Rear drums locking easy after Power Disc conversion

[hank scorpio]

Just finished up doing the power disc conversion on my c10 from the original manual drums. Brakes before stopped ok under 40mph but were pretty terrifying from anything above that. No locking issues.

After the swap the rears would lock up under any sudden application of pressure. Went round robin on bleeding, checking everything. Improved after the fronts bed in some but only a little. Ended up checking the rears and they were adjusted way too tight. Lug nuts were noticeably hot after a short trip.

Backed the adjuster (and hand brake off) and it's better. It doesn't lock if you increase the pressure gradually (normal braking) but under a sudden application it still locks the rears easily.

When I had the rear drums off the rear pads were looking a little thin so it's probably time to build them anyways. There was no fluid or grease inside the drums. Truck has 240k and while always maintained well, it probably only put 500 miles in the last five years on before I ended up with it.

For those who have done the power conversion, is the locking normal? Seems to me this is locking in an unsafe manner. The proportioning valve is marked PV2 (which should be correct) but don't know which end I'm chasing an issue here on.

[geezer#99]

You got a pic of your prop valve?

[LostMy65]

I used one of these. That way I can adjust the rears depending on the load I have in the bed.
https://www.summitracing.com/parts/s...AaAmZUEALw_wcB

[slepysal]

Proportioning Valve.... as mentioned what are you using?

[hank scorpio]

Originally Posted by geezer#99

You got a pic of your prop valve?

It’s the same PN as this one: https://www.speedwaymotors.com/GM-Di...lets,9878.html


It’s this kit (but with captain fabs bracket) https://azproperformance.com/product...ssembly-700200

[Captainfab]

Did you get good fluid flow when bleeding the front?

[hank scorpio]

Originally Posted by Captainfab

Did you get good fluid flow when bleeding the front?

Yep! Rebled three times to be sure. Pedal feel is great.

[REDROCKER652002]

I was thinking proportioning valve as well. Isn't there something about the lines being the same length on the front and backs? That is why the fronts are usually in a circle by the master cylinder? I am just trying to remember, but I am sure the pro's here will get you going. I just seem to remember something about the lines having to be equal so the pressure is the same. RR

[Captainfab]

I can't say why your rears are locking up before the front, but you might just have to plumb in an adjustable valve in the rear line. Then you can adjust to get the brake bias you are wanting.

Originally Posted by hank scorpio

Yep! Rebled three times to be sure. Pedal feel is great.

[LostMy65]

Originally Posted by Captainfab

I can't say why your rears are locking up before the front, but you might just have to plumb in an adjustable valve in the rear line. Then you can adjust to get the brake bias you are wanting.

That's what I posted above:

Originally Posted by LostMy65

I used one of these. That way I can adjust the rears depending on the load I have in the bed.
https://www.summitracing.com/parts/s...AaAmZUEALw_wcB

I like it because the rear is light unloaded, but I can dial the rears open a little more when I have a load in the back.

[Steeveedee]

You shouldn't have to use the valve from Summit in conjunction with the proportioning valve you have. Verify which part of the master cylinder pressurizes which part of the brakes. Some use the rear piston part for front brakes, some for the rear brakes.