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2003 chevy trailblazer_lt
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Discussion Starter #1
About a year ago, i had the engine replaced. Before they touched it, the 4wd worked. After they did the work, when i engage 4wd there is some new load as the truck is hard to move when hit gas and when let go of gas slows to a stop promptly. The selector light changes fine but I get the check 4wd light. turn it to 2wd and the drag is gone.

I have another pending\releated issue of leaking seals in the front differential case. Before i replace the seal, I was wondering if this behavior is from a bad bearing in the differential from lack of\low fluid before or sometihng? It was low on fluid when i got it and i topped it off. I don't see how they could have broken the part to engage the 4wd on the transfer case when changing the engine, or can they???

TIA.
 

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2002 chevy trailblazer_lt
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Make certain that the front differential was not also changed. It's an ugly possibility since they are bolted together, and depending on the circumstances of the engine swap it could happen. And if the axle ratio wasn't right the truck would do as you describe.

Granted , this is hopefully not what happened and itnis anfemote possibility, but I would want to rule that out.
 

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Discussion Starter #3
Make certain that the front differential was not also changed. It's an ugly possibility since they are bolted together, and depending on the circumstances of the engine swap it could happen. And if the axle ratio wasn't right the truck would do as you describe.

Granted , this is hopefully not what happened and itnis anfemote possibility, but I would want to rule that out.
The replacement engine was delivered to my house and i had to drive it to the shop.It didn't have a new front diff on the block. Being it wasn't a dealer, odds are very slim they had one laying around that they swapped I assume....

I need to change the driver side shaft seal anyway. I will try engage and drive it with the driver side shaft removed and see what happens.

I don't think the problem is a bad bearing in the diff box because the gear box doesn't disengage from the shaft so it always spins right??? It just engauges in the gear case when i enable, right??? Oh well. Ill find out soon.

BTW, there is some electronics on the front shaft but on the passenger side of the block. That doesn't engauge\disengauge the diff from the wheel right??

Thanks.
 

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It most definitely does disengage the front diff from the front right cv axle!! The device attached to the passenger side of the oil pan which the cv axle connects to is the front axle disconnect. That disengages the right cv axle from the intermediate shaft which goes through the oil pan and into the front differential.
 

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bearing in the diff box because the gear box doesn't disengage from the shaft so it always spins right?
Front differential as you know has one input shaft and 2 outputs.
Drivers side wheel always engaged. Passenger side is disengaged/engaged by the front axle disconnect which is bolted to the passenger side of the oil pan. Front driveshaft is connected in the transfer case through a clutch that is disengaged when in 2Hi.

So while in 2Hi the path of least resistance for spinning stuff is drivers wheel spins spider gear which then spins the opposing spider gear spinning the intermediate shaft theough the oil pan to the front axle disconnect where it is connected to nothing. I suppose the front driveshaft might spin some since the clutch in the transfer case is disengaged But I suspect most of the spinning is the freewheeling intermediate shaft in most cases.
 

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Discussion Starter #6 (Edited)
As an update, this is what i found:
I turned the shaft from the wheel end and also from the input shaft end. Both turned fairly freely.
I took off the driver's side output shaft being i was looking to repair the leaking seal on the drivers side.
I drove it engaging the the 4wd and it didn't bog down and the car rolled fine.
Conclusion\guess: the gear box was replaced with the wrong ratio.
 

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You could confirm that with this somewhat simple test. Details are written in the description of the video...
 
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