A while back I installed new Speedhut gauges in my ‘72 Supreme. The speedometer is GPS, so I’m getting around to removing the cable. I like the idea of the billet delete plug. I have seen them advertised for a TH400 but not a TH350. The CSM states the 350 and 400 are not the same, but does anyone know if they are the same diameter, if so, would a 400 plug fit? If there’s no manufactured plug that will fit, has anyone had success going a different direction?

 

I believe a 3/4 or7/8 freeze plug fits the hole.

 

Freeze plugs were used to fill the holes on cars that used the front left wheel hub to drive the cable like 98's and 88's. I am not sure of the size of the plug though.

 

The 350 used two different size speedometer housings, I don't know if it was all but some, BOP tail housings used a 2 inch diameter housing and the chevrolet used a 7/8 housing. I don't know if chevy ever used the large housing, was told it was only used on BOP. If memory serves me correct the large 350 and the 400 are close in size, maybe the seller will tell you the diameter of the plug. As others have said I just use a freeze plug.

 

Actually, most of the full size cars used a trans case that didn't have the hole machined in the first place. Yes, sometimes you'll see a freeze plug, which works just fine. Simply measure the diameter of the hole and buy a freeze plug to match. No one will be able to admire a spendy "billet" plug.

 

^^^^^^^^This right here.
The last TH400 I had built came from a 88 and the hole wasn't there. It wasn't a big deal to have it machined, just added to the cost a bit. I'd never seen a hub driven speedo before that.

 

Thanks to everyone who replied. The freeze plug wins out. Haven’t measured mine yet, looks to be about 2”