I'm having troubles with the 4x4 on my 97 2500. The 4x4 light either won't light up or flickers on and off. When on for a few seconds, the 4x4 seems to work but when off, just the rear tires spin.
I had a similar problem last Oct. and took it to a dealer who took the front brakes off and I think the front axel, and said they fixed the problem and I haven't needed the 4x4 since. Now that I need it.....
Anyway, could it be just an easy electrical connection or is it back to the $80/hr dealership ?
Thanks in advance!!

 

Check your vacuum supply to the front axle. The hose has been known to come off and not let you engage the front axle.

 

Absolutely check the vacume, on the front axle, passenger side,back there is a vacume motor. This motor holds your front axel in, or out of the engagement possition. There are two vacume hoses attached to it, check to see if it has vacume on them. Also on the top of the transfer case there is a vacume block, it has 4 lines comming out of it, you might check to see if they are all hooked up. It is a pain to get to, but can be done, just need a good flash light and stron neck. Also if you follow the two line back from the front axel, you will notice they change several time from soft (rubber) lines to hard lines, make sure they are good, tight connections, no abrasions. If they are ok, check were the run down from under the hood. Also the vacume motor could be bad, if you have access to a vacume tester, you can test it. Good luck.

 

Yeah. It's definately mechanical problem and not an electrical if the 4x4 disengages and re-engages with the light. If it stayed in 4x4 with the light blinking off and on or something that'd be another story.

 

I checked the vacume lines and there was 1 line off and was maybe off since I had a rebuilt engine dropped in a month ago. I slipped the line on again but no go. (would it wreck the vacume motor if the line was off ?) I also checked the top of the transfer case and the 4 lines were on. The 4x4 light doesn't want to go on anymore either. If the engine was running, could I feel a vacume on a line if I plugged the end with a finger or are we talking about real low suction?
Is the Vacume supposed to be loose on the motor?
I followed the 2 elec. wires from the vacume motor to the front under the bumper but it just goes into a bigger bunch of wires and I get lost. I guess I will have to see if there's power in the wires now. (should there be power in those wires if the shifter is in 4lock and the light is off?)
Thanks for input. It's real nice to have help!!
Al

 

The 2 wires just turn the light on when the vacum motor hits the senser inside the CAD unit. There should be 2 vacum lines one on the outside has vacum in 2wd, one on the inside has vacum in 4wd. Yes it should suck on your finger good, if its low you have a vacum leak somewhere.

 

It's good you find the line that was off. Now back under the truck to the vac motor, the two lines going to it are the disengage line, and the engage line. If the truck is running (please be carefull getting under a running truck), you will get vacume on one of the two lines. Mine held a steady 25 in., which was real good. Yours should be simular, and steady. If there is no vacume, I would go back to the drivers side under the hood, and find the t-fitting were the transfer case picks it's vacume up. This would be much easier if you have a vac meter. But, it you have a good vac reading there, then just follow the lines down and check. These lines change several time from hard (metal) to soft (rubber), so there could be a conection problem. If you have good vacume at the vac motor, it must be shot, or jamed. You will have to investigate. Good luck.

 

BINGO !!! Couldn't get any vacume on axel so started by motor then traced it down to transfer case with lots of suction but could get non after transfer case. I guess the soft plug on top of TC wasn't pushed on tight enough. You guys just saved me a ton-o-money!! I might replace a few rubber conectors including the big transfer case plug as they seem too soft.
I do notice however a "clunk" the odd time in H or L lock coming from the front end. I used to hear that noise in an old 92 F250 4X4 but only when in 4x4 and turning a real tight corner. Now, it seems to do it running straight ahead. Any Ideas?
Anyway, I'm real grateful for the vacume advise!!!!!!
Al

 

I hope your "clunk" isn't anything serious. The only thting is the front axel disconect is designed to be held in-or held out of engagement. When you were driving around with no vacume line hooked up, that was allowing these parts to slap around, It could have damaged something. It might be wise to drain the frontend, you could look for shavings, and if there is any, at least you would have gotten them out, no further damage. I hope that isn't the case, good luck

 

I thought I had this trouble fixed by replacing the vacume harness. The rubber on the harness was soft and spongey letting it suck air. The 4x4 light stays on now so vacume is working properly. Anyway, I needed 4x4 yesterday and popped it in. Made it 1/2 way up the hill then spun out. Doesn't seem to fully engage. I turned around and tried in reverse. Worked great. So.... why do you think 4x4 works only in reverse? Maybe damage occured when the vacume wasn't working? Any ideas?
Thanks

 

I just went through the same problem. The vacuum diaphram on the differential was bent. It is suposed to rotate some. When rotating it looked like a bent wheel. Taped it back strait with a small hammer, fixed it. A week later, a vacuum line on the firewall broke in half, no 4x4. Put on new line, fixed. When going up a steep hill tires started spining. It felt like just the back was spining. Got my friend to get out and look and only one front tire was spining ( this is normal ) . But it did feel like two wheel drive. Hope you get things fixed up, it is deer season. Good luck!

 

I would remove the shift motor from the axle and see if the shift collar or whatever its called has been damaged. You should be able to slip the collar from the one axle over so it covers the two without any trouble. While you have it off you can run the truck and see if the thing actually works properly( slides back and forth when you go between 2wd and 4wd).


NOTE!!! Be careful when you remove the shift motor from the axle as not to damage the cork gasket.


Good Luck


Jason

 

Just an update. Took the vacume motor off (making sure the cork gasket stayed in 1 piece). I found out that the little plastic clips on the fork were missing. ( they were in pieces on the floor of the axel housing). Also found that the splines on the outside of the inner axel were damaged a bit from the collar slopping back and forth (due to the faulty vacume lines not keeping the collar in or out of 4WD). I tuned the splines on the axel up with a very small chisel until the collar slipped over both easily.So, thanks to all for the info and the whole fix cost a grand total of $10.00 !!

 

Those clips broke on me too. Took out the passenger side axle seal. Ugliest job I've done on the truck to date. The dealer quoted me 4 hrs. labor to change them both. Might take him up on it if I have to do it again.