Let's talk brake boosters...question inside. I NEED AN ANSWER GUYS!!!

[BigOrange90Jimmy]

I am in the process of building a truck. The cab I am using is from an 86 1/2 ton 2wd pickup. It had the 4.3L in it. The brake booster is considerably smaller than the ones used on our K5's. I am using the stock 3/4 ton brakes on my axles, and you guys know there is no size or fluid capacity difference between the calipers. I am unsure on the size difference of the 14b's wheel cylinders compared to the 10b's.

Should I replace the booster with a larger unit or will I be fine with the smaller one that currently resides on it?

 

[BigOrange90Jimmy]

ttt

 

[sandawgk5]

The 10 bolts have a 1" wheel cylinder bore I believe and the 14FF and sf have an 1 1/8" bore on the wheel cylider. Hope that answers your question.

 

[R72K5]

theres not just one size for wheel cylinders for each axle sometimes theres more than two even, depending on the brake system installed by GM

RPO code starting with J

also bigger booster doesnt always mean is bigger truck, alot of the old 1 tons ran real small diameter boosters vs. the 3/4 tons that ran huge diameter ones

its hit and miss really

size doesnt mean crap with boosters

its the chassis/axle/brake system(GVRW rating) that determined the booster GM installed

good luck

 

[mechted]

my brother just did this (14b swap with a 4.3l engine) and the rear kept locking up on him, so he got a 3/4 ton brake booster and master to solve the issue

 

[BigOrange90Jimmy]

well which do you guys think i should run?

i have 2 weeks to get this truck ready to go...and i have driven neither the 1/2 ton cab truck that i'm using, nor the 87 K5 chassis.

Nothing on this truck has ever been driven by me. I'm combining a 73 3/4 ton drivetrain, an 87 K5 chassis, and an 86 C10 cab. Power comes from a stock, carb'd 350, a TH350 w/a reverse manual valve body, 205, sent to a 3/4 ton D44 front and 14b rear w/11.5" brakes.

 

[BigOrange90Jimmy]

ttt one more time....come on fellas!

 

[adamforsythe]

Bigger is better in my book.
Thanks
Adam

 

[fatbob]

I would keep the booster and use the master cylinder for a 3/4 ton. The difference in wheel cylinder size will affect the master cylinder more than the booster.

 

[dyeager535]

All you have to do is get it together and see how it feels, right? You've got two weeks, what are your options for getting another one at this point that won't exist when you get the truck together and decide (from use) the booster doesn't have enough assist?

As far as I can see with the braking system, a smaller booster might make brake pedal effort a bit harder, but the wheel cylinder/braking differences as related to fluid capacity/movement should be made up in the master, with the bore diameter.

Not sure if this applies to trucks or not, but on the cars in the 80's, they used a dual or single diaphram booster, and IIRC, the dual booster was smaller diameter, but fatter than the single. Still better brake assist. Is yours any different in thickness, or is the diameter the only difference between a "stock" K5 one?

 

[BigOrange90Jimmy]

The thickness is the only difference.

I have two stock brake boosters still on the trucks in my yard, but the vacuum line on one has been removed and they have been exposed to the elements for the past two years. I wasn't sure if they would still work or not.

 

[kgblazerfive]

Booster size doesn't matter, you could run it without the booster might be hard to stop but my point is it would work. the size of the master cylinder is what matters and the smaller the better to a point at least the smaller the bore diameter the more pressure, volume is meaningless its all in the pressure.

 

[dyeager535]

the size of the master cylinder is what matters and the smaller the better to a point at least the smaller the bore diameter the more pressure, volume is meaningless its all in the pressure.

Hopefully this is somewhat meaningful and borne out when the posters project is completed, but I don't agree with the above statement.

OK, higher pressure is good. Doesn't developing higher pressure take more effort? (as you mention, run without the booster. Just turn the truck off, pump brakes a couple of times, then try and stop it) Thus, you'd need more assist to develop more pressure in a similar setup. Right? I'm talking similar bore size. I understand decreasing bore size alone would increase pressure, however...

If you increase the fluid capacity of the braking system (larger calipers, cylinders, rear disks) you NEED to push more fluid with at least the same pressure as before, or braking effectiveness (both apply speed and force) is going to decrease. If that wasn't the case, GM would have gone with smaller master cylinder bores to boost pressure, and wouldn't have changed them based on the different brake RPO's, which they did.

 

[R72K5]

bottom line here is that i would recommend using brake booster off same size of truck as your axles/brake system is

its real basic/easy here

good luck