Newbie Question, Need one more gear....

[bmwhitt]

I searched but couldnt find exactly what I needed. I recently bought a 1964 GMC 3/4 ton with the 305 V6. I have been driving the wheels off and love every minute of it. It is lwb and has a utility bed on it. My question is, what is a direct replacement for the rear end, gears, or maybe a 5 speed trans that bolts to the big V6? The motor seems to be screaming at about 45 mph or so...( my speedo isnt working). This was my grandad's truck and dad said it would pull a house down if you could keep the a$$ end down. I just want it to be a little more drivable maybe 65 mph or so.....Thanks ahead of time and sorry if this is a repeater!!

[spacedebris]

Not exactly cheap, but there is always the gear vendor OD option. My grandfather had an 85 ford F250 that was the same way. 50 MPH and it was out of steam with the engine screaming near redline. Added the GearVendor and it would cruise just fine at 65-70MPH.

[bmwhitt]

Thanks for the reply. There has to be an easier way...maybe a direct swap rear end from a late model or something like that.

[FetchMeAPepsi]

Your screaming is probably closer to 50 - 55mph. That's the norm.
As for getting her to go faster, well, you can swap out the rear end gears to a 3.73 or so, but remember that you're pushing 4k lbs of thick unyielding steel. These old farm trucks weren't made to go that fast b/c the reaction time in them is crap. They become a missle.

(and who needs to haul hay and get it there RIGHT NOW, right? lol!)

Anyway, if you really want you can swap out those rear end gears and you'll be fine. You might consider bigger tires too. What kinda rear end do you have now?

[kieth]

Before changing the trans/rear end pm me your spec's. I will send you a detailed performance spreadsheet. Kieth

I need engine
transmission
rear ratio
tire diameter(ground to top of rear tire)

I will send you a excell spreadsheet that shows usable torque to the ground and speeds at 1500, 2000, 3000, 4000 rpm........

[factorystock]

Originally Posted by bmwhitt

My question is, what is a direct replacement for the rear end, gears,

GMC 3/4 tons with leaf springs came with either 4.10 or 4.56 Dana 60 axles. Direct replacement would be a Dana 60 with 3.54. This axle can be found in big block 69 thru 72 GMC 3/4 ton with leaf springs. THis would be a do it yourself job. To replace the gears in your axle would require you to take your vehicle to a professional rear end shop and buy a 3.54 ring and pinion set and a carrier, and have the shop do it, which may be more expensive than finding a whole rear axle drum to drum in a wrecking yard.

[bmwhitt]

Thanks for the help. Ill get all the info when I can. Appreciate it!
Posted via Mobile Device

[sdcfish]

I just dealt with the same ****......I have a 65 C-20 with a 4 speed that had an Eaton HO-52 rear end....check that out on google and see the images to match it up. I am guessing you have the same **** I did which was that HO-52 rear end with 4.57 gears. I couldn't get over 45 - 50 mph either. 410 gears where the best I could do in that rear end. Here are your options:
1. Buy a new 14 bolt rear end with a 3.73 or lower gear and pay $1500 or so to exchange, plus the cost of a used rear end.
2. Change the gear in the diff to a 410 which is the best you can do in that Eaton.
3. Try to find an aftermarket gear which I was lucky to have done, and it's a 390 gear...which I now can run 62-63 mph comfortably.
4. Go for a 410 gear change, and get a new transmission, like a NV4500 with an overdrive....you can achieve .75 x 410 to get your overdrive running gear number.
5. sell that truck and buy a new one that has already been swapped out on this issue

Good luck...that's what I got for ya. Just been there done that.

[sdcfish]

Oh...I paid $750 for the 3.90 gear exchange.....but it's gonna be hard to find another one....I got really lucky A 4.10 gear exchange is more like $600.00 all done. Maybe with a bigger tire too it could get your more like 55-60 mph My rims are 18" and my tire is a 255/65/18. Not that high a profile tire...just medium in my opinion.