GM discs dragging

[Colliedog3]

I installed the wildhorses disc conversion on my bronco and after driving the truck for about 15 minutes the front right brake starts dragging and recently both front brakes started dragging. New rubber lines from the knuckle out, new lines from the master to proportioning valve and new proportioning valve and plenty of clearance for the caliper to slide. Anyone ever have this problem or have any suggestions?

 

[DirtDonk]

Power brakes, or manual?
If using a vacuum booster the first place I would look would be the interface between the booster rod and the master cylinder piston.

You can narrow down the restriction (if that's what's causing the dragging) by loosening various things.
The next time it drags or locks up, loosen or remove the two nuts holding the master to the booster. If the caliper(s) release then you found the issue.

If no booster, then crack a bleeder to see if that relieves pressure.
Hydraulic pressure is not the only cause of a dragging caliper, but it's the most common. A caliper can actually "stick" too, where the piston refuses to retract back into the body just the slight amount needed.
But cracking bleeders or loosening various points is a good first step in checking.
You've already checked the previously most common reason, and that was lack of clearance for the caliper after insufficient grinding. Sounds like you're OK there.

Paul

 

[Colliedog3]

Power brakes, or manual?
If using a vacuum booster the first place I would look would be the interface between the booster rod and the master cylinder piston.

You can narrow down the restriction (if that's what's causing the dragging) by loosening various things.
The next time it drags or locks up, loosen or remove the two nuts holding the master to the booster. If the caliper(s) release then you found the issue.

If no booster, then crack a bleeder to see if that relieves pressure.
Hydraulic pressure is not the only cause of a dragging caliper, but it's the most common. A caliper can actually "stick" too, where the piston refuses to retract back into the body just the slight amount needed.
But cracking bleeders or loosening various points is a good first step in checking.
You've already checked the previously most common reason, and that was lack of clearance for the caliper after insufficient grinding. Sounds like you're OK there.

Paul

Thank you! Will check that. it does have a vacuum booster. I thought it might be a caliper and replaced the passenger side when it started dragging and still drags.

 

[Broncobowsher]

Excess preload on the master cylinder is my first thought as well.
Strange one side would start before the other, but there have been weird stuff I don't understand in the brakes before.

 

[toddz69]

I installed the wildhorses disc conversion on my bronco and after driving the truck for about 15 minutes the front right brake starts dragging and recently both front brakes started dragging. New rubber lines from the knuckle out, new lines from the master to proportioning valve and new proportioning valve and plenty of clearance for the caliper to slide. Anyone ever have this problem or have any suggestions?

Which master cylinder are you using? If it's a drum/drum master, did you remove the residual pressure valve?

Todd Z.

 

[Colliedog3]

Which master cylinder are you using? If it's a drum/drum master, did you remove the residual pressure valve?

Todd Z.

I did not, what is that? And how can I remove it?

 

[toddz69]

If you have a drum/drum master cylinder, there's a small residual pressure valve behind the conical seat in each port that keeps a little pressure in the line to keep some pressure in the wheel cylinders at each wheel.

Disc brakes don't need this and you'll likely get some dragging calipers if you still have the valve in the line.

Remove the line and fitting from the master cylinder (front brakes only - the back one). You'll then need something a tap or a fine thread sheetmetal screw that you can screw into the hole in the center of the conical brass seat in the port. This might take awhile to find something that threads in and holds. Once it's installed, carefully rock the screw back and forth to wiggle/pull the conical seat out of the fitting hole. Behind it, you'll find a coil spring and a little rubber piece. If they don't pop out, pull them out and discard. Carefully tap the brass seat back into the port (without damaging the center hole) and reinstall the brake line and bleed, etc. as needed.

Todd Z.

 

[Colliedog3]

If you have a drum/drum master cylinder, there's a small residual pressure valve behind the conical seat in each port that keeps a little pressure in the line to keep some pressure in the wheel cylinders at each wheel.

Disc brakes don't need this and you'll likely get some dragging calipers if you still have the valve in the line.

Remove the line and fitting from the master cylinder (front brakes only - the back one). You'll then need something a tap or a fine thread sheetmetal screw that you can screw into the hole in the center of the conical brass seat in the port. This might take awhile to find something that threads in and holds. Once it's installed, carefully rock the screw back and forth to wiggle/pull the conical seat out of the fitting hole. Behind it, you'll find a coil spring and a little rubber piece. If they don't pop out, pull them out and discard. Carefully tap the brass seat back into the port (without damaging the center hole) and reinstall the brake line and bleed, etc. as needed.

Todd Z.

Awesome! Thank you! I will try this, I checked my master adjustment and it’s all the way in so I don’t think it could drag, this must be it

 

[Colliedog3]

Update. Master cylinder adjuster is all the way in and no residual valve was found in the master. Any chance the soft line to the axle could be heating and causing a clog and dragging?

 

[DirtDonk]

What do you mean by the master is adjusted all the way in? I assume you mean booster rod, but all the way in isn’t how you measure it.
Whether or not it is touching the back of the master cylinder at all Is the important question.
If it is then it’s too far out and not matched to the master.
If it’s not touching, then it’s not the problem.

Most master cylinders no longer come with residual pressure check valves in them.
Even if you went out today and bought a drum brake master, chances are better than 90% that it does not have a check valve in it.
In the old days having them was standard practice, but now, in the days of saving fractions of a penny, they are no longer automatically included.
If you do find one, it’s a rarity.

 

[Colliedog3]

What do you mean by the master is adjusted all the way in? I assume you mean booster rod, but all the way in isn’t how you measure it.
Whether or not it is touching the back of the master cylinder at all Is the important question.
If it is then it’s too far out and not matched to the master.
If it’s not touching, then it’s not the problem.

Most master cylinders no longer come with residual pressure check valves in them.
Even if you went out today and bought a drum brake master, chances are better than 90% that it does not have a check valve in it.
In the old days having them was standard practice, but now, in the days of saving fractions of a penny, they are no longer automatically included.
If you do find one, it’s a rarity.

Yes I meant the booster rod. How do you measure to see if it’s touching the back of the master? Interesting that they got rid of the check valve, mine is a newer master but was for manual brakes, not sure if that makes a difference or creates a problem

 

[Broncobowsher]

Residual pressure valves were important back in the day when the master cylinder was mounted under the floor and was lower than the wheel cylinders, the wheel cylinders would drain back into the master.

I want to say my Chilton had instructions on measuring booster pushrod stickout. Books are in storage at the moments, so off memory...
With the master removed lay a straight edge across the master and measure off that to the tip of the pushrod. That is the stickout.
Then you need to know the depth of the pushrod hole in the master, but you have to reference that off the mating surface to the booster. This will probably take a couple measurements and subtract from each other to get around the step on the back of the master. There needs to be a tiny air gap. I don't remember how much and my books are in storage.
If the adjuster is turned all the way in, we are probably looking at the problem of mismatched parts and the adjuster that has run out of adjustment and is still too long. Probably caused by a master with too short of a hole, or not.

 

[Oldtimer]

Looks like gap should be .020"

And this tool simplifies the process.

https://www.amazon.com/dp/B0BNNGN47R/?tag=cbama-20

 

[DirtDonk]

An easy way to tell if it’s too far out is if you can feel the master touch down on the rod before it mates up to the booster mounting surface.
If that’s the case, then it’s too long and needs to be shortened.
If not then it’s probably not your issue.