35" tires with 3.73 gears

[jlindquist]

I currently have 3.73 gears pushing 35" tires down the road. I am considering upgrading to 4.56 gears but am afraid I will lose my 65+MPH highway driving ability. I was curious what options, if any, I may have to possibly add a fifth gear to my stock 4 speed manual transmission.

Any thoughts?

[SeventyOne]

split the difference and do 4.11s?

Do you not like the sluggishness off the line with 3.73?

Seems to me a trans swap to get that 5th gear would be the most work of your options.

[Lieferson]

Im running 3.73 with the sm465 and 35s, it goes pretty good for me. I agree with the above statement though. move up to 4.10s and you should be good to go

[jlindquist]

4.11's may be the easiest, most cost effective way. Doesn't seem like much of a jump from what i have. Do you think i will see a noticeable change?

[rsavage]

Randy's calculator shows 2565 rpms at 65mph with 35" tires with 4.11 rear gear

https://www.ringpinion.com/calculators/Calc_RPM.aspx

[Mike C]

Transmission? 3.73 and 35's should be a decent combo. I run 35's with 4.10 and SM465 in my Jimmy. The Jimmy we are screwing together for my teenager is getting 3.73 with a TH350. With converter slippage, they are both probably equal in terms of highway RPM.

Maybe a cam swap to get a little more cruising RPM torque will make the difference and a lot cheaper than swapping gears in both ends. Dual exhaust, HEI and good tune.

[jlindquist]

Originally Posted by rsavage

Randy's calculator shows 2565 rpms at 65mph with 35" tires with 4.11 rear gear

https://www.ringpinion.com/calculators/Calc_RPM.aspx

This is a great tool thank you
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[jlindquist]

Originally Posted by Mike C

Transmission? 3.73 and 35's should be a decent combo. I run 35's with 4.10 and SM465 in my Jimmy. The Jimmy we are screwing together for my teenager is getting 3.73 with a TH350. With converter slippage, they are both probably equal in terms of highway RPM.

Maybe a cam swap to get a little more cruising RPM torque will make the difference and a lot cheaper than swapping gears in both ends. Dual exhaust, HEI and good tune.

It’s a stock 4 speed. I have a newer crate motor with a mild cam in it now. The diffs are stock and due for an overhaul (bearing and seals), so I might as well replace the ring and pinion while I’m in there
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[Mike C]

I did ring and pinion swaps in my truck in the late 80's. I think I broke the 12 bolt in some way 8 or 9 times? My truck has a semi-float 14 bolt from an '86 3/4 ton Suburban and we just pulled a set of 3.73 geared axles from an '84 Sub for my kids project. Both of the 9.5" axles have Gov-Locks in them and we are putting a TransAm clutch posi in the front of his.


I can't see spending $1000 to re-gear your axles and less it is REALLY important to you. But you can probably find a beater Suburban and pull the 8 lug axles from it. (I paid $300 for the 4.10 equipped truck that was equipped with HD towing an TH400. The 3.73 truck had a TH700R4 and was $200.)

As you can see, if it were mine I would also be looking for a strength upgrade at same time.

[PSYCHO_OUTLAW]

Originally Posted by Lieferson

Im running 3.73 with the sm465 and 35s, it goes pretty good for me. I agree with the above statement though. move up to 4.10s and you should be good to go

My blazer has pretty much the same setup but I am running 33s. However, I feel like on the highway the RPMs are way to high. At 65 MPH i am at 3500 RPMS continuos. Which I feel is way to high. I have thought about getting a NV4500 for the 5th gear set up. I am also swapping to 3/4 ton axles and I believe the rear is 4:10 or 4:11. I feel like that setup would be more suitable for hwy/street

[hemi43]

Originally Posted by PSYCHO_OUTLAW

My blazer has pretty much the same setup but I am running 33s. However, I feel like on the highway the RPMs are way to high. At 65 MPH i am at 3500 RPMS continuos. Which I feel is way to high. I have thought about getting a NV4500 for the 5th gear set up. I am also swapping to 3/4 ton axles and I believe the rear is 4:10 or 4:11. I feel like that setup would be more suitable for hwy/street

3500 RPM @ 65MPH ? How is this possible ?

[PSYCHO_OUTLAW]

Originally Posted by hemi43

3500 RPM @ 65MPH ? How is this possible ?

I am not sure.. but it def dont seem like it will be good for the truck in the long run.

[SeventyOne]

Yeah Psycho you gotta check that out - The math on randy's ring and pinion calculator doesnt add up.

I had to put in 4.56 gears, 33" tires and 75 mph to get to 3500rpm...

Your speedo could be off but your gear ratio cant be that far off. Are you sure you're getting into 3rd gear in the trans (1:1)? EDIT oh its a manual..guess you'd know if you got in gear lol

[PSYCHO_OUTLAW]

Originally Posted by SeventyOne

Yeah Psycho you gotta check that out - The math on randy's ring and pinion calculator doesnt add up.

I had to put in 4.56 gears, 33" tires and 75 mph to get to 3500rpm...

Your speedo could be off but your gear ratio cant be that far off. Are you sure you're getting into 3rd gear in the trans (1:1)? EDIT oh its a manual..guess you'd know if you got in gear lol

The speedo is off.. but i use a speedo app to gauge it... and maybe the tach is wrong... since its factory and old... but I dont believe it is too far off if it is... it does not purr down the hwy like i think it should... eitherway.. hopefully soon I will be installing the 14 bolt.

[jlindquist]

i was hoping i could get by with one of these, but with the short wheel base, the driveshaft angle would be too extreme. These add 13" to the rear of the transfer case. The NV4500 may be the best option long term.

http://www.gearvendors.com/4x4.html

[Mike C]

Originally Posted by PSYCHO_OUTLAW

The speedo is off.. but i use a speedo app to gauge it... and maybe the tach is wrong... since its factory and old... but I dont believe it is too far off if it is... it does not purr down the hwy like i think it should... eitherway.. hopefully soon I will be installing the 14 bolt.

My truck runs 2500 rpm at 70 with the 4.10. With 33's, you are about 10% more but 2750 is a LOT less than 3500. One of your numbers is off somewhere.

[mongocanfly]

physco what trans are you running? I use the csg rpm calc..but using it and assuming your final trans gear is 1:1 at 65mph with 33in tires and 3.73s you should be at 2469rpm....
http://www.csgnetwork.com/multirpmcalc.html