99 Blazer 4x4 tranny thumping while driving
dogtired78
01-29-2004, 02:49 PM
I just bought my 1999 Blazer 4x4 last week. Slipped in and out of 4-hi without trouble for the first few days. Yesterday she drove it and reported that after putting it in 4-hi to climb a snowy hill and then putting it back into 2-hi, an audible thump can be heard and felt while driving.
I recreated the problem and can say that the tranny will thump in 4-hi as well as 2-hi (after being shifted out of 4-hi). If I start and drive the car just in 2-hi, there is no thump. I haven't tried 4-low because I'm worried about damaging anything further. The thump feels and sounds a lot like somebody kicking the underside of the front end.
This is my first 4x4 and I don't know where to begin. Please help!
I recreated the problem and can say that the tranny will thump in 4-hi as well as 2-hi (after being shifted out of 4-hi). If I start and drive the car just in 2-hi, there is no thump. I haven't tried 4-low because I'm worried about damaging anything further. The thump feels and sounds a lot like somebody kicking the underside of the front end.
This is my first 4x4 and I don't know where to begin. Please help!
durangodriver
01-30-2004, 01:14 PM
I just bought a 98 and it does it too. While moving after shifting from 4hi to 2hi, when the 4 wheel drive releases it jarrs the truck like if running over a large crack in the road. Feels like it is coming from front end or transfer case. Hope someone can shed some light on how serious the cause this is. thanks
skruzich
02-09-2004, 11:12 PM
Hi,
what your experiencing is a problem with the transaxle.
What is happening is that you have a cluster gear in there that slides a ring gear back to engage 2wd and forward to engage 4wd. What has happened is that the shift fork that slides this gear has three plastic pieces that slide in the groove of the ring gear. one or more of these has probably fallen out or worn out and gotten chewed up. Now when this happens, the gears wear the fork out by spinning against the bare metal. Then the ring gear that slides doesn't get pushed back far enough to totally disengage from the 4wd. Ok now what usually happens next is that there is a spring clip that holds these gears in place, and one might have popped out, and allowed one of the three little brass "i call them dogs" pieces that help lock the ring gear into place. One of these may have popped out or gotten chewed up.
At any rate, you will have to take the transaxle off of the back of the tranny. YOU DO NOT have to remove the transmission. Just unbolt the transaxle from the transmission. Unbolt the 5 bolts that go into the transaxle, not the bolts that go into the transmission. There is a spacer that fits between the two. You want to unbolt the bolts that are pointing to the back.
When you pull the transaxle, you must unbolt the wires going to the motor that engages the forks. When you slide it out make sure you break arm, a leg, your neck but DO NOT BREAK the cylindrical motor on the bottom of the transaxle. IF you do, you will be shelling out about 400 bucks for that motor.
Now once you have your transaxle out, you will need to unbolt the bolts holding it together starting with the tailshaft. You will not need any gastkets for this case, just a big tube of the blue rtv gasket sealer. Thats all that is needed.
Once you get the tailshaft off, you will need to remove some spring clips that hold the shaft together, then work on splitting the housing. Once you get it done, then you can remove the whole shaft assembly in one piece.
The fork is going to have to be replaced and it runs about 100 bucks for another one. You will also need those brass dogs and the plastic retainers that go on to the fork.
It isn't too awful bad doing this if your mechanically inclined. Just remember to put the parts in order on the table that you took them off.
steve
what your experiencing is a problem with the transaxle.
What is happening is that you have a cluster gear in there that slides a ring gear back to engage 2wd and forward to engage 4wd. What has happened is that the shift fork that slides this gear has three plastic pieces that slide in the groove of the ring gear. one or more of these has probably fallen out or worn out and gotten chewed up. Now when this happens, the gears wear the fork out by spinning against the bare metal. Then the ring gear that slides doesn't get pushed back far enough to totally disengage from the 4wd. Ok now what usually happens next is that there is a spring clip that holds these gears in place, and one might have popped out, and allowed one of the three little brass "i call them dogs" pieces that help lock the ring gear into place. One of these may have popped out or gotten chewed up.
At any rate, you will have to take the transaxle off of the back of the tranny. YOU DO NOT have to remove the transmission. Just unbolt the transaxle from the transmission. Unbolt the 5 bolts that go into the transaxle, not the bolts that go into the transmission. There is a spacer that fits between the two. You want to unbolt the bolts that are pointing to the back.
When you pull the transaxle, you must unbolt the wires going to the motor that engages the forks. When you slide it out make sure you break arm, a leg, your neck but DO NOT BREAK the cylindrical motor on the bottom of the transaxle. IF you do, you will be shelling out about 400 bucks for that motor.
Now once you have your transaxle out, you will need to unbolt the bolts holding it together starting with the tailshaft. You will not need any gastkets for this case, just a big tube of the blue rtv gasket sealer. Thats all that is needed.
Once you get the tailshaft off, you will need to remove some spring clips that hold the shaft together, then work on splitting the housing. Once you get it done, then you can remove the whole shaft assembly in one piece.
The fork is going to have to be replaced and it runs about 100 bucks for another one. You will also need those brass dogs and the plastic retainers that go on to the fork.
It isn't too awful bad doing this if your mechanically inclined. Just remember to put the parts in order on the table that you took them off.
steve
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