C2: Hi. My name is Dan and I've got FBPS

[Dan Pepper]

Flaccid Brake Pedal Syndrome... My '66 w/J50 brakes stops well on the front brakes, but the rear always goes soft after bleeding and driving 100 miles or so. Couple of questions for trouble shooting:

First: I have a tried to get an accurate runout reading on the rear rotors with a dial indicator. Trouble is, the U-joints bind because they are drooping from being elevated. This tends to make getting a decent reading tough. The needle jumps around when the half shaft passes the bind. Not sure if this dial jump in itself is a sign of execceive runout. Any tricks to get the rear halfshaft assy's to turn without binding?

Second: I have a Motive products pressure bleeder and am wondering if I could find a system leak by applying pressure, letting it sit for a while and then look for a fluid leak. Will brake fluid under pressure typically leak from where ever the air is being introduced?

[Terry F.]

Re: C2: Hi. My name is Dan and I've got FBPS

It is hard to comment. How old are the componets to your brake system? Are there any obvious leaks anywhere? When was the last time the rear bearings were gone through?

You can support the car on the frame rails just in front of the rear tires with dead man jacks. Take the tires off. Then take another jack (I use a roling floor jack and a 2x4) and lift the trailing arms one at a time. Be careful doing this and you might want to pad the surfaces slightly so you are not banging things up. Stop lifting the trailing arm before the car starts to come off the frame rail (jack stands). You should be able to check for run out at that point.

But consider this....run out is a result of the combination of bearing play and the uneven surface of the brake disk. If you are exceeding tolerances already, I would say you got problems. Your rear bearings may need to be rebuilt.

Enjoy, Terry

[Terry F.]

Hmmm, I suspect you also have "BTAB" also.....

Bad trailing arm bearings....

[Dan Pepper]

Re: Hmmm, I suspect you also have "BTAB" also.....

Could be the dreaded BTAB. The hubs still have original rivets, so bearings were installed in St. Louis. This is a 54k original mile car. At some point somebody threaded zerks into the bearing housing, so they have been greased occasionally. Don't feel play when I reef on the tire/wheel assy. But it's probably time though.

One last thought - I am suspicious of speed bleeders I have installed. Think they may be sucking air from around the threads. There is not a lot of teflon coating left on the threads. Anybody air seeping past bleeder threads?

[Terry F.]

Re: Hmmm, I suspect you also have "BTAB" also.....

Speed bleeders I have never used. I would not use them. All it takes is a little air and your brakes are no good. It also confuses things.

I had this feeling you would say you couldn't detect any play in the rear bearings. Remember, if you don't take the tension off the rear axels by raising the trailing arm, it is nearly impossible to detect the play in them. That is because as the trailing arm comes down it pulls the half shaft tight. This put considerable lateral tension on the stub axels. I am nearly certain you will not be able to flex it enough to detect any play. Just my opinion though.

I wonder where the metal filings went when they drilled those holes in the housings for the grease fittings? Just because the brake disks are still riveted on doesn't mean they have never been apart.

I bet if you lift it up like I said in the previous post, you will find play in the bearings. You may need to take the brake caliper off or pry the shoes off the disk to feel it.

Enjoy, Terry

[Wayne W.]

Re: Hmmm, I suspect you also have "BTAB" also.....

It is pretty obvious that there is runnout if the rears are sucking air. You have to support the rear of the car at the hub housing to get the suspension to flatten out so you can check the runnout. Support it under the outer strut rod at the shock bolt.

[Gerard F.]

Re: C2: Hi. My name is Dan and I've got FBPS

Dan,

If these are you original brake calipers after 54K and 39 years, consider replacing them or sending them in for an overhaul. About 25 years ago, I had the same problem on my 67 and I had to pump them up each time I pulled it out of the garage. I tried everything from speed bleeders to pressure bleeders. They bleed from the cylinders which is hardly noticable. It got so bad, that I was afraid to drive the car, and it set for about 20 years. About 5 years ago, I replaced all four calipers and the master cylinder, and I haven't had FBPS since.

The original calipers were not meant to last that long.

Jerry Fuccillo
#42179

[George J.]

Agree with Jerry

I had the same symptoms you have even after replacing the wheel bearings and checking runout. It turned out to be a leaking caliper. You could not tell this, though, until you had it out. Replaced calipers, pedal hard as a rock.

George #31887

[Dan Pepper]

Re: C2: Hi. My name is Dan and I've got FBPS

I removed the original 1st design calipers (frozen) and replaced them with 2nd design sleeved units a couple of years and 2100 miles ago - so odds are it's not the calipers. Since the problem has gotton worse over that time, it sounds like a progressively worsening runout problem. The metal shavings from drilling the zerk holes probably isn't helping the bearings regardless - that was done before I acquired the car. I'll replace the speed bleeders w/new conventional bleeders first to see if that is where air is being introduced. Then, I'll put'er up on jackstands to straighten the axels and get a good dial reading off of the rotors.

[Chuck S.]

Re: Agree with Jerry

Probably time to get them sleeved with either brass or stainless steel, and rebuilt with new pistons with O-ring seals. Rebuilding with the O-ring kits will be a little more expensive, but eliminates potential problems later with rotor runout that causes "air pumping". If the calipers are original, I would have them resleeved rather than trade in as cores...calipers are dated, but the dates are not judged.

[Terry F.]

Re: C2: Hi. My name is Dan and I've got FBPS

To set the dial indicator up you have to put it on a magnet stand or similar that is attached to the trailing arm.

If you did it that way the first time and you exceeded the run out as you rotated it through the bind (trailing arms just hanging, you already have a problem with the bearings. Your run out on the brake disk may actually be ok or they are contributing to the problem. In any case, the solution is to carefully pull the trailing arms and send them out for restoration. It is by far the best solution for the problem (vansteel or blairs). Tell them to make them like new and like original.

If your brake disks have enough metal left, they may be able to reuse them.

Im not sure if I would leave the grease fittings in them. If that was such a great idea chevrolet would have built them that way. I think the potential of blowing the seals out of the housing would be very high! As I recall, there is a seal on the front and the back of the stub axel. As you grease it and fill the cavity you would build pressure in there and the seals could pop out. I would especially be concerned if it was freshly rebuilt. I wouldn't do it.

Thanks, Terry

Good luck, Terry