need master booster pushrod help

[BAGNDRAGIT]

ok i am trying to figure out my braking issue, and i am wondering what length the rod that goes between the master and booster is on a half ton system. the one i have is 3.25" long. is there a longer one? there seems to be alot of slack in it, and i have adjusted the pushrod out of the booster and i still have to push the pedal down halfway to get any braking. any advice would help. thanks!

[Steve Hafner]

I'd like to know too, I'm still having the same problem.

[68gmsee]

This may help. (from CPP site http://www.classicperform.com/TechBo...oubleshoot.htm )

Check Booster Pushrod Adjustment
The pushrod that actuates the master cylinder must be properly adjusted. Ideally there should be only slight clearance between the booster pushrod and the master cylinder pushrod. Interference will preload the master cylinder. When the system is preloaded, it builds pressure each time the pedal is pressed. Since the master cylinder is not allowed to fully release the pressure from the previous stroke, the system will eventually lock the wheels. Too much clearance will cause excessive freeplay in the pedal. In almost every case, if you bought your booster and master cylinder from us, we pre-adjust the booster pushrod and master cylinder for you so this is not a problem.

To make 100% certain of a properly adjusted booster pushrod for your master, we offer a master cylinder depth gauge (PN: CP2003) to determine correct pushrod length. The following illustration demonstrates the proper usage of this tool. First measure the length that the booster pushrod extends past the face of the booster with the "head" of the pin. on the tool. Then measure the depth of the master cylinder piston with the other end of the pin on the tool. If the pin hits or there is too much space on step two, then adjustment is necessary.




There are basically two different master cylinders that we use for our Chevy and Ford kits, the Deep Bore master cylinder and the Shallow Bore master cylinder. To determine which master cylinder your booster is setup to mate with, you can do the following simple check. For Shallow Bore master cylinders, the pushrod should be approximately flush with or below the booster face. Deep Bore master cylinders will protrude past the face of the booster body by about 1" to 1-1/2". Note that Deep Bore master cylinders are required for manual brakes and Shallow Bore master cylinders are generally used for power brake systems. We now supply a master cylinder piston adapter to accommodate both master cylinders. You will only use this adapter when you have a Deep Bore master cylinder with a short booster pushrod.

[BAGNDRAGIT]

Thanks 68gmsee, now my question is how do you adjust the push rod? in the booster? anyone have any pics?? still wondering about the pushrod length and if there is a longer one out there. or if i just have to make one..i really dont want to go buy a new master/booster.


if it makes any difference my pushrod is not threaded into the front of the booster. i can just pull it out. is that correct?

Thanks.

[68gmsee]

Here's mine. Looks like it's about 3.5"- 4" give or take.

Also, unbolt the m.c., move it forward and check to see what master cylinder you have (reference the CPP info).

[BAGNDRAGIT]

i have a deep bore master. and my pushrod looks nothing like yours...

this is mine

[rsavage]

The end of your pushrod should adjust in and out. 5/16" hex on it?

[BAGNDRAGIT]

ok, a little headway, i went through some parts and found another pushrrod. but its for a 3/4 ton booster and is about 6" long. which is too long.

in the pic:

left: what was in my truck

middle: not sure, but way too short. i think its for a shallow bore master

right: out of the 3/4 ton booster.

so i have to assume (not a fan of assuming) that the rod 68gmsee posted is the one i need. now ehere can i find it??? any ideas? or should i just make one?

[BAGNDRAGIT]

and heres pics of my booster and master. and yes i know the vac line is disconnected lol

[68gmsee]

The one I have is a Bendix #5115 single diaphragm. You probably have a different booster on yours.

Probably the cheapest route, if you can't find a push rod, is to swap out the master cylinder. On the CPP site I posted above it mentions the two types.

[BAGNDRAGIT]

Originally Posted by 68gmsee

The one I have is a Bendix #5115 single diaphragm. You probably have a different booster on yours.

Probably the cheapest route, if you can't find a push rod, is to swap out the master cylinder. On the CPP site I posted above it mentions the two types.

i will look into that, whaere are the ID numbers located on the booster? ive never looked.

[68gmsee]

Not sure if it's the right number but it's under the Bendix name on my booster.

They have made many different types of boosters over the years. The one on my 69 is totally different.

[cdowns]

cut fit and finsh the one that is too long into one that is just right would b the oldschool way to solve the problem

[marco chevy]

Absolutely great info. You have covered every issue I have ever had with my drum brakes. I printed off everything from the brake troubleshooting guide and am reviewing it all now. I can't wait for this rain to let up so I can get these brakes safe and get this truck back on the road. Thanks 68gmsee.

[rsavage]

One of the things to watch out for in changing boosters is the different stock brackets are not interchangeable. The shorter firewall bracket is used with the fatter but smaller diameter double diaphragm booster most often found on 3/4 tons and and 1/2 ton 4X4's. The longer bracket goes with the single diaphragn (thinner but larger diameter) booster found commonly on 1/2 ton 2wd's).

[68gmsee]

One last fyi: the threaded part of the adjusting screw on my pushrod is app 1 inch long so there's quite a bit of adjustment for a recessed m.c.

Here's how I adjusted mine:

1. I placed a thin metal ruler on the master cylinder and then measured the distance the push rod protrudes out of the booster in a static condition.

2. I measured the depth of the m.c. pushrod hole.

3. Adjusted the adjusting screw out until it protruded about 1/8 inch shorter than the depth of the hole.