TJefferson2020

Since my most recent build, I had some trouble with the front wheels skidding easily on medium braking.

Only changes were new proportioning valve (previous unit wasn’t working) and replumbed lines from the master. I’ve had some issues with rear cylinders blowing. (64, added power brakes, disks on front, drums on rear, proportioning valve for rear)

I’ve opened the prop valve all the way (max pressure to rear) and while improved, still skiddy. It seems like the drivers side front is skidding.

I have a suspicion that my right rear drum is not adjusted properly. My theory is that the shoes on that drum are not adjusted close enough to the drum causing lighter braking pressure there and causing the left front to break loose.

Am I on the right track? One thing is for sure. That car really stops. I just need it to be balanced.

Plus, on the freeway a skid makes a skid mark in your pants.

TJefferson2020

Crickets

Patrick03

I did the front disk conversion on my '64 and rebuilt the rear drums. Used a '67 power master cylinder with a distribution block, not a proportioning valve. I have a pressure holding valve (can't remember the correct term) for the drum brakes that I haven't put on yet. I'm very happy with the conversion. Not sure what is going on in your case, but I'd look at whether or not you need a proportioning valve. Adjust rear drums as well.

Patrick

63 340HP

If both fronts a locking up at the same time, half the problem is resolved.

Bleed the brakes with a different color fluid, starting at the right rear, to assure you have no air in the lines.

Make sure the rear has the residual valve in-place, downstream of the proportioning valve, to keep the rear shoes close to the drums to allow the auto adjusters to work while backing up & braking, and to minimize the fluid volume it takes to get the shoes on the drums. Manually adjust the rear shoes to slightly drag, to bed-in and arc the shoes on assembly. Drive it for a while with frequent brake cooling stops, to arc the shoes without cooking the brakes and bearing grease. Test the brake bias.

If you have better rear brakes, and front to rear brake bias, with the parking brake handle pulled out, the adjusters are not working and the shoes are way out (time to pull them apart and rebuild).

If you still have the front end locking early, and essentially no rear brakes, move the proportioning valve to the front circuit. Start full open and adjust down a needed.

Good Luck.

TJefferson2020

Super helpful. And you.

I dont think I have a residual valve for the rear. IIRC the line goes from master to proportioning valve (adjustible) to the rear.

I did dial in more pressure to the year and the problem is MUCH better but still one front tire lets loose under extreme braking.

I’m going to check rears so they slightly drag and look into residual valve. I did try the backing up adjustment. Not sure t worked.

The car handles really good with larger tires. The adjustible valve is gold. I went to a big wet parking lot to figure it out. That is a good idea too. It really lets you see what is happening.

This car is really getting ironed out. Very happy with the latest round of upgrades.

davekp78

Hard braking in the wet will be different than in the dry. In the wet, the fronts will lock up more easily.
Whatever the conditions, you don't want the rears to lock up first.

TJefferson2020

Should have mentioned I used the wet skid pad to see what was happening, then adjusted and tested on dry pavement. It is very close now. When it does skid, the fronts lock first - barely. In full lock the car skids straight now.

The biggest improvement is that the threshold for skidding is much higher now. I think the tears were getting little pressure.