2nd Gen Non-Engine/Transmission four wheel drive won't engage??

[KCanepari]

my '96 2500 has been running fine and all of a sudden today it won't engage into four wheel drive. The heat controls don't work either, won't switch from floor to dash. is it a vacuum leak or is the pump shot. would I not have power brakes if the pump was bad?? Help please, snow is coming.

 

[2broke2smoke]

it's probably the big vacuum line coming out of the vacuum pump right ...

 

[KCanepari]

there's a big line from the pump to the brake booster and the a small line that t's off for everything else. if there was a leak in any of those lines I wouldn't have power brakes right??

 

[Spunkys Ram]

Not very familiar with the '96 era but I know the later 2nd genners have a Hydraboost brakes, NO vacuum. I would put a vacuum guage directly on the pump and start there.

 

[tgordon]

Don't know on the brakes other than you simply wouldn't have the boost for your brakes, they would still work just harder. I had the supply line that runs above the engine under the ledge fall onto the turbo not to long after I bought my truck. Simply got some vacume line at the auto parts store an dhaven't had a problem since. It could be the pump going out also I have not experianced that.

 

[Ragain]

Possibly a check valve at the vacuume pump? The 24 valve engines have them and the first sign was the HVAC blend doors not operating properly.

 

[JWashburn]

I've had failure to engage 4wd for two reasons. The connect at the axle came off while going through deep snow, and the connect at the vacuum pump came off while installing the 3K GSK. Neither event caused any loss in brakes. Just run the vacuum line from the pump to the axle.

 

[Dan_69GTX]

there's a big line from the pump to the brake booster and the a small line that t's off for everything else. if there was a leak in any of those lines I wouldn't have power brakes right??

Yes, you wouldn't have power brakes if the pump was bad.



So, you probably have a break in the line between the brake booster and the other side of the engine compartment. You can have a leak there and still have power brakes. Just follow the line and find the hole/rub/break.



If you do as JWashburn stated "Just run the vacuum line from the pump to the axle. " that would engage the axle ALL the time.



Please let us know what you find.



Dan

 

[KCanepari]

So I think I fixed it? There's a small line that t's off of the big line going from the pump to the booster. that line then t's of again, one half going to the hvac/4x4 and the other half goes to a little vacuum canister with some wires coming out of it mounted on the drivers side wheel well. I took the T out and just hooked up the hvac/4x4 line. Everything works perfect now. Anyone know what that thing on the wheel well is??

 

[Dan_69GTX]

I don't have my service manual with me at work, but I "think" that is the warning switch for low vacuum.

 

[JWashburn]

When I said run the line I meant trace it to find and leaks or disconnects. Terminology.