brake booster rod

[ALLAN]

I need to replace the brake booster on my 70 Polara,as far as I can tell it still has an original unit fitted(pedal goes half way to the floor then every thing locks up, plenty of vacuum at unit,pedal doesn't move when engine starts). I've been on Rock Auto and the units listed for the car have different length rods, which one do I need ? would like to buy before stripping the old one out and don't want to risk the fitted one being wrong anyway. I have the build sheet can I tell from that?

 

[Davea Lux]

I need to replace the brake booster on my 70 Polara,as far as I can tell it still has an original unit fitted(pedal goes half way to the floor then every thing locks up, plenty of vacuum at unit,pedal doesn't move when engine starts). I've been on Rock Auto and the units listed for the car have different length rods, which one do I need ? would like to buy before stripping the old one out and don't want to risk the fitted one being wrong anyway. I have the build sheet can I tell from that?

Usually the supplier will send out the rebuilt unit before you send them back the core. You can use the old unit to compare to see if everything looks right before shipping it back.
Assuming that you are replacing your booster with the same unit, the pedal rod length probably won't be an issue. The build sheet is not a whole lot of help in this regard as the only information it will give you that is relevant is if your car has disc or drum brakes. Be sure to order the proper unit, disc brakes use a bendix type booster, Drums use a single clamp mopar boster. That is why there are two different rod lengths. If you are really worried about this, you could take you current unit to a rebuilder and have them rebuild that unit. Be sure if you are going this route to get a quote before authorizing the work. Some of these folks do not work cheap. Bendix boosters currently run about $350 to rebuild, the mopar ones are about $200. Be sure to replace the vacuum hose to the unit before giving up on the old one, these cars were notorious for having the inner liner of the hose collapsing and starving the booster of enough vacuum to operate, especially if the factory hose is still on the car. By now it is rock hard and likely to fail. If your car has the bendix booster, you may need to have it rebuilt locally, these units are mostly out of stock at the rebuilders even though they still show a listing for them. Hope this helps.

Dave

 

[Davea Lux]

I need to replace the brake booster on my 70 Polara,as far as I can tell it still has an original unit fitted(pedal goes half way to the floor then every thing locks up, plenty of vacuum at unit,pedal doesn't move when engine starts). I've been on Rock Auto and the units listed for the car have different length rods, which one do I need ? would like to buy before stripping the old one out and don't want to risk the fitted one being wrong anyway. I have the build sheet can I tell from that?

One you have installed the new booster, unless you have bought a complete unit with a rebuilt master cylinder attached, you will also need to adjust the travel rod that goes into the master cylinder. Mount the master cylinder and start the car. You should have 3/4 to one inch of free play on the pedal before the brakes engage, less and the brakes will not properly release, more and they will not apply properly. The rod that goes into the master cylinder has an adjusting nut on the exposed end. Turn the nut in to increase free play and out to decrease free play. These numbers for adjustment assume that all drum brakes are adjusted properly.
Dave

 

[Davea Lux]

Detailed information available in the FSM, download free at www.mymopar.com