Redoing the Brakes... but the rear's are locking up on hard braking

[sircrunch]

I've been working on my truck brakes for quite a while now. It originally had manual brakes. I upgraded to power brakes. Soon after upgrading I noticed a few days later my brakes were starting to fade. It got so bad after a few days I realized only one wheel was braking, because the right rear tire would lock up and slide.

I have replaced the following:

Rear Drums
Rear Shoes
Rear Wheel Cylinders
Rear Spring Kit
Rear rubber brake line
Rear stainless axle brake lines
Front Rubber Lines
Master Cyl
Booster

I simply inspected the front disc brake pads and they looked like they had plenty of material left.

I bled all 4 wheels once finished.

Now that I have done all that work, the back wheels are locking up under hard braking. The good thing is that its both back wheels instead of the one before... But, this locking up tells me the fronts aren't working like they should. The bleeding process went well, I got a good hard stream from all 4 corners.

What should I do at this point?

Also, for bonus points, what do I need to replace to keep grease from splashing outward from the hub all over my front wheels?

[Gmc.guy]

There should be a sheet metal cap that goes on. They are pretty cheap. Your bearings will not last long without.

[Shugalou]

Have you thought about your proportioning valve? I see it wasn't replaced...If you are getting fluid on all 4 corners I would think it's working properly but maybe when a bleeder is open in the front it works normally?

Also I see you replaced all the stuff in the rear but not much up front, is it possible both front calipers are seized and pushing the pads against the rotor?

Have you checked the push rod length?

I'm not too familiar with changing from non power to power but I thought you had to make sure the booster and master matched?

[sircrunch]

I purchased the booster and master separately.... any additional info concerning matching...and pushrod length is greatly appreciated.

My first instinct was bad calipers but it could be something to do with the master/booster etc.???

[Shugalou]

Here is a good trouble shooting checklist to go through

http://www.classicperform.com/TechBo...oubleshoot.htm

And here is my post that has lots of great info from our members here

http://67-72chevytrucks.com/vboard/s...=684488&page=2

Hopefully this will help you out.

[sircrunch]

I read some information last night that got me thinking.... There are 3 different types of brake systems for my truck. JB1 JB2 and JB5. These codes are on the service id sticker on each truck. My truck is originally a JB1 truck. That is manual, non-power brakes. JB3 and JB5 are power but it depends on the GVW of the truck. Because of my trucks lighter weight, when I upgraded to power brakes I went with all JB3 components. From what I read, JB1 and JB3 share most components anyway.

So I read a post on another message board from a fellow that said he converted his truck from JB3 to JB5 over time, piece at a time, and he said never mix JB3 and JB5 because "it will let the rear brakes lock up easily"

Sounds like what I have going on BUT as far as I know, I don't have any JB5 stuff on my truck.... Unless perhaps... the store gave me the wrong master/booster.

So right now, I've removed the master and booster for a return. I'm going to try to return it for a booster/master combo and install that to see what happens. If I'm still getting stronger rear brakes and weaker front brakes, I'm going to go to the next step, which I think would have to be.... the proportioning valve??

[sircrunch]

I forgot to mention, I put new front calipers and pads on and it didn't help.

[Dead Parrot]

Same tires and tread front and back? Tire pressure good?

+1 to making sure the booster and MC are meant to be together.

The booster should have an adjustable pushrod. At least the replacement I got a few months ago did.

IIRC, the pin on the brake pedal that the pushrod connects to is in a different location for manual vs power.

Other then the rear lock up problem, is the truck stopping as good or better then before you started?

[sircrunch]

As stated above, I took the new master cyl and booster back to the parts house for a warranty return. When they put the new replacement up on the counter I measured the rod. It was a half inch shorter. We began looking and we believe the booster I had is either wrong or broken. In any case, there's some reason for the difference. I'm going to install these new parts tonight and cross my fingers that this was the issue all along. The rod.