454/dana 70...highway gears?

[Puglia10]

I have a 1979 GMC crew cab dually. 454, th400, and a dana70HD rear end.
I still need to figure out what gears I have in there, but I assume 4.10 or 4.56 because the motor is screaming at 60mph.

I'd like it to be more highway friendly (70 all day, 75 would be nice) I'm not terribly concerned with gas mileage because it's a toy, and will only be towing a couple Harleys, or one hot rod...nothing crazy heavy, and even that will be rare. Mostly just building a fun cruiser that I can take to some shows...and again, maybe bring a couple bikes. Pulling a car MIGHT be once a year.

I know gear vendors or 4l80e would probably make the most sense, but for a quick and inexpensive fix, I am wondering what gear ratio would make sense for the highway driving, but still be able to move the big truck (with 22" Alcoas and adapters) and go up a hill.

At what point is the gearing too high that it won't be able to move around town?
Thanks!

[Big Chip]

I have the same engine and trans and I can tell you 3.73 isn't much better than what you're describing. It's not too bad at 70 but the truck was clearly designed for the 55mph speed limit.

[Corts60]

3.42’s would probably be your best to bring the rpm’s down yet still be able to tow decent.

[kwmech]

Tire size is also a factor. Some of the trucks came with 215/75r-16s. A good upgrade is going to a 235/85r-16. I think I have a pretty good combo in my dually with 235s, 4.10s and a Gear Vendor which has a 22% overdrive

[MARKDTN]

4L80E is a .75 overdrive so even with a 4.56 gear it makes it a 3.42 in overdrive (4.11 is 3.08 in OD). That seems like to way to go to me. There are aftermarket stand alone controllers for them.

[66gmcguy]

In my opinion, the only way to get a more useable highway gear is to add some type of overdrive. I went from 3.73s to 3.08s in my chevelle to be in a more highway-friendly RPM range, and it didn't make that much of a difference on the highway, but it made it way more sluggish in 1st and 2nd. I hated it, and was out a bunch of time and money that could have otherwise gone to putting in an overdrive transmission. I would look into a 4L80E, or if you're like me and don't like automatics, get an NV4500.

[Dead Parrot]

My 75 C10 with a mostly stock 350/TH350 and 3.42 rear gears + LT 235/75 15 inch tires (approx 28" diameter) does fine at 70~75 mph on long trips. Can get 3400lbs of trailer and gravel moving as well but doesn't set any 0-60 records during the process.

Play with some of the online RPM calculators before deciding anything.

[Puglia10]

just to put some closure in this thread, I ended up ordering a gear vendors overdrive. Not cheap, but the reviews are great and after pricing out a rebuilt 4l80e and controller, plus the extra amount of work, it wasn't a big difference. I'll try to remember to report back after I drive it. It makes my 4:10s act like 3.20 on the highway.

[chris989]

Originally Posted by Puglia10

just to put some closure in this thread, I ended up ordering a gear vendors overdrive. Not cheap, but the reviews are great and after pricing out a rebuilt 4l80e and controller, plus the extra amount of work, it wasn't a big difference. I'll try to remember to report back after I drive it. It makes my 4:10s act like 3.20 on the highway.

If possible,, reconsider the 4L80... the gear vendor is nice but it does not lock up the converter.

Having the converter lock is almost like getting another gear. I swapped a 4l80 behind my 5.7 with 4.56 gears. I run a MSD atomic controller.

It is an easy swap,,check you pick a part,,, pic one up for a few hundred with everything.

Good luck

[SunSoaked]

Originally Posted by chris989

If possible,, reconsider the 4L80... the gear vendor is nice but it does not lock up the converter.

Having the converter lock is almost like getting another gear. I swapped a 4l80 behind my 5.7 with 4.56 gears. I run a MSD atomic controller.

It is an easy swap,,check you pick a part,,, pic one up for a few hundred with everything.

Good luck

Too late! He already bought the GV. I was in this situation and researched my options to death. Finally, I just swapped in a NV4500 and all was good with the universe! Best of everything. With my Edelbrock pro-flo 4, I'm getting around 14-15mpg in my 85 K20.

[SCOTI]

Originally Posted by chris989

If possible,, reconsider the 4L80... the gear vendor is nice but it does not lock up the converter.

Having the converter lock is almost like getting another gear. I swapped a 4l80 behind my 5.7 with 4.56 gears. I run a MSD atomic controller.

It is an easy swap,,check you pick a part,,, pic one up for a few hundred with everything.

Good luck

4i80e's in my area from a yard are usually in the $6-800 range.

[chris989]

Originally Posted by SCOTI

4i80e's in my area from a yard are usually in the $6-800 range.

I was grabbing some fenders the other day and there is a 90k mile 2003 2500hd, someone already got the 6.0. but the 4l80 and 14 bolt 411 with disk brakes is just hanging there.

They are only 230$ here

[SCOTI]

Originally Posted by chris989

I was grabbing some fenders the other day and there is a 90k mile 2003 2500hd, someone already got the 6.0. but the 4l80 and 14 bolt 411 with disk brakes is just hanging there.

They are only 230$ here

Wow. Core price here near DFW is ~$4-500.

[SCOTI]

Originally Posted by Puglia10

I have a 1979 GMC crew cab dually. 454, th400, and a dana70HD rear end.
I still need to figure out what gears I have in there, but I assume 4.10 or 4.56 because the motor is screaming at 60mph.

I'd like it to be more highway friendly (70 all day, 75 would be nice) I'm not terribly concerned with gas mileage because it's a toy, and will only be towing a couple Harleys, or one hot rod...nothing crazy heavy, and even that will be rare. Mostly just building a fun cruiser that I can take to some shows...and again, maybe bring a couple bikes. Pulling a car MIGHT be once a year.

I know gear vendors or 4l80e would probably make the most sense, but for a quick and inexpensive fix, I am wondering what gear ratio would make sense for the highway driving, but still be able to move the big truck (with 22" Alcoas and adapters) and go up a hill.

At what point is the gearing too high that it won't be able to move around town?
Thanks!

As for gearing changes, I'm not sure how many choices are out there for the HD70 housing. I understood there were limited options w/a 3.54 being the mildest available. 3.54's would still help your situation as far as cruise rpm goes but not by much. Simulations assuming 235/85-16's....

4.56 gear w/a th400 @ 75 = 3625rpm
4.10 gear w/a th400 @ 75 = 3259
3.73 gear w/a th400 @ 75 = 2965
3.54 gear w/a th400 @ 75 = 2814


4.56 gear w/a 4l80e @ 75 = 2719rpm
4.10 gear w/a 4l80e @ 75 = 2444
3.73 gear w/a 4l80e @ 75 = 2223
3.54 gear w/a 4l80e @ 75 = 2111

4.56 gear w/a G.V. @ 75 = 2827rpm
4.10 gear w/a G.V. @ 75 = 2542
3.73 gear w/a G.V. @ 75 = 2313
3.54 gear w/a G.V. @ 75 = 2195

My towing adventures seem to like ~2500rpm to maintain speeds w/the sbc in my CCSWB 3/4 ton & slightly lower rpm's w/the BBC CC dually.

[factorystock]

Originally Posted by Puglia10

just to put some closure in this thread, I ended up ordering a gear vendors overdrive.

IMO, a good move, seems more durable and least amount of modifications. Automatic overdrives have a short shell life if TV cable not adjusted correctly,

[SCOTI]

Originally Posted by factorystock

IMO, a good move, seems more durable and least amount of modifications. Automatic overdrives have a short shell life if TV cable not adjusted correctly,

4l80e has no TV cable to worry about.

Gear Vendor OD is a great choice as well. Be advised though... On a truck like a CC Squarebody dually, the GV will likely end up about the center of the chassis. Not an issue @ stock height but it definitely becomes one when the truck is dropped 6"F/8"R.

I was considering one but when I looked @ where the bottom of the unit was in relation to the frame it made me nervous (I looked under a 7.4l/TH400/GV equipped Burb for the visual). I decided a 4l80e was a better option w/no worries about clearance since my dually has high centered more than a few times. I didn't want to spend >3k only to whack it in a jacked-up parking lot entrance/exit @ some point.