chstitans42

So I am trying to fix my 400 auto trans from leaking in my 1973 roadster, and have narrowed down the transmission leak to the area where the speedo cable joins up with the trans. Is there some kind of gasket that i can buy to fix this? or is the problem with the cable no seating all the way?? Any help is appreciated!

Easy Mike

There is an o-ring on the sleeve where it installs in the tranny.

moosie982

Dunno if a 400 is like a T-10 , but I had a leak from the fitting (Bullet) that the cable screws to, replaced the o-ring, the seal where the driven gear rides and it still leaked. The fitting was worn internally by the driven speedo gear, it was readily apparent when it was out but not so much if you looked @ it still on the trans. Good Luck, Peace,,, moosie

chstitans42

O ring on the cable or in the round metal part where the cable attaches?

mds3013

Hey Ben. There is an o-ring on the outside diameter of the aluminum plug that inserts into the transmission. There is a small shaft seal, kinda like a wheel bearing seal only without any steel, inside the aluminum plug that seals the speedo driven gear shaft. I am betting it is the small shaft seal. There is no seal at the threaded part of the plug where the cable attaches. When you remove the plug be sure not to drop the driven gear into the trans.. mike...

chstitans42

Hmmm can this be bought at an auto parts store or is it an online corvette specific vendor part??? Any one have any pics or a step by step to demonstrate the fix?
Thanks!

mds3013

Any parts store should have them or be able to get them. My guy gets me ATP brand trans. parts. Call me and I will tell you how I did mine. mike...

jesse10886

This is what is leaking





The black Oring is gone needs to be replaced the speedo cable goes inside the blue piece and the cable cover threads over the outside large threads. BE CAREFUL BE CAREFUL. BE CAREFUL not to push the plastic speed gear into the trans while doing this o ring replacement as it will be a bitch to get or back out

jesse10886

This is the actual speedo gear it will fall out easily

jesse10886

Only real difference will be that on the th400 the fitting is the same but the actual plastic gear is MUCH bigger in diameter the stem is the same but the gear is larger

JimT

I seem to remember that the nylon speedo gear (cable end) comes in two shaft sizes depending on the number of teeth required, thus there are two sizes of housings..
Determine your gear size - number of teeth - what you have and check the requirements for your situation.
I think the number of teeth (40 or less) requires one speedo cable housing, 41 teeth or more requires another. Please verify this. This could be your leak!
The speedo cable gear teeth count is dependent on the equipped transmission gear for speedo accuracy. My tranny was set up for another car/speedometer and I had to search for the correct speedo gear and housing for a true reading.
Good luck!

bpassmore

Assuming the speedo is correct and you only have a leak, Mike is correct. My experience with these speedo adapters and gears is the gear and adapter wear allowing the gear to fit sloppy so the internal seal (the small one) allows oil to seep out and leak at the junction of the speedo cable. Check this, if ok replace the outer O ring and internal seal. if not replace the adapter, gear and seals.
I have seen an O ring put in the speedo cable nut to stop the leak, but this allows the fluid after a time to migrate to the speedo head.

sjohnson2615

I had the same leak and the o ring actually wore down the shaft a bit where it fit.The fix was to put a second o ring so it rides on a fresh part of the shaft.
There is plenty of room for 2 o rings without interfering with anything else.
This did the trick and stopped the leak.

TimAT

If you look at the cable end of the adapter, you can see a round wire clip with a blue/gray seal under it. Pop the round clip and pull that seal. That's the one that rides on the shaft of the speedo driven gear. Check the shaft of the gear for wear, replace that seal, (2 will fit as noted above) then put it all back together.

jesse10886

^ He is correct and the blue speedo gear in my picture was not correct it made my car off by 5mph I replaced with with the red 37 tooth gear an now it reads true different rear gearing will determine the amount of teeth and the amount of teeth will determine the size of your shaft sizing an cable end

chstitans42

Thanks for the tips guys. Ill be sure to let you guy know how it all goes when I have the time to fix it all. Does anyone know what to ask for when at the autoparts store? Or should I just buy the generic o ring kit?

sjohnson2615

I got mine from Napa and they looked up turbo 400 and the o rings are listed.

chstitans42

Do you think o'reilly's would have it?