gearing question

[cajun chevy]

Hello out there
I have in my 1972 c10 307 v8, 4 speed, sm465, 373 gears in rear , 245/60 r15 front tires, 275/60r15 back tires. At 65 mph, it's screaming at close to 3000 rpm, at 70mph, 3200 rpm.
My question is, would 308 gears help me out or should I change transmission to lower the rpm so it more bearable when I cruse on larger highways in the 70 mph range? Would like to keep the same tire size that I have now also.
Thanks.

[Mike C]

3.07 should lower RPM 20% or about 600 rpm. Yes, it would make a big difference. And this is much cheaper and easier than changing transmissions. The beauty of the granny gear is even with 3.07 you can get some low first gear torque multiplication if you need it.

[trkfrk]

Try this gear calculator chart, It's awesome! It takes the guessing out of the equation. You can try different scenarios by choosing different transmissions, tire sizes, and gearing.

http://www.grimmjeeper.com/gears.html

[stsalvage]

Here is the point How old are you what kinda of condition is your body in.Can you handle pushing in a clutch for the next 10 years..2 how often do you drive your truck what do you do with it is it a work truck how much traffic do you deal with where you live how are the roads up there.Do you use your truck to tow a trailer.

If your come to a point that your wife might need to drive your truck or your kids how easy is it for them to get in it and drive it.

All of these things have to be looked at.

If you make your more Utility friendly that all can drive it.Makes it worth more money when you want to turn and sell it.


Most people say i will never sell my truck.Well it happens.And you have to make sure you get your bang for your dollar.Its like your house curveaplle when you drive by your house dose it sell if self.

A 700R4 would make your driving experience so much better.Less moving parts to replace.

Doing a 700R4 change over would mean the cradle needs to be cut and removed get a trans cross member shorten the drive shaft.if you have a salvage yard around you that has one of these trucks there I say buy the full frame the rolling chassis.

it sounds like a lot of work But it pays off in the long run.

Or i hear some just buy another truck with a auto in it.

To me I don't Buy stick trucks or 3 on the tree I like auto's.But i ever so often miss not driving my 1965 3 ton bob tail flat bed wish i still had it I pull a 8 speed Allison trans in it.

Now that might be a Idea for you Allisons are sweet trans and that can bolt up to where your 4 speed is

[LockDoc]

Originally Posted by stsalvage

Here is the point How old are you what kinda of condition is your body in.Can you handle pushing in a clutch for the next 10 years..2 how often do you drive your truck what do you do with it is it a work truck how much traffic do you deal with where you live how are the roads up there.Do you use your truck to tow a trailer.

If your come to a point that your wife might need to drive your truck or your kids how easy is it for them to get in it and drive it.

All of these things have to be looked at.

If you make your more Utility friendly that all can drive it.Makes it worth more money when you want to turn and sell it.


Most people say i will never sell my truck.Well it happens.And you have to make sure you get your bang for your dollar.Its like your house curveaplle when you drive by your house dose it sell if self.

A 700R4 would make your driving experience so much better.Less moving parts to replace.

Doing a 700R4 change over would mean the cradle needs to be cut and removed get a trans cross member shorten the drive shaft.if you have a salvage yard around you that has one of these trucks there I say buy the full frame the rolling chassis.

it sounds like a lot of work But it pays off in the long run.

Or i hear some just buy another truck with a auto in it.

To me I don't Buy stick trucks or 3 on the tree I like auto's.But i ever so often miss not driving my 1965 3 ton bob tail flat bed wish i still had it I pull a 8 speed Allison trans in it.

Now that might be a Idea for you Allisons are sweet trans and that can bolt up to where your 4 speed is

Some good points to take into consideration, but I am 73 and I still prefer manual transmissions. I just put a crate 350 and NV4500 manual overdrive trans in my '72 Dually and it drives like a dream. I realize some folks have knee and hip problems but they know their limitations and can decide what they want to do from that. It's all personal choice....

LockDoc

[cajun chevy]

I f I decide to install 3.07 gears what parts would I need to order and is installation a big job? And thanks for the great info guys!

[Rich69shortfleet]

Originally Posted by cajun chevy

I f I decide to install 3.07 gears what parts would I need to order and is installation a big job? And thanks for the great info guys!

Setting up gears is a big job. The rear axle needs to be completely disassembled and setting up the proper gear lash takes special tools. This is not a backyard mechanic job unless you've done it before and know what you are doing and have the proper tools.

Parts you will need are a new ring and pinion, shims, bearings (might as well replace them while you are in there), new lube and new additive if you have a posi differential and a new crush sleeve and new axle, pinion and rear cover seals. Do not use a synthetic rear axle lube. Used gears can save you some bucks but you have to be careful to buy good used. It is also a good opportunity to closely inspect the axles and axle bearings and determine if they are still in good shape, if not, this would be a perfect time to replace them. You will also need to change the speedometer driven gear in your transmission to keep your speedometer in calibration. They are inexpensive though. Calculating what driven gear to switch to is pretty easy.

I happen to have a spare set of truck 12-bolt 3.07 gears, PM me if you are interested. These are the good GM gears which are usually better than aftermarket gears for quality and will run quieter if installed correctly.

Oh, and I should add, "screaming" the engine at 3000 RPM isn't doing any harm to the engine. You might get slightly better fuel mileage with higher gears, but it probably won't be noticeable. I actually switched from 3.07s to 3.73s since the main purpose of having my truck is to tow cars on a trailer and the 3.73s sure make that process easier on the truck and the job as a whole much easier. Also, 3.07s will make your truck feel somewhat less peppy. However, if you don't use your truck for moderate to heavy hauling or towing and mostly just for cruising, you might like the 3.07s for lower highway RPMs and noise but will be a step back in the performance feel if that's important to you. Of course with a 307 it probably doesn't feel like a rocket on wheels as it is.

[Mike C]

If you were say 1000 miles closer I'd swap you some 3.07 for your 3.73!

As mentioned above, it is a relatively complicated process to do gears. After breaking the 5th 12 bolt in my Jimmy I learned how to do it and spent money on all the tools to no regrets. But the 25+ gear sets I've done for paying customers is what made that worthwhile.

I'd be looking for a junkyard/used axle assembly with the 3.07 in it and just swap the whole housing in. Except for the time it might take to find one near you, this is usually the most cost effective way to get the ratio you want.

[Jrainman]

I just did this swap with my 68 SWB DD , 350/ Th 400 / 3.73 to 3.07 , I drive roughly 1,000 mile per week , and where I live if you drive on the interstates the speeds or more like 70- 80 MPH ,

What I did is find a 71 c/10 3.07 12 bolt rear on CL took it home , cleaned it replaced all bearings and races and seals , set the back lash and pinion crush sleeve to specs , then put on all new brakes and brake hardware and drums . total cost with buying rear and parts were about $500.00

I had a friend lend me the tools required to do this job ,I now have close to 10,000 miles on this rear . it was a not that hard to do , I did the whole job by myself

I would buy extra crush sleeve and a extra inner pinion bearing and new axle U bolts this will make the job go much quicker

I now can cruise at real highway speeds not posted highway speeds with ease.

[Stu Pidd]

edit.....

[cajun chevy]

Originally Posted by cajun chevy

Hello out there
I have in my 1972 c10 307 v8, 4 speed, sm465, 373 gears in rear , 245/60 r15 front tires, 275/60r15 back tires. At 65 mph, it's screaming at close to 3000 rpm, at 70mph, 3200 rpm.
My question is, would 308 gears help me out or should I change transmission to lower the rpm so it more bearable when I cruse on larger highways in the 70 mph range? Would like to keep the same tire size that I have now also.
Thanks.

Would anew Process 4 speed help me out?

[Mike C]

A newer one or a NP435? A 435 has less 1st gear but 1:1 4th just like all the other transmissions of yore.

A newer truck 5 speed would help with an overdrive but with the questions you are asking not sure if you are up to the task of swapping a late model trans and having to deal with clutch linkage (or hydraulic conversion) and driveshaft etc.

[cajun chevy]

Originally Posted by Mike C

A newer one or a NP435? A 435 has less 1st gear but 1:1 4th just like all the other transmissions of yore.

A newer truck 5 speed would help with an overdrive but with the questions you are asking not sure if you are up to the task of swapping a late model trans and having to deal with clutch linkage (or hydraulic conversion) and driveshaft etc.

supposedly 4th gear is .73 in the New Process 4 speed that I'm looking at getting.

[cajun chevy]

Originally Posted by cajun chevy

supposedly 4th gear is .73 in the new process 4 speed that i'm looking at getting.

help identifying this trans. thanks. this is what they tell me what the gearing is 1st-3.09 2nd-1.67,3rd-1,4th-.73

[Mike C]

That would help on the highway, but it kills your starting. Right now you have a 3.5 SECOND gear and 3.73 for an overall 13 to 1 2nd. With the granny 1st you have 23.5:1 which gives you tons of power when you need it.

The 3.05 first of the OD trans gives you a maximum low gear of 11.3 but does reduce highway rpm by 27% but low gear by more than 50%!

3.07 gears and the SM465 gives you a 20:1 first and also reduces the highway speed 20%, that would be my choice as it makes the truck more useful IMO.

That and it's a lot less work to swap an axle I think.

[cajun chevy]

Okay Mike, thanks very much for the advice.