K10 14bolt swap now rear brakes lock up before the front

[Darty03]

Did you read through that link sent you on post 9??

I looked through the brake pads shown and looked at their ratings. The wagner should be about like the raybestos performance pads. I just found them for 2 bucks more though so I might go with them instead. I'm trying to keep it under 50 bucks, preferably 40 or under. This is a trail rig and these parts should be getting replaced again in a year or so. One thing I didnt understand about the ratings on that list was that some pads had near maxed out performance but then only one notch for performance above stock. How can they be rated so high on one and low on the other for the same pad?

 

[Rustisbest]

When I put the big C30 brakes under my Suburban, I considered using the load sensing valve that came with the axle. But I eventually chose not to. I never had any issues with rear lockup, even when braking down steep, muddy or gravel roads.

Oddly enough, my old '86 C20 Burb with 13" brakes, the load valve evidently cut too much line pressure to the rear. The front brakes had a tendency to lock up in a panic stop on pavement.

Probably because theres couple hundred pounds of steel and glass over the rear vs a truck?

 

[bucket]

Probably because theres couple hundred pounds of steel and glass over the rear vs a truck?

Could be. I made sure to mention that fact in my earlier post. But GM installed the load sensing valves on the Burbs too.

 

[Blue Ox]

I've had both. The pickup had the JD7 brakes from the factory, and I duplicated the same specs when I upgraded the axles on the Suburban. Both trucks had the same issue. When the LSPV malfunctioned on the pickup, and since I hadn't initially installed it when I did the Suburban. Violent, premature rear lockup. Both corrected by a properly functioning LSPV. Maybe it's different for a 4WD. Maybe I'm just the lucky one. I know others have said it's a non-issue. Don't know what else to say except YMMV.

BTW, I didn't initially install it on the Suburban because someone else with a similar pickup said "that valve doesn't do anything." Well, it turns out it does. We tried changing the shoe adjustments and smaller wheel cylinders and it made zero difference. Added the LSPV and they turned back into civilized, drivable trucks.

 

[squaredeal91]

I put a 14 bolt out of a 1995 k2500 suburban in my 78 k10 with no issues like this. A few months before I did the axle swap i replaced my master cylinder with the 3/4 ton master. That being said. If you rears lock up its probably because the shoes are out of adjustment, ive had that issue before on something else. That's my 2 cents lol

 

[48hd]

Make sure you have the correct size wheel cylinder and pins.

 

[chevdude]

You didn't say what diameter the rear wheel cylinders are.
I believe that they come in 1" and 1 1/8".
The larger bore will give you more braking pressure than the smaller one.
So if you have the 1 1/8" rear cylinders, try the 1"

 

[Ricko1966]

I looked through the brake pads shown and looked at their ratings. The wagner should be about like the raybestos performance pads. I just found them for 2 bucks more though so I might go with them instead. I'm trying to keep it under 50 bucks, preferably 40 or under. This is a trail rig and these parts should be getting replaced again in a year or so. One thing I didnt understand about the ratings on that list was that some pads had near maxed out performance but then only one notch for performance above stock. How can they be rated so high on one and low on the other for the same pad?

All gm combination valves are not the same. In 1985 alone there were 4 different combination valves with different settings for brake bias. I've put all this up on another thread including the part numbers and people put some interesting work around. The aftermarket combination valves must be a generic works okay in most applications kinda deal since they only sell 2 to cover everything instead of dozens like original. That said see if anything had your combination of parts and try to find a used OE. combination valve. I'll look for the other thread and link it. BIAB.

https://www.gmsquarebody.com/threads/rear-brakes-locking-up-information-for-you.48473/

 

[Darty03]

You didn't say what diameter the rear wheel cylinders are.
I believe that they come in 1" and 1 1/8".
The larger bore will give you more braking pressure than the smaller one.
So if you have the 1 1/8" rear cylinders, try the 1"

They are the 1 1/8". I tried to find a definitive part number for the 1" that would fit and if the pins were the same, but I didn't find much so I went with the 1 1/8" again. I really didn't feel like they would make enough of a difference to fix the issue after reading about them. I need a lot less strength and from what I saw a lot of people were saying it made minimal change.

All gm combination valves are not the same. In 1985 alone there were 4 different combination valves with different settings for brake bias. I've put all this up on another thread including the part numbers and people put some interesting work around. The aftermarket combination valves must be a generic works okay in most applications kinda deal since they only sell 2 to cover everything instead of dozens like original. That said see if anything had your combination of parts and try to find a used OE. combination valve. I'll look for the other thread and link it. BIAB.

https://www.gmsquarebody.com/threads/rear-brakes-locking-up-information-for-you.48473/

I actually saw your post the other day and it got me back on the proportion valve being the issue. This is what I initially felt like was the solution but wasn't sure. I think I mentioned adding a manual adjustable valve early but that was going to be my "bandaid" fix before I made this post. I decided to just make the post and see what others thought first. I was going to add it after the factory valve along the rear frame rail. I figured that would let the factory valve still work correctly and not limit flow to it. This being an offroad only vehicle now it might be the most simple solution.