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Insufficient Braking on my Suburban

2546 Views 4 Replies 2 Participants Last post by  Crawdaddy
As some of ya'll may have read, I'm still working on upgrading my Suburban to a 3/4 ton. This process included upgrading the rear axle to a 14-bolt out of a 1-ton truck. So, the brakes in the rear are a lot bigger. As a result, my stock brakes weren't doing the job. So, I've upgraded the master cylinder to a JB8 master cylinder. I left the 1/2 ton booster in the truck since it appears the same one as the 3/4 ton one. So, logic dictates that since the master cylinder is rated for 1-ton usage, it should be able to make the truck stop well....not.

Now, the question is, why isn't the truck stopping well and able to lock up its brakes? My first thought is that I think I accidentally ran the master cylinder dry while bleeding the brakes. The brake pedal felt great and rock hard after bleeding the rear brakes, but went to nothing as soon as I started bleeding the fronts. When driving, I can stand on the brake pedal with both feet, and while the truck leans forward a lot, the wheels will not lock up at all. Braking distance is also considerably longer than it should be. So, I'm planning on getting some more brake fluid and re-bleeding the brakes. Should I re-bleed the master cylinder before bleeding the brakes? While I'd really rather not have to take the brake lines loose again, if I have to, I have to.

Any suggestions where I should go to get my brakes braking nice and hard?
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I will re-bleed the master cylinder then. I think the MC also might be on a slight rear lean in the truck, so I'll try to roll the truck up on ramps to get the MC level before bleeding the master cylinder. When moving up to the 3/4 ton parts, the rear wheel cylinders got bigger, but the fronts actually remained the same size, in fact, the same part number. The truck does have rear ABS, but it is the real old archaic rear abs. There isn't really an ABS valve, it's just an accumulator on the line for the rear brakes. About the only thing not new to the brake system now is the brake lines, proportioning valve, and brake booster. Everything else is brand new. The parts not changed are 1/2 ton parts, but it doesn't appear that the 3/4 or 1-ton replacements are any larger to handle more load.
Hopefully the seals aren't already destroyed. I think we were going pretty much to the floor when bleeding the wheel cylinders. When we bled the front, the front of the truck was higher because I had taken the tires off the truck to get to the bleeders. I really hope I didn't destroy the seals on the MC, it's literally brand new.
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