67 DeVille/ TH 400 speedometer seal

[ccd3]

Hi Folks,

This weekend I'm going to replace the o-rings in my leaky speedometer seal. Looks straight forward to me- anything I should watch out for? Someone told me the internal seal might be encased in a metal shroud? Sound right? The o-ring I bought is just rubber... does it matter?

Thanks for the help,
Carey King

[bcroe]

You have a large O ring in the gear support insert, but I doubt that
is causing a leak.  The plastic gear that drives the speedometer cable
has a press in seal riding on it.  Unfortunately the plastic can get a
groove worn to where the seal is no longer effective.  Solutions might
be a new gear, or adding another seal moved over enough to miss
the groove. 

TH400s have quite a list of places to develop small leaks. 
good luck, Bruce Roe

[ccd3]

Thanks Bruce- hopefully there will be one less spot on my garage floor... I was told if a TH 400 isn't leaking, it's out of fluid....

[bcroe]

Thanks Bruce- hopefully there will be one less spot on my
garage floor... I was told if a TH 400 isn't leaking, it's out of fluid....

That is about right, I have spent a lot of effort fixing small leaks.  I have a
switch pitch Cad trans like yours in my Olds, wonderful trans with electronic
pitch controller.  When you get to the NEXT leak, let us know for info. 
Meantime I have drip pans or sheets of cardboard to keep the floor clean. 

Bruce Roe

[savemy67]

Hello Carey,

I recently rebuilt my '67's TH400, and I took hundreds of photos.  Unfortunately, not one of the photos includes the speedometer assembly.  Fortunately, I have an original shop manual which helps me recall things that I forget.  Funny, some aspects of my transmission rebuild I can remember distinctly.  Other aspects I can't recall much detail - probably because those aspects were very straightforward and not troublesome.

The Speedometer drive gear is on the transmission output shaft, and is made of steel.  The speedometer driven gear is what can be removed from the side of the transmission case.  The driven gear is made of plastic.  If your '67 is original, and does not have climate control, the differential ratio is 2.94:1 and the speedometer driven gear is blue.  If your car has climate control., the differential ratio is 3.21:1 and the speedometer driven gear is yellow.  The blue gear has 38 teeth.  The yellow gear has 41 teeth.

There are two "sleeve" sizes.  The sleeve is the part that holds the speedometer driven gear, has the o-ring around its circumference, and is threaded to accept the knurled speedometer cable fitting.  Sleeves have numbers on them (facing outboard).  A sleeve for a blue gear will have numbers 36, 37, 38, and 39 molded on the sleeve.  A sleeve for a yellow gear will have numbers 40, 41, 42, and 43.  They are not interchangeable.

Sleeve assemblies have two seals - the o-ring which goes on the circumference of the sleeve, and a lip seal which goes inside the sleeve and which is retained by a C-wire retainer.  If you are sure your speedometer assembly is leaking, check to see that it is correct for your car using the above information.  Second, get a new lip seal as well as a new o-ring.  Be sure to clean the area around the sleeve before removal.  A little petroleum jelly (Vaseline) - not grease - will help when re-installing the sleeve with a new o-ring.

Respectfully submitted,
Christopher Winter