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Rear diff can't take it?

46K views 123 replies 55 participants last post by  pmrracing 
#1 ·
FYI, I got this off the MS3 forum when asking about JBR parts



The RS's rear diff is not capable of handling any real extra power, maybe only another 30-40 hp at the crank. The driveline was optimized to the engines specific power output for weight savings. PM me for specific questions on the RS platform, I work in Ford Performance
 
#3 ·
#4 ·
That may be true, if you are looking at from Ford's official standpoint. Especially when they need to consider how the car can last 100k miles plus when designing components. Can the RDU handle more power? Yes. Can it handle it for 100k miles when you don't even drain and replace the fluid for the clutch packs? Who knows right now.
 
#6 ·
I just read an article about the car on trackmustangsonline.com titled "Keep Your Mustang!". Its a pretty in depth look at the car from a mechanical and functionality standpoint and they said that the diff is pretty damn small along with some other disconcerting observations when the vehicle was taken apart. Worth a read all be it a sad one. I am still eagerly awaiting the car and will be so extremely happy with it though. Its a brilliant car.
 
#8 ·
When will all this hearsay stop!!!!!!!! When the first diff goes then we can all talk about it but until then people need to stop spreading rumors. I would love it if the first weak point was a driveshaft or something just to rub it in all these so called inside engineers. Every vehicle has weak points, even full on race cars, the fact is these claims are extremely exaggerated. 30-40 crank, we are pushing 50+WHP with no issues(very easy to get power BTW). The Diff which is actually a spool (reason for being compact and very smart move) only take power from the front and only takes what is programmed. The RDU is basically self protective until some one unlocks the module, you can add all the power in the world but the RDU will only use up to it's specified TQ limits at that given moment.
 
#11 ·
When I told him about tune+ and whatnot



Im not sure I understand, yes, people are making 30-40 hp gains. that is the limit of what the rear diff can safely handle, anything else is a ticking time bomb. Additional diff cooling could be an answer for moderate power bumps and track driving
 
#12 ·
So he works for FP but doesn't know that the RS doesn't have a rear differential?
 
#13 ·
That was what I caught as well. All these internet FP employees floating around, but don't know the car's components yet when it has been on the streets since February in Europe?
 
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#18 ·
It is CLUTCHES. If anyone can explain how they would not just slip when you apply too much torque I would be willing to say the RDU is a weak point. However, it sounds like there is no way to break the RDU, you would just throw off vehicle dynamics and overheat the RDU which would cause it to stop engaging the clutches until it cools down.
 
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#21 ·
Over the years I have really only ever had problems with side gears or pinion gears never crown wheels and pinions, THE RDU has no side gears/pinion gears, I doubt there is going to be many problems, the crown wheel and pinion will be fine. The clutches will be fine up to a point then will slip but I doubt they will explode or anything like that, they have ben using clutches in auto trans for years, his tech will be fine, so much hearsay, I call bulls!t.
 
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#23 ·
Damn, all these Ford Performance (Mazda) and GKN employees (NASIOC) posting everywhere but here, lucky competitor's car forums get all the people that designed the Focus RS's tech. Someone go check on the Golf R forums to see if Raj Nair is there talking down the RS.
 
#26 ·
30+ passes at the track with 400whp and on a full set of drag radials with no issues yet. We have been even launching it in drift mode from time to time which is near full rear lock and again no issues. Car has been making that power for almost a month now.

If the rear diff is going to break, we are going to be the ones that break it. Remember the rear diff is only being used if there is wheel speed error so the transmission is taking the brunt of the torque. The RDU always has an initial pressure lock and then tapers off as it reads multiple inputs and realizes it is not needed. It is a reactionary system, so it is only being used when it needs to be.

Also, I work for the company that makes the O-rings that go into the rear differential. I also am contracted by the company that supplies the aluminum for the casting to point and say "uh huh, yes right there". So, I know a few things... Also, I go to the Ford dealership sometimes and they know me by name.

:)
 
#42 ·
More from the FP guy

MikeBavaro said:
Im in performance chassis. The RS was mostly developed in Cologne Germany but we have had some input. I know its not a conventional diff but the electronic diff was optimized for the current power levels. I would recommend keeping it stock for a year or 2 until the aftermarket finds out how far they can push the drivetrain. We have nuked several pre production RDU's from track abuse. Did Ford say if the car was built yet?
......P.S. Congrats on the new ride, I wish I had the coin to get one right now.
 
#54 · (Edited)
Since the RDU was designed by GKN for Ford, I am betting this guy knows about as much about it as I do. Which is to say only what he has heard through the grapevine. Even if he is an accountant at FP chassis :rolleyes:

Of course the RDU was optimized for the stock power levels, but that has nothing to say about its limits. In developing a new product, I am sure they broke plenty of things on purpose. The RDU was probably broken a few times to re-write their algorithms to perform properly, find out limits, and to get the packs functioning reliably under harsh conditions; all in getting ready for production.
 
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#43 ·
I'm just worried how much the RDU costs to replace when I break mine
 
#53 ·
Rear diff can't take it

I'm sorry if this is ignorant but surely just like a manual transmission that is struggling for bite because of excessive torque, if that is the major weak point a simple clutch pack upgrade could be in order to deal with the issue. Should bump up the capabilities to the level of the next weak link. If these rdu's fail, the clutches will fail and need replacement not the whole unit.


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#56 ·
I'm sorry if this is ignorant but surely just like a manual transmission that is struggling for bite because of excessive torque, if that is the major weak point a simple clutch pack upgrade could be in order to deal with the issue. Should bump up the capabilities to the level of the next weak link. If these rdu's fail, the clutches will fail and need replacement not the whole unit.


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From a genuine perspective the clutches aren't available as a separate part only the complete RDU, I doubt Ford will be changing this, but I would think more than likely someone in the aftermarket will make a suitable replacement/upgrade (just going from experience with other clutch based diffs)
 
#55 ·
pretty sure the clutches are always in a state of various slip in the RDU. I would find it very hard to "break" like one thinks a conventional LSD will break. I think if anything the clutch packs will wear out faster than usual on a car making more power.
 
#58 ·
The ford performance guy isn't exactly wrong. I work for a supplier that isn't GKN. Most likely, GKN designed the unit to handle at least 110% of the rated torque for the life of the car (100,000 or possibly 150,000 miles).

That would mean that a 35lb-ft torque increase should be fine for the life of the car. Ford isn't going to tell you that anything more would be acceptable, because from an automotive engineering standpoint, a failure of a component designed to last the life of the vehicle is exactly that, a failure.

Anything more than that, and you risk decreasing the life of the components. Will it handle am extra 100lb-ft of engine torque? Probably. But, will it last 150,000? Maybe, but they won't tell you because there is a good chance that some borderline component designed meet that mileage would fail first.

Take what I said with a grain of salt. But, in my experience, we don't design components to exactly engine torque without some safety.

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#59 ·
My gut tells me that with hundreds if not thousands of these cars running around, many of them modded, ONE would have grenaded by now if they were really as weak as some people are making them out to be. We saw GT-R transmissions blowing up within weeks of them being out.
 
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#69 ·
I'm still not sure why this argument is still going on? Until some one cracks the programming for the RDU and is able to change the TQ limits there shouldn't be any issue. You can add as much power to then engine as you want but the RDU is only going to apply up to it's limits. This means power output should have no effect on the reliability of the RDU, just how much you burn your front tires off lol.

If the limits are removed from the RDU in theory it could apply as much power as it wanted to rear as long as traction allows it.
 
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