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Hello all! I have a '65 mustang with a 289 engine and a C4 trans. My differential was whining so we had new gears put in it. Now my vin plate says that the axle should be 2:80:1 but the machanic replaced them with 3:55. Now it still whines and the engine runs at high rpms at 65 mph. When the car is actually traveling at 65 mph the speedometer shows 80mph. I have not been able to find any ring and pinion set at 2:80:1. Does anyone know where i might find a set?? All help will be deeply appreciated.
 

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IIRC, 2.79 was the most commonly used rear-end ratio on Classic Mustangs...

Dave
 
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IIRc 2.80 is a stock ratio for your 8 inch. Putting 3.55 gears in will make the engine run at higher rpm's. If the new gears still whine then they may have been incorrectly installed
 

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The 3:55's will cause the speedo to be out and the engine will rev a lot higher at any speed. What you've done is change the relationship between the drive shaft and the rear wheel. Niw the drive shaft is spinning 3.55 times for every tire revolution as opposed to 2.8 times. This means an increased torque to the rear wheels.

You should have also noticed that you get to 65 mph a lot faster than before. Stick with the 3.55's and change the speedo gear in the transmission to bring the spedometer back in range.

The whine that remains could be berarings also.
 

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You have to change the speedo gear to match your new rear end gears. If you are not doing a lot of highway driving I'd stick with the 3.55 gears. If it is still whining it is either; (A) Not the rear gears making the noise or (B) The mechanic installed them incorrectly. If you want to change to a different gearing Summit racing sells there own brand of rear gears at a very affordable price. You should be able to find whatever gear ratio you would like. The 3.55 is a good rear end for better performance, and you should still be able to drive on the highway occassionaly. If the majority of your dring is on the highway a 3.00 or 3.25 might be the way to go.
 

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I concur that it is probably the gears that are whining. Your speedo will be off until you get the proper speedo gear into your transmission. The trade off for smaller gears (going from 2.80 to 3.55 is the extra torque trade for higher rpms at higher speeds. That will probably decrease your mpg slightly, but I don't think too much. At least in my 07 it didn't. ;)
 

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Why did you/he put 3.55 rear in?
 

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DaveSanborn said:
At least in my 07 it didn't.
You had 3.55's installed in your '07?

Dave
When I had the v6 coupe, I had 3.73's installed (came with 3.31s). It was a nice change. The GT I traded up for still has 3.31s. With the amount of highway driving I do, they are staying that way for awhile. There is a factory 3.55 option also.
 
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