The P.O. told me that my truck would barely hit 60 going downhill with a tail wind. Can I swap (if I can find one!) a 51 5 speed tranny into my 51 F5 Marmon-Herrington?

 

I'm not sure if changing just the transmission will do much of anything. It's the gear ration in the rearend. With the MH 4x4 you'll have to change the front and rearend. If your going to do that, you may as well find a more modern complete running gears and just drop the body on it.
These were built for power not speed.

 

The rig is too valuable to start modifying. I'm not looking to cruise at 80 just 60. Depending on the O.D. ratio it and if it would fit it could be exactly what I'm looking for. Anybody have experience with the 5 speed? What is the O.D. ratio?

 

I'd bet you'd have space concerns, Rab. I'd bet they are bigger/longer trannies. On a normal truck a guy could maybe just shorten the drive shaft to compensate, but on yours the transfer case mount dictates the space available. If yours is like mine, the connector shaft between the tranny and the transfer case is already pretty short. I guess you could move the transfer case back in the frame and make it work, but that causes secondary changes like moving the transfer case linkage back too. If you're wanting to keep it stock, that would be a problem.

This is why I had Chuck change my gear sets from the 4.86 to the 4.11 while he had them apart. Whether new gear sets would be available for your Timkens I don't know. You might ask Chuck. But be aware it's not cheap.

 

I think your right Stu. I think the 5 speeds were only available on F7, F8's and were dimensionally bigger. But thought I'd ask.

 

Yeah, the big trucks used Clark 5 speed O/Ds according to the Chassis Manual. There was also a New Process 5 speed O/D used on the medium duties from 53-55 but I know nothing beyond that. It just stands to reason that more stuff packed into the box will make the box bigger.

 

me and my dad tore apart a 56 f600 that had a 5 speed. my dad said it was a clark. kinda strange in that 1st is where 5th would usually be. i can look again at it, it was one of the few things we kept.

 

Initially the Bonus Built F7 came with a Clark 5th over and the F8 came with a 5 direct, and you could get the 5th over as an option. As to trans size and bolt mount pattern of these I do not have info available.

On the NP540 - 541's, I read and saved somewhere that the case is similar or same as the NP435 4 spd, which was in about everything.

I have run across pics of F7's with a 5th over and the pattern displayed on the dash. I also have included a picture of the **** from my NP541 with 5th over (.85) and it has a like shift pattern - 5th middle and up. My NP541 came out of a '62 B750 with a 332 Y-block.

 

yeah it was probably closer to that, i can look on saturday. good chance it wasn't stock, it had a ford bellhousing, but also had an adaptor between it and the chebbie 283 it was bolted to.

 

I do know that the 5 speed transmissions are bigger all the way around versus the 4 speed out of the F4-F6. I just swapped motors on a 52 F6 to the 337 Flathead with the 5 speed transmission over from the 239 flathead and 4 speed.

I had originally planned on using the 4 speed out of the F6 but the bellhousing bolt pattern for the transmission is different but the big difference is the imput shaft on the 4 speeds was why to short. The 5 speeds behind the 337 motor have a really long input shaft. All this could have been modified to fit but it was easier to just use the 5 speed that was suppose to go behind the motor.

Now I don't know if they changed after 1952 or not. All my trucks, 2- F4's and 2-F6's are the 1950-1952 YOM. The 5 speed transmissions are about one third bigger than the smaller 4 speed. The 5 speed also need supported with another cross member. There are pictures in my gallery and I could send more pictures of a 5 speed transmission vs a 4 speed if any one is interested.

Also with the 5 speed you may not pick up the speed you think you will. On mine the 5 speed really slowed the truck down. Now I haven't had it on the road and into high gear yet but driving the truck down the back road to see how things worked after the switch, the truck has slowed down a lot. I have the two speed rearend and without shifting to the high side, reverse, first, second and third are really really slow versus what it was before the swap out of motor and transmission.

 

Roger~
Any idea which 5 spd you have behind your 337, direct or overdrive? By being in the lower gears and not getting into high gear yet, I'm guessing you're feeling the difference in the different gear ratios. Here are the gear ratios for the various period transmissions in question:

Trans ratios:
Clark 205VO 5 spd o/d . . . 6.06, 3.50, 1.80, 1.00, .799, R 6.0
Clark 205V 5 spd direct . . 7.58, 4.38, 2.40, 1.48, 1.00, R 7.51
Borg Warn T-98 4spd . . . . . . . . 6.40, 3.09, 1.69, 1.0, R 7.82
Borg Warn T-9 4spd . . . . . . . . . 6.40, 3.09, 1.69, 1.0, R 7.82

 

I have no idea what transmission I have in mine. There really isn't any numbers other than casting numbers. There is either a W over a W or an M over an M, depending on how you look at it, thats on the top of the transmission where it bolts to the bellhousing. Once I figure out were 4th and 5th gear will tell me at least if its a direct drive or overdrive. 4th and 5th shift paterns are opposite of one another for direct and overdrives.

Right now the truck is tucked away in the garage preparing for the long north east Ohio winter. I'll get the F6 rolling in the spring and on the road and know more then.

 

Sorry to dig this thread up but My Bus has the same pattern and I've been having a tough time identifying the trans. It's a 56 Blue Bird. Repowered at some point with a 390