Can't find my copy. The GMC for our daughter is at 2400 RPMs. At 60 MPH. 3:21? The case is gray. And I see no numbers on it. Bob Dunahugh
FD Ratio Chart
- Thread starter Bob Dunahugh
- Start date
> Can't find my copy. The GMC for our daughter is at 2400 RPMs. At 60 MPH. 3:21? The case is gray. And I see no numbers on it. Bob Dunahugh
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Jim K. has one on page 2 of his final drive products.
--
Mike K.
'75 PB
Southeast Michigan
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> GMCnet mailing list
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Jim K. has one on page 2 of his final drive products.
--
Mike K.
'75 PB
Southeast Michigan
Bob,
See this for visual differences between the 3.07 and the 3.21.
http://www.gmcmhphotos.com/photos/g4399-fd-visual-differences307-vs-321.html
HTH
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
See this for visual differences between the 3.07 and the 3.21.
http://www.gmcmhphotos.com/photos/g4399-fd-visual-differences307-vs-321.html
HTH
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
--
Steve W
1973 : 23'
Southern California
--
Steve W
1973 : 23'
Southern California
These are great charts but they don’t take into consideration the various tire sizes of tires and how they affect the final drive ration. I have attached the charts done by Don Brown several years ago (2002) that show the results. I have always run the 225 size tire to take full advantage of the available gear ratio. I presently run a 3.21 final drive with a Manny 3.50 chain drive for an effective ration of 3.66.
http://www.gmcmhphotos.com/photos/final-drive-ration-2f-tire-size-chart/p3373.html
and
http://www.gmcmhphotos.com/photos/final-drive-ration-2f-tire-size-chart/p3374.html
This Chart is also available including GMCES and GMCMI and others.
J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan
>
> http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
>
>
> --
> Steve W
> 1973 : 23'
> Southern California
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
http://www.gmcmhphotos.com/photos/final-drive-ration-2f-tire-size-chart/p3373.html
and
http://www.gmcmhphotos.com/photos/final-drive-ration-2f-tire-size-chart/p3374.html
This Chart is also available including GMCES and GMCMI and others.
J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan
>
> http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
>
>
> --
> Steve W
> 1973 : 23'
> Southern California
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> I presently run a 3.21 final drive with a Manny 3.50 chain drive for an effective ration of 3.66.
Doing it this way makes the tranny spin a bit slower than changing the final drive, what are the pros and cons to this, or is it a wash?
--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model
Doing it this way makes the tranny spin a bit slower than changing the final drive, what are the pros and cons to this, or is it a wash?
--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model
Bob,sounds like a 342.
I have a 342 from Cinnabar and that rpm is about the same as mine, if it's a 342 from Cinnabar,there should be a small alum. ID. tag on it, they are
also painted gray.
Joe
--
Joe Williams
1978 Royale rear twin
I have a 342 from Cinnabar and that rpm is about the same as mine, if it's a 342 from Cinnabar,there should be a small alum. ID. tag on it, they are
also painted gray.
Joe
--
Joe Williams
1978 Royale rear twin
Burl,
I am checking with the 3.21 guru for the correct answer and as soon as I get his email I will respond.
JR
>
>> I presently run a 3.21 final drive with a Manny 3.50 chain drive for an effective ration of 3.66.
>
> Doing it this way makes the tranny spin a bit slower than changing the final drive, what are the pros and cons to this, or is it a wash?
> --
> Burl Vibert
> Kingston, Ontario
> 1976 GMC 26 foot, Sheridan reno, don't know original model
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
I am checking with the 3.21 guru for the correct answer and as soon as I get his email I will respond.
JR
>
>> I presently run a 3.21 final drive with a Manny 3.50 chain drive for an effective ration of 3.66.
>
> Doing it this way makes the tranny spin a bit slower than changing the final drive, what are the pros and cons to this, or is it a wash?
> --
> Burl Vibert
> Kingston, Ontario
> 1976 GMC 26 foot, Sheridan reno, don't know original model
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
Bob,
Based on my math, it could be a 3.50. Attached is a spreadsheet I just put together based on 225/75/R16 tires at 92 inches in circumference, which
works out to 688.7 tire revolutions per mile. Also assuming 3rd gear is a 1:1 ratio with engine rpm.
http://www.gmcmhphotos.com/photos/general-maintenance/p68229-speed-based-on-rpm-vs-drive-ratio.html
However, the 3.42, 3.50, and 3.55 are very close, and its difficult to maintain a constant RPM while driving and trying to get an accurate speed
measurement. Ask me how I know. Of course tire wear makes a difference, so does torque converter slip, if any.
My numbers are slightly different than these:
http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
for the 3.50
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.50 eng rev) x (1 mile/688.7 tire revs per mile) = 59.7 mph
for the 3.21
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.21 eng rev) x (1 mile/688.7 tire revs per mile) = 65.1 mph
for the 3.42
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.42 eng rev) x (1 mile/688.7 tire revs per mile) = 61.1 mph
for the 3.55
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.55 eng rev) x (1 mile/688.7 tire revs per mile) = 58.9 mph
It would probably be easier to pull the cover and count the teeth, than the figure out while driving.
Russell
--
Russell Keith,
1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
Onan, Dunedin, Florida
Based on my math, it could be a 3.50. Attached is a spreadsheet I just put together based on 225/75/R16 tires at 92 inches in circumference, which
works out to 688.7 tire revolutions per mile. Also assuming 3rd gear is a 1:1 ratio with engine rpm.
http://www.gmcmhphotos.com/photos/general-maintenance/p68229-speed-based-on-rpm-vs-drive-ratio.html
However, the 3.42, 3.50, and 3.55 are very close, and its difficult to maintain a constant RPM while driving and trying to get an accurate speed
measurement. Ask me how I know. Of course tire wear makes a difference, so does torque converter slip, if any.
My numbers are slightly different than these:
http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
for the 3.50
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.50 eng rev) x (1 mile/688.7 tire revs per mile) = 59.7 mph
for the 3.21
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.21 eng rev) x (1 mile/688.7 tire revs per mile) = 65.1 mph
for the 3.42
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.42 eng rev) x (1 mile/688.7 tire revs per mile) = 61.1 mph
for the 3.55
(2400 revs/min) x (60 min/hr) x (1 tire rev/3.55 eng rev) x (1 mile/688.7 tire revs per mile) = 58.9 mph
It would probably be easier to pull the cover and count the teeth, than the figure out while driving.
Russell
--
Russell Keith,
1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
Onan, Dunedin, Florida
Go to our web site and you'll see the # of teeth for the ring and pinion..
> Bob,
>
> Based on my math, it could be a 3.50. Attached is a spreadsheet I just
> put together based on 225/75/R16 tires at 92 inches in circumference, which
> works out to 688.7 tire revolutions per mile. Also assuming 3rd gear is a
> 1:1 ratio with engine rpm.
>
> http://www.gmcmhphotos.com/photos/general-maintenance/p68229-speed-based-on-rpm-vs-drive-ratio.html
>
> However, the 3.42, 3.50, and 3.55 are very close, and its difficult to
> maintain a constant RPM while driving and trying to get an accurate speed
> measurement. Ask me how I know. Of course tire wear makes a difference,
> so does torque converter slip, if any.
>
> My numbers are slightly different than these:
>
> http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
>
> for the 3.50
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.50 eng rev) x (1 mile/688.7
> tire revs per mile) = 59.7 mph
>
> for the 3.21
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.21 eng rev) x (1 mile/688.7
> tire revs per mile) = 65.1 mph
>
> for the 3.42
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.42 eng rev) x (1 mile/688.7
> tire revs per mile) = 61.1 mph
>
> for the 3.55
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.55 eng rev) x (1 mile/688.7
> tire revs per mile) = 58.9 mph
>
> It would probably be easier to pull the cover and count the teeth, than
> the figure out while driving.
>
> Russell
>
>
> --
> Russell Keith,
> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock
> Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
> Onan, Dunedin, Florida
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
> Bob,
>
> Based on my math, it could be a 3.50. Attached is a spreadsheet I just
> put together based on 225/75/R16 tires at 92 inches in circumference, which
> works out to 688.7 tire revolutions per mile. Also assuming 3rd gear is a
> 1:1 ratio with engine rpm.
>
> http://www.gmcmhphotos.com/photos/general-maintenance/p68229-speed-based-on-rpm-vs-drive-ratio.html
>
> However, the 3.42, 3.50, and 3.55 are very close, and its difficult to
> maintain a constant RPM while driving and trying to get an accurate speed
> measurement. Ask me how I know. Of course tire wear makes a difference,
> so does torque converter slip, if any.
>
> My numbers are slightly different than these:
>
> http://www.gmcmhphotos.com/photos/member-galleries/p68228-final-drive-ratios.html
>
> for the 3.50
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.50 eng rev) x (1 mile/688.7
> tire revs per mile) = 59.7 mph
>
> for the 3.21
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.21 eng rev) x (1 mile/688.7
> tire revs per mile) = 65.1 mph
>
> for the 3.42
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.42 eng rev) x (1 mile/688.7
> tire revs per mile) = 61.1 mph
>
> for the 3.55
> (2400 revs/min) x (60 min/hr) x (1 tire rev/3.55 eng rev) x (1 mile/688.7
> tire revs per mile) = 58.9 mph
>
> It would probably be easier to pull the cover and count the teeth, than
> the figure out while driving.
>
> Russell
>
>
> --
> Russell Keith,
> 1978 E2 "Harry" 403 (still carbureted), Danny Dunn Tranny, Thorley, Stock
> Brakes w/Remote Vacuum Brake Booster, Quad Bags, Dakota Digital Dash, 6.5 kW
> Onan, Dunedin, Florida
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
--
Jim Kanomata ASE
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
