Brake Upgrade - 1/2ton to 3/4ton

[cleszkie]

Yesterday I took the advice of others on this board and upgraded my 1/2ton brake booster and master cylinder to 3/4ton equipment in order to work with my 3/4ton running gear. Man what a difference! A couple of points to help those out that are considering doing this:

1) If you just replace the booster and keep the 1/2ton master cylinder, you will end up using the longer push rod between the booster and master cylinder (MC) that you were using with the 1/2 ton booster. The short rod that comes with the 3/4ton booster will not work at all. Anyways, THIS LONGER ROD WILL END UP DAMAGING THE 1/2TON MC BY PUSHING TOO FAR INTO THE MC. I know this because this is how I set it up initially and it worked fine for two days until I pushed the brake peddle to the floor and damaged the MC. The rod damaged the internal MC seals.

2) You will note that the 1/2ton MC has two different size line fittings corresponding to the front brake reservoir and rear brake reservoir (the rear brake reservoir is closest to the firewall and has the larger fitting and the front brake reservoir is towards the front and has the small fitting). The 3/4ton MC has the fitting sizes reversed, however the rear reservoir is still for the rear brakes and the front reservoir is for the front brakes. TO OVERCOME THIS, SIMPLY INSTALL PIPE FITTING ADAPTERS TO MAKE THE REAR FITTING LARGER AND THE FRONT FITTING SMALLER. Contrary to some theories, you do not reverse the hard lines to the MC to make it work.

The difference the upgrade makes is unbelievable. In case anyone was wondering, the 3/4ton MC has a much firmer peddle and shorter stroke than the 1/2ton MC (when the 1/2ton MC was working).

If I stated anything incorrectly above, please correct me. I think this info is invaluable to all those that are running 1/2ton brake equipment with 3/4ton (or 1ton) running gear.

[bouncytruck]

Thanks for the info. The booster and MC you used were just standard 3/4 ton 4x4 for a 72? Do you have any pics of the final install? Other than the fitting attapters, did you have to do any modifications to the system beyond the MC and Booster? Can this modification be done on 1/2 running gear and get better braking power?

[cleszkie]

Bouncy-

The MC and booster were both for a 72 3/4ton 4x4. I do not have any pics. As seen on other threads, the booster is about 3 or 4 inches longer than the 1/2ton unit. The MC is approximately the same length, however the reservoirs are wider and shorter than the 1/2ton MC. The front and rear reservoirs on the 3/4ton MC are the same size, and I'd say they are probably a bit larger than the 1/2ton reservoirs. When bleeding the front and rear systems, I noticed that it took only 4 cycles to drain a reservoir. With the 1/2ton MC it took many more cycles to drain a reservoir. That tells me that the 3/4ton MC moves a lot more fluid to operate the larger rear brake cylinders with less pedal effort and movement.

The only other modification I had to do was to rebend the suport arm that extends from the firewall to the junction of the MC and booster. I retained the stock combination valve as I think they are the same between 1/2ton and 3/4ton models.

Total cost: $80 for MC, $180 for booster with $90 core refund.

Not sure how going to 3/4ton stuff will affect 1/2ton brakes. It couldn't hurt in my opinion. Probably get a firmer pedal with a shorter stroke.

[bouncytruck]

Cool, thanks for the info. I've seen others talk about upgrading, but nobody has gone into the detail you did. I'll probably wait until/if I upgrade to 3/4 ton.

[pound41]

What about the porportioning valve was it the same as the 1/2ton

[cleszkie]

I kept the 1/2ton combination valve (same as proportioning valve). The valves are identical between 1/2ton and 3/4ton models.