New brake system, but brakes are dragging

[4thesporty]

Hello all,

Been busy on my 71 the last couple of months, but regarding my brakes, i have the following new parts installed;

New rear axle, 8.8 from '98 grand marquis with all new disk brake hardware
New front brakes (everything), using 2014 Mustang GT disk brakes with an adapter
New hard lines, all of them
New soft line at each corner, and the soft line going to the rear axle
New Willwood MC (1-1/8" bore) with Willwood proportioning valve (eliminated factory combination valve)
New fluid (obviously) and bled well with a pressure bleeder
*Factory original brake booster (the only part not new)

I can drive the car for a few miles and it stops fine, I get an expected pedal when braking, but after a couple of miles with some stop and go the brakes start dragging (all four wheels).

I figure that my booster pushrod to my MC was too long and engaging the brakes so I bought this pushrod checker tool:

https://www.amazon.com/dp/B0C6G7NY6M?ref=ppx_yo2ov_dt_b_fed_asin_title

It was indeed a bit long so i cut some off of it (the screw in part is long gone from who knows when) so I now have an 1/8" air gap per that checker tool. When i drove it yesterday a short distance the brakes didn't seem to drag like they did the first time i drove it, but they were still doing it towards the end of my short trip to town and back (approx 8 miles). As soon as i pulled in the garage I went to my driver's side rear wheel and cracked open the bleeder and it shot fluid out and i could hear that caliper release a bit.

My question is this, is there any way that my power booster could be causing this. It holds a vacuum and seems to be operating correctly but it seems that the pedal does not have the travel that I remember from the last time I really drove this car, which was 2008. Before I replace the booster, are there any checks I can do on it to eliminate it as a cause?

 

[tony-muscle]

What brake pads are you using? Some race or high performance pads will tend to drag at the lower temps found during street use. This assumes that your calipers are new and shouldn't be the problem. Also, did you bed your new brakes? bedding may help with pad release.

 

[4thesporty]

I don't recall the brand of pads used, nothing special though, all brake hardware came from rockauto, OE replacement stuff.

And no, I did not bed them either. I'll give this a shot.

Thanks!

 

[turtle5353]

Are the calipers new? If not, make sure the pins are well lubed and allow the caliper to move in and out freely.

 

[TheDude]

Sorry not an answer to your question and sort of a long shot but a proportioning valve can cause this kind of thing. Basically it won't release pressure from the other side. I'd expect that to be on just the back though, but I've seen OEM valves fail and cause something like this.

 

[mach1sc]

you have too much "residual pressure" or you are just not satisfied with the amount of residual pressure. i can not really say it is to much, but it sounds like you are not happy with it.

my car did the same thing until i bypassed these red and blue things. i just drilled a hole thru them as they were not wanted, caused excess pad wear for me.

 

[cjstaci]

Sounds to me like a master cylinder. Either the pushrod is still too long or maybe a sticking piston. Just because it’s new doesn’t mean it can’t be defective.

 

[4thesporty]

Are the calipers new? If not, make sure the pins are well lubed and allow the caliper to move in and out freely.

Yes, all the calipers are new. This weekend I'm going to pull all the wheels and check them all for free movement again though.

Sorry not an answer to your question and sort of a long shot but a proportioning valve can cause this kind of thing. Basically it won't release pressure from the other side. I'd expect that to be on just the back though, but I've seen OEM valves fail and cause something like this.

I bought the willwood proportioning valve with the MC. I did remove all bias for now until I get this issue straightened out (turned couter-clockwise all the way)

you have too much "residual pressure" or you are just not satisfied with the amount of residual pressure. i can not really say it is to much, but it sounds like you are not happy with it.

my car did the same thing until i bypassed these red and blue things. i just drilled a hole thru them as they were not wanted, caused excess pad wear for me.
View attachment 96447

I don't have any residual pressure valves in my system, the entire circuit is new, from MC to calipers

Sounds to me like a master cylinder. Either the pushrod is still too long or maybe a sticking piston. Just because it’s new doesn’t mean it can’t be defective.

All signs really point back to this in my opinion.


Going to get the car up in the air this weekend and do these things

• Check all calipers for free movement and centered on the rotors
• Disconnect the MC again and to bench bleed once more and check pushrod length again
• Bleed the system again with a helper on the brake pedal this time. Previously I did it with a pressure bleeder attached to the MC
• Drive and bed the brakes well

If these don't solve my issue I'll get on the phone with Willwood and see about an RMA on the MC. Thanks all for the suggestions. I'll report back what i find.

 

[Don C]

I agree, likely either a pushrod length or a master cylinder problem. While you have it out for bench bleeding check the pistons for free and complete movement. You might also pull the piston to make sure there isn't any debris in the cylinder that is impeding the piston reaching full movement.

 

[turtle5353]

Was the car originally a drum brake car? I believe there are residual pressure valves built into the MC. Can’t remember for sure though.

 

[Cleveland Crush]

Was the car originally a drum brake car? I believe there are residual pressure valves built into the MC. Can’t remember for sure though.

@mrgmhale has pertinent information on the mc residual valve. Perhaps he'll chime in...

 

[mrgmhale]

@mrgmhale has pertinent information on the mc residual valve. Perhaps he'll chime in...

Thank you for tagging me. Luckily I got an alert in my email about this post. Otherwise I would have overlooked it as during the past few weeks I have been buried on some other projects. But, when it comes to braking, suspension, and tire issues, I feel those are areas where nobody can afford to duck his/her responsibilities if they know something that may help others. These are arenas that directly impact the safe operation of automobiles, after all.

Anyway, a shout out to Cleveland Crush for getting my attention. I just hope the information I have is helpful. I placed some brake information I feel may be relevant into a PDF document. Please feel to share it with others as you see fit, and to use for yourself as well, of course. If the information I incoude in the attached document is helpful please let me know.