Click on image for the lowdown. 
====
| | | Forums66 Topics128,090 Posts1,056,369 Members48,442 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Oct 2015 Posts: 94 'Bolter | | 'Bolter Joined: Oct 2015 Posts: 94 | hello, i have a 1939 1.5 ton chevy truck with 6.17 rear gear ratio, any way to go to a higher gear ratio with an open drive line using the origonal axle housing . i was thinking of a gear ratio around low to high 4s . this is new to me . thank you for looking . 1pete1 | | | | | Joined: Mar 2004 Posts: 6,214 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,214 | Why? The rest of the truck won't be able to handle going any faster safely and the stock engine is way under powered for it as well. Mike B  | | | | | Joined: Mar 2010 Posts: 10,286 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,286 | Gear ratio of low to high 4s would actually be a lower gear ratio than what you have (6.17 to 1).
I too, wonder why you want to change what you have.
Is the truck mostly stock?
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: May 2001 Posts: 7,438 Extreme Gabster | | Extreme Gabster Joined: May 2001 Posts: 7,438 | Excuse me, but a 4.xx rear ratio is higher than a 6.17.
I don't think there is anything in that range that will fit in a 1.5 ton housing. | | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | What size tires do you have on it now? Larger OD tires, if they will fit the rims, will help the speed but not the speedometer.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Mar 2010 Posts: 10,286 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,286 | Excuse me, but a 4.xx rear ratio is higher than a 6.17. I don't have a problem calling 4.xx gear "higher" than a 6.17 gear. It is, however, patently inaccurate to state that a 4.xx to 1 set of gears are a "higher ratio" than a 6.17 to 1 set of gears. That would defy the basic rule of mathematics. Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Oct 2002 Posts: 4,066 Bolter | | Bolter Joined: Oct 2002 Posts: 4,066 | higher the number more pull/ torque lower the number less pull/torque rule of basic mathematics ponder on this deal awhile
Redryder pixMy HotrodA veteran - whether active duty, retired, national guard, or reserve - is someone who, at one point in his or her life, wrote a blank check made payable to The 'United States of America', for an amount of "up to and including my life."I am fighting cancer and I am winning the fight | Pain is part of life; misery is an option. | | | | | Joined: Jan 2016 Posts: 21 Wrench Fetcher | | Wrench Fetcher Joined: Jan 2016 Posts: 21 | I think that Mr Ribbett(sp?) (on this forum), search the classifieds, had a set of 5:38 torque tube gears. In my research for the later gear sets (u joint style) there is a listing for 4:86 gear but always with the notation Marmon-H(armon? name is escaping me this second) and discontinued, and 4:30 (also discontinued) for p-30 step vans till 1982 when the H110 went metric. I wanted a set of 4:86's for my truck, but settled for the last 2 sets of 5:38s in the country at $850.00 shipped EACH. My truck would not have looked right with any other axles in it so I bit the bullet, shed blood out of my eyes and paid the price.
My suggestion is:
Examine the HP your engine produces divided by the weight of the truck and the stopping power of the brakes. If the sum total of the above equals the truck being safe to travel above 45-52 mph (no this isn't a matmatical formula just something you must think about) then the most economical way to do it is to swap in a newer axle.
Proud caretaker of U.S.A. truck 3219442-S 1943 Chevrolet Cab Over Engine 1 1/2 Ton 4x4
| | | | | Joined: Sep 2011 Posts: 1,456 'Bolter | | 'Bolter Joined: Sep 2011 Posts: 1,456 |
I don't have a problem calling 4.xx gear "higher" than a 6.17 gear.
It is, however, patently inaccurate to state that a 4.xx to 1 set of gears are a "higher ratio" than a 6.17 to 1 set of gears. That would defy the basic rule of mathematics.
Carl [/quote]
Transmission gearing uses same logic, high gear is 1:1 (unless you have an over drive i.e. 1 : 0.76), LOW gear in 1 : 4.03 (in my T5).
BC
1960 Chevy C10 driver 261 T5 4.10 dana 44 power loc
1949 GMC 250 project in waiting
1960 C60 pasture art
Retired GM dealer tech. 1980 - 2022
| | |
|
|
