Backlash in the Transaxle?

[DoctorDex]

I took my car to the stealership because they told me that the clunk I hear when going from decel. to accel. was caused by excessive backlash in my rear dif. It took them 8 hrs to adjust the rear dif. and the "clunk" still had not been fixed. After pulling my transfer case they are now telling me that the clunk is coming from my transaxle and it has to do with too much forward to reverse play (15 thousandths whereas spec. = 4 thousandths) in the output shaft going to the transfer case.

Does anybody have any idea what exactly is causing this excessive amount of backlash in the output shaft? Could this be VCU related?

Thanks.

Declan

[DoctorDex]

Anybody have any suggestions?

[Toni]

the splines on the output shaft may be worn, but I don't think it would be enough to cause alot of clunk. You can "check" the backlash on the rear diff by jacking up the rear(+ stands of course), rotating the shaft until it stops, make a mark on the shaft/diff. Then roate the other way and make a mark, then measure the spread of the two marks. If its out of spec then they didn't do a good job. I forget what spec is.

Two other possibilities, worn read diff mounts, or worn driveshaft/carrier bearings.

-Antoni

[eyeluvmy3kgt]

I have the same problem man. I have backlash IN THE TRANSMISSION. I can grab the output shaft and rotate it by hand back and forth some, causing the horrible slack in my driveline. I can't get any answers on this from anyone and I dont know enought about transmissions to know what parts need to be fixed or replaced.

[DoctorDex]

The dealership said that they adjusted the backlash in the rear dif. to within spec. and they also said that I don't have any issues with my driveshaft or carrier bearings.

They said that most, if not all, of the backlash I have is from the output shaft of the transaxle being out of spec.. The splines on the transfer case of the output shaft look good, but I'm wondering what the other side of the output shaft looks like (the side that is in the VCU).

If the output shaft (that's in the VCU) is stripped, then can it be assumed that the VCU is screwed and I need a new one (along with new output shaft)?

Or is there a better/cheaper/easier way to do it than replacing the VCU/Output Shaft?

Declan

[DoctorDex]

I found this info that I thought might be helpful. From this post, by Bret Brinkman, it sounds like it isn't a bad VCU/output shaft problem causing the backlash:

"First off, the floppy carrier bearings every one points the finger at came floppy from the factory. Sorry to inform every one, but you all wasted your money. I have never heard of a bad carrier bearing. All though I will say a CFDS is an excellent mod as it eliminates the noises and vibrations the carrier bearings made even when new. It is easy to see if one of your U-joints is bad because it will have back lash in between the two shafts it connects. Some times they will develop a squeaking sound when they fail also.

If the sound is coming from the rear it could be excessive backlash in the rear diff. You should consult your repair manual for details on checking and adjusting the back lash. Any one that doesn’t have a manual should stop screwing around and get one. They are an invaluable and nessisary diagnostic add as well."

Here's the part I found really interesting:

"If the sound is from the front then it is probably excessive back lash from the center diff in the tranny. The back lash is caused by very hard and very sudden launches such as high RPM clutch dumps. During such an event the dowel pins in the planetary assembly (part of the center diff) SLAMS against its aligning holes in the VCU (also part of the center diff). This hammers the holes out to make them a larger diameter which results in increased back lash (there is some from the factory keep in mind). Once it starts it becomes easier and easier to make it worse. What I would like to see some one try (I’ll probably end up trying it myself) is to tap out the dowel pins in the planetary assembly (they tap out with a hammer), find a drill bit the same size as the holes for the pins in the planetary assembly, line up the planetary assembly with the VCU, and drill holes into the VCU that are the same size as the holes in the planetary assembly. That way you could tap the pins through the planetary assembly and into th VCU. It would be a press fit and thus zero back lash to begin with. Which none to begin with it would eliminate the hammering effect altogether. The other fix would be to replace both components. I did not add this as a weakness of the drivetrains because it doesn't actually fail. It is just annoying."

The post I'm referring to can be found here: Everything you need to know about your AWD drivetrain.

[DoctorDex]

I have a number of questions I'm hoping someone can answer

1. Does anyone know if it is as easy as it looks to swap the output shaft?

2. When one pulls the output shaft, how hard is it to get out the VCU and the planetary assembly? Can it be done without having to drop the entire transaxle?

Edit: Answer: Yes. The hardest part seems to be getting the case off of the transaxle. Need to take off a plate that has three little balls. However, still haven't figured out what this is yet.

I'm anxious to try the fix posted by Bret Brinkmann, but I'm a little worried that I'll get the whole thing apart only to find that my VCU is bad.

3. Can a VCU be tested, before pulling it out, to see if it works properly?
Edit: Answer (quoted from WoodroweBones):

Test #1:
Pull E-brake, put car in 1st gear and slip clutch a little. The car should dip in the rear and rise at the front

Test #2:
Hold 3 wheels and have someone try to spin the free rear wheel. Should be lots of resistance

Test #3:
With the rear tires on the ground and the front in the air try to spin both front tires in the same direction. Should resist.

4. What kind of symptoms will a bad VCU give, other than wheel spin?

I haven't been able to find anything about removing the VCU, but I have found some good how-to's regarding the output shaft:

Output shaft replacement without tranny pull: EASY
http://www.3si.org/wiki/index.php/Ch...e_transmission
http://hireznet.com/swap.htm
http://www.vr4stealth.com/output_shaft.htm
TC O.S replacement pics & tips
http://www.3si.org/forum/showthread...ht=output+shaft

Here's some good illustrative information on stealth316.com:

http://www.stealth316.com/2-awd3.htm#cdvcu

[maddog]

I have a number of questions I'm hoping someone can answer

1. Does anyone know if it is as easy as it looks to swap the output shaft?

i personally beleive the proper way to swap it is to take the trans out of the car and take the trans apart the right way but it can be done the other way but make sure u know wut ur doing

2. When one pulls the output shaft, how hard is it to get out the VCU and the planetary assembly? Can it be done without having to drop the entire transaxle?

if u take the trans apart with it out of the car its not hard. if its still in the car you have to pry gears away and etc which is a pain

3. Can a VCU be tested, before pulling it out, to see if it works properly?
Edit: Answer (quoted from WoodroweBones):

Test #1:
Pull E-brake, put car in 1st gear and slip clutch a little. The car should dip in the rear and rise at the front

Test #2:
Hold 3 wheels and have someone try to spin the free rear wheel. Should be lots of resistance

Test #3:
With the rear tires on the ground and the front in the air try to spin both front tires in the same direction. Should resist.

4. What kind of symptoms will a bad VCU give, other than wheel spin?

drain the fluid, usually if its bad the fluid that comes out is a lot darker and thicker than usual

[/quote]

[DoctorDex]

I tested my VCU today and it seems like the one in the front is bad. When I jacked up either front wheel, the wheel would spin with only a little resistance. When I tried jacking up either of the rear wheels and spinning them, there was a great deal of resistance when compared with the front wheels.

It looks like I'm in the market front VCU and there isn't much use in trying to fix/re-drill my old one.

Declan

[blindmist]

there isnt a front vcu.

that means your vcu is shit in the planetary gear case. get a hammer and a screw driver, knock the 4 pins in, hit the end of the output shaft and it should all come out.