Home » Public Forums » GMCnet » 3.55 or 3.70 Final Drive Gear?
| 3.55 or 3.70 Final Drive Gear? [message #313178] |
Tue, 14 February 2017 08:22  |
rviguet
Messages: 6
Registered: December 2016
Location: Texas
Karma: 0
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Junior Member |
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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 455, quadra-bag, Thorley headers, 3.70 w/LSD,
2016 Jeep Wrangler Unlimited Rubicon Hardrock,
Dallas (primary)/Orlando (as often as I can)
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313180 is a reply to message #313178] |
Tue, 14 February 2017 08:59  |
jknezek
Messages: 1057
Registered: December 2007
Karma: 5
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Senior Member |
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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
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313182 is a reply to message #313178] |
Tue, 14 February 2017 08:59 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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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@list.gmcnet.org
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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Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313183 is a reply to message #313182] |
Tue, 14 February 2017 09:23 |
Mike Kelley
Messages: 467
Registered: February 2017
Karma: -2
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Senior Member |
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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
> On Feb 14, 2017, at 8:59 AM, Keith V wrote:
>
> 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@list.gmcnet.org
> 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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| Re: 3.55 or 3.70 Final Drive Gear? [message #313186 is a reply to message #313178] |
Tue, 14 February 2017 11:22 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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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
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313188 is a reply to message #313178] |
Tue, 14 February 2017 11:40 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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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
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313189 is a reply to message #313188] |
Tue, 14 February 2017 11:44 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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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,
> On Feb 14, 2017, at 12:40 PM, John R. Lebetski wrote:
>
> 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
>
>
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313191 is a reply to message #313180] |
Tue, 14 February 2017 11:49 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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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,
> On Feb 14, 2017, at 9:59 AM, Jeremy wrote:
>
> 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
>
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313192 is a reply to message #313178] |
Tue, 14 February 2017 12:22 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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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.
On Feb 14, 2017 6:23 AM, "Ross Viguet" wrote:
> 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
>
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313210 is a reply to message #313178] |
Tue, 14 February 2017 15:12 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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rviguet wrote on Tue, 14 February 2017 09:22I 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 - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313214 is a reply to message #313178] |
Tue, 14 February 2017 15:44 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Those jeeps tow nice, but are not light, and I doubt you will let it sit empty, so I would opt for the 3.70 if you have the choice, especially if you plan to tow all the time.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313218 is a reply to message #313178] |
Tue, 14 February 2017 16:46 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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'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
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313220 is a reply to message #313218] |
Tue, 14 February 2017 16:56 |
rviguet
Messages: 6
Registered: December 2016
Location: Texas
Karma: 0
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Junior Member |
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Johnny Bridges wrote on Tue, 14 February 2017 16:46'16 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 455, quadra-bag, Thorley headers, 3.70 w/LSD,
2016 Jeep Wrangler Unlimited Rubicon Hardrock,
Dallas (primary)/Orlando (as often as I can)
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313238 is a reply to message #313220] |
Wed, 15 February 2017 10:39 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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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. GMCSJ and GMCMI member
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| Re: [GMCnet] 3.55 or 3.70 final drive gear? [message #313246 is a reply to message #313193] |
Wed, 15 February 2017 11:18 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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Senior Member |
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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@list.gmcnet.org
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
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| Re: 3.55 or 3.70 Final Drive Gear? [message #313268 is a reply to message #313178] |
Wed, 15 February 2017 15:13 |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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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
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| Re: [GMCnet] 3.55 or 3.70 Final Drive Gear? [message #313271 is a reply to message #313268] |
Wed, 15 February 2017 16:45 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Jims 3.70 can be a bit whiny at first but it definitly quiets down. a couple thousand miles and I don't hear mine anymore
________________________________
From: Gmclist on behalf of Jack Christensen
Sent: Wednesday, February 15, 2017 3:13:54 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] 3.55 or 3.70 Final Drive Gear?
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
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Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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