It appears the brake booster on my 1078 F100 is shot and is causing the truck to come out of gear when brakes are applied, etc.

If I am replacing the booster, should i go ahead and do the master cylinder as well?

 

No mention of what the engine and transmission is and what type of brake booster. If the MC has ever leaked between the MC and into the booster, this would break the booster diaphragm down and cause a vacuum leak and poor brake operation.

A photo of the MC/booster would clarify exaclty which booster type it is.

 

Sorry...it is a 302 with the C6 tranny.

aside from being stiff(has been since first bought) the brakes work fine..but when you apply the brakes and come to a stop, it takes the truck out of gear. The vaccum lines look ok, so i assume the booster is shot...i will likely just buy a new booster w/ a new master attached.

 

I'm not sure how a brake booster can cause the transmission to slip out of gear. Those don't have a direct relationship to each other. Maybe the braking motion is causing the shifter (worn?) to move...

 

Another member gave me the idea...there is a main vacuum line going from the booster to the vacuum tree behind the manifold....i guess if the diaphram in the booster goes bad it can leak off that vacuum. Sounds weird, but it is the only time the truck comes out of gear.