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| | | | Joined: Apr 2009 Posts: 94 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2009 Posts: 94 | Hi, I just bought and am fixing a 1942 Chevy 3/4ton. I want to keep the original motor tranny and rearend. It has the original 216 and 4 speed tranny. Is there anything i can do to get better cruising speeds with the original drivetrain?
Last edited by Jordi55; 02/15/2010 2:22 AM.
| | | | | Joined: Oct 2003 Posts: 5,152 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Oct 2003 Posts: 5,152 | Taller tires. Jet engine in the bed.
1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble... | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | He's kidding, but he's right. To increase vehicle speed or reduce engine speed, one of those has to change significantly:
O/D added to existing transmission (Gear Vendor, etc., $$$).
New O/D transmission (T5).
Lower numerical axle (3.55 instead of 4.11).
At least 2" taller tires. | | | | | Joined: Apr 2009 Posts: 94 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2009 Posts: 94 | Where or what kind of vehicle does a t5 tranny come out of? | | | | | Joined: Oct 2003 Posts: 5,152 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Oct 2003 Posts: 5,152 | I want to keep the original motor tranny and rearend. I'm not sure I was kidding. If you are not willing to change the motor, trans and rear you have very limited options to increase your speed. Another helpful thought would be to always drive downhill. The T-5 transmission was available in Jeep Cherokees, S-10 pickups and Camaros and Firebirds. And Mustangs and Astro vans. How do you plan to use this truck? Some description of your plans and intended usage might better match the suggestions you get to how you'll use the truck.
1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
It's true. I really don't do anything but browse the Internet looking for trouble... | | | | | Joined: Nov 2005 Posts: 1,048 'Bolter | | 'Bolter Joined: Nov 2005 Posts: 1,048 | What kind of drive line does your '42 have?? Does it have 6 or 8 bolt wheels? | | | | | Joined: Apr 2009 Posts: 94 Wrench Fetcher | | Wrench Fetcher Joined: Apr 2009 Posts: 94 | It has a 216 and the original 4 speed tranny with 8 bolt rims. | | | | | Joined: Jan 2000 Posts: 2,074 'Bolter | | 'Bolter Joined: Jan 2000 Posts: 2,074 | I went with a set of 4:11 gears in my 53 3/4 ton, not sure if that swaps back to the '42 or not. This was a bolt-in deal, lots of sweat but it all bolted up and now I can cruise at 'near' highway speed, ok not interstate speed but without a line of cars with horns blaring. Found the gears with a wanted ad here on the Stovebolt site, from a late 60s 3/4, 4:11s are a huge improvement over the 4:56s.
Best of luck.
Jim | | | | | Joined: Dec 2004 Posts: 1,897 Shop Shark | | Shop Shark Joined: Dec 2004 Posts: 1,897 | It has a 216 and the original 4 speed tranny with 8 bolt rims. Your 42 3/4 ton may not be a 42 3/4 ton. A 42 3/4 ton would have 6 lug wheels, just like the 1/2 ton. Maybe post some numbers so we can identify what you have. 1946 was the first year for 8 lug rims on a 3/4 ton. John | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | 4.11/4.56 = 11% faster.
60 becomes 66.5, etc.
There is no free lunch with axle ratios.
There is no magic "high speed + best power", those are opposing goals.
The engine RPM reduction in high gear is exactly the same as the torque reduction in every gear. 4.11/4.56 (and every other swap) reduces both RPM and torque by the same amount: divide new by old, in this case it's about 10%.
The exceptions:
1. wider transmission ratios
2. more gears (4 instead of 3)
3. overdrive | | |
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