So, I installed a TKO600 in my Swinger earlier this year, and I've been struggling with a persistent leak at the speedo cable entry into the tail shaft. First I thought it was a compromised o-ring, so I put a new one on. No good. I had a spare cable on hand, so I installed it, and it looked as if that may have fixed the problem, but after about 150km of highway driving, the leak re-appeared. So, tore it apart again, and found that there was gear fluid inside the cable jacket, and I'd almost bet that its leaking out where the jacket has been crimped onto the gear assembly. No techs I've spoken to at various Tremec dealers have been able to shed any light on this problem, so I'm just throwing it out here. Surely somebody here has a Tremec, maybe somebody here has seen this problem, or knows of somebody who has?

I've done plenty of Tremec swaps Mopar/Ford/GM, never seen/experienced any speedo cable leaks, who's supplying your cables? where both cables from the same vendor? is there a possibility your tremec is overfilled? do you have a vent on your Tremec?

First cable came in the kit supplied by Keisler. Ya, I bought this a while ago. The replacement cable was supplied from SST. The vent is happy, and I find it hard to believe a plugged vent would force a leak at the cable. I'd expect the rear seal would fail first, no? The box certainly isn't overfilled, it's topped up to the point where it's trickling past the threads of the fill plug.

I have no first hand experience with that brand and model tranny but I use to work in service stations back in the day when people would have their cars service around every 3000 miles. I've seen many standard tranny and rear ends be over filled when hot, I would pull the filler plug and the fluids would run out a bunch. None of them had ever issues when we let the fluids reach their warm or hot levels, almost all liquids expand when hot
I would drain a 1/2 pint or so out of it when cold and see if that helps or not
BTW I have seen speedo cables leak like your has, not many but a few

It blew out over a litre of oil, and was still leaking. I feel that rules out the over filling theory. The vent cap was pulled apart, I looked at it and made sure the spring wasn't stuck, everything seemed fine. Perhaps it's time to buy a plug and change the speedo to the VSS output.

I would double check that vent. Pull the vent and fill plug, blow air in the fill port and make sure the air is escaping from the vent port.

Here is some info.

Well then.....I never had instructions shipped with my cable, so first off, thanks a bunch for sharing that info. My cable was also sent without the small o-ring. So, that would be the most likely culprit, what with the oil getting into the cable sleeve and all.