TH-350 Speedometer Plug Size
 

What's the best way to plug the speedometer cable hole on a TH-350? Use an old cable setup or what size plug?

Re: TH-350 Speedometer Plug Size
 

There is no fractional fit for the drive, which is about 2.075.You have to go to 2.100 and run it on a belt sander.
I usually use a rubber expandable plug ..Just install it dry. I mean brake clean dry!

Re: TH-350 Speedometer Plug Size
 

Mark

I knew you would know the diameter but where the hell would I find that plug? I'm going to the junk yard tomorrow to finish stripping a 305 short block. What would I need from a TH-350 to plug the hole properly?

Re: TH-350 Speedometer Plug Size
 

If you have an old head I would just use it...has an o-ring if I remember right.

Re: TH-350 Speedometer Plug Size
 

how about a metric freeze plug?
I'm assuming it's the large speedo adapter rather than the small "bullet"....

Re: TH-350 Speedometer Plug Size
 

Depending on the size you might consider a boat/livewell type expanding plug.

Re: TH-350 Speedometer Plug Size
 

Sonnax Transmission Parts

Part # 35922-01K. TH350 Speedometer Hole Plug. During high performance rebuilds, the speedometer gear is often removed and replaced by a freeze plug. However, in addition to being used for driving the speedometer, the gear is also critical to lubricating the rear output shaft bushing. This new speedo plug supports the speedometer gear and allows lube to flow as the original design intended. The gear shaft has to be cut to 1.320" long. Cost $24.00

http://www.transmissioncenter.net/35922-01K.jpg

http://www.transmissioncenter.net/So...uper_Store.htm

Re: TH-350 Speedometer Plug Size
 

That being the case then the original stock head would seem to be the way to go after all. ;)

Re: TH-350 Speedometer Plug Size
 

I will need solid engineering proof about the statement "helps lube rear bushing"

Just consider the units in service with speedo adapter hole plugged yet they experience normal rear bushing service life.

Re: TH-350 Speedometer Plug Size
 

The spinning governor provided the needed lube for the rear bushing. This was true for the 700-R4 also. When the transmissions were redesigned to the "e" versions, a hole was drilled that pee'd fluid back to lube the bushing.

Re: TH-350 Speedometer Plug Size
 

I believe it is safe to assume if one is plugging the speedo drive hole the trans is seeing limited service on the street. That being said the impact of the deletion of said gear will have minimal impact on the lifespan of the transmission or any of it's components.

Re: TH-350 Speedometer Plug Size
 

Agreed..Plus where does the fluid go to on a drag car? ;-)

Re: TH-350 Speedometer Plug Size
 

On the track in some cases...:p

Re: TH-350 Speedometer Plug Size
 

governor is one thing but the speedo gear is another...aside from always leaking and the speedo gear wearing out at the seal,how does it do anything else?

Re: TH-350 Speedometer Plug Size
 

Interesting discussion! I found a 87' Caprice type thing in the yard today that the same diameter speedo plug. I took that and cut the speedo cable for the screw on part and put it on the trans. So far so good. First race this weekend. Alignment shop Tuesday. Will sort thru everything that was said here and re-think what I did but I needed the trans to stop leaking right now. Thanks guys.

Re: TH-350 Speedometer Plug Size
 

Good to go. ;)