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Car front wheels spinning slower than rear wheels? AWD
Hi guys,
So I’m at a loss here, I am usually pretty good at diagnosing most issue on my CLS63 but this one has me stumped. About a month ago I was doing some pulls against my friends C7 and after beating him around 3 times he decided he wanted to try again in manual. The next two times we tried it at 60mph on 3rd S+ the car acted like it spun/slipped when I floored it and I had to back off. It did that two times before I gave up. From that day forward the car started to act like a RWD CLS and spinning tires everywhere in 1st, 2nd, and 3rd. I put new tires on the car cause the old 255/285 were worn thinking it would help and went with 255/295 and nothing still spinning.
Fast forward to this weekend I went to a car show and there was a dyno. After about 20cars my car was going to be dynoed but he could not launch it because the front tires were spinning slower than the rears. The fronts were going at 30mph while the rear were at 50mph. I’ve scanned the car multiple times with STAR with no codes for anything except a couple bulbs. Took the car to the dealer yesterday cause I thought the front diff was shot since I saw what seemed like a leak, but SM said all is good and the substance on the diff was the wax they applied after the steering bolt recall they did for me last week. He also said it makes no sense that the tires would be spinning at different speeds especially 20mph difference as something would have broke already.
Any idea what could be causing this? A RWD like CLS seems fun, but doesn’t seem like the car I bought that would launch from zero with minimal wheel spin. I can’t find anything on the internet that would remotely point me in the right direction.
I always thought the fronts spun faster, since they always get everywhere before the rear tires. Just kidding. OK, I didn't do a Google search for this (and neither did you, so you know what they say about free advice!). This is just off the top of my head; most AWD systems, incl. what I think M-B uses for their cars are non-locking, viscous coupled differentials with a bias towards the rear wheels. In my car, I think its a constant 66-33 bias rear:front. In my head, this is a propeller-like device spinning in thick fluid that "grabs" once you reach a certain speed/load combination. Again, in my head, this is like when, at low speeds, my hand drill spins the wood block I'm trying to drill through, instead of going through the wood. So, I don't think that 66:33 split is consistent at all speed and all loads. Can't be, unless its all mechanical.
So, when you load up the transmission, like at high transmission speed or under launch, my guess is that you may exceed the viscosity level at which the propeller grabs and spins the front wheels, esp if the fluid has reached its end of life.Like when the drill goes through the wood instead of spinning the wood block.
That's my guess as I sit here in front of the PC....too lazy to do a Google search!
I always thought the fronts spun faster, since they always get everywhere before the rear tires. Just kidding. OK, I didn't do a Google search for this (and neither did you, so you know what they say about free advice!). This is just off the top of my head; most AWD systems, incl. what I think M-B uses for their cars are non-locking, viscous coupled differentials with a bias towards the rear wheels. In my car, I think its a constant 66-33 bias rear:front. In my head, this is a propeller-like device spinning in thick fluid that "grabs" once you reach a certain speed/load combination. Again, in my head, this is like when, at low speeds, my hand drill spins the wood block I'm trying to drill through, instead of going through the wood. So, I don't think that 66:33 split is consistent at all speed and all loads. Can't be, unless its all mechanical.
So, when you load up the transmission, like at high transmission speed or under launch, my guess is that you may exceed the viscosity level at which the propeller grabs and spins the front wheels, esp if the fluid has reached its end of life.Like when the drill goes through the wood instead of spinning the wood block.
That's my guess as I sit here in front of the PC....too lazy to do a Google search!
Bro that’s some big assumptions, trust me, if I’ve done anything at all is search using different terms almost everyday I get an idea for over a month now. You can try searching and I guarantee you that you won’t find much about it even if you don’t make it Mercedes specific. Also I have my own STAR Diagnostic and can tell you the car does not thrown any codes whatsoever about 4Matic or VGS.
What you’re saying does make sense and I was thinking about buying a trans service kit from FCP and doing it anyways as it will be due in 10k miles at 80k anyways. I bought the car with 60k and can’t with certainty say that it was performed at 40k because even though CarFax shows that it was serviced including all recommended services at 40k, it does not say anything about the transmission. Also the car has never had any issues shifting and it shifts smooth even after the day I raced the C7.
Also while writing this post you gave me another idea, ask my SM for a VMI to see if transmission was serviced, thanks!
Sounds to me like it may be the center diff in the transfer case. If it is damaged, could be not splitting the torque properly sending all power to rear wheels.
Huge update, all is good. I bought the FCP trans service kit and flushed about 7L of fluid from trans pan and trans cooler. The magnets had a very normal amount of metal particles and tiny too so I’m surprised at how well the MCT protected itself after 70k in possibly original fluid even though I was spinning the rear tires all the time. I also changed front diff fluid but that one was still brown unlike trans fluid which was black. Now the MCT launches like it used and is not slipping anymore. Also took care of a RPM related whining I started hearing right before it started to slip. I’m not sure if the whining was the diff as only 500ml of fluid came out of it when it needs 650ml so it was low but I’m glad I did it anyways.
I can’t believe someone who spent 120k on a car would skip on a $500 transmission service after 40k miles but oh well. CarFax does say recommend services performed at 40k, but says nothing about the transmission. Also nothing in the VMI from dealer. From now on, when in doubt, do it anyways.
Glad you got it sorted out. However sometimes I wish my car is rwd. much more fun.
so ignore service and it’ll be rwd? Lool
Nah bro, trust me you don’t want what I had. While it was fun turning off TC and burning some tires by just smashing the throttle, it became really annoying how the car would bog down at any sign of heavy throttle or kick down as the trans slipped and the car cut power. TC off was pretty fun though lol.
Nah bro, trust me you don’t want what I had. While it was fun turning off TC and burning some tires by just smashing the throttle, it became really annoying how the car would bog down at any sign of heavy throttle or kick down as the trans slipped and the car cut power. TC off was pretty fun though lol.
yeah I hope I never have that issue lol
I got for a ride in my friends 2012 rwd and every time it dances at the back I regret buying awd lol.
awd is cool, but rwd is more fun for sure. Pros and cons for both i guess
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much more fun.
