VCCA Home Forums TECHNICAL - 1945 AND NEWER 1965-1970 68 speedo cable leak

I'm buying a 68 Chevelle SS396 (325 hp). It's been very well restored. It's got a TH400 transmission. There's a little fluid leaking at the speedometer cable connection. Can you guys give me some advice on what's it going to take to fix it?

Thanks!

Happy Motoring!

That was a problem back then. If I remember correctly there is a seal inside of the fitting the screws into the trans. case that has to be replaced....or the complete fitting.

The nylon driven speedo gear shaft wears inside the metal sleeve.This sleeve was made from aluminum on some GM trans of the 65-72 era.My Powerglide was leaking here like yours does.You need to get a new nylon driven gear,a new black o-ring seal and possibly the driven gear housing like in the picture I linked here in this message.If your Turbo 400 has the steel driven gear housing then just do the o-ring and nylon gear.If you have the aluminum gear housing do all three.All three can be found on ebay. Jim

And be very sure of the driven gear color.My nylon driven gear in the pic is not red! It is brown,but over time/temperature and exposure to trans fluid thay do take on a different color look.
Hope this helps. Jim

I had a new 1968 Chevelle SS 396 while I was in college. I left It stock, but changed the wheels and tires. This caused the speedo to be wrong. I remember experimenting with different color gears ( different ratios ) to correct the speedometer reading. They came in several ratios ( colors ). This may have been done on yours also if it has other than stock wheels and tire sizes.
Richard

The cure that GM made was the lip seal in the fitting.

As always, you Chatter guys know your stuff. I've received major help restoring my '31 Special Sedan from those guys. Now, you are helping me with my new '68.

Had the same, common problem on my Chevy. If the speedo is reading correctly and the nylon gear is in good shape, you just need to replace the rubber O-ring. Go to a Ace hardware store in your area and they have a huge selection of rings...for about $1.00 each. Choose one that fits snug in the groove, but a little bigger 'round than your old one. Put it on by rolling it over the housing, spray a little WD40 on it and gently slip in back into the tranny. Takes about 15 minutes to fix. Bobalouie

When the fluid is coming up the inside of the cable and leaking under the dash it is NOT the O ring on the outside of the fitting..It is passing the stem of the nylon gear.

Be careful when buying standard O-rings from hardware store.Many are metric sized and not SAE like we need for our old Chev's.
Just went through this with a trans dipstick tube gasket.

bought some at hardware store......all still seeped.

Finally ordered a set from my local NAPA in SAE....no leak.

Jim