RDU Questions

[only_1]

Sorry, but I have more questions.
My RDU doesn't ever seem to engage in the snow. I am essentially driving a FWD car.
I recently had some fluid coming out of the RDU. Its only been a month since I replaced the fluid. So I pulled the plug to check it. It was like I had overfilled it by a quart. So I don't know if the fluid in the coupler went into the carrier?
So here is my question to you, who know more than I do. Is there a way to test the RDU clutches?
My thought would be to: Lift one rear wheel. Leave the other 3 on the ground. Put a pry bar into a ujoint to keep the driveshaft from spinning. Put the trans in neutral. Apply 12v to the RDU. Apply torque to the free wheel. See how much torque the clutches resist before slipping.
Is there some easier way?
Will the car set a code if it engages the RDU but the rear wheel speed sensors do not detect them approaching the front wheel speeds?

Thanks!

 

[Sgtmeatsauce1]

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[only_1]

I decided to just buy a second RDU. I will take my current one apart once I have the new one in. All the videos I see of the SHO in the snow show all 4 wheels spinning. That is definitely not the case for my car. No error codes so it is trying to work. Guessing friction plates are shot.

 

[xFallenxCripplex]

Wow where you find them I couldn't find any earlier?
I did get my car stuck in mud with the summer tires on and someone told me all 4 where spinning that's great if they really do!
I know on my Subaru I could get two spinning opposite sides.

Sent from my Pixel 4 XL using Tapatalk

 

[only_1]

Here is a couple

 

[Johnbigdog]

The Active Torque Coupeling clutch, attached to the front of the rear differential does not have any fluid in it to leak into the differential. There is some fluid in the clutch pack, however it is sealed in the clutch. If its leaking, it's not going to be seen. The two do not exchange fluid either. So if you pulled the rear fill plug and fluid come out, it was over filled or your car was not level.

If you put the car on Jack stands and it's in neutral spinning one rear wheel will be enought to rotate the drive shaft and most likely one front wheel. There is enough drag in the clutch for quite a bit of torque transfer. You should be able to drive it on the stands (wheels off the ground safely) and get all 4 wheels to spin.

The car itself does monitor front and rear wheel speed. If you get into a slippery surface, and punch it and there is a significant difference in speed I would expect an AWD fault message or a wrench light in the cluster and or dtcs set.

I haven't seen too many clutches that get smoked where torque isn't transferred, usually it's the opposite where there is too much and you get windup when turning, but that doesnt mean it's not posible. I have also seen the ptu fail in many ways with similar problems.

I'm not going to recommend putting power and ground directly to the rear solenoid. It is PWM by the AWD relay. I dont like doing that. The solenoid (ATC Clutch) should read about 10 ohms (16MY spec) and should not read continuity to the case.

The new clutch does have to be programed to the pcm to work properly.

 

[b4black]

Why would it be the RDU and not the PTU?

Since the RDU is a differential, shouldn't one wheel at least be getting power if the PTU was OK?

 

[Johnbigdog]

Why would it be the RDU and not the PTU?

Since the RDU is a differential, shouldn't one wheel at least be getting power if the PTU was OK?

The PTU is a 90 degree gear box splined to the front carrier. It works or it doesnt.

The RDU has a clutch on the front of the unit that modulates the torque provided to the pinion from the drive shaft.

The system is not "locked" together at any point in normal operation unless something is broke.

Secondary thought.

B4black does have a good point if you are only getting traction with one rear tire, the other would be spinning but bs should kick in. If you have a stripped out half shaft, a similar concern would be present.

 

[only_1]

I am not getting any real force from the rear end. When I drive it on jack stands the rear tires do spin. When I put it on the ground and actually drive the thing, dry/wet/snow/ice the front wheels spin and the rears do nothing. I can spin the front tires for 15 seconds straight on the snow/ice. I get noise from the antilock, but the rear wheels never do anything.

 

[only_1]

I guess what I am saying is that its like there is a viscous coupler with no friction material in the plate set. It will spin the wheels when no opposing force is present. When there is a force, the coupler does not have the torque to overcome it.

In either video above, my car in those scenarios gets neither wheel to do anything.

And I have no error lights on in the cluster.

 

[only_1]

The new RDU is in place. My SHO is AWD again. Clutches were out on the old one.

 

[Johnbigdog]

Good to hear!

 

[only_1]

After Christmas break I got a chance to drive the car. The new RDU also fixed my vibration. As suspected the clutch fluid was intermixed. The pinion bearing was toast. The pinion was eating into the carrier. It was a mess in there.

 

[Billy VK]

After Christmas break I got a chance to drive the car. The new RDU also fixed my vibration. As suspected the clutch fluid was intermixed. The pinion bearing was toast. The pinion was eating into the carrier. It was a mess in there.

Man, I have vibration in my car that is from 60 to 75 mph and I swear this is my issue too....Nothing else I have done has fixed my issue and you feel it in the seat but not in the wheel. Sound about right? Can you tell me what it cost you for a new one?

 

[only_1]

I found one on car-part.com with 45k miles on it for $75 with a 1 year warranty. I went this way because I could make sure I got the right gear ratio. I have a non-pp car, so I needed the 2.77 ratio. There are a number of RDU's that bolt in with other ratios from vehicles like Explorers. So, you just have to make sure you get the right ratio.
The vibration I was getting also came through the steering wheel some. But yes, I could feel it translate through the body/seat etc. It was more noticeable on acceleration, which makes sense after seeing the damage.

 

[Billy VK]

I found one on car-part.com with 45k miles on it for $75 with a 1 year warranty. I went this way because I could make sure I got the right gear ratio. I have a non-pp car, so I needed the 2.77 ratio. There are a number of RDU's that bolt in with other ratios from vehicles like Explorers. So, you just have to make sure you get the right ratio.
The vibration I was getting also came through the steering wheel some. But yes, I could feel it translate through the body/seat etc. It was more noticeable on acceleration, which makes sense after seeing the damage.

Good point on the gear ratio.

 

[ticoscen]

I have a 2010 PP SHO. Looking to rebuild the RDU clutch pack. I'm thinking of going with the AKD upgraded clutch pack kit for the RDU. No reprogramming necessary and get to keep my PP rear ratio instead of risking buying a used RDU with the wrong ratio. (PP ratio is 3.11)

 

[ticoscen]

The new RDU is in place. My SHO is AWD again. Clutches were out on the old one.

Anyone have the PN for the PP RDU so I know I'm buying the right used unit?

 

[Bluezone]

Anyone have the PN for the PP RDU so I know I'm buying the right used unit? the rear end gear ratio is the same regardless of PP or not performance pack. The gear ratio is set by the differential in the transmission.

IIRC the gear ratio of the rear differential is the same in all cars. The rear wheels turn at the same speed as the front wheels. They're both receiving power (RPM) from the front differential, which has already done the gear reduction. The differential in the transmission sets the final gear ratio. The PTU steps up the RPM and the rear differential steps it back down. So it works out that the output from the transmission to the rear wheels is 1 to 1.

 

[802SHO]

I have a 2010 PP SHO. Looking to rebuild the RDU clutch pack. I'm thinking of going with the AKD upgraded clutch pack kit for the RDU. No reprogramming necessary and get to keep my PP rear ratio instead of risking buying a used RDU with the wrong ratio. (PP ratio is 3.11)

All 10-12 RDU or (carrier assembly) will not work with AKD’s coupler and clutches. The magnet is different. You’ll need a 13+ carrier assembly.