My turbo trans speedometer connection at the trans is leaking trans fluid 

When replacing the seal there  — I read in the library I will need to get  that from Jason
 What will be the issue dealing with the trans fluid leaking out when  replacing that seal ?

Do I have to drop the oil pan and remove the trans fluid  to do that ?  
I did take a 1/4 to half turn on the connection there and hoping that may solve the leak 


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I've done this repair many times on newer TH 400's, so my info comes from that, the 64 is a rare duck, so i don't know if it is even the same.

On the 65-up trans, the speedo driven gear is nylon plastic, and the seal cuts a groove in it.  This must be changed or the trans will still leak.  The gear has to be matched by tooth count, or the speedo will read incorrectly.  
If you let the transmission sit before doing the repair, some fluid will definitely come out, but not all of it, just what is an inch or so over the pan.  say a pint or so tops.  The pan will hold the rest of the fluid and won't need to come off.

the seals for this (on a 66 TH400) are included in any over haul kit for a TH400.  again, i've learned that the parts may not be shared, so go fatsco, they have dealt with this trans for years.

When I installed the previously rebuilt 1964 Turbo Hydra-Matic transmission in my 64 CDV, I only remember having to replace that outer O-Ring. See yellow arrow in pic below. From memory I think there is a small internal o-ring or seal but don't remember having to change it out and need to look at one close up again. Here is the O-ring I changed ... really had nothing to do with the nylon gears:


My leak looks like it is the seal for the speedo cable —that would be the seal  in front of the one with the yellow arrow in the picture on the open treads that are showing 

Mark   Thank you 


On later models, it has a small lip seal, just like your fave, the main seal....
it looks like the same assembly.  The gears are color coded by the # of teeth for easy selection.   I can't assume they started the color coding in 64, but maybe.  count the teeth to be sure. 
at least do yourself a favor and take it apart.  if there is a groove in the shaft, replace it.  they are very available in almost all numbers of teeth.  use vaseline as a prelube, if you don't have any transjel or assemblee goo on hand.  vaseline has no body, like lithium or aluminum grease, it will dissolve completely.  it's what you use on transmissions.  and other things i guess.

Appreciate your thoughts and experience

 Jason  Love your photo with the arrows —Thanks 

So the part in your picture has a second seal on the shaft that is not shown in the photo

That seal is causing the leaking and possibly a worn shaft issue and the speedo cable will leak from its connection until the internal seal is repaired or the assembly replaced with the correct gear for the rear end ratio 

Will contact Fatsco and see what they have to say 

From my discussion with Fatsco  transmission parts they confirmed Marks thoughts on the speedo gear shaft being scored by the old seal and will need a  new seal and speedo gear ( with shaft  attached ) for replacement or the area will continue to leak 

Looks like I am getting away on the easy side of this trans  leak repair that is always a blessing of some kind 

Thanks for the help that Jason and Mark provided  for me to understand what I was looking at —-that is priceless ! ( with pictures and arrows — to boot !! ) 

You GUY’s are the best !!! 


no need to drop the oil pan 

just completed the trans speedometer gear seal replacement of both seals and the plastic gear with its shaft 

both the seal and shaft were worn down in my case as the step down on the plastic gear shaft was greater than that of the new shaft were the seal rides ( worn ) 

mine was a 40 tooth gear that was stamped on the one coming out which means I have a 3.21 rear end ratio so the speedo records the correct speed for my 64 convert ( need to count the teeth for replacement )

the small seal the shaft rides on is removed from the front of the housing and has a small metal O ring that keeps it in place  

seal pops  in and out the front of the housing 

both the old and and new shafts were black plastic but the new one did not have the number 40 printed on it and the new shaft was neuraled ( lines cut in shaft ) to be feeding some trans fluid towards the seal and old one was not 

Applied Vaseline to all moving parts and around the larger outer O ring for an easy slide in ( per Mark Anderson )

All parts came from Fatsco who told me there would be no issue with the gear properly messing correctly when installed 

Part cost was $ 40 shipped from NJ to FL ( parts 20 shipping 20 )

Just tightening the speedo cable nut might give you the illusion you can stop the leak there —but that is not the case at all as you have a seal leaking in front of the speedo cables nut 

you must remove the assembly and replace the seal  In front of the speedo cables nut to stop the leaking fluid  ( per Mark Anderson )

I loosened  the speedo cable nut but left it attached so I could pull the assembly out more easily with that attached and then remove the speedo cable from the housing 

The housing came out easily but the plastic gear and shaft stayed in the channel until I fished it out ( an UHOH moment ) 

going back in you have to have the face of the housing in the right location turning the housing from the cable nut 

There is a slightly raised surface — the hold down clamp needs to fit into and on top of — that allows the hold down clamp to apply a kind old sideways hold down pressure to the housing ( bolt is 9/16 ) 

you will only be loosing a bit over a quart of trans fluid when removing the housing but I did have my car jacked up  high from the driver side which is the side the fluid would run out of reducing the loss of fluid 

This is a very easy fix —after the heart attack one has seeing trans fluid suddenly in the drain pan

To find  the leaks location  I clean the drip pan put it back under the car to see were the drip was originating from 
Replacing the now missing trans fluid  ( AC Delco Delco Dexron VI ) and check level with car at operating temp

note - dipstick is in Pints 

This is the first and only issue ( knock on wood ) that I have ever had with my Turbo 400 since the car was new 

this trans is known for the fact it is Bull - it Poof  very very reliable design and a desired trans those reasons 

A big part of the reason I chose to go with the 64  convert model over the 63 myself 

Back in Action just in time to enjoy the crazy good convertible weather here in FL we start to get after Halloween for 6 months 




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