JB6 to JB7 brake upgrade

[Supercharged111]

Presumably you’re using the OE 1” cylinders.

See my prior post in this thread:

Post in thread 'JB6 to JB7 brake upgrade'
https://www.gmt400.com/threads/jb6-to-jb7-brake-upgrade.58607/post-1248959

I glossed right over that. I'd figured the bigger ones were a different dimension, that's pretty sweet.

 

[94K3500PROJECT]

So I have a 98 k1500 with a 6 lug 14 bolt rear end and JB6 brakes. I'm looking at switching to the JB7 calipers (pn: 18-4123) and the JB7 master cylinder. (pn: 131-66008) My original plan was to switch to rear disks but @Schurkey made some good points in a couple different threads about those conversations and I ditched that idea pretty quick. I guess my question is should I swap my drum brakes or can I run my oem 11" JB6 drums? Also do I need to do anything with the pressure valve (not sure if thats the rught term) for the drums since im going from a low drag JB6 set up, to a non-low drag JB7 set up. I've done a lot of reading on this site and I believe I don't have to change my drums because there doesn't seem to be any big changes from the JB6 to JB7 drums considering they are both duo-servos. but I can't quite get the solid answer I'm looking for. Part numbers are a big help too!

I couldn’t find posts about the disk brake conversions.
What were the issues addressed?

My old K1500 had a gmt800 Tahoe MC, gmt800 single piston rear disks and 8 lug front calipers and that was by far the best K1500 brakes I’ve ever driven

My K3500 is getting the Lugnut4x4 rear disk conversion with JB7 calipers so I’m curious to hear feedback on the negatives of that setup

 

[DamHoodlum]

They're are a few members that disagree with Disc on rear, however if you use the correct parts and install them correctly they work flawless. I used the Little Shop kit and I am pleased with my results.
Its your truck, do what YOU want to do and don't worry about the ones that disagree

PS The block members feature work great here...................................

 

[Schurkey]

They're are a few members that disagree with Disc on rear,

I haven't heard of anyone who "disagrees" with rear discs...if they're engineered properly.

Horse-shiit hack-job bottom-feeder disc conversions are another story.

My old K1500 had a gmt800 Tahoe MC, gmt800 single piston rear disks and 8 lug front calipers and that was by far the best K1500 brakes I’ve ever driven

OEM assemblies wouldn't suffer from the poor engineering of some aftermarket "kits".

My K3500 is getting the Lugnut4x4 rear disk conversion with JB7 calipers so I’m curious to hear feedback on the negatives of that setup

Post a link, or photos.

Its your truck, do what YOU want to do and don't worry about the ones that disagree

But if the brakes fail, you may need to worry about the lawyers of the folks you collide with.

 

[1998_K1500_Sub]

I couldn’t find posts about the disk brake conversions.
What were the issues addressed?

This thread from earlier this year generated some buzz…

Thread 'Disc brake upgrade'
https://www.gmt400.com/threads/disc-brake-upgrade.57241/

@Schurkey’s comments are spot-on.
From from I’ve seen, the OE designs are superior for the reasons stated.

 

[94K3500PROJECT]

This thread from earlier this year generated some buzz…

Thread 'Disc brake upgrade'
https://www.gmt400.com/threads/disc-brake-upgrade.57241/

@Schurkey’s comments are spot-on.
From from I’ve seen, the OE designs are superior for the reasons stated.

I found it.
At the same time there have been 10’s of thousands of those kinds of kits available for years now.
Cup cars use the exact same brackets on all of their cars including super speedway cars.
The calipers do function different being fixed but that’s a pretty solid testament to that designs durability

I’ll run my Lugnut setup with no worries at all

 

[94K3500PROJECT]

They're are a few members that disagree with Disc on rear, however if you use the correct parts and install them correctly they work flawless. I used the Little Shop kit and I am pleased with my results.
Its your truck, do what YOU want to do and don't worry about the ones that disagree

PS The block members feature work great here...................................

One thing is certain I’ll never run garbage drum brakes on anything longer than it takes me to convert one to disk.

Another thing, of all vehicles I’ve owned over the years that did have drums the gmt400’s were by far the worst functioning of all of them.

 

[Erik the Awful]

OEM assemblies wouldn't suffer from the poor engineering of some aftermarket "kits".

*Cough* JB3 *cough*

Rear discs are only an improvement in that you don't need to keep adjusting your drums. Past that, most conversion kits are just racer-wannabe garbage.

 

[1998_K1500_Sub]

I found it.
At the same time there have been 10’s of thousands of those kinds of kits available for years now.

Well, that's speculuation, but yeah, certainly "many"...

Cup cars use the exact same brackets on all of their cars including super speedway cars.

My buddy uses similar brackets on his pro drag car.

Suggestion: Draw inspiration from applications similar to the task at hand. Look at other designs on other truck rear brakes (GM, Ford, Toyota...) and auto front brakes with comparable GAWR.

Race cars and other vehicles have a different design objective... budget, materials, longevity, reliability, serviceability, to name just a few.

I’ll run my Lugnut setup with no worries at all

Then probably most any vendor's setup will do, as most of them are similar if not copy-cat identical. eBay might offer the best value for you.

 

[Schurkey]

Cup cars use the exact same brackets on all of their cars including super speedway cars.

Fatigue life isn't really a problem on "Cup cars", since everything gets examined or replaced after five hundred miles.

The calipers do function different being fixed but that’s a pretty solid testament to that designs durability

The Little Shop caliper brackets don't have fixed calipers. I bet the Lugnuts brackets don't have fixed calipers, either. The calipers float on the pins/sleeves/O-rings.

The GM brackets support the caliper so that the thrust of the caliper is taken between the pads--balanced, so no twisting force. The pins and sleeves allow side-to-side movement only. The Little Shop brackets rely on the pins/sleeves to retain the caliper entirely, and caliper thrust is taken way off-center, so the pins bend with brake application. The pins were never intended to accept thrust loading or bending forces.

Again, I don't know about the Lugnutz conversion--but I suspect it's the same as the Little Shop.

I’ll run my Lugnut setup with no worries at all

Okee-dokee. Make sure you don't collide with me.

Suggestion: Draw inspiration from applications similar to the task at hand. Look at other designs on other truck rear brakes (GM, Ford, Toyota...) and auto front brakes with comparable GAWR.

Race cars and other vehicles have a different design objective... budget, materials, longevity, reliability, serviceability, to name just a few.

Thank you. Great wisdom there. And to reinforce the first part--make sure the disc conversion kit is AT LEAST as powerful as the drums you're replacing. Doesn't do any good to replace huge drums with small rotors.

One thing is certain I’ll never run garbage drum brakes on anything longer than it takes me to convert one to disk.

Another thing, of all vehicles I’ve owned over the years that did have drums the gmt400’s were by far the worst functioning of all of them.

Drum brakes PROPERLY SIZED stop just as well as discs, once. Drums do have issues with retaining heat.

The biggest problem with brakes on GMT400s is the leading/trailing shoe system on half tons, followed by ABS issues, and (I suspect) low-drag caliper issues. Are you blaming the drum brakes for problems that actually happen because GM undersized the rear brakes, or occur somewhere else due to lack of maintenance; specifically lack of PROPER brake fluid flushing?

GM had no damn business installing the crappy and too-small 254mm leading/trailing drums on American vehicles, knowing that Americans don't use the park brake any more.

*Cough* JB3 *cough*

Yeah. Acknowledged. And the "5" was no better at the rear, but considerably more powerful up front.

Rear discs are only an improvement in that you don't need to keep adjusting your drums. Past that, most conversion kits are just racer-wannabe garbage.

IF everything is working right, and if the customer knows how the self-adjuster works, the drums stay in adjustment.

Discs don't self-adjust if the caliper piston and square-cut seal aren't in good condition; and some calipers need the park brake worked to stay in adjustment. There's problems with everything. Anything can fail. The bigger questions are "how often in normal use", and "how often in severe use".