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#830515 - Tue Feb 28 2012 05:32 AM Highway speed  
Weeds  Offline
Shop Shark
Joined: Mar 2003
Posts: 1,477
Brodhead Wi 53520
Friend of mine is doing a 58 Chevy 1 ton and is wondering how to get 60/65 mph. 235/4 speed, rear end ratio unknown. What have some of you guys done to keep up with traffic?

Weeds



#830574 - Tue Feb 28 2012 02:41 PM Re: Highway speed [Re: Weeds]  
Grigg  Offline
Joined: May 2005
Posts: 8,995
Lexington, VA
If you're not going to change the engine for a faster running one or the transmission to one with an OD then the only variables you have left are tire size, auxiliary transmission, and rear axle gear ratio.

Run the numbers here
http://www.onlineconversion.com/bigger_tires.htm


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-

#830597 - Tue Feb 28 2012 03:53 PM Re: Highway speed [Re: Grigg]  
Whitedog  Offline
Shop Shark
Joined: Mar 2008
Posts: 1,616
IL
One method would be a center section from a 60-72 truck with the GM/Eaton axle. They typically have the 4.11 gear, you may luck out and find a 3.90.

Another option is a complete rearend swap. I don't know if the truck in question is a dually or single wheel, or even if axle width is an issue, but here it goes. GM has a full float 63" WMS-WMS (wheel mounting surface) and a 67" 14 bolt rearend. The good thing about them is that they are fairly common and they were made from 72 to present day, with only minor changes and a pretty good selection of gear ratios. Rearends from Dodge and Ford vans seem to be another popular swap. The Dana in the Ford is kind of hard to come by. They mostly were built with the Sterling axle, which is still a possibilty. You'll want to look for a full float Dana axle in the Dodge vans otherwise it'll probably be the Dodge semi float 9.25 rear.



1954 3600 Chevy Truck
"The Fake Truck"
In the Stovebolt Gallery
More pix on Photobucket

#830708 - Tue Feb 28 2012 10:52 PM Re: Highway speed [Re: Whitedog]  
EdPruss  Offline
Shop Shark
Joined: Jun 2011
Posts: 1,560
Longmont, CO
At some point, you're going to run out of HP, w/ a high rear gear or load, then you can look for a 261(looks same as 235,) 292(modern looking,) or GMC 302(move radiator to front of core support) to maintain your choice of higher road speed.


#830767 - Wed Feb 29 2012 01:43 AM Re: Highway speed [Re: Whitedog]  
LONGBOX55  Offline
Master Gabster
Joined: May 2006
Posts: 9,469
DANVILLE IL
Originally Posted By Whitedog
One method would be a center section from a 60-72 truck with the GM/Eaton axle. They typically have the 4.11 gear, you may luck out and find a 3.90.



A little clarification; The third member you would want is from a '68-'72 C20, generally with a 350 and automatic transmission. All others will be either a 4.56 or 5.13. The 3.90 mentioned is not an oem gear, they were a low production aftermarket run that seem to be impossible to find. The company that had them made seems to no longer be in business, though their website is still up.


Bill Burmeister

#830871 - Wed Feb 29 2012 07:53 AM Re: Highway speed [Re: LONGBOX55]  
Murraydave  Offline
Shop Shark
Joined: Jan 2002
Posts: 400
Ft Lauderdale, F:L
When I came to the realization that my 1941 1 Ton Long Bed pickup was not going to move over 45 mph without some changes and the fact that parts to get me up to speed were going to be hard to find/duplicate I replaced the whole drive/running gear assembly.

I started with a narrowed modern 3.73 rear end with wider rear brakes, single drive line instead of 2 piece, a 700R4 transmission (.70)overdrive and a small block stock 350, a radiator to match engine size and cool transmission and finally disc brakes on the front. If you want to cruise fast you need to be able to stop fast.

End result is 70mph at 2000 rpm. I got tired of chasing hard to find parts trying to make the truck do what GMC did not engineer it to do.


#831604 - Fri Mar 02 2012 07:17 PM Re: Highway speed [Re: Whitedog]  
aggie jon  Offline
Shop Shark
Joined: Nov 2008
Posts: 542
Temple Texas USA
My 49 1 ton would do 40 tops and sounded like the engine was going to fly out straight out of the hood. I bought a 3rd member from a 71 3/4 ton w/ auto and it has a 4.10 rear end. They are hard to find, and harder unless you know it is/was originally a 3/4 ton w/ and automatic. otherwise, you have to crack into it and count teeth.

Excited to get it back out on the road and see what switching from the 5.14 to the 4.10 will do. Everyone says it doesn't affect the low end too badly but improves the higher gears. Mine spent a good life working. In retirement, she's just gonna cruise to farmers markets and parades. Maybe the lumberyard on a fine sunny Saturday.


#831632 - Fri Mar 02 2012 09:34 PM Re: Highway speed [Re: aggie jon]  
Dirty_Gurty  Offline
Wrench Fetcher
Joined: Apr 2011
Posts: 81
Cleburne, TX
Actually you don't have to open it up to determine what the ratio is. All you have to do is make sure that only one wheel end will turn, and then count how many turns of the yoke equals one turn the wheel. If it's just a little over four turns that would make it a 4.10 to 1 ratio. 4 1/2 turns would make it a 4.56 to 1 ratio etc.


#834404 - Mon Mar 12 2012 03:09 AM Re: Highway speed [Re: LONGBOX55]  
GMCpanel  Offline
Shop Shark
Joined: Apr 2002
Posts: 2,664
Springfield, MO
Originally Posted By LONGBOX55
[quote=Whitedog]One method would be a center section from a 60-72 truck with the GM/Eaton axle. They typically have the 4.11 gear, you may luck out and find a 3.90.



A little clarification; The third member you would want is from a '68-'72 C20, generally with a 350 and automatic transmission. All others will be either a 4.56 or 5.13. The 3.90 mentioned is not an oem gear, they were a low production aftermarket run that seem to be impossible to find. The company that had them made seems to no longer be in business, though their website is still up. [/quote]

I've been told by a knowledgeable person that there was indeed a factory 3.90 gearset, used only in some big block 3/4-ton pickups in the 1969-71 era. He's the only person I've ever talked to who has seen one.

Some manual and leaf spring applications would also have the 4.10, but the auto/coil combo is the most common.

No need to count gear teeth, either use the method outline above this post or look for the markings on the edge of the ring gear.


Get a REAL truck, get a GMC! www.oldgmctrucks.com
1954 GMC De Luxe COE

#834704 - Tue Mar 13 2012 01:17 AM Re: Highway speed [Re: GMCpanel]  
LONGBOX55  Offline
Master Gabster
Joined: May 2006
Posts: 9,469
DANVILLE IL
Originally Posted By GMCpanel
[quote=LONGBOX55][quote=Whitedog]One method would be a center section from a 60-72 truck with the GM/Eaton axle. They typically have the 4.11 gear, you may luck out and find a 3.90.



A little clarification; The third member you would want is from a '68-'72 C20, generally with a 350 and automatic transmission. All others will be either a 4.56 or 5.13. The 3.90 mentioned is not an oem gear, they were a low production aftermarket run that seem to be impossible to find. The company that had them made seems to no longer be in business, though their website is still up. [/quote]

I've been told by a knowledgeable person that there was indeed a factory 3.90 gearset, used only in some big block 3/4-ton pickups in the 1969-71 era. He's the only person I've ever talked to who has seen one.

Some manual and leaf spring applications would also have the 4.10, but the auto/coil combo is the most common.

No need to count gear teeth, either use the method outline above this post or look for the markings on the edge of the ring gear. [/quote]
GM says different. Cross referencing the available ID guides to the GM Heritage site, there's no listing for a 3.90 in any 3/4 ton. The factory big block truck did have an option for a 3.54 gear, but those were Spicer/Dana axles, not Eatons.


Bill Burmeister

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