Frustrated - Front Brake Issue

[Fresh Air Inspector]

Hello All,

I'm still plugging away on my '88 Plymouth Caravelle (aka Gran Fury). The rear axle, rear suspension and rear brakes have been rebuilt. Along with the rear brakes (wheel cylinders, shoes and all mounting hardware [all new]), I also replaced the hard lines (copper / nickel), and flex line to the rear along with the power brake servo (rebuilt), and master cylinder (new). I did not touch the front brakes as the engine / transmission was coming out along with the K frame.

After rebuilding the back half of the car I bled the complete hydraulic system - brakes were great. Fast forward a few months, engine /transmission is out and work started on the front end. K frame is finished and installed. Time to move on to the front brakes.

I replaced all the front hard lines (copper / nickel), the front flex hoses (new), and the calipers (rebuilt). Brakes have been gravity bled and no bubbles to be seen now when the bleed nipple is cracked. My better half is away at the moment so I can't ask her to pump while I bleed.

However, no matter how many time I pump the brake pedal I can't build up any pressure and the calipers do not move (still have ~3mm [1/8"] gap between outside pad and disc). I don't want to push the brake pedal too hard as I can feel it hit a stop (not floor), after moving about 50 mm (2") or so. I've never had an issue like this with any brake job I've ever done (the above is probably number 20 in my life).

The only brake component I haven't replaced is the proportioning valve but I can't imagine that being an issue. Hopefully one of you can shine some light on this and end my frustration. Looking forward to the feedback.

 

[AMC Diplomat]

The only brake component I haven't replaced is the proportioning valve

My guess is you still have air in the system, something isn't tight and you're leaking in a weird spot, your brake booster rod isn't the right length, or it's the proportioning valve.

The proportioning valves in these are cast iron and they rot on the inside.

 

[Oldiron440]

I can’t remember if you can get the calipers on the incorrect side of the car on the mopar or not but make sure the bleeders are at the top of the caliper.

 

[M_Body_Coupe]

I can't remember, but do you have access to the FSM?

If YES, look up 'Brake System Bleeding Procedures' in CH5.

Specifically, look at the Hold Off valve mention and just check that out to see if for some reason maybe the way it's currently positioned happens to be blocking off the pressure apply to the FRONT brakes.

Beyond that, check the 'Bleeding Master Cylinder' section as well to be safe.

 

[Oldiron440]

It could be that you have a leak at one of your fittings, I got into a Corvette that I had trouble getting a non factory joint to seal. It didn’t leak fluid but it did air.

 

[69-]

Doesn't The proport valve have position to block off one circuit?

 

[Fresh Air Inspector]

Hello All,

First, many thanks for all the feedback. As I always highlight; it is times like this that make it clear how valuable these forums are. When you encounter a difficult problem someone in our group has probably run into it and found a solution.

And the winner is ..... M_Body_Coupe - he suggested the 'Hold Off Valve' in the proportioning valve. (FSM, Chapter 5, page 5-3 - see pictures below)

I pulled out the FSM, read the write up about bleeding the brakes. Because I was on my own I had to make my own 'tool' using the taper on a set of needle nose pliers to hold the valve pin in position coupled with a small vise-grip to keep the needle nose jaws tight on the valve pin.

As soon as I pushed on the brake pedal I got significantly more travel and within a few pumps the pedal started to firm up. A quick check of both front brakes indicated that the each piston had taken up the gap between the pads and disk. Next test was to spin each wheel and see if the brakes would stop it - both worked. Neither of these tests had worked prior to today! Next I removed my 'tool' and tested again with the same results. I know I still have some air in the front system, when my better half arrives home over the weekend I'll do a proper bleed.

Oldiron440 makes a very good point. It is VERY easy to mix up the front calipers. I had taken my new (aka rebuilt), ones out of the box to paint them but accidently put them back in the wrong boxes. The passenger caliper had just been bolted to the bracket when I looked at it and thought 'why would they have placed the bleed nipple on the bottom of the piston cylinder'? Then the 'doh!' moment hit - wrong side!!





Hope it helps.