup? I really want to do my homework on this, as it is probably the most critical system of my rig.

Step hills, no brakes = BAD.



Thanks for everyone's help.
-Chris

The location of the valve is not particularly important. I prefer to keep it all in the engine compartment, so I put my residual valves on the firewall along with my line locks. I always put the adjustable prop valve at the M/C, upstream of the OEM prop valve. You could put the residual valve closer to the wheels, but there is no reason too.

You probably could install a residual valve from the front brake circuit into the rear brake circuit in the M/C. I have considered this, but have not actually done so.


The monte carlo brakes are a lot more powerful than the stock FJ40/FJ60 brakes... a big part of the difference in behaviors is the reduced braking forces that can be applied to the rear end as the weight transfers forward under deceleration. this lightens the tail and reduces traction for the tires. The rear brakes need to be less powerful than the front.

You can swap later model Toyota front calipers into your Cruiser... the V6 4runners were the first to use a caliper with 4 equally sized pistons (instead of a pair of small and large) and a slightly larger pad. You will still have to reduce the braking power if the GM stuff in the rear, but this will gain you a bit of braking at the front.


Mark...
 
4Runner calipers will offer a significant increase in "clamping pressure" over the mini calipers, although I don't know how they compare to the Monte Carlo calipers. I think that 60 calipers have larger pistons also (but I'm not 100% sure of that).


The early minitrucks used a nonvented rotor... so heat disipation is reduced as well is thermal mass.... the Cruiser and later minitruck vented rotor is more effective.

The "4runner" caliper will not work with the non-vented rotor.

The calipers on the '60s are the same as the ones under the '40s.



Mark...
 
FWIW in my experience with the 4-runner calipers (4 big pots) and monte carlo rear using 2lb residual and adjustable prop valve will not provide enough bias to have the fronts lock up before the rears. I am looking at putting my OEM prop valve back in. It is a 40 no top doors etc. empty cargo area, stock MC.
 

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