Brake Issues - SRO codes

[Doppleganger]

The codes on my truck (85 K20) says it has the JB7 brake system. Apparently it does not. I dont know if this is a case of someone swapping things out (doubt it - but possible) or was one of those instances where GM used what they had on the shelf.

My rear drums are 11" not 13". My fronts look to be the bigger brakes, but I cant find any specs on what size the fronts are in JB6 or JB7. The GVW is 8600 so it should have JB7 anyways. My master cylinder was the smaller plastic reservoir, but had yellow paint marker all over it like a junkyard part. The original owner's modified this truck so bad anything is possible.

Now, in light of the setup it 'should' have, I found / bought an NOS GM booster and master cylinder for that brake (JB7) setup. New JB6 GM Pro MC's are cheap - boosters however, are NLA. I cant even find a PN to look for one. I am beyond p.o.'d with this whole truck at this point. Doesn't help the person doing my axles is going on month 9 now with the front.

So before I seriously consider cutting bait, I have a few questions that hopefully someone has already done.

Can I use the booster and MC from the JB7 with the "smaller" brakes (I know the rears are, but not sure on the fronts)?

What is required to upgrade the rear axles to 13" and the fronts (if they also turn out to be smaller)? I would imagine its all bolt-on parts.

Can the rear axles be pulled without removing the diff cover? I know some do - some dont. No idea on this one.

Does anyone know the PN for the JB6 booster (if I cant use the one I have)? I would rather find an NOS one than anything reman'd.

Thanks fellas.

[VileZambonie]

What is someone doing for 9 months to your axles? Incubating? 

Don't get hung up on NOS brake parts. Get what is readily available to you. You buy a 30 year old MC and fails, now what? If your truck came with 13" brakes and has 11" brakes, someone probably swapped in a JY axle, brakes and all, however, K20 JB7/JD7 came with 13" and 11" brake shoes.

Full floating axles can be unbolted without removing the meatball cover. Doesn't sound like you have a full floater. Identify your axles

[Doppleganger]

Thanks for the response.

Clown who has my axles got them in October. Winter was coming so no hurry. Took him 4 months to disassemble them so I could get the housings cleaned and powder coated. All they needed was new seals. He has since claimed he couldn't find parts - then he did and a seal was missing. Now its 'maybe' end of this week. I'm not holding my breath. My issue with his is why didn't he say something, oh, like 6 months ago?? His main job is he builds motors. He's lost 3 BBC's and a 401 AMC job over this from others watching.

So can I use the JB7 booster and MC I have with the 11" rear brakes? Not sure what the fronts (in a JB7 setup) are supposed to have. My rotors are 12.25". If I can use the bigger booster/MC with these, I can swap the bigger parts later. Have heard mixed reviews if thats possible.

THX

[VileZambonie]

So can I use the JB7 booster and MC I have with the 11" rear brakes?

Yes

[Doppleganger]

THANK YOU!

 

[Doppleganger]

Is the front brakes (JB6 to JB7) a complete bolt on upgrade? I cant find any different part numbers between the rotors. I need new calipers anyways....this just seemed too easy.

btw.....my rear axle is a 9.5 semi-floater.

Does anyone know if I have to open the diff up to pull the axles? I know some Dana's do - some dont.

Sorry for the 1000 questions.

Thanks.

[VileZambonie]

The JB7 larger caliper bore requires a longer stroke, so different length push rod, minor differences in the booster but everything will bolt on. Just buy the JB7 parts and try to keep everything correct for the application.

C clip axles require the cover to be removed.

[Doppleganger]

Thanks VileZ.

I read an article from a company that does brake conversions - they suggested swapping out the larger front calipers, MC and booster - and if you regularly tow less than 15,000 lbs, the 11" rears will be fine.

I'm set.

Thanks again!