E brake light on after disc brake conversion

[ethanmccll]

I recently did a disc brake conversion on my 8.625” 10 bolt using Cunningham brackets and 1985 eldorado rear calipers. The truck is a 1998 c1500 with a k1500 10 bolt swapped into it and 4 wheel abs with a recently replaced master cylinder and booster. I have bled the brakes till no more air was coming out, and properly adjusted my parking brake. During regular braking it feels like the first half of my brake pedal is a lot softer or mushier than the last half. I found that if I quickly pump the pedal a few times that brake pressure builds up quickly and I am able to stop a lot quicker, and after a good bit of driving I find that my rear rotors are relatively cool compared to the front ones. Any guidance would be greatly appreciated.

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[Schurkey]

I recently did a disc brake conversion on my 8.625” 10 bolt using Cunningham brackets and 1985 eldorado rear calipers.

You have my sympathy.

recently replaced master cylinder

Please tell me you didn't downgrade to a so-called "NBS" master cylinder.

You still have the OEM-style three-chamber, Quick Take-Up master cylinder...right?

I have bled the brakes till no more air was coming out

...using a scan tool to auto-bleed the ABS, of course.

Any guidance would be greatly appreciated.

Shitcan the disc brake conversion. You've already got a six-lug rear axle, therefore you've already got six-lug wheels. Replace the entire rear axle with a 6-lug K2500 9.5" "14-bolt" of the proper gear ratio. This gets you an enormously better axle than the craptastic ten-bolt axle you've got now, and you'd get the wonderful 11.x Duo-Servo rear drum brakes in the process. You'll need a conversion U-joint and four U-bolts and hardware, and the U-bolt plates from the donor vehicle.

Install the CORRECT master cylinder if that's been replaced with an incorrect one. Booster too, if that's been screwed-up as well.

Flush the brake fluid front and rear, using a scan tool to chatter the ABS solenoid valves. Procedure attached.

Make sure the front brakes work properly--calipers not sticking on the pins, caliper pistons not sticking in the caliper bores, etc.

 

[ethanmccll]

You have my sympathy.


Please tell me you didn't downgrade to a so-called "NBS" master cylinder.

You still have the OEM-style three-chamber, Quick Take-Up master cylinder...right?


...using a scan tool to auto-bleed the ABS, of course.


Shitcan the disc brake conversion. You've already got a six-lug rear axle, therefore you've already got six-lug wheels. Replace the entire rear axle with a 6-lug K2500 9.5" "14-bolt" of the proper gear ratio. This gets you an enormously better axle than the craptastic ten-bolt axle you've got now, and you'd get the wonderful 11.x Duo-Servo rear drum brakes in the process. You'll need a conversion U-joint and four U-bolts and hardware, and the U-bolt plates from the donor vehicle.

Install the CORRECT master cylinder if that's been replaced with an incorrect one. Booster too, if that's been screwed-up as well.

Flush the brake fluid front and rear, using a scan tool to chatter the ABS solenoid valves. Procedure attached.

Make sure the front brakes work properly--calipers not sticking on the pins, caliper pistons not sticking in the caliper bores, etc.

I replaced the master cylinder with an oem style replacement.

I put a Eaton trutrac and 4.56 gears in the 10 bolt I’ve got now so I don’t think I’ll be switching to a 14 bolt lol

Also saw a few things about switching to 3/4 front calipers and then switching to the nbs master cylinder. I believe these posts might’ve been from you. Would that be something worth doing?

 

[Schurkey]

I have no use for the "NBS" master cylinder whatsoever on a GMT400. Others will disagree.

Going to the non-low-drag calipers could be a benefit. Bigger piston = more force on the front pads. OTOH, I don't know how big you can go without losing proper front/rear balance. My '88 K1500 stops just fine with the equivalent to JB6 brakes--including the low-drag front calipers and OEM-style master cylinder.

Did you THOROUGHLY bench-bleed the master cylinder? Doing a proper job of that takes much longer and is more-involved than most folks realize. You can run ten gallons of brake fluid through the master cylinder, and NOT get the air bubble out if it wasn't properly bench-bled to start with. Raising the rear of the vehicle, or unbolting the master from the booster WITHOUT removing the brake tubes, and forcing the front of the master down so the master cylinder is tipped somewhat "down" from level, and then tickling the big piston at the rear with a Philips screwdriver or wooden dowel can help.

If you've assured that the bleeder screws are located at the TOP of the calipers--not at the bottom, not angled on the brackets kinda-sorta but not really at the TOP of the calipers, then I'd say that the next thing you need to do is to flush the brake fluid front/rear, following the bleeding procedure in the attached .pdf in my post above. You WILL need a scan tool. The Tech 2 listed in the .pdf is the official "dealership" tool, but SOME other scan tools can do the same thing. I used a Snap-On Solus Pro with 14.2 software to do my '97 K2500. The 8.2 software will NOT do it, however.