The Nut Behind the Wheel: Summer 1998

I’d like to share with you some of the other fixes I’ve made over the years to my 100 to prevent it from leaking precious fluids. In previous articles I concentrated on the engine. This time I want to talk about everything else that can leak that refined Cretaceous crude.

The BN1 three-speed gearboxes all tend to leak oil, much more so than later boxes, due to the additional “holes” in the bottom. Here are the usual suspects. The adapter assembly for the overdrive gear switch is a potential source. The oil seal in the case under the interlocking shaft is another. Also, over-tightening of the cast iron drain plug in the alloy case can crack the case, and even if not cracked, the threads tend to leak anyway! There is a “scroll” seal in the front cover that urges oil to go back into the transmission instead of into the bell-housing. It’s not very effective, as gearbox oil seems to have a mind of its own and is always looking for a way out!

What are some of the fixes for these potential leaks? Glad you asked.

The adapter assembly gaskets are available in the gearbox gasket set. Make sure you have the right ones and install them correctly. Sometimes, it’s the gear switch itself that leaks, and only replacing it will solve this problem. Fortunately, it’s the same type of gear switch used on later Healey gearboxes and is available.

The oil seal under the interlocking shaft is another problem. To get to it, you will need to drive the retaining pin out and remove the shaft. To remove the shaft, you will need to gain access to the side cover and remove the interlock mechanism that attaches to it. Now you can extract the shaft and get to the seal. If you can’t locate a new one, why not use the O-ring technique like I described in an earlier article regarding the tachometer drive? A proper size O-ring can be fitted together with the seal, and that should eliminate this leaker.

As for a crooked case, only Heliarc welding or another case will fix this problem. If the threads on the drain plug are stripped, sometimes you can tap to a larger size. However, the drain plug on the BN1 transmission is a standard pipe thread, and a larger size is just too large! Best to weld it up and have it re-tapped to a standard size. If the threads are just worn, try Teflon thread tape. But don’t get any of it inside the transmission, as oil possibly could clog up the works in the overdrive. One problem I solved here was trying several different drain plugs, both new and used, until I found one that fit tightly and didn’t leak. Maybe you can be so lucky!

Ahhhh, the transmission front cover! That scroll seal is present here on the BN1 transmission and on the 100/6 transmission. All the others have a modern neoprene spring-loaded lip-type seal to keep oil from the transmission from leaking around the first motion shaft. You know that leak that occurs right under the low spot on the transmission? Well, it’s probably transmission oil, if it’s clean. If it’s dirty, it’s probably engine oil leaking past the rear main bearing.

The fix for a 100/6 is to use a later bellhousing. The fix for a BN1 is to machine an O-ring groove into the front cover and use an O-ring to staunch the flow. The front cover is small enough that it can be chucked up in a lathe and then a groove machined in the cover’s first motion shaft inner diameter. I know of only a few of us who have done this. One member did it back in the ’50s, and I did it in 1982. My transmission doesn’t leak from this area at all, and you don’t need to totally disassemble the entire transmission to do this! Just remove the front cover and take it and a spare first motion shaft to your local machinist and tell him/her to FIX!

Steering boxes tend to leak due to a perished oil seal or a worn rocker shaft where the seal bears on it. Two seals sometimes can be inserted to maximize sealing. Another source of leaks is in the front cover shims and gaskets as well as the “olive,” or compression fitting, that seals the stator tube to the front cover. All original olives are split so that they will then compress to seal when the securing nut is tightened. However, a regular un-split olive or compression fitting works just fine. Don’t over-tighten the nut, as removal of the olive in the future becomes difficult, as you may squash the stator tube.

That about wraps it up for my tips on oil leaks for this time. I really hope you have found my tips useful and possibly interesting. If you have any questions, drop me a line care of the Editor. The only item we haven’t covered is the rear axle, and I’ll mention it briefly in the future.