SonnysSweetTea
Newbie
That's the exact route I'm fixing to go. Run the old style lines, a proportioning and call it a day.88-94 brake lines are how I deleted mine and I've never regretted it.
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That's the exact route I'm fixing to go. Run the old style lines, a proportioning and call it a day.88-94 brake lines are how I deleted mine and I've never regretted it.
That's the exact route I'm fixing to go. Run the old style lines, a proportioning and call it a day.
Two pages, not one word about quick-take-up master cylinders or low-drag calipers.
Failing to use a quick-take-up master cylinder when you have low-drag calipers results in a low pedal that can't be fixed...until you install a QTU master cylinder.
Do you even know if your calipers are regular-style or low-drag? How about those eight (!!!) master cylinders?
"Regular" and "Low-drag" calipers with the appropriate master cylinders were both used on GM400 trucks.
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The rear of the QTU master cylinder has a "step" in the casting, that accommodates a huge rear piston. The 1" bore master has a 32mm rear piston. The 1 1/8 bore master has a 38mm rear piston. (I think. I may be off a bit.)
No promises on the GM800 masters. Never held one in my hand.
Calipers are harder. I have low-drag calipers on my K1500; when I pulled them apart I didn't see anything that caught my eye. When these first came out, low-drag calipers had a wider, tapered groove for the square-cut seals. My calipers didn't seem to have a wide groove, though. So maybe I'm just not seeing the difference, or maybe GM has changed the design.
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HOWEVER they work, low-drag calipers MUST have a gush of fluid (high volume, low pressure) when you first push the pedal. The bigass rear piston is what provides that gush of fluid. That pushes the disc pads up to the rotor, then the high-pressure section of the master cylinder takes over and actually squeezes the rotor. If there's no big piston to provide that gush, the pedal goes way down because the high-pressure section of the master has to supply the large volume of fluid.
Oh, yeah. Forgot to mention. I converted my front brakes on my standard-cab K1500 to the more-powerful brakes that come on an extended-cab. The caliper pistons are bigger. Bigger pistons require a larger-bore master cylinder, or the pedal goes way down.
My truck came with a 1" bore QTU master. I have to convert to a 1 1/8 bore QTU master, to handle the larger fluid volume needed by the bigger caliper pistons. I got the calipers, master cylinder, and bigger booster all from the same Treasure Yard donor truck. The bigger, extended-cab parts are what's in the photos above. (Truck came with JB3 (?) brakes, and I'm installing JB5 (?))
You start playing games with brake parts, and pretty soon you're in deep **** and changing everything.
Does the O.P. have the correct master cylinder bore to go with his bigger calipers?
Pretty much what ive gathered is all the upgrades suck. As far as Oem style m/c theres a 1" and 1-1/8". Im assuming mine already had the bigger of the two being an extended cab.Easy solution: DON'T buy a master cylinder intended for a vehicle that's set up differently than yours, when you can get one that fits properly. There's no magic in the GM800 master cylinder.
Good info from Schurkey.........
My thoughts: improper rear drum brake adjustment would cause low pedal as you describe. Drum brakes WILL self-adjust. but only after they get fairly loose, and the self-adjuster mechanism is set up so that it only adjusts when going in reverse.
Anyway, I have been using this method to adjust drum brakes for almost 50 years, and it works perfect....... carefully mount all hardware and then rotate adjuster until you can just get the drum onto the hub. Rotate the drum by hand a few times to make sure it's free, then (using adjuster tool or flathead screwdriver) tighten the adjuster (through the slot in backing plate or drum) until the drum is locked. Now slowly back off the adjuster until the drum rotates freely with just a tiny bit of drag. This ensures the shoes are positioned where they need to be.
Good luck. Please keep us posted. I'm curious to see what your solution ends up being.