2003 AWD problem

[Dobaroy]

This is our 3rd Astro/Safari. The first 2 were 2 wheel drives and they were troublefree. Now we ended up with a 2003 all wheel drive and 3 months later we find that when you turn the wheel to the left or right to make a turn it doesn't feel smooth. Feels like something is not right, maybe binding or something. We have driven 4 wheel drive before but never had this problem. Has anyone ever had this kind of problem . . . don't have a clue what it could be (could it be the posi-trac?)

[old_master]

4WD can encounter what's called "crow hop". It's usually described as the vehicle jerks, hops, or binds when turning on dry pavement. 4WD transfer cases are direct drive, (there is no clutch system between the front and rear differentials). Crow hop is usually caused by the tires being different sizes or tire inflation is not equal. Bottom line, anything that makes the circumference of the tires different. What you are feeling is the transfer case binding caused by speed differences between the front and rear differentials. This is why it's not recommended to operate 4WD on dry pavement.

The AWD transfer case has a clutch that allows for slight slippage between the differentials to reduce or eliminate crow hop tendencies. If the clutch is not able to slip, you will experience crow hop. AWD transfer cases use a special fluid that requires changing on a regular basis. If the fluid has not been changed often enough, it may require a couple of fluid changes to "free up" the clutch. If the fluid changes do not correct the problem, the clutch itself may need attention. The proper fluid is available at GM dealerships. A similar fluid might be available at an auto parts store, but I'd recommend the GM stuff.

[Dobaroy]

Originally Posted by old_master

4WD can encounter what's called "crow hop". It's usually described as the vehicle jerks, hops, or binds when turning on dry pavement. 4WD transfer cases are direct drive, (there is no clutch system between the front and rear differentials). Crow hop is usually caused by the tires being different sizes or tire inflation is not equal. Bottom line, anything that makes the circumference of the tires different. What you are feeling is the transfer case binding caused by speed differences between the front and rear differentials. This is why it's not recommended to operate 4WD on dry pavement.

The AWD transfer case has a clutch that allows for slight slippage between the differentials to reduce or eliminate crow hop tendencies. If the clutch is not able to slip, you will experience crow hop. AWD transfer cases use a special fluid that requires changing on a regular basis. If the fluid has not been changed often enough, it may require a couple of fluid changes to "free up" the clutch. If the fluid changes do not correct the problem, the clutch itself may need attention. The proper fluid is available at GM dealerships. A similar fluid might be available at an auto parts store, but I'd recommend the GM stuff.

Thanks for the info. We are going to get the GM Fluid for the transfer case, Part #10953626, just not sure if we should change the fluid in the front and rear differentials and wondering which fluid would we use? According to the code on the passenger door, this van does not have posi. (the code is GT4 which it would appear is a 3.73 axle ratio).

[old_master]

If you don't know the history on the axle fluid, it would be a good idea to replace it, then you know for sure. SAE 80W90 gear lubricant with a GL5 rating.

[Dobaroy]

Thanks Old Master, bought the fluid today but it is too cold up here to get under that van today . . . its supposed to warm up a bit in the next couple of days.

[old_master]

Know what ya mean, I'm just outside of Detroit and you're a bit North of me! Did you pick up new gaskets for the differentials? They're cheap, only a few bucks each.

[Blue Bowtie]

Good info from the Master.

If you do get new diff cover gaskets, make sure you get an aftermarket rear cover gasket or alter the factory gasket to open the oil holes from the axle tubes:

[Dobaroy]

No, Old Master . . . completely forgot about getting gaskets. Thanks for the reminder. We are about 3 hours from Detroit, sure wish this cold snap would get over. Thanks Blue Bowtie for the reply. Good info about the gaskets, seems like Fel Pro would be the way to go.

[Dobaroy]

Got the fluids changed but haven't driven it much yet to see what the results are gonna be.
Does this van have CV joints in it and wonder how you would know if one of them is going bad?

[Dobaroy]

Been driving the van quite a bit the last couple of days and there has been a big improvement in the steering. Thanks for your suggestions.

[Blue Bowtie]

Yes, both front half-shafts have CV joints. They typically make some noise when they are failing, but since they are unloaded 99% of the life of the vehicle they are not as prone to wear as on a FWD vehicle. They should be inspected for play and leakage of the bellows whenever chassis lubrication is performed.

[Dobaroy]

Thanks Blue Bowtie, will have them checked next time we have it serviced. Find this van to be very rough on bumps, thinking maybe we should look at putting Sensa Trac shocks on it but not sure if they would be heavy enough for this van.