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Rear Differential

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I know the issue of the noise from the rear diff when turning has been beaten to death on these forums. I have the noise in my 2011 non-SVTPP. I'm going to drain the fluid and refill and add 3-4oz of friction modifier soon. I don't want to just add modifer in case there already is some in there from the factory. Hope that works.

 

The question I have is related to inner tire spin. When I pull out of my driveway and out of my neighborhood, the inner tire spins on turns even with light throttle. I've never had a solid rear axle car before. Is this normal? i think it does it only when cold (and it IS cold here in MD). Just wondering if this might be related to the noise, i.e. I'm low on fluid. I'm sure it's just related to the solid axle, but just wasn't sure.

 

Thanks guys.

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I know the issue of the noise from the rear diff when turning has been beaten to death on these forums. I have the noise in my 2011 non-SVTPP. I'm going to drain the fluid and refill and add 3-4oz of friction modifier soon. I don't want to just add modifer in case there already is some in there from the factory. Hope that works.

 

The question I have is related to inner tire spin. When I pull out of my driveway and out of my neighborhood, the inner tire spins on turns even with light throttle. I've never had a solid rear axle car before. Is this normal? i think it does it only when cold (and it IS cold here in MD). Just wondering if this might be related to the noise, i.e. I'm low on fluid. I'm sure it's just related to the solid axle, but just wasn't sure.

 

Thanks guys.

 

 

I don't think it's a solid axle issue. More likely your temp is in the 40s or lower - and these tires are really not designed for that low of a temp.

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I don't think it's a solid axle issue. More likely your temp is in the 40s or lower - and these tires are really not designed for that low of a temp.

 

 

Thanks.

It's about 30 degrees.

But I've had high powered cars (Porsche, BMW M, Audi) with high performance tires (P Zero, Mich PS2, Toyo Proxes, Etc) and I've never had an issue. They all have independent rears.

Maybe it isn't a solid axle vs independent issue, but a Ford differential issue? In any case, does this happen to you (and others)?

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The tores on these cars are like Hockey pucks when it gets cold out , but both tires should spin. Try doing some figure eights in a parking lot this will get the rear end fluid in the clutch packs . Then spin the tires you should get two strips on the pavement. Has your car been sitting for any length of time ?

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The tores on these cars are like Hockey pucks when it gets cold out , but both tires should spin. Try doing some figure eights in a parking lot this will get the rear end fluid in the clutch packs . Then spin the tires you should get two strips on the pavement. Has your car been sitting for any length of time ?

 

 

The car has sat for awhile at a dealer before I bought it a couple hundred miles ago. It only has about 2,200 miles now.

I'll try the figure eights. Thanks.

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Just to be clear, the inner tire is spinning when turning, NOT on a straight hard acceleration. I believe the straight line acceleration is fine, and both tires lose grip on hard pulls.

 

So imagine this... when the car is started in the morning and I am parked parallel to the curb, if I turn the steering wheel to the left for example, and then gently drive away, the inner (left) tire spins a little. I know it's because the outer rear (right side in this case) has to spin more than the inner rear during a turn like this. So if the inner tire is spinning, it means the differential isn't doing its job very well. Just wondering if this is a characteristic of this car.

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Just to be clear, the inner tire is spinning when turning, NOT on a straight hard acceleration. I believe the straight line acceleration is fine, and both tires lose grip on hard pulls.

 

So imagine this... when the car is started in the morning and I am parked parallel to the curb, if I turn the steering wheel to the left for example, and then gently drive away, the inner (left) tire spins a little. I know it's because the outer rear (right side in this case) has to spin more than the inner rear during a turn like this. So if the inner tire is spinning, it means the differential isn't doing its job very well. Just wondering if this is a characteristic of this car.

 

 

No it's not. The stock tires are horrific in the cold, but if you have one spinning and the other one isn't - sounds like it's time to take it in to the dealership.

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The rear end is a posi t-rack & has clutch packs need lub . to work if they sit for any period of time they become dry by doing figure eights you are forcing the fluid into the clutch packs . There have been several people that have had this problem .

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The rear end is a posi t-rack & has clutch packs need lub . to work if they sit for any period of time they become dry by doing figure eights you are forcing the fluid into the clutch packs . There have been several people that have had this problem .

 

 

What would you consider a period of time 2 weeks / 4 weeks / more? As I live in the Northeast and with all that snow outside my car will not be seeing the roads for a while. Thanks.

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What would you consider a period of time 2 weeks / 4 weeks / more? As I live in the Northeast and with all that snow outside my car will not be seeing the roads for a while. Thanks.

 

 

Yup 4weeks will do it to prove it when you first take her out boot it & spin the wheels , then check the marks you left on the pavement

one may be more prominent than the other. Then go do some figure eights , & boot it again & check the marks on the pavement you will have two solid tire prints.

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...So if the inner tire is spinning, it means the differential isn't doing its job very well. Just wondering if this is a characteristic of this car.

 

You shouldn't have just one spinning. Adding friction modifier may make the problem even worse. I'd put up with a little groaning noise, and not add any friction modifier. I have the carbon clutch packs in both my Bullitt and the KR. They groan after I get on it hard, and then turn. Normal driving seems to loosen 'em back up, and they get quieter again. :)

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Did the figure 8's and the groaning sound was reduced but did not go away. Car still had some inner tire spin when pulling away from a stop while turning.

Drained the fluid and refilled with 2qt of lube and a 4oz bottle of friction modifier. Didn't want to add just friction modifier in case there was some in there already.

Groaning sound on turns is gone. Issue with inner tire spin is greatly reduced, if not gone.

Edited by MDGT500

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Did the figure 8's and the groaning sound was reduced but did not go away. Car still had some inner tire spin when pulling away from a stop while turning.

Drained the fluid and refilled with 2qt of lube and a 4oz bottle of friction modifier. Didn't want to add just friction modifier in case there was some in there already.

Groaning sound on turns is gone. Issue with inner tire spin is greatly reduced, if not gone.

 

 

Great now spin the tires & check the marks should be the same in lentgh & colour.

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. I've never had a solid rear axle car before. Is this normal? i think it does it only when cold (and it IS cold here in MD). \

 

It's not as directly related to the solid axle as it is the diff and tires.

 

At least my SVTPP the tires turn to rock in the cold. Combined with the increase in HP/torque the last couple weeks have been fun. Breaking the rear end lose at 50 MPH+ on the highway in 3rd gear type of fun. I also think that the limited slip diff gets really grabby with the cold fluid. I didn't really notice the diff noise other complain about until the cold came (well cold for N. Cal - 30-40 degrees). After the car is warmed up, things settle down and the noises go away on mine.

 

I've experienced cold weather tire traction issues on my (ex)Porsches with summer tires. It is different as rear engine makes the it more likely the slippage occurs in the front while cornering or braking rather than acceleration. I also suspect the Porshe traction control was a bit better than Fords, or just less overwhelmed with torque.

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Its normal, in tight turns one tire wants to spin faster than the other, these cars have a tight posi and the inside tire will spin if traction is limited. Normally the clutches in the rear would slip on tight turns (thats what the 'groan' is that a lot complain about), but the diff oil being cold, summer only tires and cold streets the inner tire will spin with a good working posi. An open differential wont do that, nor will a torsen type or a G80 that work on RPM before it locks. My BMW M3 will spin the inner tire when its cool out and the tires arent very grippy, it has an very tight posi, even has the same groan in tight turns as these 8.8s when its hot and dry ;)

Edited by kpevin

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It's not as directly related to the solid axle as it is the diff and tires.

 

I've experienced cold weather tire traction issues on my (ex)Porsches with summer tires. It is different as rear engine makes the it more likely the slippage occurs in the front while cornering or braking rather than acceleration. I also suspect the Porshe traction control was a bit better than Fords, or just less overwhelmed with torque.

 

 

I had a 997, and agree with what you said. My initial question about why the car does this was due to my comparisons with my past cars. I think the answer is probably a little bit of everything: different type of diff, a lot of power, cold, cold tires, Ford vs Porsche/BMW.

 

Its normal, in tight turns one tire wants to spin faster than the other, these cars have a tight posi and the inside tire will spin if traction is limited. Normally the clutches in the rear would slip on tight turns (thats what the 'groan' is that a lot complain about), but the diff oil being cold, summer only tires and cold streets the inner tire will spin with a good working posi. An open differential wont do that, nor will a torsen type or a G80 that work on RPM before it locks. My BMW M3 will spin the inner tire when its cool out and the tires arent very grippy, it has an very tight posi, even has the same groan in tight turns as these 8.8s when its hot and dry ;)

 

 

Thanks, I think you are right about the posi vs open diff. Except, I have had an E36 M3 and E60 M5 and none of these, and none of the other several cars I have owned over 19 years, have ever done it. That's why I thought it was a live axle/Ford thing.

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Thanks, I think you are right about the posi vs open diff. Except, I have had an E36 M3 and E60 M5 and none of these, and none of the other several cars I have owned over 19 years, have ever done it. That's why I thought it was a live axle/Ford thing.

 

 

Tighter the posi clutches and more you see it happen, GT500s (and even my 2011 GT) has an extremely tight clutch pack. Same with my E92 M3, I have had plenty of other cars with a posi/limited slips that didnt do it, and like I said there are various types of limited slip rears that arent capable of doing it by design. Take a car for a drive with a detroit locker and everything else will seem quite :) If one wheel spins only in a straight line then you have problems, but the inner wheel in a turn wants to go the same speed as the outer wheel even though its covering less distance, doesnt really matter if its IRS or not, just some differentials handle it better than others. Not to mention some tires make more noise than others when they slip, so thats another factor.

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