Question about 1991 GMC S-15 Jimmy

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GMC '91 Jimmy, Transfer case. When in two wheel drive I hear a slight grinding noise and rattling noise. When in 4 wheel no noise. 330,000 miles, could something be worn? What keeps the transfer case gear from slipping into 4 wheel drive? I know that I have to back up to change from 4 wheel to 2 wheel. Transfer case lever shifted all the way forward to 2 wheel drive. What ever keeps the transfer case in 2 wheel drive could be worn? Thanks.

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  • Michael Schaffter
    Michael Schaffter Dec 27, 2010

    Its officially fixed thanks to daylongdrive. It has worked for as long as I fixed the cable thanks to daylongdrive. But today it snowed and hopefully putting it into 4 wheel drive wont cause any problems to return. Well see.



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Yeah your right about waer but you might be blaming the wrong part. With the truck up on jack stands ( all wheels off the ground) have a helper drive the truck at the speeds that make the most noise you'll find it in the front axel or fround U joints or drive shaft splines ( drive shaft jumping ) You watch the parts moving and the joints or the cable that shifts the ront axel in and out not moving all the way it uses a vacume motor under the battery that has a cable going to the front axel. the clutches that are in the front axel have clips on them that hold the side gears that engage and disingage as you turn it on and off the clips break get lost fall off were out and let the side gears do as they please and they runinto each other a click and pop/ the cable and the shift fork that move them also fail but not htat much as the cable fails and the vacume leak pulls on a spring in two wheel and it may not be pulling hard enough/

Posted on Sep 17, 2010

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  • Michael Schaffter
    Michael Schaffter Sep 18, 2010

    Thank you Daylongdrive! Fixed! Hopefully. So far I took out the battery and got to the bellows vacuum and found that the tube attached to it wasn't as secure as it could be so I added a hose clamp and tightened that up and was able to get some oil down the cable after removing the boot on the cable and found some insulation on the cable to be broken, but the cable wasn't damaged and found a little rust there so I put some wd 40 and taped it up. Everything was reassembled and have driven about ten miles in 2 wheel drive with no noises. I did get an oil change and lube though and don't know if that helped at all, though I did find that oil may be seeping out of my front main oil bearing, though when I checked oil level it was good. Does oil level have any thing to do with vacuum system?

  • John P Schwantes Jr Sep 19, 2010

    the question does the oil level have anything to do with the vacume system? and the answer is; the oil provides, the lubercation, for the engine and the oil in the trans lubes it. If it takes less power to turn these parts their'll be more vacume as the engine won't be pushing as hard to turn all the parts and go easier down the raod as the gas pedel won't be pushed down as far to do the same things so more vacume. Same goes for lighter oils or even synthic oils as they resist turning less so everything works better. don't get carried away in this area though as you can get into the area of dimishing returns as the better oils cost more and they get containanted just as easy as cheap oil but ib a gear box like the transfer case and a manul trabsmission and the front and rear rear ends the exonomal gears oils that are full synthic ( I got some from my parts store for $7 per quart and put it in the rear end of my truck and it's quiter and gets better gas mileage (2 mile per gal. )) The repair manuel shows the transfer case shifted with a soliod and there's no mention of the cable to the frount axel I just have fixed them before and that's hopefully all you need to do. Hose is cheap at the store and you can buy it by the foot. Cut off the end and take it with you to the store as theirs lots of different sizes and the fuel line is better than vacume hose and it only cost a little more.

  • Michael Schaffter
    Michael Schaffter Apr 02, 2013

    Thank you very much for your solution Mr. Schwantes Jr. you saved my truck.



Remove the transfer case and strip it down,wash it out and replace whatever is worn.
330,000 miles is unrealistic
Your chain is worn and stretched for sure, and rattling and may be cutting into the case.
Don't install another salvage yard unit, unless you can not repair yours. Then strip down whatever you purchase, and go thru it also.

Posted on Sep 17, 2010

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  • Michael Schaffter
    Michael Schaffter Sep 17, 2010

    Yes 330,000 is the true mileage, still runs good, burns a little oil though. Do I need to loosen the transmission bolts to remove the transfer case? Or can I just remove the rear shaft? Why would 4 wheel work if the chain is worn? I only drove about 200 miles total in 4 wheel drive. Thank you.

  • Anonymous Sep 17, 2010

    You need to separate the transfer noise from daylongs solution. I was avoiding those issues as you leaned toward the transfer in your question. You don't have to back up, to go to two wheel,the front axle will release as you drive either direction,once you shift the transfer into 2wd.
    You can leave the trans bolted to the engine,if that is your question. The chain being stretched doesn't stop it from working, it just makes a noise and could cause wear to other components.
    Get someone at a repair facility to print out some pictures of your front axle and check out what solution 2 is referring to

  • Michael Schaffter
    Michael Schaffter Sep 03, 2012

    I currently have 348900 miles, and 350k looks good with no problems. Though noise comes back when first starting at idle, but goes away druing idleing after driving for sometime.

  • Michael Schaffter
    Michael Schaffter Jan 30, 2014

    Ok I had the vacuum switch replace on the transfer case and two weeks later the grinding noise has come back but I never reattacched the vacuum actuator for the front engagement. But if I put it into 4wd the noise goes away, and it doesn't have force of driving the front wheels. What do I do? I know the front actuator cable is not pulling to engage the front axels.


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Output shaft retaining ring snapped off shaft

Posted on Dec 27, 2010

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