Mine are 5/8-11 NC

 

I know this is a really old topic but I've been offered two t98s but owner says they have 1 3/8 input shafts. My 52 Mercury M3 has an 8ba and the non synchronized 4 speed.
I can find no reference to t98s with a larger shaft and he says they are from larger trucks with the 6 cylinder in them.
I've not pulled mine yet as I'm using the truck and he's 20 hours away. Assuming mine is 1 1/8 input can I have the shaft ground down, resplined? Will a T5 match my bellhousing? What is the input shaft size on a T5?
Speedway says the T98 is 1 1/16 but I think they are mistaken or they may be referring to the T5 input.
Any insite is appreciated as I'd really like to get rid of the crash box.
Oh, and yes I'm aware of the rear end issues so we don't need to go done that path.

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The larger shaft on the t98 is no problem ,get the 11'' clutch disc and pressure plate and your good to go ,pilot bearing diameter is the same. If your flywheel is not drilled for the 11'' there are shops that can do that too. Alan

 

If you plan to retain the flathead, then the T98 from a flathead truck is only what you can use. The bellhousing-to-T98 bolt pattern is cast into the T98 case, which is different than all T98 cases after (gonna say) 1952. Visually compare the two side by side, and you can see it.

As for the T5, there are conversion kits to use one behind the flathead, and ultimately easier to install than an original T98 in anything other than an F4-F6, due to frame heights and crossmembers.

I added a couple pics to show a flathead T98 Notice the bolts are only accessible through the inside of the bellhousing.

 

You can see my crash box has the bellhousing cast with the trans case. So I would need trans and that bellhousing half?

 

Your crash box is a Warner T9 or T8 transmission. The pre world war two transmissions were one piece castings like yours, post war in the USA got the half bell bolted to the crash box case. The T98 is the same casting half bell as the crash box half bell, but the hole where the transmission input bearing retainer centers is larger diameter in the T98 half bell. A good machine shop could bore out a crash box half bell for you if you found a T98 that was missing the half bell (hogs head).

 

the bell half mounted directly to the T98 is needed. The hogshead is used from what engine it was mated to. In my case, it's the hogshead from a 254CID. A V8 hogshead may very well need machining like 38coupe said. Personally, I have not tried fitting a V8 hogshead to it yet.