Home » Public Forums » GMCnet » 3.21 final drive, any opinions
| 3.21 final drive, any opinions [message #304824] |
Wed, 03 August 2016 11:29  |
Scott Nutter
Messages: 782
Registered: January 2015
Location: Houston/San Diego
Karma: 4
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Senior Member |
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Hello,
I am Getting ready to pull out my 3.07 FD because it is getting a little noisy. First of all, I have a rebuilt 455 with a RV cam and headers in a heavy Royale and I pull a 92 Tracker. I have been fairly happy with the 3.07 and I normally cruise between 65 to 75 mph, probably closer to 75 mph.
Has anyone out there replaced their final drives to the 3.21 and been really happy? Or really disappointed? Wished they would of gone with a 3.55?
I have searched past posts and have only found opinions with the 403 engine.
I would think a 3.70 would be overkill for me. I don't pull extra heavy loads or travel the Rockies.
Thanks all!, Scott.
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, Dave Lenzi super duty mid axle disc brakes, tankless water heater, everything Lenzi. Alex Ferrera installed MSD Atomic EFI
Houston, Texas
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| Re: [GMCnet] 3.21 final drive, any opinions [message #304833 is a reply to message #304830] |
Wed, 03 August 2016 12:39  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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If you regear to a 3.55 final drive while running a 26 foot coach with a
455 Olds, about the only thing you will notice is something similar to
adding 50 horsepower to your engine. How you handle this new found power
will affect your fuel economy. All other things being equal, this is about
the best performance upgrade you can do to a GMC for the money spent.
Opinions vary. If you balloon foot the go pedal, your mileage might
improve. If you stomp on it, it will get worse. Should see 8 to 10 mpg in
good state of tune with sane driving style.
Jim Hupy
Salem, Or
78 GMC ROYALE 403 w/3:70 final drive.
On Aug 3, 2016 10:17 AM, "Todd Perkins" wrote:
> great questions. I drive in the 70s pull 3,000 to 5,000 loads also.
>
> Another question is what kind of mileage before and after would be
> interesting. I'm getting around 7 MPG. Too many WOT runs up the hills I
> guess. I
> assume i would get a little better buy staying out of the secondary
> throttles :)
>
>
> please share what you find.
>
>
> Todd
> --
> Todd
>
> Owner of a 1976 Eleganza II 26’
> other toys:
> 93 Vette
> 84 Goldwing
>
> and gone but not forgotten
> 72 CB750 Chopper
> 96 Caprice Classic
> 34 Ford roadster
> 94 Fleetwood
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] 3.21 final drive, any opinions [message #304835 is a reply to message #304833] |
Wed, 03 August 2016 13:07 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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I have 3.70's with posi in my Royale and love them. I'm really glad I didn't go lower.
BUT, I drive 60mph MAYBE 65, but the copilot starts to squeal above 65 :D and I'm rarely in a hurry in the GMC
If I liked to drive 70, 3.55's would be a good choice
>
> If you regear to a 3.55 final drive while running a 26 foot coach with a
> 455 Olds, about the only thing you will notice is something similar to
> adding 50 horsepower to your engine. How you handle this new found power
> will affect your fuel economy. All other things being equal, this is about
> the best performance upgrade you can do to a GMC for the money spent.
> Opinions vary. If you balloon foot the go pedal, your mileage might
> improve. If you stomp on it, it will get worse. Should see 8 to 10 mpg in
> good state of tune with sane driving style.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403 w/3:70 final drive.
> On Aug 3, 2016 10:17 AM, "Todd Perkins" wrote:
>
>> great questions. I drive in the 70s pull 3,000 to 5,000 loads also.
>>
>> Another question is what kind of mileage before and after would be
>> interesting. I'm getting around 7 MPG. Too many WOT runs up the hills I
>> guess. I
>> assume i would get a little better buy staying out of the secondary
>> throttles :)
>>
>>
>> please share what you find.
>>
>>
>> Todd
>> --
>> Todd
>>
>> Owner of a 1976 Eleganza II 26’
>> other toys:
>> 93 Vette
>> 84 Goldwing
>>
>> and gone but not forgotten
>> 72 CB750 Chopper
>> 96 Caprice Classic
>> 34 Ford roadster
>> 94 Fleetwood
>>
>> _______________________________________________
>> 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
_______________________________________________
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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] 3.21 final drive, any opinions [message #304840 is a reply to message #304835] |
Wed, 03 August 2016 13:46 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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I have had a 321 planetary with Caspro reduction chain set which reduced
the effective final ratio to about 3:62 and later a limited slip 3.55 from
Kanomata in the same coach and I liked them both. I think for traction the
3.21 and Caspro was actually a little better than the 3.55 lim slip. Power
and cruise Rpms were similar. Coach loved 65 mph and towed very well.
Current coach is a 3.07 with a switch pitch from manny. I have to say that
I absolutely love the switch pitch. Mileage cannot be fairly compared
between the switch and the others since they are two different coaches.
Both coaches are 77 with 455
Sully
77 eleganza 2
Seattl
On Wednesday, August 3, 2016, Keith V wrote:
> I have 3.70's with posi in my Royale and love them. I'm really glad I
> didn't go lower.
> BUT, I drive 60mph MAYBE 65, but the copilot starts to squeal above 65 :D
> and I'm rarely in a hurry in the GMC
>
> If I liked to drive 70, 3.55's would be a good choice
>
>>
>> If you regear to a 3.55 final drive while running a 26 foot coach with a
>> 455 Olds, about the only thing you will notice is something similar to
>> adding 50 horsepower to your engine. How you handle this new found power
>> will affect your fuel economy. All other things being equal, this is
> about
>> the best performance upgrade you can do to a GMC for the money spent.
>> Opinions vary. If you balloon foot the go pedal, your mileage might
>> improve. If you stomp on it, it will get worse. Should see 8 to 10 mpg in
>> good state of tune with sane driving style.
>> Jim Hupy
>> Salem, Or
>> 78 GMC ROYALE 403 w/3:70 final drive.
>> On Aug 3, 2016 10:17 AM, "Todd Perkins"
> wrote:
>>
>>> great questions. I drive in the 70s pull 3,000 to 5,000 loads also.
>>>
>>> Another question is what kind of mileage before and after would be
>>> interesting. I'm getting around 7 MPG. Too many WOT runs up the
> hills I
>>> guess. I
>>> assume i would get a little better buy staying out of the secondary
>>> throttles :)
>>>
>>>
>>> please share what you find.
>>>
>>>
>>> Todd
>>> --
>>> Todd
>>>
>>> Owner of a 1976 Eleganza II 26’
>>> other toys:
>>> 93 Vette
>>> 84 Goldwing
>>>
>>> and gone but not forgotten
>>> 72 CB750 Chopper
>>> 96 Caprice Classic
>>> 34 Ford roadster
>>> 94 Fleetwood
>>>
>>> _______________________________________________
>>> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] 3.21 final drive, any opinions [message #304842 is a reply to message #304835] |
Wed, 03 August 2016 15:32 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Todd,
Back in 1980 we ran the 3,21 as that was the only option.
I did not notice much of differencce and avantage.
Our 3.70 has been the most populer unit.
I run it in my 540 cid Cad powered Royal and pull 6,000 pounds of toad with
show materials and pull 7-8 mpg at 65-75 mph.
If your getting 7 now you'll still get 7+ with the 3.70.
I have many that are now running the 4.10 and pulling and the milage is the
same.
We also have limited slip units also.
On Wed, Aug 3, 2016 at 11:07 AM, Keith V wrote:
> I have 3.70's with posi in my Royale and love them. I'm really glad I
> didn't go lower.
> BUT, I drive 60mph MAYBE 65, but the copilot starts to squeal above 65 :D
> and I'm rarely in a hurry in the GMC
>
> If I liked to drive 70, 3.55's would be a good choice
>
>>
>> If you regear to a 3.55 final drive while running a 26 foot coach with a
>> 455 Olds, about the only thing you will notice is something similar to
>> adding 50 horsepower to your engine. How you handle this new found power
>> will affect your fuel economy. All other things being equal, this is
> about
>> the best performance upgrade you can do to a GMC for the money spent.
>> Opinions vary. If you balloon foot the go pedal, your mileage might
>> improve. If you stomp on it, it will get worse. Should see 8 to 10 mpg in
>> good state of tune with sane driving style.
>> Jim Hupy
>> Salem, Or
>> 78 GMC ROYALE 403 w/3:70 final drive.
>> On Aug 3, 2016 10:17 AM, "Todd Perkins" wrote:
>>
>>> great questions. I drive in the 70s pull 3,000 to 5,000 loads also.
>>>
>>> Another question is what kind of mileage before and after would be
>>> interesting. I'm getting around 7 MPG. Too many WOT runs up the
> hills I
>>> guess. I
>>> assume i would get a little better buy staying out of the secondary
>>> throttles :)
>>>
>>>
>>> please share what you find.
>>>
>>>
>>> Todd
>>> --
>>> Todd
>>>
>>> Owner of a 1976 Eleganza II 26’
>>> other toys:
>>> 93 Vette
>>> 84 Goldwing
>>>
>>> and gone but not forgotten
>>> 72 CB750 Chopper
>>> 96 Caprice Classic
>>> 34 Ford roadster
>>> 94 Fleetwood
>>>
>>> _______________________________________________
>>> 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
>
> _______________________________________________
> 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@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: 3.21 final drive, any opinions [message #304874 is a reply to message #304824] |
Thu, 04 August 2016 08:59 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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I went from 3.07 to 3.42 and only have one trip in so far. My first impression is that I have to apply more pedal to maintain the same highway speed. From a non sceintific viewpoint that can't help mileage. Vehicle launch is much better without so much converter slip time And no mountain driving yet. My first impression would be to want the 3.21 as the best overall compromise, though I bet I may change my opinion after altitude driving. There just isn't enough gear spread in the 400/425 family, though that does make the shifts less extreme in terms of RPM drop.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] 3.21 final drive, any opinions [message #304877 is a reply to message #304874] |
Thu, 04 August 2016 09:36 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Our first coach started out as a 403 with the 3.07 final drive. It was a real dog in the hills! Coach never ran well until were running 75+mph. Went to a 3.55 ratio and the coach really woke up. Drove that coach for 11 years. The current Stretch coach has a 3.21 final drive, but has a Manny 3.50 chain drive making it an 3.66 ratio and the coach really moves and with the toad and coach loaded for 4 months of winter travel we tip the scales at close to 19K pounds. I have a 3.42 final drive in the shop a I am considering putting that in to lower the ratio to 3.9. Still undecided on that. I am with Jim K on the minimum of a 3.55 with the 3.77 as the best all around gear.
JR Wright
78 Buskirk Stretch
75 Avion
Michigan
> On Aug 4, 2016, at 9:59 AM, John R. Lebetski wrote:
>
> I went from 3.07 to 3.42 and only have one trip in so far. My first impression is that I have to apply more pedal to maintain the same highway speed.
> From a non sceintific viewpoint that can't help mileage. Vehicle launch is much better without so much converter slip time And no mountain driving
> yet. My first impression would be to want the 3.21 as the best overall compromise, though I bet I may change my opinion after altitude driving. There
> just isn't enough gear spread in the 400/425 family, though that does make the shifts less extreme in terms of RPM drop.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> Source America First
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: 3.21 final drive, any opinions [message #304917 is a reply to message #304824] |
Thu, 04 August 2016 21:44 |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
Karma: 1
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Senior Member |
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I know there are a lot of opinions already, but we've got the 3.70 and love it (with the 403). When we got the coach it had the OEM final drive still in it, and the 3.70 made a world of difference. We do not pull anything, but it really helps for climbing larger hills on the highway (like the Tennessee & Kentucky hills!), also going downhill it will coast really well without having to brake much. We usually travel between 65-70 on the highway and it just goes, it helps the cruise control climbing the smaller hills, too. I'm sure the 3.55 is close, that you would see similar benefit.
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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