Gearing up 37 pickup

[kiwitony]

Hi guys I'd like some advice from your collective expertise. My 37 is running a stout 284 5 speed and 4.11 diff and 650-16 tires. I would like to gear it up a bit as I go everywhere in 5th gear. I have a 3.78 diff but would need to convert to open drive. I'm wondering if bigger rear tires would help me,either 700 or 750-16's. Has anyone done this? I don't want too much rake as I'm Tall and look through the top of the windscreen now. Looking forward to your reply's. Cheers Tony.

[V8COOPMAN]

Talkwrench down there near your side of the planet has 7.50s on the rear of his truck, below! I love the look! DD

[drolston]

If that 284 is a flathead, it probably has 4 1/8" stroke and a bunch of torque. It should be fine with 3.54 or 3.78 rear end gears, particularly if you have a 29 tooth cluster gear in the transmission to give you a lower low. Gears are available for the banjo rear end from various sources. I got mine from VanPelt. No need to go open drive. Swapping out rear end gears is not for the faint hearted or inexperienced, but there are folks around with the skill and setup needed.

[Talkwrench]

Yep mine is little 221 with a 28 gear set, 3.78 diff and the 7.50x16's turns over easy, yours should be no problems at all [unless you have a silly cam and a very light fly wheel]. so bigger tyres or change of gear no problem.

[Phil Gillespie]

Have a 38 Barrel Nose fitted with an 8BA Max 1 cam with 97 Carb. it has 3.78 rear end 38 g/box.
When I got it it had 7.50 x 16 on the rear. I personally felt they were to tall on the hills.
Now have radials all round, Front:185/75 R x16 and Rear: 205 R x16
These work just fine for me as New Zealand driving has its fair share of hills and not all flat going.
Phil NZ

[Brian]

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Boys...read the original post he's running a 5 speed transmission, hence the open drive requirement.

[V8COOPMAN]

Originally Posted by kiwitony

I have a 3.78 diff but would need to convert to open drive.

Originally Posted by Brian

Boys...read the original post he's running a 5 speed transmission, hence the open drive requirement.

Brian..........YOU should read his original post AGAIN! He "would need to convert to open drive". You know, it IS possible to run a 5-speed with a closed drive line. Click on my "T5 W/TORQUE TUBE" at the lower left. DD

[kiwitony]

No I run an open drive jailbar diff, hence the 4.11 ratio, if I use my 3.78 I need to convert it to open drive. Thanks for the input so far,especially the picture it looks good as the rear guards need filling up. cheers Tony. PS it is a flatty built by Brian.

[A bones]

Originally Posted by kiwitony

No I run an open drive jailbar diff, hence the 4.11 ratio, if I use my 3.78 I need to convert it to open drive. Thanks for the input so far,especially the picture it looks good as the rear guards need filling up. cheers Tony. PS it is a flatty built by Brian.

Tell me if I'm wrong, what I think is being said is there are two banjos. In the truck is an open 4.11, the spare 3.78 is torque tube.

The question is, can rubber make a enough difference without affecting visibility?

Would the fenders allow clearance, if the rear were to be lowered, to avoid excessive rake?

[JSeery]

What 5 speed are you using? Is the 5th gear overdrive? If so what ratio? Some missing information here to get a good response. You can do the rpm calculations to compare different tire sizes to what the corresponding rear axle ratio would be. The final drive ratio would be 5th gear ratio times rear axle ratio.

[JM 35 Sedan]

Based on my personal experience running different gear ratios (4.11, 3.78, & 3.54) and tire sizes (6.00x16 & 7.50x16) on my '35 fordor with a basically stock 21 stud engine bored 0.030" over and slightly higher compression, I'm thinking with your built engine, & 5 speed transmission, you would do fine with 3.54 R&P gears and your existing 6.50 tires, or possibly 7.00's.

[blucar]

If the transmission in the '37 is a 5 spd, is it an OD version, or is it direct. If it is an OD 5spd then re-gearing it to a higher ratio and/or increasing the tire size might not be a good idea. I know several guys that have put OD trans in their vehicles with no regard for the rear axle ratio, which was in the 3.08 range, typical for a late '70's rear axle. The vehicles can't be driven in OD at speeds below 7o mph.
Is the actual rpm's the engine is turning is known, if not they should be. A modern vehicle with an OD type of trans will generally be 3.42/3.73 with 28" tires. The RPM's at 70 mph will be in the 2,100 range.
My '36 Ford has a well built 59AB, trans is 28 tooth 46-48 Merc column shift, rear end is a 46-48 Ford Columbia with 3.78 gearing, tires 600x16.. The car runs very well on the open road at 65+ in OD. Out of OD the car is very fast, use to street race it on a regular basis when I was younger.

[kiwitony]

Hi Guys, The gearbox is overdriven in 5th at .78. The 3.78 diff is a torque tube so would need converting to open drive. A higher ratio diff would do what I want, but is a lot of work to change over. A couple of new bigger rear tires is a twenty minute job at the tire shop and probably cheaper. I have enough torque to run around in 5th at anything over 30mph so am looking at a more relaxed cruise at the 60mph range. Thanks again. Cheers Tony.

[JSeery]

Run the numbers and see how they compare, that's about as simple as it gets.

RPM = (MPH x Gear Ratio x 336) / Tire Dia

MPH = (RPM x Tire Dia) / (Gear Ratio x 336)

Pick a mph and play with the numbers to see what you get.

Example (if I have the tire dia correct!)

(60 x 4.11 x 336) / 29.4 = 2818 RPM

(60 x 3.78 x 336) / 29.4 = 2592 RPM

Your actual final ratio would be OD x Rear Gear Ratio. So,

.78 x 4.11 = 3.21 & .78 x 3.78 = 2.95

So using final drive numbers

(60 x 3.21 x 336) / 29.4 = 2201 RPM

(60 x 2.95 x 336) / 29.4 = 2023 RPM

Now do you really think it is worth all that effort for 200 RPM?