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Front Brake (8 lug conversion) question

Phil513

Phil513

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So, I'm getting ready to order calipers and rotors for my 8 lug front conversion.

When I look at parts, there seems to be 2 types for the K20. They distinguish by having an 11 inch or 13 inch rear drum.

I have a 1 ton rear axle, so pretty sure it's 13 inch.

However, the fronts that match that size rear are the "JB7" rotors and calipers, the "JB6" are for lighter duty. I read even where the "JB7" were for hydroboost, but that info seemed iffy. I think there were "JB8" for that.

Anyhow, I guess my question is, in my scenario, should I be looking at the smaller or larger ones? I don't want to get into a whole master cylinder kerfuffle either.

Any thoughts?
 
My best guess is JB7. Because JB7 is a 3/4 ton set up, and trucks that had an 8-lug Dana 44 or 10-bolt would be a JB7 option code. Just my best guess. Also, you are corect that an JB8 brake option code is a Hydroboost only set up as far as I know.
 
Phil513 said:
So, I'm getting ready to order calipers and rotors for my 8 lug front conversion.

When I look at parts, there seems to be 2 types for the K20. They distinguish by having an 11 inch or 13 inch rear drum.

I have a 1 ton rear axle, so pretty sure it's 13 inch.

However, the fronts that match that size rear are the "JB7" rotors and calipers, the "JB6" are for lighter duty. I read even where the "JB7" were for hydroboost, but that info seemed iffy. I think there were "JB8" for that.

Anyhow, I guess my question is, in my scenario, should I be looking at the smaller or larger ones? I don't want to get into a whole master cylinder kerfuffle either.

Any thoughts?
Click to expand...
Yeah, Im thinking yus got the small hublock sized drive rotors from Martin?
Calipers and brakes off of your 10b should be the same.

At one point there was a large hub front D44, is that the JB7?
 
The K20 front calipers differ only in the size of the piston; the outer castings themselves are interchangeable (ie the calipers are the same physical size as each and the 1/2 ton's, and use the same D52 pad.)

If I remember my hydraulics properly, the larger diameter piston will apply more force but will require more pedal travel to do so. Especially if you're using a vacuum master (I.e. no hydroboost), you might stick with the smaller piston. Which I think is actually the same as the K10 caliper.

Don't get too caught up in the RPO's as they're tied to the GVWR and the booster type, as mentioned.

-- A
 
The difference between JB7 and JB6 calipers is the size of the pistons. Everything else is the same. Same pads and same rotors. I would use the JB7 so they match the rear drums better and bias will be closer. I used JB7s on the front and JB6 on the rear with a stock K5 master. I have since changed to a D60 up front and kept the one ton calipers (for now). When I first installed the D44 with JB7 front and JB6 on the rear the brakes (master cylinder) felt funny but I think it was just because it was different. I don't even notice it now. They work just fine with a stock master.
 
Cool, thanks everyone. Yes, I'm using the caliper brackets and hubs that Martin sent me.

I guess JB7 it will be. One other small question, since I'm putting 8 lug 15 inch wheels on (so I don't lose my brand new tires) would the JB7 require more caliper grinding than the JB6?
 
No, the calipers are the same casting. Same grinding either way.
 
Phil513 said:
Cool, thanks everyone. Yes, I'm using the caliper brackets and hubs that Martin sent me.

I guess JB7 it will be. One other small question, since I'm putting 8 lug 15 inch wheels on (so I don't lose my brand new tires) would the JB7 require more caliper grinding than the JB6?
Click to expand...
Check them first, you may get lucky

The rear, if they be 13", might be different issue
 
bent72 said:
Check them first, you may get lucky

The rear, if they be 13", might be different issue
Click to expand...

Good call on the 13 inch drums. 15s may not fit over them. Good reason to change to disc out back too. I love mine. It will never have drums again.
 
AV8TER said:
Good call on the 13 inch drums. 15s may not fit over them. Good reason to change to disc out back too. I love mine. It will never have drums again.
Click to expand...

I just can't go rear disc. I have a manual trans, don't have a "Park". I can't go without an ebrake.
 
AV8TER said:
Well crud! Dang manuals!
Click to expand...

I love having the manual. It's just cool. hahaha.

Martin seemed pretty certain a 15 inch steel wheel will fit over the rear drum. I guess if worse comes to worse, I'll sell my set of ralleys with 35 inch tires and go larger. It's just that much longer for me to do this project.
 
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