Backing off front disc brake pads.

Michael Dimock

Michael Dimock

IH Parts America Sales Assoc.
I have a 1962 International Scout with a 1975 j@@p wagoneer front axle that has been converted to 5x5.5 lug pattern and a 1973 rear j@@p wagoneer axle that was 5x5.5 from the factory. When I was having the axle worked on for hi-steer and SOA I had new balljoints and calipers/brake pads installed. I took the Scout out for a drive on Sunday and the front brakes didn't disengage all the way as the smoke coming out from the front let me know in a hurry.....:yikes: at first I backed off the master cylinder push rod as it was putting a slight bit of preload on the mc, but I still had the same problem. Could a slight bit of air in the lines cause the pistons to not fully back off? What else could cause this? The drivers side is a bit tighter on the clamping then the passenger side. I am new to disc brakes, so any help would be appreciated.
 
I'm no brake expert michael, but do you have a db proportioning valve in place? If not, you need one. That dawg won't hunt w/out it.
 
No, I was going to see if the mc that I got that was for disc front/drum rear was correctly proportioned or really close to what I needed before I dished out the $50 for a proportioning valve..... But, at this point it's kinda hard to do that.....:icon_rolleyes: I know a proportioning valve will limit the amount of fluid that will move to the brakes when pedal pressure is applied, but would it have an effect on the brakes when the mc is fully retracted?
 
After sitting for a bit, do the calipers release there death grip?

Any residual valves in the master or hydraulic system?



I doubt it is a hydraulic issue, but to verify, loosen a bleed nipple on either caliper and see if allowing the pressure to vent will free it up.
 
michaeldimock said:
no, I was going to see if the mc that I got that was for disc front/drum rear was correctly proportioned or really close to what I needed before I dished out the $50 for a proportioning valve..... But, at this point it's kinda hard to do that.....:icon_rolleyes: I know a proportioning valve will limit the amount of fluid that will move to the brakes when pedal pressure is applied, but would it have an effect on the brakes when the mc is fully retracted?
Click to expand...

The proper master cylinder is a different issue as compared to the proportioning valve! Two independent devices.

I'd not screw with the oem-style proportioning valve, pick up an adjustable valve and run the front brakes and rear brake plumbing in a split configuration, put the adjustable proportioning valve only in the rear plumbing, you don't need a dam "warning light"...make this simple.

The oem proportioning valve serves three functions,...switch for "warning" light (the combination function), proportioning, and as a junction block for front/rear plumbing distribution.

The very earliest sii (810/sii) used only a combination valve (not proportioning). The "proportioning" function was handled by making the early caliper piston size different along with rear wheel cylinders that were smaller. And...that design did not last long because it didn't work very well.

As I stated in my email...are the calipers truly new (or reman) loaded calipers, or simply "new" to you and really boneyard shit? If boneyard, they need to be rebuilt (same for a boneyard master cylinder). If they are boneyard, they have been open to the atmosphere and are now badly contaminated.
 
Mm, as far as the calipers, they are either new or reman, as the old ones had been exposed to the elements and were toast. I only bled them initially and haven't touched them since I drove it on Sunday. It is quite possible that air has migrated down to the calipers and is causing this. This is a reman dual mc with a small rear brake resevoir and very large front brake resevoir. I was definitely going to only use an adjustable proportioning valve and not an oem one as I have an entirely different mc than a Scout 2.

Robert, idk if there are any residual valves in the mc but I know there aren't any in the rest of the brake system, as it is all new. I had my local napa buy a 25' roll of tubing and make me all new lines. I also have all new soft hoses. The only thing that hasn't been touched is the rear drum brakes, but they are next on the list. I have the e-brake to install next. I will go ahead and bleed them again and see if that works. :idea:
 
When you crack the bleeder the first time it will release and residual pressure and should allow the calipers to release.

Try pumping the pedal before cracking the bleeder. Watch for a release of pressure. There should not be any, if there is see if your master cylinder push rod is backing off enough to uncover the little hole in the bottom of the resevoir.
 
To further clarify what Robert is saying...did you "bench bleed" the master cylinder? If not, then bench bleed it while it's on the rig now. That gets the air out of the master. Make certain the master can fully "retract" when the stroke is released and that your pedal pushrod has a noticeable amount of freeplay and the pedal has a return spring on it (that mikeemouse spring in the hole in the lip of the dash). Then work your way through the wheel ends, beginning with the rear that is farthest from the master, then next farther, etc.

You May have to go around the pattern several times.

But if you are going to open the plumbing again to install a proportioning valve or whatever, then don't bleed until all the repairs are made! Otherwise ya will have to bleed anytime any connection is opened.

If the master cylinder has residual pressure valves for either end, they will be inside the ports on the casting and retained by any "adapter"-type fitting. They are simple one-way "check valves" that look like a small rubber disc with a nipple in some cases. A disc brake caliper set needs about 2psi residual...the drum set needs 8>10psi.
 
X2 on an adjustable prop valve. Get the 'summit' brand one -- it is a wilwood part in a summit box -- and you save some cash.

The factory combination valve is fine for stock applications but it just doesn't work as soon as you change anything.

As for a residual valve inside the mc -- some disc brake sawp writeups I have seen have you pull them out of the mc by jamming a pick into the outlet port and popping them out... I've never needed to do it on any of the swaps I have done.
 
The problem with residule valves is if they are reversed. Like 10 to the front instead of 2#. I have only needed them for hotrod chassis and similer where the master is close in elevation to the calipers or wheel cylinders. In many case the master is below the calipers etc. Kinda scary to grab a foot full of nothing in a panic stop. :yikes:
 
I bled the master into a bottle of old brake fluid when it was in the truck, but just enough so the master pushed a fair amount of fluid out and had a much firmer piston stroke. I'll be bleeding the entire system again this weekend and will let you know how it all pans out. Thanks for the suggestions!:icon_up:
 
Git yore azz back to class kid! Yore daddy tole me I could kick yore azz when needed! Scruu this junkiron and I-net stuff...git sum learnin' or you'll end up a dumazz like me.
 
I'm at work now, class is over.... Until later that is!:ciappa: got all my homework done for the week and some for next week! So, I'm gonna devote a little weekend time to my Scout! Afterall, it is just a slight bit of rolling resistance away from being driveable again....:yesnod:
 
I bled the front lines on Friday night and I was able to push the Scout around on flat ground... Saturday morning though I wasn't able to! I decided to take it for a drive anyway and same problems as before, front brake pads were dragging, so I headed back home. I had the local napa guy call around and I'm running the lines off of the correct reservoirs and it should be a 2 lb residual valve in the disc brake reservoir and 6 lbs in the drum brake reservoir.... Now, if I have a leaking brake line fitting, which I can't seem to find and air gets in the line, can the calipers increase the pressure that they are pushing on the rotors when the master cylinder is backed off? If the residual valves are wrong, will an adjustable proportioning valve lower the residual pressure when the master cylinder is backed off? Or does it only limit the working/pedal pressure? I guess I could bleed it again and take it for a drive immediately....:icon_rolleyes:
 
Don't need to bleed them again, only loosen a caliper bleeder ans see if there is residual fluid pressure in the lines. If so I would say the master is the culprit.

Did you say the proportioning valve was installed?? It won't help but can cause grief if installed backwards.

Any chance the rotor is to thick for the caliper to accomidate? May be binding after the pads get hot and expand.
 
chris pucci said:
you need to get rid of the prop. Valve. The stock drum/drum valve is not going to work.....
Click to expand...

There is no proportioning valve.... Robert, loosening the bleeder screw to find if there was any residual pressure is definitely next on my list. I'm sorry that I misinterpreted your post before, as I won't be able to test this until I head home on the weekend. So, basically when I loosen the bleeder screw I should receive no fluid? Is this correct? If fluid flows out, then I can ascertain that the master cylinder has the wrong residual valves in it and I should take it out of the disc brake port of the mc. Do I just use a pick and pull out the brass nipple and behind it should be a rubber valve? Then, obviously I will need to remove this and then should I leave it out or should I try and get a new 2 lb one? I jacked the front up and the drivers side wheel is very hard to turn ( it has 24" less hard line than the passenger side so less fluid flow) and the passenger side was turnable but it still had too much drag.

The rotors haven't been touched, as they were in good shape when I got it. As far as the calipers and pads idk.... I bled them a little yesterday and was able to roll the Scout around, so I jumped in it and drove it. By the time I made it 100 yards, I could feel the brakes grabbing again, so I headed back down the driveway. Basically I can assume from the lack of drag immediately after I bleed them that the calipers and pads are right for the application, but there is something wrong with the mc. If I find fluid coming out of the bleeder screws, then this will be confirmed.:icon_up:
 
You May have already proven my theory. When you bleed the brakes you say it would roll around easy but after the first brake application, the binding would return. This points to a holding of residual line pressure.

Line length has no effect on the residual pressure because the lines are all parallel.

When you get a chance to bleed again, make sure you apply the brakes and verify the binding exists, then loosen the breeder. At that time the binding should go away after the pressure is released. You May see a small amount of brake fluid released under pressure and a resultant end of the binding.

Hard to say what residual valving mechanism the master is using as many types are used. Some are internal to the piston assembly others are a simple spring loaded poppet in the line port.

The brake pan deal is only an outside possibility.
 
Uhhhh..... Well, I took the brass male fitting out of the brake line port and there was no residual valve behind it!:shocked: when I got home, I loosened the bleeder screw and fluid slowly came out, so I tightened it back up. Then, I found out there was no residual valve. So I opened the bleeder screw and the fluid came out again, and never stopped, so I presumed it was gravity providing the 1-2 lbs of pressure. I jacked the Scout up and turned the wheels. The passenger side turns with a little drag while the drivers side is fairly hard to turn. Allowing the fluid to flow out a little made them easier to turn, but it is still more difficult than they should be. I don't have a 3/8" allen wrench to take the calipers off with, but is it possible that they were installed wrong/ spaced too much? They are the only thing left.... Either that or the pistons are sticking... I don't really know what to think at this point.
 
michaeldimock said:
I don't have a 3/8" allen wrench to take the calipers off with, but is it possible that they were installed wrong/ spaced too much? They are the only thing left.... Either that or the pistons are sticking... I don't really know what to think at this point.
Click to expand...

Find the needed allen and loosen the caliper mounting screws. Possible the alignment is off.

You should be able to push the caliper pistons back so the rotor fits between the pads with room to spare.
 
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