Transfer Case Problems (i think)

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Aug 12, 2010 | 12:15 PM

nowafordman

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Transfer Case Problems (i think)

Hi all,

I'm having some issues when using 4x4 on my truck: 1986 F250 4spd (t18) 4x4, 4.9L six (300cid). 250k.

The truck shifts beautifully from 2hi to 4hi, neutral and into 4lo. Locking hubs operate fine (lock and unlock eaisly).

When driving with hubs locked but transfer case in 2wd there are no issues, but when in 4hi the transfer case seems to skip with a serious thud/clunk when it does. Whatever it is it doesn't sound healthy.

I'm wondering if anyone has had similar experiences and what the fix is. Also if anyone knows a little about the makeup of that transfer case. From what I understand it is chain driven? Could the chain be loose and thus slipping?

Any info would be greatly appreciated.

Thanks,

Drew

Aug 12, 2010 | 12:45 PM

Franklin2

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From: Virginia

If this truck is not all original, I would double check the ratios of the front axle and the rear. Someone may have slapped a rearend in it with a different ratio and then sold the truck.

Aug 12, 2010 | 02:49 PM

nowafordman

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Funny you should mention that... I recently had an axle failure a long way from home and had to get one from a junker and install it myself in a parking lot behind NAPA. Long story short I now have a full floating sterling 10.25" upgraded from my previously semi-floating setup.

I checked both axle codes and they are both 3.55 gearing. The speed/rpm ratio is still the same (i.e. 120 km/h at just under 3000 rpm; before and after the switch). The front axle code reads that it is a 3.54 gear ratio; from the research i've done this seems to be normal.

I used 4x4 very rarely (i.e. i just got the truck) before the switch but never experienced this skipping/clunking. I'm tempted to think that there was a gearing change on the axle that I got from the junker that doesn't match up to the tag on it. But seeing as the speed/rpm ratio is still the same I feel this means the gearing is correct; unless this is an incorrect assumption...

Thanks for any input; greatly appreciate it...

Drew

Aug 12, 2010 | 04:16 PM

bashby

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From: Charles Town, W bygod Va

your tach and speedo relation wont change with gear changes, You might want to jack it up and turn the wheels while watching the driveshaft to be sure. To check chain slop in the transfer case, put it in 4hi with the hubs unlocked then turn the ft driveshaft back and forth and see how much slop there is. You might be able to see or feel the chain through the transfer drain or fill hole. I was told that all the cast iron cased transfer cases were gear driven and aluminum ones have chains.