rear end

S

stoker

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i bought a 91 cummins a while back and its slow wats the best thing to do to the rear end to get it geared faster thanks for ur imput
 
Auto or manual. If auto, is it 3 speed (727) or 4 speed (A518 w/ OD).
Figure out what rear end you have. They made 4.10, 3.54, and 3.07's as far as I know. The first thing I would do is put a higher GSK in it. Search on here, there good info.
 
It can have 3.07's, 3.54's and 4.10's. Best way to know is jack up the back and count how many times the wheel spins for 1 driveshaft spin.

3.07's have their own special housing so you can't really regear them.

Slow as in 75mph top speed or slow to get to 60?
 
i doubt the top speed is even 75 like 3rd gear should be 1st gear so how many spins should u get if i have 3.07s
 
3.07...

Sounds like you have 4.10's. Look for 3.55's or get bigger tires.
 
Pretty sure you've got 4.10's. We have the same truck at the farm.
 
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thats where this truck came from i grew up on the neighbors farm and once i got outa school i wanted him to sell it but he nv wuld finally he did but at this point in time the body was rough but im in the works of fixing the hole body
 
Best way to know is jack up the back and count how many times the wheel spins for 1 driveshaft spin
Click to expand...

Actually it's count how many times the driveshaft spins for one wheel revolution isn't it? The driveshaft would spin basically 3 times around exactly for 3.07:1 gears. And basically 4 times around for 4.10:1 gearing. 3 1/2 times for 3.55:1 gearing. Etc Etc.
 
My truck with 4.10s would eventually break 90 if you stayed in it long enough That was with turned up pump, 33s and aftermarket turbo. Runs a lot better with the 37s. 3rd gear ran out at around 35 and 4th was right around 60-65
 
NeilLB7 said:
Actually it's count how many times the driveshaft spins for one wheel revolution isn't it? The driveshaft would spin basically 3 times around exactly for 3.07:1 gears. And basically 4 times around for 4.10:1 gearing. 3 1/2 times for 3.55:1 gearing. Etc Etc.
Click to expand...

You're correct...if it has a locking differential, welded spiders, or a spool.
If it's an open, or non-locking differential and 1 wheel is blocked so it doesn't spin, it splits the ratio in half.
At which point TWO full tire revolutions, counting the turns of the driveshaft would end up with the correct ratio.

Mark.
 
Look for the steel data tag on the diff cover which has the BOM number and gear ratio stamped in it. Typically on the left side of the cover. Assuming it's completely stock and hasn't been modified or re-gear in the past.
 
jimbo486 said:
Look for the steel data tag on the diff cover which has the BOM number and gear ratio stamped in it. Typically on the left side of the cover. Assuming it's completely stock and hasn't been modified or re-gear in the past.
Click to expand...

That, too! :D
It'll also say if it's a Limited Slip, denoted by an L or LS on the same tag.

It's been my experience that about half are missing that tag, which means it is kinda' 50/50 on the condition, good or bad, of the rear axle.

Mark.
 
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