Overdrive Possibilities...

[maineSS]

Started looking at OD possibilities and decided to share what I've found- be interesting to see if anyone's tried them.

Transmissions:

NP 435- According to the January 91 issue of 4 Wheeler, a company in Colorado offered a 5-speed conversion using "mixed and matched 2 ton parts" that offered 5th direct or a .80 OD. This would be a 20% OD, equivalent to 4.66:1 diff gear. Interesting thread at http://classicbroncos.com/forums/arc...p/t-96958.html . Kit was not cheap- $1850, company no longer exists. PTO is on passenger side of tranny.

NP 540- "O" version had a .82 OD, 18%, equal to a 4.78:1 diff. Very, very rare in OD, parts not stocked. PTO on both sides, but too wide to fit with underfloor brake bracket on PW. Don't know if it would fit with a hanging pedal conversion.

Dennan/Laycock Auxiliary- Electrically switched, .78 OD, 22%, equal to 4.54:1 diff gear. Mounts behind transfer case, requires shortened driveshaft. Will be instantly destroyed if operated in reverse, should not be operated in lower gears or in T-case low range. In OEM use (Volvo, Jaguar, etc.) it was set up with circuitry to allow operation in high gear only, and was cut out in reverse.

Gearing- 4.89:1 diff gears will give 16% OD. Required front and rear, as the difference between 4.89 and 5.83 exceeds the 2% allowance. When combined with the Dennan, a .62 OD ratio (38%) results, equal to a 3.6:1 diff gear. Need high end torque for this combo.

Others- The Spicer transmission used in the 6x6 can be set up for OD, and has been fitted to some PW's. It's bulky, and requires crossmember mods, don't know what OD ratio is, or if you can mechanically drive a winch after the conversion. If you go with a modern engine, then more modern stick shifts and auto's are possible, but that's getting beyond the parameters of my search...

[Dozerman51]

How do you figure the 2% differential in gearing using a 4.10 ratio and a 4.30 ratio. Is there a 2% or less differential between these ratio's. Thanks for any help.

[Charles Talbert]

Started looking at OD possibilities and decided to share what I've found- be interesting to see if anyone's tried them.

Transmissions:

NP 435- According to the January 91 issue of 4 Wheeler, a company in Colorado offered a 5-speed conversion using "mixed and matched 2 ton parts" that offered 5th direct or a .80 OD. This would be a 20% OD, equivalent to 4.66:1 diff gear. Interesting thread at http://classicbroncos.com/forums/arc...p/t-96958.html . Kit was not cheap- $1850, company no longer exists. PTO is on passenger side of tranny.

NP 540- "O" version had a .82 OD, 18%, equal to a 4.78:1 diff. Very, very rare in OD, parts not stocked. PTO on both sides, but too wide to fit with underfloor brake bracket on PW. Don't know if it would fit with a hanging pedal conversion.

Dennan/Laycock Auxiliary- Electrically switched, .78 OD, 22%, equal to 4.54:1 diff gear. Mounts behind transfer case, requires shortened driveshaft. Will be instantly destroyed if operated in reverse, should not be operated in lower gears or in T-case low range. In OEM use (Volvo, Jaguar, etc.) it was set up with circuitry to allow operation in high gear only, and was cut out in reverse.

Gearing- 4.89:1 diff gears will give 16% OD. Required front and rear, as the difference between 4.89 and 5.83 exceeds the 2% allowance. When combined with the Dennan, a .62 OD ratio (38%) results, equal to a 3.6:1 diff gear. Need high end torque for this combo.

Others- The Spicer transmission used in the 6x6 can be set up for OD, and has been fitted to some PW's. It's bulky, and requires crossmember mods, don't know what OD ratio is, or if you can mechanically drive a winch after the conversion. If you go with a modern engine, then more modern stick shifts and auto's are possible, but that's getting beyond the parameters of my search...

Correction: The Spicer 5-speed OD does not require crossmember mods, and can be fitted with a .69 overdrive. A winch can also be PTO driven.

[maineSS]

Dozer- you can do it two different ways. The first is to multiply one of the ratios by 2%- i.e. 4.10 x .02 = .082. Add the result to find a higher gear- 4.10 + .082 = 4.18, subtract to find a lower gear- 4.10 - .082 = 4.01. Or, divide the lesser of your two ratios by the greater -4.10/4.30, subtract the answer from 1.0 (1.0-.953), and that's the per cent difference- .046 = 4.6%.

Charles, was the Spicer used in later model 6X6's that didn't use the flathead? I have about the thickness of a sheet of paper between the brake bracket and the PTO on my '49, if the bracket were removed you'd gain another 4" width. Have you ever fit the Spicer behind the 230/251?

[Charles Talbert]

Spicers are used behind both the OA331 gold comet gasser and the later multifuel engines in the 6x6 trucks. The OD version was used only behind the multifuel, the ones used in gassers were a 5th gear direct. Same basic trans though.

I wouldn't waste my time putting it behind a 230-251, not enough vitamins under the hood to support the OD. We have used many behind Cummins.

[danlen]

Charles, a question about a Spicer swap

Charles, you said the 230 engine doesn't have the guts for an overdrive, fair enough, My situation is that the trans is bad on my WC-52. I will eventually do a diesel swap, perhaps the QSB 4.5, but can I bang a Spicer 3053 in there until I do? Any bell housing or other issues?

Many thanks in advance,
Daniel Leonard

[danlen]

other ideas

Or a nv4500?

[Charles Talbert]

Charles, you said the 230 engine doesn't have the guts for an overdrive, fair enough, My situation is that the trans is bad on my WC-52. I will eventually do a diesel swap, perhaps the QSB 4.5, but can I bang a Spicer 3053 in there until I do? Any bell housing or other issues?

Many thanks in advance,
Daniel Leonard

Bottom line, you can do anything virtually with enough time and money invested.

However, the same issue exist, not enough vitamins to support the overdrive 5th gear in a 230, so definitely not worth the trouble when it will not perform well anyway.