3.55 or 3.70 Final Drive Gear?

R

ross viguet

New member
Feb 14, 2017
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I am having my new to me early '77 model Eleganza II with a 455 worked on at Cooperative Motor Works and now is the time to change the final drive
gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair amount so I think I need to change the gear ratio. I live in the Dallas
Texas area and have a house in Orlando, both pretty flat areas. However, I do plan to make trips to the Ouchita and Ozark mountains (more like tall
hills) in Arkansas and the hill country in Texas. I will also be driving between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
preferably around 65MPH if I can.

Thoughts and suggestions on 3.55 or 3.70 final drive gear?

TIA
Ross
--
Ross Viguet
1977 Eleganza II
2016 Jeep Wrangler Unlimited Hardrock
 
I have a 3.55 and it works fine, but I always wonder if I should have got the 3.70. For the incremental added cost, especially since your towd is
fairly heavy, I'd just go with the 3.70 and never wonder...
--
Thanks,
Jeremy Knezek
1976 Glenbrook
Birmingham, AL
 
I have the 3.70 with limited slip, absolutely love it.

On the freeway at 60 it just walks up the hills, you barely notice them, no downshifting, no struggling.

On highways when you are stuck going 55 or slower, it's so much better, the engine seems much happier.

I have a heavy Royale, close to 13k lbs but I don't tow. Towing a wrangler, I would definitly not go lower than 3.70, I almost wish I went 4.11 !

But I do drive slow, 55 - 60, almost never 65 and spend a lot of time on back roads.

And the limited slip is awesome, well worth the extra $$

________________________________
From: Gmclist on behalf of Ross Viguet
Sent: Tuesday, February 14, 2017 8:22:19 AM
To: gmclist
Subject: [GMCnet] 3.55 or 3.70 Final Drive Gear?

I am having my new to me early '77 model Eleganza II with a 455 worked on at Cooperative Motor Works and now is the time to change the final drive
gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair amount so I think I need to change the gear ratio. I live in the Dallas
Texas area and have a house in Orlando, both pretty flat areas. However, I do plan to make trips to the Ouchita and Ozark mountains (more like tall
hills) in Arkansas and the hill country in Texas. I will also be driving between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
preferably around 65MPH if I can.

Thoughts and suggestions on 3.55 or 3.70 final drive gear?

TIA
Ross
--
Ross Viguet
1977 Eleganza II
2016 Jeep Wrangler Unlimited Hardrock

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Talk to Bob Dunahugh.
He is an expert on final drives (w/ lots of experience) and he tows HEAVY loads.
I think he prefers the 3:70
Mike/The Corvair a holic

Sent from my iPhone

>
> I have the 3.70 with limited slip, absolutely love it.
>
> On the freeway at 60 it just walks up the hills, you barely notice them, no downshifting, no struggling.
>
> On highways when you are stuck going 55 or slower, it's so much better, the engine seems much happier.
>
>
> I have a heavy Royale, close to 13k lbs but I don't tow. Towing a wrangler, I would definitly not go lower than 3.70, I almost wish I went 4.11 !
>
> But I do drive slow, 55 - 60, almost never 65 and spend a lot of time on back roads.
>
> And the limited slip is awesome, well worth the extra $$
>
> ________________________________
> From: Gmclist on behalf of Ross Viguet
> Sent: Tuesday, February 14, 2017 8:22:19 AM
> To: gmclist
> Subject: [GMCnet] 3.55 or 3.70 Final Drive Gear?
>
> I am having my new to me early '77 model Eleganza II with a 455 worked on at Cooperative Motor Works and now is the time to change the final drive
> gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair amount so I think I need to change the gear ratio. I live in the Dallas
> Texas area and have a house in Orlando, both pretty flat areas. However, I do plan to make trips to the Ouchita and Ozark mountains (more like tall
> hills) in Arkansas and the hill country in Texas. I will also be driving between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
> preferably around 65MPH if I can.
>
> Thoughts and suggestions on 3.55 or 3.70 final drive gear?
>
> TIA
> Ross
> --
> Ross Viguet
> 1977 Eleganza II
> 2016 Jeep Wrangler Unlimited Hardrock
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Don’t worry about the Hill Country in Texas. The elevations vary from 984 to 2461 feet. About any gear ratio will work there.

Emery Stora
77 Kingsley
Frederick, CO

>
> I am having my new to me early '77 model Eleganza II with a 455 worked on at Cooperative Motor Works and now is the time to change the final drive
> gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair amount so I think I need to change the gear ratio. I live in the Dallas
> Texas area and have a house in Orlando, both pretty flat areas. However, I do plan to make trips to the Ouchita and Ozark mountains (more like tall
> hills) in Arkansas and the hill country in Texas. I will also be driving between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
> preferably around 65MPH if I can.
>
> Thoughts and suggestions on 3.55 or 3.70 final drive gear?
>
> TIA
> Ross
> --
> Ross Viguet
> 1977 Eleganza II
> 2016 Jeep Wrangler Unlimited Hardrock
 
I've a 3.07 in the 23'. Works, but it's marginal. It wants second on the steeps, but walks over them then. I have a 3.7 in the 26' coach, it's
overkill. I'd go for the 3.55. I tow either a Kia Soul or an 88 Ranger - both lightweights.

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen
 
I have a 3.42 in a 77 455 and at first wanted the 3.07 back due to high speed limits in some states. But got used to it and the long 6% Rockies grades
are pulled in 2nd at about 50 MPH on the primaries. Going to WOT long term just washes the oil off the cyl walls and raises temp to go just a little
faster. My guess is 3:55 if you like keeping up with traffic I have no toad but think it's more powerband vs speed.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The 3.70 is about 3200 rpm at 70 mph. Toes the car trailer just fine.

Dolph Santorine

DE AD0LF

Wheeling, West Virginia

1977 ex-Palm Beach TZE167V100820
1-ton, Sullybuilt Bags, Reaction Arms, 3.70 LSD, Manny Transmission, EV-6010,

>
> I have a 3.42 in a 77 455 and at first wanted the 3.07 back due to high speed limits in some states. But got used to it and the long 6% Rockies grades
> are pulled in 2nd at about 50 MPH on the primaries. Going to WOT long term just washes the oil off the cyl walls and raises temp to go just a little
> faster. My guess is 3:55 if you like keeping up with traffic I have no toad but think it's more powerband vs speed.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Tows. *%*%ing Autocorrect.

Dolph Santorine

DE AD0LF

Wheeling, West Virginia

1977 ex-Palm Beach TZE167V100820
1-ton, Sullybuilt Bags, Reaction Arms, 3.70 LSD, Manny Transmission, EV-6010,

>
> I have a 3.55 and it works fine, but I always wonder if I should have got the 3.70. For the incremental added cost, especially since your towd is
> fairly heavy, I'd just go with the 3.70 and never wonder...
> --
> Thanks,
> Jeremy Knezek
> 1976 Glenbrook
> Birmingham, AL
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
You could use either one effectively. For heavier towing, a 3:70 gives a
better mechanical advantage, the 3:55 a few less rpm, but it becomes a
personal choice. Durability of both units is the same. Fuel economy, also.
Jim Hupy
Salem, Or
78 GMC ROYALE w/3:70. I tow light but have a 403.

> I am having my new to me early '77 model Eleganza II with a 455 worked on
> at Cooperative Motor Works and now is the time to change the final drive
> gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair
> amount so I think I need to change the gear ratio. I live in the Dallas
> Texas area and have a house in Orlando, both pretty flat areas. However,
> I do plan to make trips to the Ouchita and Ozark mountains (more like tall
> hills) in Arkansas and the hill country in Texas. I will also be driving
> between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
> preferably around 65MPH if I can.
>
> Thoughts and suggestions on 3.55 or 3.70 final drive gear?
>
> TIA
> Ross
> --
> Ross Viguet
> 1977 Eleganza II
> 2016 Jeep Wrangler Unlimited Hardrock
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I've got 78 Royale that I put a 3.70 in back in 2004. Absolutely love it. One of the best things I ever did. Mileage went up some because you end up running a higher intake vacuum. Trans temps went down. Thinking of going to a 4.10. On our last trip down South of 3800 miles. Pulling Linda's 5000lbs Chevy Uplander lift van. Thus a 17,000 LBS GVW. We got 10.2 MPG. Stock exhaust, carb, and distributor. But I must confess. I tried a lot of different carb jets, and timing mods to get there. That 403 78 Royale had 152,000 miles on it. Now this 78 Royale has about 5,000 miles on it's 403. I'm at 9.0 MPG using that other 403 carb. So now I need to tune to the cam in this 403. I'm short cutting the mods this time. Installing an EFI with spark control. Spark control is the real key to efficiency in conjunction with the 3.70. There's a reason that GM never put a 3.55 to 3.07 gears in anything with a GVW of 10,000 Lbs or more. And that weights not towing. Bob Dunahugh
 
> I am having my new to me early '77 model Eleganza II with a 455 worked on at Cooperative Motor Works and now is the time to change the final drive
> gear if I want to. I will be towing a 2016 Jeep Wrangler Unlimited a fair amount so I think I need to change the gear ratio. I live in the Dallas
> Texas area and have a house in Orlando, both pretty flat areas. However, I do plan to make trips to the Ouchita and Ozark mountains (more like tall
> hills) in Arkansas and the hill country in Texas. I will also be driving between Dallas and Orlando some. I prefer to cruse at least at 60MPH and
> preferably around 65MPH if I can.
>
> Thoughts and suggestions on 3.55 or 3.70 final drive gear?
>
> TIA
> Ross

Ross,

Welcome to the group, family, cult, asylum.....

You have a good plan. The 3.07 was wrong for everything when they were built..
With a 455, either the 3.55 or the 3.70 will be good. If you are towing I would edge toward the higher number. You are thinking of where you are
planning to go now and what you are towing now. Even with more of everything, the 3.55 will still be good, but with a 77 ELII, I think I would go for
the lean a little more toward the 3.70.

It is very good that you found your way here. This is where to come to get the good answers when you need them. Your sig is a great help, but please
put a geographic reference in there those the get this as e-mail can't read the location in the header. This matters as it both tells us the climate
you are dealing with and if you are in striking range when someone might choose to help you with something.

You should be planning to make it to the spring international rally in Shawnee in a about five weeks. Even if you can't spring the whole time, at
least make the weekend. You will get to meet a couple hundred brand new old friends. If you just stand in one place (closing your mouth is optional)
you can learn more in day than you knew you could learn. Speaking of such, you are now a part of a community like so few others. These are wonderful
supportive and helping people. But, be aware that everybody here has a personal agenda. It just so happens that we all have the same personal agenda
and that is to see that you can enjoy your coach as much as possible.

Speaking of the community, the only other community that is like this is that of the watermen that are my world. Those people have a welcome for any
new owner or vessel and for that reason I have taken to welcoming new owners here in a similar manner, So,

May the Good Lord bless this coach and all those that set forth within her.

Welcome Ross

Matt

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
'16 Wrangler Unlimited is listed at 4397 pounds. That wants some sort of braking system. If it was back there a lot of the time, I'd lean towards
the 3.7, for occasional I'd still favor the 3.55. I don't like to spin that motor up that fast for sustained periods.

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen
 
> '16 Wrangler Unlimited is listed at 4397 pounds. That wants some sort of braking system. If it was back there a lot of the time, I'd lean
> towards the 3.7, for occasional I'd still favor the 3.55. I don't like to spin that motor up that fast for sustained periods.
>
> --johnny

Thanks for all the replies. As of right now, I am leaning toward the 3.70. I think I will be pulling the Jeep more than 50% of the time. As for
braking, I have the Brake Buddy with the proportional braking, so I think I am good on that front. Jim B at the Coop is going through the motorhome
brakes now, so they should be up to the job when he is done.

--
Ross Viguet
1977 Eleganza II
2016 Jeep Wrangler Unlimited Hardrock
 
It is all about the torque curve.
Even on my 540 Cad that has tons of torque, the torque is strong at 3,000
rpm plus, the moment you slow down, you'll fall out of the strong torque
curve.
I run 3.70 towing or not, speed determines ratio. You'll never drive at
65mph , but fall down to 50 and your out of the torque curve.
There are several of us that is running 4.10 ratio.
Also we have the LSD (Limited Slip Differential)

> > '16 Wrangler Unlimited is listed at 4397 pounds. That wants some sort
> of braking system. If it was back there a lot of the time, I'd lean
> > towards the 3.7, for occasional I'd still favor the 3.55. I don't like
> to spin that motor up that fast for sustained periods.
> >
> > --johnny
>
> Thanks for all the replies. As of right now, I am leaning toward the
> 3.70. I think I will be pulling the Jeep more than 50% of the time. As for
> braking, I have the Brake Buddy with the proportional braking, so I think
> I am good on that front. Jim B at the Coop is going through the motorhome
> brakes now, so they should be up to the job when he is done.
>
> --
> Ross Viguet
> 1977 Eleganza II
> 2016 Jeep Wrangler Unlimited Hardrock
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
I think you'll like the 3.70. That's what I have and I tow almost all the time. My towd ('03 Tracker) is quite a bit lighter at just under 3000#,
than a JK Jeep, but I also tow my '53 CJ-3B on a trailer (~4000#) on occasion. The route I take while towing the Jeep/trailer is relatively flat, but
it still helps to have the lower gearing.

Most 1-ton trucks of that era had 4.56 rear end gears with about the same size tires as we have, and their GVW rating was about 2000# less than ours.
3/4 ton trucks generally had 4.10 gears with a GVW of 8 - 9000 The 3.07 is just too high.

Fuel economy goes down exponentially as your speed increases much over 60 mph, no matter what your final drive is, just the laws of physics. To some
it doesn't matter, but I notice a big difference when I am in California where the towing speed limit is 55, so I usually cruise at around 65, with
occasional passing speeds of 75 plus with no problems.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging
 
What Jim is saying is what is missed. You drive torque. You BS horse power. You pick the speed you like to drive. Then install a final drive that puts your engine in the top of it's torque curve. That's part of the formula for getting the best mileage. Don't get wrapped up in RPM's, and piston speeds. You'll never get there with your GMC attached to the engine and transmission. 4000 to5500 RPMs isn't a problem with these engines. You will NOT burn them up. But our torque curve isn't there. It's in the 2800 to 3200 RPM range. And were you're at in that range is determined by your cam shaft, and distributor that's in your engine. That's why there are so many different cam profiles to choose from. And different distributors. Just because you find an Olds distributor cheep somewhere. And it fits in the hole. It may be totally wrong for our use. Bob Dunahugh

________________________________
From: Bob Dunahugh
Sent: Tuesday, February 14, 2017 12:38 PM
To: gmclist
Subject: RE: 3.55 or 3.70 final drive gear?

I've got 78 Royale that I put a 3.70 in back in 2004. Absolutely love it. One of the best things I ever did. Mileage went up some because you end up running a higher intake vacuum. Trans temps went down. Thinking of going to a 4.10. On our last trip down South of 3800 miles. Pulling Linda's 5000lbs Chevy Uplander lift van. Thus a 17,000 LBS GVW. We got 10.2 MPG. Stock exhaust, carb, and distributor. But I must confess. I tried a lot of different carb jets, and timing mods to get there. That 403 78 Royale had 152,000 miles on it. Now this 78 Royale has about 5,000 miles on it's 403. I'm at 9.0 MPG using that other 403 carb. So now I need to tune to the cam in this 403. I'm short cutting the mods this time. Installing an EFI with spark control. Spark control is the real key to efficiency in conjunction with the 3.70. There's a reason that GM never put a 3.55 to 3.07 gears in anything with a GVW of 10,000 Lbs or more. And that weights not towing. Bob Dunahugh
 
I tow a Honda CRV and feel the 3.70 is a good addition, even when I'm not towing. I'm not experienced with the 3.55 so I can't evaluate that. My
only complaint with the 3.70 is that it's definitely noisier than the original. I noticed it as I drove away the first time. I guess I'm use to it
now. Jim did offer to change it, but that's a lot of trouble for both of us and why should that make a difference. I'm guessing it has something to
do with the design/manufacture.

--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
 
G'day,

GMC folklore says that they had a 3.42 to 1 on the drawing boards which I
believe can be purchased from Cinnabar.

I have absolutely no experience with that final drive I'm only mentioning it
as it is another way to go.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
 
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