Brake performance

[85ckaz]

I have a 1985 K20 suburban.  The vehicle has a 2" lift on it and I put new 33x12.50 r16 load range E tires on it. I have the rear brake height sensing valve is removed in the style of Service bulletin 88-T-151.  I have new brake pads, machined Disc, new drums and new shoes on it. I have no fluid leaks and the brake fluid is clear with no debris in it. The rear brake slack adjuster is expanded out and I have done the stopping in reverse to self-adjust the shoes several times. The brake pedal feels firm and if you stop from 45 mph a couple of times all the brakes get hot. 

My question is how well do these trucks stop? Is there a specification on braking distance? Did any auto magazines did a review of theses and get stopping distance measurements?

My brakes work fine for normal driving but at 65mph during a fast stop the brakes feel weak.  If you are driving at 45 mph and hammer the brakes hard the tires do not lock. I know I am driving a 5500 lbs., 8 passenger, and “super wagon I do not expect this thing to perform like a Corvette or a brand New 2014 2500 HD.  A 1982 Ford F150 4x4 with 36" tires will stop a lot faster than my Suburban. My friend and I side by side brake tested his F250 and Suburban from 45 MPH and his F150 stopped around 40 feet shorter The F150 will lock up all four tires if you push the pedal hard. I know there is a major weight difference but if you drive his F150 with a 4000 pound dual axle trailer the brakes feel good    

I am wonder what other people think about square body brakes? Is this normal performance for a brake system?

P.S. I am not trying to start a flaming war about Chevrolet vs Ford.

[1967KaiserM715]

One, the F150 is lig hter so a shorter stop is expected.
But at least your rears should lock up, fronts too ideally. I would say look at vacuum booster, it is possible it is leaking giving the indication it is working, but not completely. Does the pedal get harder to push the longer you hold it? Other considerations are air in lines still, master on the way out(although unlikely)

And you were doing fast hard reverse stops? Not just pumping pedal while moving backwards, the auto adjust won't work right that way

Sent from my LGL34C using Tapatalk

[werewolfx13]

My trucks have always stopped fine unless there was an issue...And the issues were either known or easily realized. I would consider looking for an incorrect combo of brake parts..IE, wrong (mismatched) master cyl/brake booster for the rest of the brake code package, such as a JD3 master on JD5 or 7 booster, or vice versa, JD3 booster with JD5 or 7 master....Unless its hydroboost (JD8), in which case this is mostly a non issue, except a non hydroboost master on a JD8 booster.

Did that make sense?


On related note, I'm experimenting with my 76 k20, since I get a lot of parts dirt cheap through work (O'Reillys), I'm trying a hydroboost master cyl on my vacuum booster...the hydroboost is a larger bore, possibly longer stroke, and I expect I might have to try extending the pushrod from the booster if brake performance is not up to snuff when I finish putting the truck together, but with a rear disc conversion, theoretically more fluid movement, and carbon metallic pads, I'm crossing my fingers for even better braking. Once I put the system through the paces, I'll create a thread relating my findings, then any changes required, for future reference.

[frotosride]

Even with the 35's I know for a fact that all 4 of mine will lock up and smoke the tires espe ially if someone spit out the window and I find it during hard braking. Getting heat in them makes a huge difference as with all brakes. I use semi-metalic pads because I hate taking the hubs off of the front to replace rotors!

My trucks have always stopped fine unless there was an issue...And the issues were either known or easily realized. I would consider looking for an incorrect combo of brake parts..IE, wrong (mismatched) master cyl/brake booster for the rest of the brake code package, such as a JD3 master on JD5 or 7 booster, or vice versa, JD3 booster with JD5 or 7 master....Unless its hydroboost (JD8), in which case this is mostly a non issue, except a non hydroboost master on a JD8 booster.

Did that make sense?


On related note, I'm experimenting with my 76 k20, since I get a lot of parts dirt cheap through work (O'Reillys), I'm trying a hydroboost master cyl on my vacuum booster...the hydroboost is a larger bore, possibly longer stroke, and I expect I might have to try extending the pushrod from the booster if brake performance is not up to snuff when I finish putting the truck together, but with a rear disc conversion, theoretically more fluid movement, and carbon metallic pads, I'm crossing my fingers for even better braking. Once I put the system through the paces, I'll create a thread relating my findings, then any changes required, for future reference.

I'm definitely interested in this! Especially for heavy loads like my haul down here to GA. People on the interstate don't seem to understand how weight prevents that big blue truck the just cut off from stopping before I'm on to of their hood.

[85ckaz]

I will try to get some heat in them tonight. I have JB7 brakes on the truck according to the decal in the glove box.  I have a new part # NMC1872 master cylinder, Part # MKD153 pads and Part # 451 shoes from O'Reilly auto parts. The vacuum booster is what was on the truck when I bought it. As far as I can tell I have no air in the brake system. The petal is not spongy and it stays consistence on matter how long you hold it down.

Is there a way to identify if the power booster is a JB7group part?

I am also interested in the JB8 master cylinder install.

Thank you

[werewolfx13]

I didnt get to check those part numbers to verify they are correct for your brake package today, but i work for a few hours on thanksgiving, if we dont get much traffic ill look them up for you just to be sure you have the correct parts.

[werewolfx13]

Those parts should all be correct, if you want a pad upgrade ask for performance friction carbon metallic pads, they might have to order it, but they dont cost a ton, about $50