RTS 4 speed OD trans info needed

[Jack 34pu]

I’m considering an RTS 4 speed OD behind a Merc flathead. I found a chart someone posted that indicates that the 26% OD is only found on the mid ‘80’s F150 with 302V8. It also noted that the 300 6cyl had the 37% and 41% OD. I’m interested in the 26% as most seem to indicate that it is the best combo with a 4:11 rear. So, is the 26% only found behind the 302 V8?

 

[flatjack9]

With 4.11 gears, I would think you would want the 37% OD. That's what I have in my 39 with 3.70 gears. With 225R15s I'm going 73 mph at 2500 rpm.

 

[Ross F-1]

I've heard a lot of guys in cars who run super-low OD ratios, all I can say is even fat fendered cars must be a lot slipperier than the trucks. Either that or flatheads pick up a lot of power at lower altitudes. I had a 3.25 ratio in my truck (9") and it was a struggle getting around corners in 2nd, anything more than a small short hill and my speed was dropping fast.

I'm running a 3.50 axle now (stock trans) with 28" tires, and it's just about right. If I had an OD for flat ground it would be nice, or a normal (non-granny) 4-sp so I had a 3rd gear to hit, that would be nice, but the wind resistance above 55 is just enormous.

A 4.10 with 26% OD is right at 3.0, I can't imagine pulling a taller gear in a truck with any kind of hills.

BTW, Novak/Advance Adapters shows different ratios:

Gear Ratios

Truck
1st Gear 3.25:1
2nd Gear 1.92:1
3rd Gear 1.00:1
4th Gear 0.78:1
Reverse 3.25:1

Car
1st Gear 3.29:1
2nd Gear 1.84:1
3rd Gear 1.00:1
4th Gear 0.81:1
Reverse 3.25:1

http://www.advanceadapters.com/tech-vault/ford-tc-overdive-transmission/

 

[Bassman/NZ]

Jack34pu.... I have that same RTS, the 302 model. My rear is 3.78 and I'm running 31" tall tires. On the flat it works great, probably about 1900 rpms at 60mph (our speed limit here) but no tach so I'm guessing. New build, so have'nt tried any hills yet, but the 3rd gear (1:1) should be good for that. On the limited running I've done so far, just the awesome synchros alone make the swap worth while. I welded an early Ford shift lever to the F150 stub, so just looks like it's stock.

 

[Matt in Alameda]

Four-speed OD transmissions in Ford F150 4X4 trucks in the early 80's came with 3 engines...the 4.9 liter (6 cylinder) had a 0.71 OD ratio....the 5.0 liter V8 had a 0.78:1 OD ratio and the 5.8 liter had a 0.72:1 OD ratio. I suggest you use the 0.71 or 0.72 transmission........Matt in Alameda

 

[Ol' Ron]

Very interesting thread. Do you need an adapter, or just redrill the stock bell housing.. What kind of shift system do you need to run a column shift. This looks like a nice substitute for the T-5 in many applications. What years were thes trans available. The Michael OD behind a 276 flathead works very well ay 26% even around town.