Weird 'brake loss' problem...

[madmike]

'68 Charger, I recently converted my stock manual drums to manual disc 11 3/4" front, 10" drum rear.  I had no problems with this set-up, everything seemed to work fine.  Two weeks ago, I replaced both rear axle wheel bearings with new tapered Timkens, so I did have the rear brakes apart.  I re-assembled the rear end, drove it, and everything seemed normal at that time.

This morning, I decided to drive the car to work, after it had been sitting the last week and a half or so.  I backed out of the garage and down the driveway, and rolled down the slope to the stop sign and DIDN't have any brakes!  I pumped the pedal a few times, and they pumped up and came back.  I drove around the block (back to the house) and checked the fluid level in the master cylinder, and it was full.  The brakes acted normal too.  So, I thought, screw it, I'm taking the Charger to work.  I backed out of the driveway, rolled down the slope, and the same thing happened, I lost my brakes!  I pumped them back up with a few pumps, and they're normal again.  It's weird...

I never had this problem before, and I'm thinking that maybe I don't have the rear brake shoes adjusted correctly (too loose or too tight).  Usually, I adjust the shoes so that I can hear/feel them dragging slightly on the drum.  And, that's what I did when I first installed the disc brakes several weeks ago, and had no issues.  My other thought was that maybe there is still air in the lines, but this seems unlikely.  I drove about 25 miles to work, used the brakes aggressively several times, and had no issues.  The only other thing I noticed, is that at the beginning of the drive, The brake pedal would go down maybe 2", before I felt actual resistance in the pedal.  At the end of the drive, the pedal goes down only an inch or so, and the resistance is already there.

My other thought was that maybe I really need some sort of additional isolation or proportioning valve, since I've added the discs up front.  But honestly, the car seems to brake really well, until this problem popped up this morning.  Right now, the car has only the factory proportioning valve for 10" manual drum brakes in it.

What do you guys think?  Where is a good place to start looking?  Tonight after work, I plan on popping the rear drums back off, to see what I can see...  Thanks!

[bill440rt]

Did you bleed the brakes after putting everything back together again? Sounds like you may have air in your system.
Check all fittings at the lines as well for leaks.

If you still have the drum brake prop valve, you will need to add the disc brake hold-off valve. They are available repro. And, swap out the front/rear drum line for a disc line, or modify your existing line.
I went thru something similar when I did my drum/disc conversion on my '68 as well. Just had to add the hold off valve & swapped the main front/rear line.

Here is the hold off valve:
http://www.ebay.com/itm/67-68-69-70-Mopar-B-body-Disc-Brake-Hold-Off-Valve-NOS-/390166088986?hash=item5ad7b60d1a&item=390166088986&pt=Vintage_Car_Truck_Parts_Accessories&vxp=mtr

[madmike]

Bill,

Thanks for the link.  I guess my train of thought this morning was along the lines of, since I lost brakes backing up (well, actually moving forward right after backing up) that I might have an adjuster problem.

The car doesn't 'seem' to need another valve added in the system, but maybe I'm flat wrong about that...

[bill440rt]

Do you have brakes with a firm pedal then when backing up?

Might be a shoe problem if it only occurs when backing up, but if you have brakes again after several tries or a low pedal that leads me to believe you still have air in the system.
Sometimes after a first few drives I like to bleed them again. Vibration from driving could stir up any small trapped air bubbles.

[resq302]

If you do decide to add the proportioning / hold off valve, try and get one NOT made by In Line Tube as I had problems with both of mine causing the back breaks to lock up as the valve would only let fluid through and not back up to the master cylinder.

[bill440rt]

Inline Tube (unfortunately), looks like the only company that is making them repro. I got mine thru Fine Lines, but it is still made by Inline Tube. I try not to buy anything direct from I.T., their customer service leaves little to be desired.

FWIW, I have no problems with my valve.

[myk]

I say bleed the lines again.  Also, I was under the assumption that you had to have a different proportioning valve or....had to change "something" when going from drums to discs? 

[resq302]

Bill, I had mine on the charger for a little over a year and without warning, boom.  My back breaks were locking up.  The replacement valve I put in did it immediately.  Im not saying that they couldn't have refined something but the one that was on the car was supposed to be after that "bad batch" and it still ended up causing problems like they were said to do.  I figured that after a year I had lucked out and got a good one.   

[bill440rt]

Bill, I had mine on the charger for a little over a year and without warning, boom.  My back breaks were locking up.  The replacement valve I put in did it immediately.  Im not saying that they couldn't have refined something but the one that was on the car was supposed to be after that "bad batch" and it still ended up causing problems like they were said to do.  I figured that after a year I had lucked out and got a good one.   

My rears locked immediately too, but only after a few short tests until the front pads set in. Now it works fine.
Trouble is we are at the mercy of one supplier of these things, unless you want to find a used one (risky) or a NOS one (expensive).

[resq302]

I ended up getting a used one and had it rebuilt.  Best of both worlds    Like I said, mine was fine for about a year and then it just went south fast!  The replacement I put on was fine until I went down the street and started coming back.  On the way down to the turn around point it was fine then when I was coming back I noticed more effort was needed to keep the car moving forward.  I agree we are at the mercy of one company however, if one company makes crappy parts, why support them?