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- - Gear ratio speed question (https://67-72chevytrucks.com/vboard/showthread.php?t=708476)

5Tractorguy

05-29-2016 10:55 PM

Gear ratio speed question

Got a quick gear ratio question.

I have a '61 GMC 5000 with a NP540 trans (direct drive in 5th) and split rear. 9.00-20 tires. Right now I top out at 35-40ishmph, 30mph cruising comfortably. My gears in the differential are 6.50HI and 9.04LOW.

Is this speed about right for what I have in my truck? Anyone have one similar? I realize it's old and all but it would be great to get at least 45mph, but I think that's going to take some serious gear changing to do.

Any help would be appreciated....

mrolds88

06-04-2016 11:59 PM

Re: Gear ratio speed question

Jake, check your 2 speed. Sounds like it's in low range.

5Tractorguy

06-05-2016 09:29 PM

Re: Gear ratio speed question

Quote:

Originally Posted by mrolds88 (Post 7615230)

Jake, check your 2 speed. Sounds like it's in low range.

Will do 88. I'll check back mid-week. Going to bring it to the house Wednesday (storing it at uncles place).

greywuuf

06-06-2016 09:49 AM

Re: Gear ratio speed question

I would have to agree....I have a '75. 7500 (two of them actually) with 9.00x20's and 5 speeds... .One with the 6.xx or 8.xx two speed one with and undetermined single speed axle and the top out around 48- 50 mph .....Though both of mine are Detroit powered and tact out at 2800....slower than that would almost HAVE to be either "low range" or truely "deep" rear end gearing.

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