Choosing the right transmission gear ratios

[pippinmader]

looking for some advice. I am working on swapping the transmission on my 1950 ford f-1 pickup. This was my first car that I drove to high school. It came stock with a BW T8 spur gear non-synchro transmission. It requires double clutching in all gears which is important because the brakes suck so it is nice to be able to down shift to slow down. Also has a top comfortable cruising speed of 55 mph. So working on making it more fun to drive has been on my wish list for a while. My goals were: As much synchromesh as possible, good cruising speed, look as stock as possible.
Although I considered a lot of transmission options (from T5, old school BW car style overdrive, to ford truck RTS, T18, T19) I ended up choosing a T19. The T-19 is the direct descendent of the T8 and so it looks the same where it comes up through the floor, it also has synchro in all 4 gears. It does have three issues: 1. The input shaft diameter and length is different. 2. It is about 6 inches longer. 3. It does not have overdrive.

The solutions were:
1. Find a adaptor "hogs head" that converts to the truck style bell housing and used a mustang 10" clutch to make the transmission bolt up to the engine.


2. The stock cross member only allows for a transmission that is 11 inches long and also holds the brake and clutch peddle and master cylinder I chose to add a second cross member behind the original one and cut the stock one to make it all work.

3. This is where things get complicated. The truck originally came with 3.73 gears in a Dana 41 axle. I switched it to a 1952 truck axle which is a dana 44 so I can actually get parts and change the rear gear ratio to 3.08. All the engine cares about is combined gear ratio (rear end ratio x individual gear ratios). The gear change (3.08/3.73) has the same effect as a .82 overdrive.



I found and bought all the parts had the rear end re-geared (with a 19 spline LSD), did all the fab work, had the driveline cut down, found a speedometer cable (one from a bronco fit perfectly!) and got it running again yesterday.



Problems solved! Right?

Well sort of, the T19 I used has a kind of weird gear ratios that make for a really big jump from 3rd to 4th:

[pippinmader]

So this is where I am looking for input. They make T19 transmissions with three different gear ratio sets, I keep track of them based on their first gear ratio which are 6.6 or so, 5.1 (which is the one I used) and 4.0 (used in diesel pickups). I ended up collecting both a 5.1 and 4.0 version and used the 5.1 one. I wanted some of that granny low truck feel to be authentic but as mentioned above there is a really big jump from 3rd to 4th. The engine is only happy spinning to 3500 or so and only likes to cruise at 2500 or so. So I crunched the numbers two ways and included the stock transmission option as well as a few other transmissions that I know are liked (T5 and BW car style overdrive):

First based on MPH at 2500 rpms

My concern here is that if I am climbing a hill and need to downshift I can't until my speed falls to around 40 mph, it doesn't give me much flexibility.


Second looking at RMP after each shift (when shifting out of the previous gear at 2500)

IMO in an idea situation shift RPM should increase as you go through the gears because friction (linear) and wind resistance (exponential) increases with speed. Do any of you have experience with this? Any advise? like I said, currently has the 5.1 T19 in there but considering switching to the 4.0 T19, thoughts?

[Lars]

Memories... My first experience driving a pickup was in my friend's '49 F1 with a BW T8. Eventually he swapped the flathead 6 for a flathead V8, a fun upgrade.

Speaking to your conundrum, I'd say get over the granny low and use the 4.0 diesel T19. With the limited power of even the V8 (assuming that's what you have) the 3rd to 4th split is the most important and it looks from the graphs to have the smallest split. This is one of the situations where a broad flat torque curve is your friend.

[pippinmader]

I know you are right Lars! It does have a flathead v8 with RV cam, mercury stroker crank, larger carb so it is probably at 150 hp or so. And the torque curve is probably about the same as a diesel. It does also have a cracked block between the cylinder and the exhaust valve on one cylinder that is the result of a race with a second gen Cummins in 1996 or so (I won!).

[Lars]

OMG. Thanks for the photo! Yet more memories... Would love to have one of those...