Jerk or bucks in four wheel drive

LITTLEE_DOMN8R

MEMBER
2000 CHEVROLET BLAZER
4.3L
V6
4WD
AUTOMATIC
193,000 MILES

My vehicle jerks or bucks in wheel drive every one hundred feet or so. It feels like the wheel drive is engaged, but just sounds like something is not engaging, or possibly something is broke in the hub? There was no vacuum line connected to the actuator under the battery, but I ran a temporary line to a tee under the hood to see if it would engage, and now have this problem. Hoping someone has an idea of what this would be as I do not want to start tearing into it without knowing where to start.

3 Replies

STEVE W.

MECHANIC
13,414 POSTS

Do you have the same sized tires all the way around?
Are you trying to drive in wheel drive on pavement or dry ground?
Why was the actuator disconnected?
Has anyone ever replaced the rear axle assembly?
The front actuator is supposed to have a line that goes back to the vacuum switch on the transfer case. Not a constant vacuum.

From the description it sounds like you are driving in wheel drive on a high traction surface and the system is experiencing torque wrap because the wheels are not slipping.

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Sunday, April 25th, 2021 AT 11:26 AM

LITTLEE_DOMN8R

MEMBER
3 POSTS

Yes, the tires are the same size. I have only owned it for a few months so have no idea why the actuator was disconnected or the history of it. I do believe the prior owner told me they had replaced one of the rear axles. Along with the buck, there is a noise coming from underneath, sounds like in the front axle or hub. I was driving on dry pavement, but we had some ice and snow overnight so I tried it this morning and the four wheel drive is not engaging at all, but the buck/noise is still there when I put it in 4hi or 4lo. I am probably going to take it to a shop next week as I need to sell this to buy something else and it will not sell for much if the four wheel drive is not working.

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Sunday, April 25th, 2021 AT 11:26 AM

STEVE W.

MECHANIC
13,414 POSTS

It may be that they replaced the entire rear axle and used one that doesn't have the same gear ratio. That would cause the bucking in 4 wheel. It would also explain why the actuator was unhooked. They disabled the 4 wheel drive because it can't be used. The noise is probably damage in the transfer case from the mismatched gears.

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Sunday, April 25th, 2021 AT 11:26 AM