MTFCA Forum

Looking for opinions on the ball bearing/seal 4 th main made by Birdhaven. I have the rear end out so nows the time.
Thanks, Bob Giles

If you can get tail piece TIR to less than .001" or use a modern two piece transmission shaft it would probably be fine.

Since you do not know the condition of the transmission, TIR of tail piece or if the transmission has a modern 2 piece transmission shaft (my assumption) I personally would not use it.

I'm an "old school" guy; while I do have updated pinion bearings in my cars, I think ball bearing 4th mains are a complication to the design just something "new" to go wrong. I think that particular bearing are requires more "give" than a ball bearing can provide.
BUT! That's just my personal opinion. Consider the source--a guy who is still on dial-up (but not by choice! Nothing else available at my home site).

Some of the ball bearing fourth mains are loctited to the shaft, when the trans heats up it has to expand and if it can not go out the rear it will go forward and push on the thrust of the rear main or get into the magnets and field coil?

Thanks for the reply’s, I heard enough.
Bob Giles

I’ve run ball bearing 4th mains for many years (over 40 years). I took to making a light press fit to the output shaft and close slip fit of the outside race. NEVER have I had a problem and this is before I invented the “floating transmission shaft “.
I can’t personally speak to the Birdhaven design as I always have made my own.
The inspiration for using the ball bearing came from reading the old era go fast books!!

I've fitted a few at owners request over the years with no problems so far with the exception of the last rebuild to come in with one.
Now in saying that it had a early crankshaft in it that was ground .060" mains and big,ends. we know that that crank would have been in it for some 20 years before it broke. Do we blame the ball bearing 4th? I sure don't.
As for the movement of the trans growing with heat, there is at least .015" to .020" clearance\float in the drums to allow for that.

Les

I would bet that it's fair to say that you invented the two piece shaft as an answer to excessive runout of tail shafts and based on other older posts from you, you had extremely small runout on your tail shafts when installing your ball bearing 4th main (even prior to the two piece transmission shaft), correct?

I think that a casual reader could come away from your post thinking "gee, I have .018" runout on my tail shaft, so the best way to hang on to that puppy is a modern solid ball bearing 4th main and I'll be fine since Les has used them for years with no trouble". I don't think that's what you're saying, but I think someone could come away with that idea.

Personally, I don't have any heartburn over these things, but also realize they are not an answer to a badly fitted transmission and can under the right conditions, speed the eventual destruction of things if fitted without regard to other unresolved faults. On the other hand, while they won't wear similarly to babbit (like every babbit bearing still in the engine), they are expensive and provide a solution where there wasn't a problem, thus don't really interest me.

BTW, my next transmission will have one of your transmission shafts. I just think it's an excellent idea. That is a solution to an actual problem...not another solution in search of a problem. Kudos to you in imagining it and developing it.

With a bearing rather than Babbitt, how do you keep oil from migrating into the torque tube?

Mark
The bearing includes a seal on each side

I have been looking for month's to get my hands on a 4 rear main sealed bearing ball cap