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Both front discs brakes dragging(?) 72GTS

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fordismyboss View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fordismyboss Quote  Post ReplyReply Direct Link To This Post Topic: Both front discs brakes dragging(?) 72GTS
    Posted: 17-December-2017 at 6:11AM
Read all the posts on this subject, but still cannot understand what could do this:

First the background. A year ago, about 1200 miles, I converted my factory original brake system, which was working OK, by having my original booster rebuilt, new dorman disc/disc master cyl.(1977 Lincoln Mark V), used Prop valve (77 Mark V), kept the original steel brake lines, new rubber flex hoses all around, rebuilt the original front calipers myself, used caliper bracket(78 Marquis), new 12" rotors (72 t-Bird), new wheel bearings, rear discs(00 Lincoln Town Car), rebuilt steel calipers, new hoses, lines and bearings.

Problem. The last two times I drove it I thought the front wheels went out of balance, but when I got home the car smelled different after I parked it in the garage and I noticed that both front disc pads were dragging at what seems to be the same pressure. With the wheels off I can turn the disc but the pads are clearly dragging at the same pressure on both sides of the front. Rears are fine. I have yet to touch anything to try to fix the problem because I found this:

When I opened the master I saw a distinct difference between the rear and front reservoirs:


Rear brake reservoir:


Front brake reservoir:


Could it be the rebuild I did myself on the calipers, or the prop valve, or the master cyl? But why does the fluid look contaminated? Is it full of air? Burnt?Confused


My plan:
Since it appears there is a gap at the brake pedal before it touches master cylinder push rod, I plan to open the front brake fitting at the master to see if the calipers release. If not, open at the prop valve. If not, open the bleeder at the caliper. If they still don't release it is the caliper or the bracket. Is my plan correct? Thanks for reading!



Edited by fordismyboss - 17-December-2017 at 6:32PM
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aquartlow View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote aquartlow Quote  Post ReplyReply Direct Link To This Post Posted: 17-December-2017 at 6:56AM
It may be possible the front circuit's metering valve(and/or the supply tubing from the MC)has some sort of internal obstruction, doesn't allow brake fluid to reverse flow back to the MC, keeping fluid pressure at the calipers. Hearing that both calipers are dragging, this seems a possible culprit. Most times a dragging caliper is due to internal scoring of caliper bore and/or brake fluid contamination(rust) not allowing the caliper pistons to fully retract, usually happens one at a time, but both of yours are new. Another culprit to look at are the brake hoses, but you have already changed them both as well. Try loosening the MC off the brake booster(about 1/4") and see if the front calipers quit dragging, if so the pushrod length is "off". Good luck and hope this helps. 
www.supermotors.net/22468
Yeah, It's a Hybrid...It burns gas and tires.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 17-December-2017 at 7:18AM
contaminated / stuck residual pressure valve in the master or distribution block?
72 GT Ute
   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 17-December-2017 at 8:28AM
usually the calipers rust between the o-ring and the dust seal and don't retract causing a dragging but like todd said usually 1 at a time, looks like old fluid backflushing from your original lines? probably not a real big deal but if it had big chunks of crap clogging it! flex lines usually swell internally and cause this but if they are new that shouldn't be the problem? i'd start at the caliper bleeder then work your way back to the master or loosen the master like todd said that could very well be the issue!!!
JOHN
74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fordismyboss Quote  Post ReplyReply Direct Link To This Post Posted: 22-December-2017 at 7:23AM
Thank you for these comments. When I unbolted the master cylinder it seemed to release the brakes a bit. So I pulled the MC and measured the booster push rod and master piston hole depth. The push rod protrudes .998" from the booster face. The depth of the piston hole is 1.023" from the booster face. .025" clearance is not enough in my view.

What is the typical clearance? Anyone have a recommendation?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 22-December-2017 at 1:36PM
IIRC the end of the booster rod is adjustable.
 somewhere on here way back i saw some mention of the clearance or adjusting the rod but no idea where i read it?
 i just now though of this... my buddy dave's torino acted like the calipers were dragging and sometimes it didn't? come to find out his pedal wasn't retracting all the way, due to rust or something on the pivot bushing or something?
JOHN
74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fordismyboss Quote  Post ReplyReply Direct Link To This Post Posted: 23-December-2017 at 6:09AM
Yes, the rod is adjustable. I plan to call the guys that rebuilt the booster and get their input.



I checked the pedal and it is clear and working correctly...thanks for the suggestion.

With everything apart now and the outside of the caliper still dragging slightly, I'm thinking the sliding mechanism of the caliper is tightening as the pads wear making it unable to retract now. But(?). 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote aquartlow Quote  Post ReplyReply Direct Link To This Post Posted: 23-December-2017 at 6:33AM
IIRC, the end of the pushrod should be .993-.995" from the face of the booster(measurements taken near where the MC bolts to booster), there are online diagrams showing a measurement tool to fab up to allow accuracy of this measurement.
  Looking at the pic, could the MC be leaking internally(wet booster/MC mounting area). Have you tried "cracking" the front bleeders to see how much residual pressure exists when no brake pedal pressure is present? If you have tried this, did the move allow the front rotors to turn more easily?
www.supermotors.net/22468
Yeah, It's a Hybrid...It burns gas and tires.

No matter how good she looks, somebody, somewhere, is tired of her sh*t.

Beauty is skin deep, ugliness goes clear to the bone.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fordismyboss Quote  Post ReplyReply Direct Link To This Post Posted: 23-December-2017 at 6:43AM
My push rod measures .998 from the booster face. I will measure it again and adjust.

The only relief came when I unbolted the MC from the booster, but it was only a slight improvement. No other improvement as I worked my way disconnecting lines as I got to the caliper bleeders. I think I may have a combo of errors going on, a small MC pre-load and a caliper glide impingement.

Great de-bug fun during the Holidays!

Thank you for your inputs!     


Edited by fordismyboss - 23-December-2017 at 6:46AM
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Post Options Post Options   Thanks (0) Thanks(0)   Quote californiajohnny Quote  Post ReplyReply Direct Link To This Post Posted: 23-December-2017 at 7:06AM
your always going to have a slight drag of the pads and caliper but you should be able to turn it by hand.
 you could remove the calipers and clean the sliding surfaces with emery or sand paper  especially if any paint or rust got in there also check for any dings or nicks on those surfaces Wink
 as far as the ugly fluid... may be some stuff from inside the calipers when they were assembled??? there shouldn't be anything from the master lines i had them on my car for a while and all worked fine! plus i thoroughly blew them out before shipping them to you so no fluid would be dripping Wink in fact i'm using that master from that car it was perfectly clean inside i wouldn't have ever believed that if i hadn't seen it with my own eyesShocked i'm running that master on my car!!!
JOHN
74 GRAN TORINO S&H CLONE
74 CORVETTE COUPE CUSTOM
90 S10 BLAZER 4X4 LIFTED
77 CELICA CUSTOM
75 V8 MONZA SUPERCHARGED
79 COURIER VERT. SLAMMED
75 VEGA V6 5 SPD
70 CHEV C10 P/U
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fordismyboss View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fordismyboss Quote  Post ReplyReply Direct Link To This Post Posted: 24-December-2017 at 5:46AM
Yes, the items you sent me were clean, and after testing, I'm confident the prop valve is working as it should. And, of course, I've just rechecked everything. The ugly fluid has me stumped as the entire brake system was clean one year ago and the rear circuit does not show the contamination.  

Hopefully after I adjust the pushrod, reclean/lubricate the caliper glide faces, double check the piston movement, rebench-bleed the MC, and fill with new fluid I'll have a firmer pedal than when I finished this brake redesign process a year ago.  

I really like this Mark V (master and prop valve) and 2000 Lincoln Town car (rear disc calipers and backing plates) disc brake upgrade.
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