Transmission or gear ratio

[cdg1994]

Just picked my new project yesterday. She is a 1969 c20 with a 350 and a 4 speed on the floor. I am slowly going to build this truck but would like to be able to cruise at around 60mph instead of 40mph. Motor has he power but the trans is too small or geared too low. Does anyone know a solid trans that would fit year and motor or gear ratio if I were to rebuild it. Still want a 4 or maybe a 5 speed. Thank you

[TwoFiftyShifter]

Your best bet may be to look into an axle swap. If you can find a Dana 60 from this era GMC, you could get 3.54 gears. If you get a later model 14 bolt rear you could do 3.23, 3.42 or 3.73 gears. You most likely have 4.57 now.

[cdg1994]

So from what I said you believe it is the rear that needs to be geared and it will give me more power out of the trans

[Bigdav160]

Less torque but less rpm's.

A five speed with overdrive would be nice but your options are pretty limited and, in most cases, expensive.

If you don't work the truck too hard (and it's 2WD) a NV3500 could be swapped in.
A more heavy duty choice (also available in 4WD) would be a NV4500. They are much more expensive.

Other car transmissions like the T5 and TKO have also been used. Do a search on here.

[Mr Handy]

I have a 350 and 4 speed in my truck and I can cruise at 70 and still be under 3k.
I have the stock 3.07 rear gears, and I don't have any issue with the steps between gears.
one day I do plan to go to a 3.73 or 3.42 gears and add a gear vendor overdrive. should be a bomb proof combo and be able to do anything I want.

[Alex V.]

If your truck is truly wound out much above 40 MPH, it's got some stupid low gears. Do you know what diff. ratio you have, also tire size?

[Mike C]

The Granny 4 speed gives lots of gear options and would match up well with a 3.54 gear.

The Eaton axle has a 4.10 gear set on the low numeric side so not a good choice for the highway cruiser.

3.23 can be had in a later 14 bolt common in vans. 3.42 can be had but the most common is 3.73 in a full float 14 bolt. That's the swap I would do keeping the granny 4.

[Alex V.]

Not trying to be caustic here, but it seems this bears saying.

If you are used to vehicles - especially cars and mid-size/half ton trucks - from the early 90's-present, and you assume your new truck is supposed to behave the same it will sound stressed in comparison. To truly be what some call "wound out" above 40 MPH, with roughly stock tires, your rear end ratio would have to be above 6:1 which wasn't even available. Assuming near-stock tire size and 4.10 rear, your truck is turning around 2,700 RPM at 60 MPH - which is right in the power curve of the original engine. In more recent years GM made changes to the 350 (as all manufacturers did to all engines) to flatten the power curve and allow for the use of higher diff. ratios and overdrive transmissions, which did improve fuel economy and, of course, cuts down on engine noise at cruising speed, etc. For example, my parents' '97 1/2 ton Suburban sits right on 2,000 RPM at 70 MPH (4L60E/3.43 gears w/29" tires) and can get just over 21 MPG in good conditions, and it has enough torque at that speed to negotiate fairly hilly terrain without downshifting. However, your older small block's sweet spot is a bit higher than the Vortec's and it's right at home there - 4.10 gears with 32" tires or 3.73's with 30's (both of which I have) and no overdrive both cruise along at 60-65 just like it was made for it. My '72 Honda 175 motorcycle redlines at 10,500 and torque peak is at 8,500 - am I hesitant to run it there because what I'm used to redlines at half that speed and peak output is at 2,500 RPM? No, because it's a different animal. Overdrives and faster axle ratios are good mods for some purposes, but these trucks are very capable of highway speeds as they are - they're just a different animal and can't be judged on the same scale as modern rigs.

[TwoFiftyShifter]

Good post Alex. We are conditioned for lower rpm at cruise. I will say however, my DD pickup will cruise 65mph at 1900rpm due to OD. My '71 runs 2800rpm. If I decide to go out on a 100 mile highway trip, it's the other things that will keep the '71 at home - the DD has A/C cruise CD and so on, not the revving!

[Alex V.]

Thank you, twofifty.

[MidLifer]

cdg1994 welcome from a fellow Philly-area member.

Your C20 has a high-ratio (4:10) rear in it, which is what makes it seem wound-out at highway speed. If it's the stock rear, it is the GM "Corporate" 14-bolt rear. The 3/4 ton trucks were meant to haul loads, so they geared them lower than the C10s.

You can re-gear your existing rear down to as low as 3.42. Probably a 6-700 job if you pay a mechanic, if you can set clearances and all that yourself, you can get the gears for about $350. Yukon Gears among others makes them. You have the "10.5 inch" variety of the rear (later models are 9.5").

The NV4500 is another good choice and if you look around you can find them used for $6-700, but you'll need either to run the bellhousing that comes with it, with hydraulic clutch (they are notorious for leaking and blowing slave cylinders) or get an aftermarket bell to use your mechanical clutch. Another $300 there. I was this close to putting one in my C20 frankentruck then I went all LS swap and ended up putting an auto in. I sold the one I had (in a day- they are a hot commodity).

The SM465 trans that you have in that truck is not called the rockcrusher for nothing - they are bulletproof and last forever. So if you don't mind having 3 usable gears I would say re-gear your rear down a bit and be done with it.

[Bigdav160]

A 1969 C20 most likely has an Eaton axle. The choices of gear ratios would have been 4.10 or optional 4.57. The corporate 14 bolt didn't arrive until 1973 models. There are no other real gear choices for the Eaton.

A small percentage of trucks (mostly GMC) had the Dana axle which has allowed a 3.54 gear behind the big block.

A lower overall gear ratio (read overdrive trans) allows for longer engine life, better fuel economy, and less vibration/noise in the cab.

Can I cruise all day in my Corvette at 3500 rpm? Sure. But it would be more comfortable closer to 2000 rpm.

[MidLifer]

Sorry for the mis-info. Like I said my truck is a frankentruck. I mistakenly thought that the 14-bolt was offered in our vintage trucks.

Originally Posted by Bigdav160

A 1969 C20 most likely has an Eaton axle. The choices of gear ratios would have been 4.10 or optional 4.57. The corporate 14 bolt didn't arrive until 1973 models. There are no other real gear choices for the Eaton.

A small percentage of trucks (mostly GMC) had the Dana axle which has allowed a 3.54 gear behind the big block.

A lower overall gear ratio (read overdrive trans) allows for longer engine life, better fuel economy, and less vibration/noise in the cab.

Can I cruise all day in my Corvette at 3500 rpm? Sure. But it would be more comfortable closer to 2000 rpm.

[cdg1994]

Thanks for all the input everyone. im doing some research on 3.73 gears so i can still put power to the wheels. i would like to be able to cruise around 60mph like i said but would also like to spin the tires and be able to beat a honda at a green light. The previous owner did not know much about it he bought it cause he liked the look spent a ton of money and redid the brake system then parked it in his barn before i bought it. I had owned a 78 camaro a couple years ago with the same setup of a 350 and a 4 speed and im looking to drive like that. Any ideas will help thank you.

[cdg1994]

instead of a new trans is there anyway to rebuild the 4 speed i have (granny gears) or is a different trans a better idea?

[Wide Open]

I don't think there is anyway to have fourth gear be an overdrive for that transmission.
I believe you are limited to changing the rear gears (assuming they are available), changing to an overdrive transmission or adding a gear vendors unit.

[chevyremod]

I also have a 69 C20, 350, 4b Edelbrock, 4 speed w/granny and I can't go more than 2 mph in 1st without winding it out. I can cruise around my neighborhood in 4th gear at 35 mph. I too need something to change.

[MidLifer]

First is entirely optional on a SM465. I only used it when pulling my boat out of the water or pulling a stump. Entirely acceptable to pull off the line in 2nd.

Lots of choices as this thread and others on this forum go over. IMO if you want to continue to row gears find yourself a NV4500.

Originally Posted by chevyremod

I also have a 69 C20, 350, 4b Edelbrock, 4 speed w/granny and I can't go more than 2 mph in 1st without winding it out. I can cruise around my neighborhood in 4th gear at 35 mph. I too need something to change.

[my67c20]

You leave us with more questions than we have the knowledge to answer.

1) What rear gears do you currently have? Several places you can look for this. SPID tag on glovebox door, tag on the rear axle, or spin a wheel and count driveshaft rotations, remove cover and look for markings.

2) What size tires are currently on the truck?

3) What is your budget?

4) What are your plans with this truck?

5) What set of fabrication or mechanical skills do you possess?

6) Do you have a camera (cause we like pictures)?

And last but not least welcome to the board. You have made an excellent choice in seeking the wisdom of the many members of this community.

[Orange Crate]

First find out what rear end you have and what ratio is in there. Then decide if it is easier or cheaper to re-gear the one you have or swap in a new rear end (from an Eaton) that might have more gear options (say 14 bolt). To re-gear the rear end is the cheapest option, next cheapest would be a different rear axle and the last thing (most expensive) would be to swap out the trans."Rebuilding" your trans won't get you different gear ratios. If you can do any of this work yourself you can save some cash on all of these options.

[demian5]

I have a 70 with 31" tall tires, a turbo 350 and a 308 rear end. 2500 rpm at 70. Didn't lose any bottom end on the fairly stock and old target motor.

[67 chevelle]

I like this , especially with 3.42s or 3.23s

Originally Posted by Mike C

The Granny 4 speed gives lots of gear options and would match up well with a 3.54 gear.

The Eaton axle has a 4.10 gear set on the low numeric side so not a good choice for the highway cruiser.

3.23 can be had in a later 14 bolt common in vans. 3.42 can be had but the most common is 3.73 in a full float 14 bolt. That's the swap I would do keeping the granny 4.