Rear axle question

[1989k2500]

now that my 89 k2500 has a TBI 454 swapped in it. I am eye balling the 8 bolt fully float rear axle with limited slip and 4.10 gearing.
Now I’m not sure if it’s a good idea, being that I have a 3 speed manual transmission, so no overdrive.

Right now I have a 3.73
I’m not doing much highway driving , but I dont want that engine to fly out at 55mph, either
Good input is much appreciated

 

[454cid]

I assume you mean 8-lug.

If you want a limited slip, that would be aftermarket. It's either open, or a locker, from GM.

There are calculators online to help you pick gearing. I think I would be staying with the 3.73s, but that also depends on what kind of tire you want to run.

 

[geeeee89]

for what it's worth, my 89 c3500 with a 454 and 4.10 rear end doesn't rev that high on the interstate. I have a 3-speed auto. I don't drive it over 65. Sounds like maybe 25 or 2600 rpm at 65 mph, but i'd have to calculate it to know for certain

 

[PlayingWithTBI]

With a 1:1 trans final ratio, 4.10 gears, and 28.9" tires you're spinning ~3,000 RPM @ 60 MPH. Here's a calculator that might help.

https://www.tciauto.com/racing-calculators

 

[stutaeng]

for what it's worth, my 89 c3500 with a 454 and 4.10 rear end doesn't rev that high on the interstate. I have a 3-speed auto. I don't drive it over 65. Sounds like maybe 25 or 2600 rpm at 65 mph, but I'd have to calculate it to know for certain

Is that a TH400? I think I forget the TH400 was in the early GMT400s. I was reading a '89 literature the other day and looks like even the C/K1500s 4.3/5.0 were listed with a 3 speed auto. I'm guessing those were also TH400? Interestingly, the 5.7 had the 4 speed auto.

Didn't make much sense to me...like the stronger engine got the less robust tranny? Or the stronger tranny got the weaker engine. Of course this is 30 years later, LOL. Not certain on the C/K2500s (both 3 speed and 4 speed Auto were listed?,) but it was clear that the C/K3500s got the 3 speed auto.

Page 9:
https://www.gmheritagecenter.com/do...evrolet-trucks/1989-Chevrolet-Truck-PCK-2.pdf

 

[geeeee89]

With a 1:1 trans final ratio, 4.10 gears, and 28.9" tires you're spinning ~3,000 RPM @ 60 MPH. Here's a calculator that might help.

https://www.tciauto.com/racing-calculators

ah okay, maybe i miscalculated. I used this one https://www.crawlpedia.com/rpm_gear_calculator.htm

i have 235/85/r16 tires currently. it gave me 2800ish rpm

Is that a TH400? I think I forget the TH400 was in the early GMT400s. I was reading a '89 literature the other day and looks like even the C/K1500s 4.3/5.0 were listed with a 3 speed auto. I'm guessing those were also TH400? Interestingly, the 5.7 had the 4 speed auto.

Didn't make much sense to me...like the stronger engine got the less robust tranny? Or the stronger tranny got the weaker engine. Of course this is 30 years later, LOL. Not certain on the C/K2500s (both 3 speed and 4 speed Auto were listed?,) but it was clear that the C/K3500s got the 3 speed auto.

Page 9:
https://www.gmheritagecenter.com/do...evrolet-trucks/1989-Chevrolet-Truck-PCK-2.pdf

yea that's right i have the th400, shifts SUPER smooth but an O/D would definitely be nice.

 

[stutaeng]

ah okay, maybe i miscalculated. I used this one https://www.crawlpedia.com/rpm_gear_calculator.htm

i have 235/85/r16 tires currently. it gave me 2800ish rpm




yea that's right i have the th400, shifts SUPER smooth but an O/D would definitely be nice.

TH400 was the cat's meow of the era. We had a '72 C20 truck with a Buick 402 and that truck I remember had a super smooth shifting tranny. I find that little "whine" pleasant to hear, LOL. Cars like the Rolls Royce, Bentley, Jaguars, and even a Ferrari had the TH400/4L80e, among others.

My 4L80e with 4.10 and LT265/75/R16 (D = 31.5") turns roughly at 2400 RPM.

OP, if I were to have a 3 speed with 7.4, I would just keep the 3.73. How does it drive? I would think it would be a good combination, unless you are doing some super heavy hauling/towing.

 

[1989k2500]

I have a 3 speed manual actually and am planning to get s set of HMMWV tires for her

 

[1989k2500]

TH400 was the cat's meow of the era. We had a '72 C20 truck with a Buick 402 and that truck I remember had a super smooth shifting tranny. I find that little "whine" pleasant to hear, LOL. Cars like the Rolls Royce, Bentley, Jaguars, and even a Ferrari had the TH400/4L80e, among others.

My 4L80e with 4.10 and LT265/75/R16 (D = 31.5") turns roughly at 2400 RPM.

OP, if I were to have a 3 speed with 7.4, I would just keep the 3.73. How does it drive? I would think it would be a good combination, unless you are doing some super heavy hauling/towing.

As I probably wasn’t clear enough, I have a 3 speed manual transmission. The 454 drives very nicely, it’s got good torque,that’s for sure. I want the other axle mostly for the 8 lug hubs and 14 bolt full float. I am going to get a set of HMMWV wheels. They are 37x12.5 16.5” that’s equivalent to an 85” tall tire

 

[JWOK]

37” tire and 4.10 gears isn’t too bad, so long as your engine is in decent shape. Your talking 2400-2500 rpm at 65mph. I have 35” tires and 4.56 gears with a 4 speed manual (no overdrive) in one of my trucks. It is spinning nearly 2900 at 65mph which is screaming, but liveable within reason. If you spend much time off road you will appreciate the lower gear ratio since the 3 speed doesn’t have a deep 1st gear.