73-76 sliding calipers not sliding?

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slmiller243

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We are trying to wrap up a drum to disc brake conversion on the front of a 69 Barracuda. Been quite a few year since I worked on the mid year A body disc brakes. We got all of the necessary parts from a 73-76 donor car and purchased new rotors, pads and calipers.

My question is that once I tighten the bolts on the 2 retaining brackets the caliper is very tight. It seems to me that the caliper needs to be able to freely slide back and forth. I am pretty sure I have the retainers installed correctly. What did I do wrong?
 
before pads and hardware the caliper should slide in the ways. once assembled they aren't supposed to be so loose they'll move by hand. With aftermarket calipers... maybe you will need to file dress their ways a little.
 
Thanks. I definitely can't move them by hand. The calipers moved freely until i tightened the retainer bolts. I suspect that the force of the piston when the brakes are applied will move the caliper on the "ways". I was concerned with how the caliper would move back after the brakes are released so the pads don't drag. Sounds like the pads self adjust by wearing slightly against the rotor.
 
The springy retainers apply some pressure. I do smear a light coat of anti seize compound on the ways. Anything there will collect brake dust. Bolt it down without the pads and see if a rubber mallet bump will move the caliper. This type of bearing hub setup cant run a rotor so true that it wouldn't bump the outer pad away a few thousandths. So long as the outer pad stays attached to outer caliper, all good.
 
The caliper only needs to move now and then, to compensate for padwear.
Seal retraction will pull the inboard pad away from th rotor, and rotor wobble will pop the outboard pad back.
But non-the-less, the ways should be smooth, and the loaded calipers should slide back and forth with the pistons pushed back, and the retainers fully secured, on dry ways,with just a bit of effort. The key is that the pistons be retracted.
Op you know what seal retraction is right? That's when the square section O-ring seal, inside the caliper, relaxes after an application and returns to it's former square shape. To do this, the piston has to be free to move in it's bore. That means no rust/no sludge inside the bore,and no rust/gunk/gravel/etc in the receiver groove for the sq. section O-ring. The dust boot is pretty good at keeping that stuff out from the atmospheric side. But when new pads are installed in old calipers, that's when the trouble starts. To get the new pads to fit, the pistons have to be pushed back into their bores.Where the rust and gunk have been accumulating. But often overlooked is also the oxidation that occurs on the outside of the pistons,under the dustboot, and which gets jammed into the sq O-ring during this resetting process. This External problem can prevent seal retraction from properly working, and can also lead to leaks.
And don't forget to pump the brakes up to hard pedal before putting the tranny into gear for the first time.
 
AJ/FormS said:
The caliper only needs to move now and then, to compensate for padwear.
Click to expand...

And then only less than a thousandth of an inch at a time.

A good palm thump should be able to move it if it's working normally.
I put them together with the retainers tightened and palm thump it while the pads are still backed off.
If it moves, great and done (well besides pumping the brakes back up before it's driven) :D
Also the anti seize on the slide surfaces is widely accepted.
 
TB, you know I like you, and you know I like my anti-seize, but I cannot imagine what anti-seize would do if allowed to get into a brakepad, so for me, Ima gonna keep on putting those calipers on, dry. Besides, between heat,dirt and rainwater, I also cannot imagine the stuff staying on that long.
 
Caliper brackets were media blasted and powder coated so the "ways" are very smooth. I'll check how much pressure needs to be applied to move them. Can the retainers be bent up to relieve pressure?
 
AJ/FormS said:
TB, you know I like you, and you know I like my anti-seize, but I cannot imagine what anti-seize would do if allowed to get into a brakepad, so for me, Ima gonna keep on putting those calipers on, dry. Besides, between heat,dirt and rainwater, I also cannot imagine the stuff staying on that long.
Click to expand...

I don't put anything on them either, but that's mostly because it gets driven every day and new brakes twice a year.
Grease and antiseize both collect dust and can cause the caliper to bind up solid because of it.
If it sat for lengths of time I would use a light coat of grease like Lithium or something along that nature.
(just enough to "wet" the slide surfaces only and no more.)

So we're ok and I didn't disappoint you then after all right? :D


slmiller243 said:
Can the retainers be bent up to relieve pressure?
Click to expand...

I wouldn't because that's what holds the entire caliper in it's bracket.
You could probably get away with it if you really needed or wanted for some odd reason, but they work fine the way they are.
 
Is there any chance that the powder coat is interfering?
The retainers are not a problem, leave them be. If you remove tension, they will rattle. If they rattle they will chew up your PC.

TB thanks for setting me straight.
 
AJ/FormS said:
Is there any chance that the powder coat is interfering?
Click to expand...

Of course. :D
That being the case I'd sand it off the slide surfaces, because that could cause it to bind and drag also.

Seems to me it could anyway.
 
slmiller243 said:
Caliper brackets were media blasted and powder coated so the "ways" are very smooth. I'll check how much pressure needs to be applied to move them. Can the retainers be bent up to relieve pressure?
Click to expand...

In my opinion powder coating should not be on the moving / mating surfaces. I dont know for sure that is your problem but I wouldn't want it. Factory didn't even put a thin coat of paint on them.
 
I just did (today) Brake Conversion on my 64 Barracuda with the same set up that you have, except I kept the Small pattern, my 65 has the Big Pattern and both have the sliders. They both operate like other saying.

The Caliper moves hardly ever, and it will slide inboard as the pads wear down. Its not to bad of a set up.

I noticed a difference in pedal throw with power brakes on my 64 Barracuda, seemed the throw is longer than the 65 Signet is a Manual, press the brakes and lock up you go.

MY QUESTION FOR YOU...Did you use a proportioning valve? And did you convert your master cylinder?
 
We did convert the master cylinder and added a 7" booster. We are still undecided on a brake proportioning valve. Seems to be varying opinions on whether one is needed however logic is leaning us towards needing one.
 
We just changed all 4 wheels to disc brakes but have not driven the car yet. Previously had rear drum and front disc from Scarebird. Didn't stop great
 
Wow that's the first negative I have heard on scarebirds brakes. I would think if you are going 4 wheel disk to put a proportioning valve in and if you don't use it, by not restricting and fluid and keeping it wide open then no big deal.


I have a feeling the rears will lock up though if you don't just because there is no weight back there, remember that is why there is a valve, so the rear will have pressure but not enough to lock up or at least not before the front.

Will be interesting to see how this turns out, what kind of disks did you put in the rear?
 
I agree on the proportioning valve. I didn't mean to imply that Scarebirds brakes were not good. I think we may have a bad booster. Got the rear disc brakes from Dr Diff along with new axles. Very good quality.
 
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