4:88's with 31's?

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Hello, I searched and couldn't find the answer. So... I just bought my first 80 and I've had to do some repairs. For one, the front diff was messed up, so I needed new gears. I looked for 4:56's, but couldn't find them in stock anywhere so I bought 4:88's! It should be fine in the long run once I add a lift and some bigger tires, but has anyone driven with 4:88's and 31inch tires and if so what is the result? Really high RPM's? Thanks.
 
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EXTREMELY high RPMS that thing will drive live a turbo...report back with the launch ability, should be quite nice.
Don't forget to break the gears in no driving more that 20min at speed and change the diff fluid after 500 miles.
 
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Hello, I searched and couldn't find the answer. So... I just bought my first 80 and I've had to do some repairs. For one, the front diff was messed up, so I needed new gears. I looked for 4:56's, but couldn't find them in stock anywhere so I bought 4:88's! It should be fine in the long run once I add a lift and some bigger tires, but has anyone driven with 4:88's and 31inch tires and if so what is the result? Really high RPM's? Thanks.

Just a question, you did change the 4.88's front and rear right................ Not just the front I hope.

-Ammo
 
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Yep-swapped both. I took the third members off and took them to a specialist. I figured I'd save some labor cost that way and I could re-seal the front axle and replace the brake pads while I had it apart.
 
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The 91 has a 3FE and will benefit tremendously with 4:88's and 31's if they are a true 31" tire. I wouldn't put any less gear in there, especially if you eventually plan to run up to a 33" tire.

I'm running 4:88's with 32" BFG AT's on a 15x10" rim that measure about 31"es tall. At 70 MPH I'm running 2700 RPM
s. At 80, right around 3G's. Will easilly go 90 MPH before she starts to run out of legs.

I love the 4:88's. My MPG's have improved, the auto shift points match the engine almost perfectly (33's I think would be the best). The torque curve is awesome compared to stock, and merging into traffic on the interstate is a breeze now. The whole driving experience is improved over the original stock gears.

I also tightened the throttle, and tranny kick-down cables. Tune-up, and advanced timing, runs on 91 octane though.

I really love it. I will be adding some 33's in the next year. My only problem after the gear swap has been the front d-shaft. I had a vibe around 70MPH with the stock gears. With the 4:88's it's starts around 50 MPH and gets very bad at 70. I've had it balanced, new joints, and found that the shaft had been bent at some point in it's life. Recently the d-shaft shop in town tried to starighten it, but marginally better. I'll be adding a new d-shaft soon.

If you can drive the speed limit (here it's 70 MPH), you won't have a problem with your 4:88's.
 
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Thanks a lot for the reply! I'm not positive when I'll be able to upgrade the tires and that eases my mind a bit. Hopefully, I have results as good as yours. I'll have to measure my tires. I'll probably move up to 33's next. Do you happen to know if 33's will fit without a lift?
 

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