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Another rear disk question...

mrdrinksalil

mrdrinksalil

1/2 ton status
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Ok. So I've read way too much info we've got on the rear disk set-ups and the "official disk brake thread" is enough to make you go insane. I want to get this right the first time. And please dont refer to things as "stock" parts. There are lots of different parts that came "stock" and with a brake system any one part can change how the whole system works.


What I have is a Chevy Dana 60 front and a 14 -bolt rear with the mid 80's 3/4ton calipers. I also have a 1 5/16 master cylinder. I want to start plumbing things up, but am unsure if I should be using the front proportional valve or not... I want this thing to be safe on the street. Anyone running this set-up, or those of you that KNOW what you're talking about please help...
 
I don't know what I have for the master cylinder as far as size. It's the factory hydroboost unit. I'm running my rear discs with all the same plumbing as it came from the factory. It works just fine. Well outstanding actually!
 
Oops, forgot to add my point. My point is you may need to "test and tune." I know there are others that haven't needed to add an adjustable proportioning valve. Haven't heard of anyone doing anything with the factory proportioning valve, but then I haven't heard it all either. :D
 
I totaly understand the "test and tune" part, but im a big fan of "doing it right the first time" too. Thats why my build-up is taking so long.
 
I think the test & tune......

He is talking about involves adjusting the proportioning valve, with the additional stopping power coming from the rear you need to turn it down a bit. I have found the best area to test is a smooth gravel road. On Gravel it becomes obvious when the rear locks up before the front.
 
my truck came with a d44 up front... so I am not sure if that means I have a different proportion valve and master cyl than you..

but I upgraded to a d60 front and had d44 calipers for the rear.. but have since upgraded to caddy calipers in the rear.. I think my d44 calipers worked way better.. but to have an ebrake (working or not) to pass inspection is a beautiful thing.....
 
my brakes came off of a 79 gmc 2500. I used the front 10 bolt 3/4 ton calipers in the rear for the conversion. I used the factory master cylinder and lines, steel braided flex lines, and factory proportioning valve as well. Took the truck for a spin after bleeding everything, had a problem, the rear tires would skid easy. Bought an adjustable proportioning valve and mounted it where the 1/4 inch rear brakeline meets the rear flex line that is 3/16 and used the adj. prop valve as the adapter. So im using the factory proportioning valve and the adj. proportioning valve in conjunction with each other, I can skid my 40's no problem. If your motor is pumped up and has very little vaccum, it will effect how your brakes perform.
 
I've got enough vaccum for the booster so I should be ok there. Looks like I'll just use the factory proportioning valve and see where that gets me. The valve I have is from an 85 K5. I'm not sure what the master cylinder is from, other than its a 1 5/16".
 
mrdrinksalil said:
I've got enough vaccum for the booster so I should be ok there. Looks like I'll just use the factory proportioning valve and see where that gets me. The valve I have is from an 85 K5. I'm not sure what the master cylinder is from, other than its a 1 5/16".
Click to expand...
mine would lock up the rear way easy.i found it it was because on the rear of the master side there is a sustaining 10 psi valve in there that keeps a constant pressure on the rear brake cylander in a front disk rear drum setup.i took out the pressure valve in the master and they work a lot better now.
 
There is a disc/disc prop valve that you may or may not need. You can get it from GMpartsdirect.com for alot less that other places.
The rear disc swap can actually be a truck by truck thing. Some need parts, others don't. Get them on there, bleed, bleed, bleed, and see how it feels to you.
Each truck is different, each driver is different. What may be fine to me, may be totally unaccepable to you. Vise versa
 
I have run all the stock plumbing and had good luck. On my blazer I eliminated the proportioning valve entirely and still works better than the factory drums ever worked.
 
Leper said:
There is a disc/disc prop valve that you may or may not need. You can get it from GMpartsdirect.com for alot less that other places.
The rear disc swap can actually be a truck by truck thing. Some need parts, others don't. Get them on there, bleed, bleed, bleed, and see how it feels to you.
Each truck is different, each driver is different. What may be fine to me, may be totally unaccepable to you. Vise versa
Click to expand...

hey leper, would you happen to have this part nubmer you speak of?
 
I have a Dana 60 front with stock calipers. Dana 44 calipers in the rear. A stock 1986 half ton short bed master cylinder (not sure of the size) and all of the stock plumbing. It locks the rear brakes up before the fronts, only in a panic stop situation though. I will be adding an adjustable proportioning valve some time before spring, I will update this post with my results.

Mike
 
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