brakes

[sidevalve]

hi my name is mark I have a 1987 suburban 2500 I bought about 6 months ago, I am a bus mechanic for Monrovia unified school district for the past 25 years. The vehicle I bought needed a lot of work,to make a long story short the brakes stop fine under normal conditions.but when you would have to panic stop or apply the brakes hard it comes to a rolling stop,the brakes do not lock up the wheels.i have turned the front rotors and rear drums replaced wheel cylinders rebuilt front calipers adjusted rear brakes.looks like the booster was replaced don't know if its the correct one it has a cast iron master cylinder.i know you can botton out a vacum booster which is normal , this one seem  to seems to easy to bottom out acts like the stroke is to short jb7 is what is on my id tag any suggestions thanks

[80Chevy4x4]

Here are the codes.

JB5 BRAKE POWER, DISC/DRUM, 6,400 LBS
JB6 BRAKE POWER, DISC/DRUM, 7,200 LBS
JB7 BRAKE POWER, DISC/DRUM, 8,400 LBS
JB8 BRAKE POWER, DISC/DRUM, 10,000 LBS

[Irish_Alley]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=28592.0
what conditions are your brakes hoses? wonder if they could be expanding under the higher pressure. does it pull or anything while braking?

[zieg85]

I would get the correct master cylinder for your particular application.

[sidevalve]

thank you will see if this one is correct

[sidevalve]

this is a 4x4 does have the 13'' drums with the 2 1/2 inch shoes semi floater vacuum booster the one picture that shows jb7 jd7 are they interchangeable THANK YOU VERY MUCH

[bd]

If the brakes are properly adjusted, there is no air in the system, the combination valve is not tripped, and the truck has the correct master cylinder (GM 18014705), then take a new look at the vacuum booster.  JB7 brakes used a dual diaphragm vacuum booster (GM 18011339).

JB7 and JD7 both use 13" x 2.5" rear shoes (GM 15596619).

[roundhouse]

Get a brand new master cylinder
Not a rebuilt one
And make sure it's made in the US or if you can't find that , Mexico ,
Check the box and do NOT accept one that's made in China
Cost a few bucks more but totally worth it

If you bleed the brakes on an older vehicle and don't put a block of wood under the pedal to limit the down travel  to normal range ,
If you let it go all the way to the floor when bleeding it , it damages the rubber O rings on the piston from all the dirt and stuff that the O rings never touch in normal operation




Sent from my iPhone using Tapatalk

[Irish_Alley]

this is a 4x4 does have the 13'' drums with the 2 1/2 inch shoes semi floater vacuum booster the one picture that shows jb7 jd7 are they interchangeable THANK YOU VERY MUCH

yes they are interchangeable same part number and all, its just a diffrent booster. im kind of confused about the 13"x2.5" brakes, not saying its wrong as im still learning. but that axle is the S.f. axle which would be found in the lighter duty trucks so why would a light duty truck/axle have the heavy duty brakes?

also heres another page you might want to take a look at