Front drive shaft question

tomsmith

Original poster
Member
Mar 12, 2013
30
Hello,

I've got the vehicle lifted and supported with jack stand on the front, and the rear wheels chocked and the parking brake applied. The car is in 2HI mode and I'm trying to remove the front differential (see my other posts). I've removed 3 of the front bolts connecting the front drive shaft to the front diff, but 1 of them is in an awkward place and I can't get a socket or wrench on it.

What I'd like to do it is turn the drive shift a half turn so I can get to the bolt but I just can't get the drive shaft to turn.

I thought when the vehicle is in 2HI, the front drive shaft is disconnected from the transfer case so it should spin freely but it seems 'stuck'.

Both front CV shaft are out and I can spin the splined shaft in the front diff by hand very easily. When I spin the shaft manually, the other side turns so they are connected - not sure if that's important or not.

I don't know if the front drive shaft is 'seized' or there's something else I am missing?

On more thing, if I rotate the rear tires, the front drive shaft doesn't turn, regardless of whether or not the vehicle is in 2HI or 4HI. I would have thought with the vehicle in 4HI, turning the rear tires (and therefore the rear drive shaft) wold cause the front drive front shaft to spin .. but it doesn't.

I welcome your thoughts and advice.

2004 TrailBlazer LS 4x4
 

BRomanJr

Member
Dec 9, 2011
371
tomsmith said:
Hello,

I've got the vehicle lifted and supported with jack stand on the front, and the rear wheels chocked and the parking brake applied. The car is in 2HI mode and I'm trying to remove the front differential (see my other posts). I've removed 3 of the front bolts connecting the front drive shaft to the front diff, but 1 of them is in an awkward place and I can't get a socket or wrench on it.

What I'd like to do it is turn the drive shift a half turn so I can get to the bolt but I just can't get the drive shaft to turn.

I thought when the vehicle is in 2HI, the front drive shaft is disconnected from the transfer case so it should spin freely but it seems 'stuck'.

Both front CV shaft are out and I can spin the splined shaft in the front diff by hand very easily. When I spin the shaft manually, the other side turns so they are connected - not sure if that's important or not.

I don't know if the front drive shaft is 'seized' or there's something else I am missing?

On more thing, if I rotate the rear tires, the front drive shaft doesn't turn, regardless of whether or not the vehicle is in 2HI or 4HI. I would have thought with the vehicle in 4HI, turning the rear tires (and therefore the rear drive shaft) wold cause the front drive front shaft to spin .. but it doesn't.

I welcome your thoughts and advice.

2004 TrailBlazer LS 4x4

The "Front" side of the Transfer Case is driven by way of a mechanically applied wet clutch. The Fluid changes for the TC need to be up-to-date for the clutch to have proper amount of partial friction when "disengaged". The Auto-Trac II Fluid has a special Friction Modifier and a Blue color, it wears out over time and use. (even if only used in 2WD). If the fluid has not been change regularly at 50k mile intervals, it is probably "stuck" in a mostly engaged situation. You might be able to break it loose if it truly is in 2WD.

If you are turning the rear with both wheels off the ground, and the rear drive shaft is actually spinning (make sure the rear wheel are not turning in opposite directions), then for the front drive shaft not to spin in 4WD, something must be damaged in the TC.


BTW, Why are you changing the front Diff? More info will help the troubleshooting.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Thanks for the info. When I turned the rear wheels, they did spin opposite to each other. I didn't see if the rear drive shaft was turning though .. I'll have to try it again and see.

As for why I'm changing the front diff, my front diff had been running for a long time with no fluid in the front diff. I know I should have checked it, but I neglected to do so and so I guess I only have myself to blame.

A couple of weeks ago, we got a good 12" of snow so I left my main car in the garage and figured I'd drive to work in the Trailblazer. Around 1km from home, there is an inclined road that is impossible to get up without 4WD when there's snow so right before the hill starts, I slow right down and put it in 4HI. Drive up the hill just fine and then drive another 0.5 km when the vehicle comes to a grinding stop. It's like the front tires were completely locked. I couldn't even get off the road, but thankfully the roads were empty and it was around 7am so wasn't too dark. I get out of the car and inspect the front, thinking I either hit something or something is tangled up. Nothing. Everything looks fine.

I get back in and try to drive off, the rears break traction but the front tires won't budge. I change it into 2HI and try driving off .. no luck. Turn it off and back on, cycle it from 2HI to 4Hi and back and all of a sudden, I can start driving again. Drive all the way to work and back in 2HI just fine.

Got it back in the driveway, change into 4HI and again, the front is jammed up. I did a bit of research and the first thing I check is the front diff fluid .. it is completely and utterly dry. I stick a bent zip tie in and it comes out dry, with metal shavings stuck to it. I filled up the diff with fluid, turn the front wheels by hand for around 100 revolutions and then attach some very strong rare each magnets to the drain plug. Let it sit for a day and then empty the fluid. There was a LOT of metal shavings :sadcry: No big chunks but enough shavings in there to suggest something had gone very wrong.

I followed the instructions in this forum to diagnose the problem and it all pointed to a front diff. The metal shavings kinda confirmed it as well.

I figured I'd try and replace the front diff myself since I want to learn a bit more .. and frankly I don't really have the $2500 to spend all at once either. I've done pretty good I think:

1. Got the front CV shafts off
2. Removed the bolts holding the front drive shaft to the front diff yoke (I managed to get that last troublesome bolt out by using a 11mm nut driver attached to a 1/4 extension (the type that attach to a handheld drill to extend the reach of a bit) and then getting a 1/4 wrench on the extension to turn the driver. A regular socket wouldn't fit because of the bolt that holds the diff to the oil pan.
3. Removed the 2 bolts on the front of the diff
4. Loosened the 1 bolt that is in the middle of the diff. I can't quite remove it because it's hitting the frame but none of the threads are engaged.
5. That one bolt that is right next to the yoke is a bit troublesome. I can loosen it, but it's hitting the front drive shaft so my next step is loosen the drive shaft from the yoke and hopefully get that last bolt out.

Once all 4 bolts are removed, will it be easy to move the diff away from the oil pan or is there a trick to it?
 

RayVoy

Member
Nov 20, 2011
939
No trick, normally the front shaft should turn, I think the damage in the diff is jamming it.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Does the inner driveshaft that goes through the oil pan need to be removed in order to remove the diff? I've unbolted it but can't get it off the oil pan. I haven't removed the inner splined drive shaft yet
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Yes, the intermediate shaft has to be removed. The passenger side of it has a threaded hole so you can thread something in there and pull or attach it to a slide hammer.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Thanks, i threaded a bolt into the shaft, gripped it with a locking plier and pulled - came out with little resistance.

I'm still having some problems getting the front diff off though. I've undone the 4 bolts:

View attachment 26828

I've highlighted the 3 visible bolts here and I've also removed the one near the yoke. I tried hitting the diff from the passenger side with a drift bit it's not budging. Is there another bolt I need to remove or is there a trick to removing the diff?
 

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tomsmith

Original poster
Member
Mar 12, 2013
30
FINALLY got it out. Wow, what a PITA.

This is what worked.

1. Place a 1x3 piece of wood against the backside of the front diff, just under where it connects to the oil pan and give it a couple of good whacks with a 3lb hammer and piece of rebar acting as a drift. Do this until it separates slightly from the oil pan.

2. From the drivers side wheel well, knock it back into position.

3. Do 1. and 2. around 5 times to break up any corrosion.

4. Place a pry bar between the lower bolt hole and the oil pan and, very gently, apply pressure until it pops loose. With each push on the prybar, I could see it separate a little each time until it finally popped off.

Now, onto getting the front diff actually out :smile: I'm going to drop the entire oil pan and get it out that way .. I'm don't think I'll be able to wiggle it out the top by loosening the engine mount and disconnecting the alternator, a/c compressor, radiator etc. Some of the bolts for those accessories are in seriously awkward places
 

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