Rear differential failure - Page 3

MPowrd · 5th February 2011, 02:08

I don't think it was the friction difference. I think the mileage got better because I'm running in the sweet spot of the power band more and seem to have the throttle pressed down less because of it (at least it feels that way).

Or maybe it's because I accelerate faster to highway speed and then spend more time crusing along.

gsfent · 6th February 2011, 18:44

Quote:

Originally Posted by Schuttsr1

That's interesting. Your diff had enough friction to decrease milage that much.

Probably. All things being equal (and assuming you are not lugging the engine), more rpms will consume more fuel. Expect a 1-2 mpg hit going from 3.15 to 3.45. Most people who make the change feel it is a fair tradoff.

Quote:

Last I check at my dealer with my account the diff was about 2k that included 650 core charge. There are some places that rebuild them that start at 1k depending on the options and gearing you want.

That is very good pricing, I would have though the price did NOT include the core charge. If you can get that kind of pricing, you may be able to help out board members who from time to time find they need a new diff. If you are rebuilding, you should very seriously consider changing the static and dynamic lockup "while you are in there". Just replacing ring and pinion should be around $600.

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My other car is a viper now I don't know if you'd consider it a super car or not but it's pretty hard to beat in a straight line. Even with the extra 200hp and the two extra cylinders it still gets 25 mpg on the open road. Now my m5 is my summer dd and gets 19mpg with about the same driving style.

I would say the Viper is as much a supercar as the M5. However, not a fair comparison. First, you are comparing 8L (V10) with an almost 5L (V8). The Viper puts out a lot more torque. So, the Viper is geared MUCH taller at the top to take advantage of that for highway cruising. Overall top gear is much taller, exact number depending on year. One that I looked at is 1.54 to 1 (3.07 diff). M5 is 2.61 to1 (3.15 diff). Much lower rpms at a given speed. So as noted above, lower revs = less fuel.

And the Viper weighs about 500 pounds less than the M5. Another advantage.

So I would expect the Viper to get much better mileage (similar to a Vette). Interesting, most M5's here beat the original EPA estimates (13/21) and the updated lowered estimates of 12/19, at least for highway numbers. Most of our members report low to mid 20's highway, and I don't think many of them are acquainted with the "suggested" speed limit signs!

My M5 can get 25 mpg in a straight line at normal highway speeds, but I cheat a little

(check my sig).

Regards,
Jerry