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Discussion Starter #1
Hello fellow members:

I have read several places that the rear drive unit was purposely engineered to slip. I have actively searched and cannot find where exactly I read that. If someone can find the article, please post it in this thread.

My question is this: The design sounds like a disaster for long-term reliability. In fact, I am so worried about this potential problem, and the incredibly expensive repair this may be 4 years into ownership, that I am considering NOT purchasing the RS. I want to own this vehicle for 12 years, and so am very worried about this. Can anyone else with insight into this matter explain whether or not this is a legitimate concern?

Variables:
- Potential major problems with long-term reliability of rear drive unit?
- Potential for an extremely expensive part, due to such small numbers of production?
- Potential for difficulty finding replacement parts, also due to small numbers of production?
 

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The clutch packs in the RDU are a wet type. The fluid in the unit acts as a coolant and friction modifier. With proper maintenence I'm sure the RDU clutches can go 120k+ without any issue.
 

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So we know that this unit was based on the rear drive unit that is currently found in Land Rovers. On that application it is directly driven. In this application it is overdriven. I read somewhere on here that it was overdriven ~1.5%, which is small but constant. Ford's literature seems to indicate that it behaves like a FWD car when cruising in normal mode but Top Gear's passenger seat write-up said that it sends 70% torque to the rear during normal driving. I'm assuming that was a typo or hearsay and that the RDU is pretty much disconnected normally.

There is nothing else out there like this system. The Evoque is the closest so if there are major problems with the design we will see it there first since it has been on the market since 2011, but Ford claims that they had to redesign the whole thing to handle the power in a sporty way.

Personally I'm not concerned. Clutch-based LSDs aren't new and the original Audi TT had a clutch-based AWD system. I certainly hope that I'm right but only time will tell.
 

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I have the same question fundamentally. I am buying the car regardless, but it would suck having to sink a few Ks into the RDU every 50k or something. Hoping it can go a 150-200k per change, so this is a once in a decade cost.
 

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Hello fellow members:

I have read several places that the rear drive unit was purposely engineered to slip. I have actively searched and cannot find where exactly I read that. If someone can find the article, please post it in this thread.

My question is this: The design sounds like a disaster for long-term reliability. In fact, I am so worried about this potential problem, and the incredibly expensive repair this may be 4 years into ownership, that I am considering NOT purchasing the RS. I want to own this vehicle for 12 years, and so am very worried about this. Can anyone else with insight into this matter explain whether or not this is a legitimate concern?

Variables:
- Potential major problems with long-term reliability of rear drive unit?
- Potential for an extremely expensive part, due to such small numbers of production?
- Potential for difficulty finding replacement parts, also due to small numbers of production?
It's not constantly slipping, but it does slip when vectoring torque. It is a wet clutch based system, just like any Double clutch automated manual, such as the Nissan GTR, Volkswagen GTI auto, Ford Focus auto, Alfa Romeo 4c, etc, etc.
It is not even engaged in 99% of driving, so unless you are beating the absolute crap out of your car, i doubt you will see reliability issues.
 

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Hello fellow members:

I have read several places that the rear drive unit was purposely engineered to slip. I have actively searched and cannot find where exactly I read that. If someone can find the article, please post it in this thread.

My question is this: The design sounds like a disaster for long-term reliability. In fact, I am so worried about this potential problem, and the incredibly expensive repair this may be 4 years into ownership, that I am considering NOT purchasing the RS. I want to own this vehicle for 12 years, and so am very worried about this. Can anyone else with insight into this matter explain whether or not this is a legitimate concern?

Variables:
- Potential major problems with long-term reliability of rear drive unit?
- Potential for an extremely expensive part, due to such small numbers of production?
- Potential for difficulty finding replacement parts, also due to small numbers of production?

What?

You essentially contradict your own self. You said "I have read several places that the rear drive unit was purposely engineered to slip." Then you go on to name it as "potential problem", without any justification, even though you said it was designed and engineered to do so.

-All clutches in all transmissions slip, that is what they do.
-Potential expensive and rare part..? (see GKN.. whom Ford & others gets their part from)



There is potential for anything, but after 10 years of ownership, I don't see the RDU needing to be replaced, just rebuilt like any other trans abused unit. I also bet the aftermarket will have their own solutions to GKN's clutch packs in the future. I don't think the durability of the RDU is a major concern at all.
 

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Consider the fact that you're covered for 60,000 miles under Warranty. That should take a little of the edge off. But your worries bring up some interesting issues that deserve to be thought through. As was mentioned, the RS is only using its AWD capabilities when you demand it. And that's surprisingly infrequently. The RS is designed to handle at least thirty minutes on a track. A type of thrashing that you will almost certainly never be able to replicate on the road. In any event, should you push the car past the limits for which it was engineered, it will shut down the RDM. And it will notify you. Not only that, the car will maintain an accounting history of just how much abuse you've dished out, and will notify you of the service procedures needed to keep the RDM in top condition. I don't think you have a great deal to worry about. Like all machines, the RS has its limitations. But it's very likely that you will reach yours before the RS reaches its.
 

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Yeah a wet clutch in .86 liters thats never been done before, sounds like a time bomb
 

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Less fluid the shorter the change interval. Even if you replaced it every oil change you wouldn't break the bank. If you want something that'll last forever go buy a landcruiser.
 

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I am so disturbed by all this RDU angst that I am simply going to select "FWD Only" every time I drive my new RS. My life will go back to being carefree and optimistic.

Jim
 

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It's not constantly slipping, but it does slip when vectoring torque. It is a wet clutch based system, just like any Double clutch automated manual, such as the Nissan GTR, Volkswagen GTI auto, Ford Focus auto, Alfa Romeo 4c, etc, etc.
It is not even engaged in 99% of driving, so unless you are beating the absolute crap out of your car, i doubt you will see reliability issues.
Ford focus double clutch is dry not wet.
 

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Didnt the manual say basically not to worry with RDU maintenance until the computer tells you it needs a fluid change? And it automatically goes to FWD only when there is too much heat build up... Sounds pretty straightforward to me. All e-diffs (including the center diff in the STI) slip constantly... That's why it has 7 plates, to reduce the amount each plate must slip to a manageable level. It actually looks to me to be a pretty robust design, and I plan to drive the hell out of it (after the break in period) to see how long it takes before it needs a fluid change.

Isn't the entire car also supposed to be able to take 30 minutes of track abuse at a time before overheating? We'll see how true that actually is once non-Ford people are driving it, but if that is the case then I'll be impressed that the RDU can take that much abuse before overheating.
 

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Yes, the RS RDU clutch packs are bathed in hydraulic fluid, separate from the gear oil in the center section. Maybe hbphil was thinking of the main clutch at the tranny?

Jim
 

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The AWD system is pretty much the same as Honda's SH-AWD system, which overdrives the rear as well. I don't think GKN supplies it, but the concept is the exact same. They've been using this system since 2006 and I haven't heard of any problems.
 

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The AWD system is pretty much the same as Honda's SH-AWD system, which overdrives the rear as well. I don't think GKN supplies it, but the concept is the exact same. They've been using this system since 2006 and I haven't heard of any problems.
Yes, the SH-AWD system from Honda is very similar to the Twinster. And you're right, it's not made by GKN. The SH-AWD from 2006 was a little different, but the system from 2014 is nearly identical.
 

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Discussion Starter #16
Thanks guys. This was super informative and helped put my mind at ease. Also, everyone seemed very knowledgeable, other than w3rkn. He did not seem to understand how something might be purposely engineered to provide greater performance but less reliability. I'm glad to hear that the system seems pretty robust, though!
 

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Careful about asking questions on here about the RDU, some people getting mightily upset about that topic, (see RDU and auto-shut down). Seeking information and an open forum to ask questions should be OK, but it you even raise a question here about the unknown some feel the need to slam the door shut...the RS should be a great fun car and give all who buy a nice value for the money. Let's all try to remember why forums like this exsits...to ask questions, seek information, share advise and keep the excitement going while we ALL wait for the RS to arrive.
 

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Thanks guys. This was super informative and helped put my mind at ease. Also, everyone seemed very knowledgeable, other than w3rkn. He did not seem to understand how something might be purposely engineered to provide greater performance but less reliability. I'm glad to hear that the system seems pretty robust, though!
Except you asked theoretical potentials.. and avoided the "understood" part of your question, in that Ford cars have a warranty and that Ford engineered their cars for reliability in mind, more than performance. Warranty and reliability are the understood part of your question. Thanks for playing..

Also.. what super informative info did u not know... that you now know.. that clutch packs are bathed in oil?




It is like asking how does water taste wet..
 

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Diff or hydraulic fluid? Link?
I was being sarcastic, like every dirtbike ever made uses this setup. Its durable enough and can handle plenty of torque.
 
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