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72 Cuda disc brake issue #2732075
01/11/20 09:20 AM
01/11/20 09:20 AM
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cdstl Online content OP
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My DS brake caliper has been dragging for a while. Another problem was that the pads were only contacting on the inside of the rotors on both sides. So I threw parts at it.

All new steel lines from Inline Tube, I also replaced the 3 rubber lines as well. The calipers got a rebuild kit thrown at them as well, they were really tight. I did pull the prop valve apart and blasted some cleaner through it. It seems to be ok as all of the O rings and seals were in good shape. I have had it apart before, and I replaced one of the big O rings.

I used the Motive Products pressure brake bleeder with the plate. It seems to have done a good job but the plate has to be really tight on the master cylinder. I'm going to have my son come over and we'll do a bleed check via the "pump the pedal 3 times and crack the bleeder".

After stepping on the pedal a few times, the DS caliper is still tighter than the PS caliper when I release the brake pedal. The only part that didn't get "rebuilt" is the prop valve. I have yet to crack the bleeder on the DS to see if the rotor will spin more freely. I'm going to wait until my son gets here.

Any ideas?

Thanks


1972 Cuda 340 auto, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 2001 Ram 5.2 4x4 auto, 1996 Ram 5.9 2x4 auto
Re: 72 Cuda disc brake issue [Re: cdstl] #2732101
01/11/20 10:44 AM
01/11/20 10:44 AM
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VA
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dragon slayer Offline
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If this is factory original set up the Prop valve is the Combination valve that does the following: Distribution valve which is primarily a block to distribute fluid to the lines with a moveable piston to identify when you have a pressure difference rear to front and trigger your brake warning light. Additionally you have the Meter Valve which holds off pressure to the front disc until sufficient pressure on rear. This valve is separate on the 3 piece set up and combined with the 2 piece. But since you said 72 it is all in one valve. It also has the proportioning valve to regulate rear brake pressure less then front after a set value.

Since only one front disc affected, I would say a block in that line not allowing pressure to bleed off, or despite the rebuild the piston is sticking. Get a new caliper. The 70-72 stuff is inexpensive at the local auto store. Or put a pressure gauge on the line to see if pressure is not releasing. Can compare good to bad side.

Re: 72 Cuda disc brake issue [Re: dragon slayer] #2732117
01/11/20 11:36 AM
01/11/20 11:36 AM
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NEW JERSEY
AARCONV Online content
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AARCONV  Online Content
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The prop valve doesn't differentiate left or right just front..I would look closer at the caliper or the mounting for binding

Re: 72 Cuda disc brake issue [Re: AARCONV] #2732184
01/11/20 04:00 PM
01/11/20 04:00 PM
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Freeport IL USA
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poorboy Offline
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Upon the first disassembly, was there any rust pitting on the caliper bore or the caliper piston? The caliper piston needs to be clean and smooth and the bore also has to be clean and smooth. any roughness will cause the piston to drag inside the caliper and its effect will show up first with the brake release.
The next area of concern is the condition of the caliper and brake pad resting surface. Over the years, they tend to wear minor grooves (or dips) in the top surface. These groves or dips will interfere with the calipers ability to "float freely" as the piston moves in and out of the caliper. If the caliper can not float freely, it may keep the brake from releasing as quickly as it should.

Both of these areas are the 1st things I look at when there is a caliper issue and the caliper has been rebuilt, and the brake hoses have been replaced. Gene

Re: 72 Cuda disc brake issue [Re: cdstl] #2732250
01/11/20 07:29 PM
01/11/20 07:29 PM
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cdstl Online content OP
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I bought a caliper rebuild kit that included new pistons, O rings, dust seals and caliper slide pins. I didn’t bother to put the anti rattle clips on. The bores looked really good with no pitting.

It’s a 70k mile car and the caliper mounting brackets and any other wear points look good.

When I rebuilt the calipers the pistons seemed to slide into the bores easy enough.

It is a one piece proportioning valve that is not available new.

I had planned on doing a manual bleed in the morning, but now it may be next weekend.
I may need to simply replace the DS caliper and see what happens.

Thx


1972 Cuda 340 auto, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 2001 Ram 5.2 4x4 auto, 1996 Ram 5.9 2x4 auto
Re: 72 Cuda disc brake issue [Re: cdstl] #2732403
01/12/20 10:13 AM
01/12/20 10:13 AM
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Calgary, Alberta Canada
a12rag Offline
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Have you replaced the brake hose on DS ? If not, might be a bit of rubber inside, acting like a one way valve, holding some residual pressure . . . .

Re: 72 Cuda disc brake issue [Re: cdstl] #2732405
01/12/20 10:17 AM
01/12/20 10:17 AM
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cdstl Online content OP
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Originally Posted by cdstl


All new steel lines from Inline Tube, I also replaced the 3 rubber lines as well.


Yep, from the initial post.

Do you guys know of anyone who can go through proportioning valves?

Last edited by cdstl; 01/12/20 10:17 AM.

1972 Cuda 340 auto, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 2001 Ram 5.2 4x4 auto, 1996 Ram 5.9 2x4 auto
Re: 72 Cuda disc brake issue [Re: cdstl] #2732416
01/12/20 11:11 AM
01/12/20 11:11 AM
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Posts: 1,365
Nebraska
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4406bbl Offline
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Originally Posted by cdstl
My DS brake caliper has been dragging for a while. Another problem was that the pads were only contacting on the inside of the rotors on both sides. So I threw parts at it.

All new steel lines from Inline Tube, I also replaced the 3 rubber lines as well. The calipers got a rebuild kit thrown at them as well, they were really tight. I did pull the prop valve apart and blasted some cleaner through it. It seems to be ok as all of the O rings and seals were in good shape. I have had it apart before, and I replaced one of the big O rings.

I used the Motive Products pressure brake bleeder with the plate. It seems to have done a good job but the plate has to be really tight on the master cylinder. I'm going to have my son come over and we'll do a bleed check via the "pump the pedal 3 times and crack the bleeder".

After stepping on the pedal a few times, the DS caliper is still tighter than the PS caliper when I release the brake pedal. The only part that didn't get "rebuilt" is the prop valve. I have yet to crack the bleeder on the DS to see if the rotor will spin more freely. I'm going to wait until my son gets here.

Any ideas?

Thanks


Are you sure both are not dragging just a little? I had a new bendix master cylinder do that on a 72 cuda, turns out the compensating port, they said, for the front piston was drilled wrong, allowing a slight drag. Could have veen the wrong residual valve, who knows. I had the original rebuilt and it is fine. The bad batch of masters had a cap that was not the same as the original, slightly smaller. If you let the car sit the calipers would release after an hour or so, as the engine warmed up they would slightly drag. I would go drive the your car then feel the wheels. I took the line lock off figured it was going bad chasing that one down, real pain in the rear to diagnose when everything is new.

Re: 72 Cuda disc brake issue [Re: cdstl] #2732417
01/12/20 11:16 AM
01/12/20 11:16 AM
Joined: May 2012
Posts: 1,149
South Bend
John Brown Offline
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Originally Posted by cdstl
Originally Posted by cdstl


All new steel lines from Inline Tube, I also replaced the 3 rubber lines as well.


Yep, from the initial post.

Do you guys know of anyone who can go through proportioning valves?


They're easy to do yourself. Buy the kit you need at the link below.

https://www.musclecarresearch.com/mopar-parts


July 19th should be "Drive Like Rockford Day". R.I.P. Jimmie.
Re: 72 Cuda disc brake issue [Re: John Brown] #2732467
01/12/20 01:42 PM
01/12/20 01:42 PM
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cdstl Online content OP
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Cool

Thanks


1972 Cuda 340 auto, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 2001 Ram 5.2 4x4 auto, 1996 Ram 5.9 2x4 auto
Re: 72 Cuda disc brake issue [Re: cdstl] #2732472
01/12/20 02:14 PM
01/12/20 02:14 PM
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Posts: 1,540
Phila. Pa.
Mattax Offline
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Proportioning valve wouldn't have any effect on the front brakes.
The prop valve reduces the increase in hydraulic pressure to the rear brakes starting areound 350 psi.

It's more likely that a problem with the from brakes involves a metering valve.
Metering valve is supposed to hold off application of presure to front brakes under very light braking.
They were used on E-bodies, at least in '70.
See here
http://www.imperialclub.com/Repair/Lit/Master/274/page09.htm

Also possible that something in the safety switch & distribution block.
Same link will get you rebuild kit info for them.

It looks to me like '72 model year e-bodies got a combination meter valve, safety switch and proportioning valve.
see here
http://www.imperialclub.com/Repair/Lit/Master/293/page10.htm


Because the metering valve holds off hydaulic fluid moving to front brakes under light braking, some form of pressure bleeding or pumping the brake pedal will be needed.
So check out the recomendations for bleeding those if you haven't already.

Final thought is there a residual valve somwhere in the front lines.

Re: 72 Cuda disc brake issue [Re: cdstl] #2732474
01/12/20 02:21 PM
01/12/20 02:21 PM
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Lake Orion, MI
goldduster318 Offline
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Originally Posted by cdstl
Another problem was that the pads were only contacting on the inside of the rotors on both sides.


Sounds like the calipers weren't sliding on the pins. Do they easily slide back and forth with the brake released and the piston pushed back? The pins need to be straight and also slide through the bushings. If they bind anywhere you'll get a drag.

597921.jpg

'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
Re: 72 Cuda disc brake issue [Re: goldduster318] #2732480
01/12/20 02:34 PM
01/12/20 02:34 PM
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Phila. Pa.
Mattax Offline
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Originally Posted by goldduster318
Originally Posted by cdstl
Another problem was that the pads were only contacting on the inside of the rotors on both sides.


Sounds like the calipers weren't sliding on the pins. Do they easily slide back and forth with the brake released and the piston pushed back? The pins need to be straight and also slide through the bushings. If they bind anywhere you'll get a drag.

Very true!
I just fixed a slight hangup in my '85 grand Wagoneer's just by tapping the caliper and pulling the pins and relubing. (GM calipers but basically the same design) And those were new disks and 'rebuilt' calipers put on this year.

Re: 72 Cuda disc brake issue [Re: goldduster318] #2732600
01/12/20 09:53 PM
01/12/20 09:53 PM
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Originally Posted by goldduster318
Originally Posted by cdstl
Another problem was that the pads were only contacting on the inside of the rotors on both sides.


Sounds like the calipers weren't sliding on the pins. Do they easily slide back and forth with the brake released and the piston pushed back? The pins need to be straight and also slide through the bushings. If they bind anywhere you'll get a drag.


I'd have to agree, but I've lubed the hell out of the sliders, rubber and pins with Silglide. Slicker than a cat's azz. Pins are new with the kit.

I've been leading towards the metering portion of the Prop valve myself.

I got called off to work and probably won't get to it until next weekend, maybe.


1972 Cuda 340 auto, 2001 Ram CTD 4x4 6 speed, 1970 Duster 408 4 speed, 2001 Ram 5.2 4x4 auto, 1996 Ram 5.9 2x4 auto
Re: 72 Cuda disc brake issue [Re: cdstl] #2733253
01/15/20 08:27 AM
01/15/20 08:27 AM
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Grosse Isle, Mi
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Hemidavey Offline
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Replace the brake hoses, we see them fail internally, keeping residual pressure on the pistons.

Re: 72 Cuda disc brake issue [Re: Hemidavey] #2733339
01/15/20 12:02 PM
01/15/20 12:02 PM
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Lincoln Nebraska
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RapidRobert Offline
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crack a bleeder & see if it frees up


live every 24 hour block of time like it's your last day on earth

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