Layshaft torque wierdness

[Ted Idlof]

The layshaft tightend up all by itself. Anyone hear of this problem? I've sent this question to Scotty at Taylor, but thought I'd see if any of you have run into this and what it meant.

I've been doing the gear box for the 7 years and always torque the layshaft nut to about 100 and it always feels like the same 100 each time I take it off.

This time, maybe 6 hours since the last service, the layshaft nut was very tight; in fact so tight, I put a torque wrench on it to see exactly what it was and it loosened at 236. And the draw bolt was exceptionally tight as well when it's normally loose (backed off 1/2 turn from tight). And when putting it back together, the draw bolt now does not "bottom out' and and stop like it has. This time I can keep turning it past the point where it starts to get snug and should stop. And where the cotter pin hole lines up.

The car had run great and shifting was normal. Everything else looked and felt normal taking it apart; the pinion nut loosened with the effort I normally expect and both cotter pins were in place. Gears and everything inside looked great and it all looked and felt normal going back together.

Anyone seen this before? What causes it and is this a problem waiting to happen? I'd like to know before I button it up and go to the track next Friday.

[Steve Demeter]

Ted,

The break away torque will always be higher than a properly applied tightening torque.
But not from 100 to 236.

The only thing that could make it tighten up is if the gear stack grew, the layshafy sorhtened or pissibly the bearing in the bearing carrier grew as in somehow balls got wedged in the race and pushed it out.

Or the case could have grown.

This all assumes that the nut was cotterpinned.

Does the drawbolt ever tighten up or bottom out against the counterbore in the layshaft?

If it never gets tight, that sould seem to point to possibly stripped threads just making it feel like it is tight but not actually holding anything. Or the shoulder on the drawbolt or the counterbore in the layshaft could be destroyed somehow.

Or it mught have gotten stretched since you said it was way more tight than normal.

One perplexing pair of problems. Kind of like the laws of physics got changed.

I would start by carefully visually inspecting EVERYTHIING then finding the correct lengths of the layshaft and drawbolt and compare yours to them.

Then do something similar to that with the case.

Actually the case somehow growing would account for the drawbolt being real tight on disassembly, but not the layshaft nut.

Really would bet that it will turn out to be something silly that all of us would have missed.

?

If not that would seem th

[carl correll]

Normally, structural failure makes stuff get loose, as in a stub axle is stretching and the comment is "my centerlock wheel nut keeps coming loose".

The layshaft gearstack is clamped to the aft bearing. Layshafts normally fail with a spiral fracture. I'd wonder if the shaft is beginning to twist, thus getting "shorter".

Or not.

[john f]

Normally, structural failure makes stuff get loose, as in a stub axle is stretching and the comment is "my centerlock wheel nut keeps coming loose".

The layshaft gearstack is clamped to the aft bearing. Layshafts normally fail with a spiral fracture. I'd wonder if the shaft is beginning to twist, thus getting "shorter".

Or not.

That, or are the threads starting to fail, causing the problem?

john f

[Ted Idlof]

....The layshaft gearstack is clamped to the aft bearing. Layshafts normally fail with a spiral fracture. I'd wonder if the shaft is beginning to twist, thus getting "shorter".

Or not.

I suppose there would be no hint of this failure as the gear meshing would be unaffected, right? And it would be difficult to see any twist with a casual eyeball inspection? I know failures happen but don't know what to look for in a routine inspection.

[Nardi]

I had spiral cracks in a layshaft once and it was not exactly an obvious thing to see. No twisting was visable to my eye, but I could just make out the finest appearance of a line in the metal that sort of cork screwed along the length of the shaft. Today I would need my glasses to see it!

[carl correll]

This is just pure speculation from a distance. Assuming the nut is pinned, there is really no way for the torque to change unless the shaft gets shorter. Since one end of the drawbolt is also pinned at the nut, it's not going to be too happy about the situation either.

[kea]

When metal such as we are talking about twists, it draw the material and thus it gets longer, not shorter. To get shorter, there would need to be a force on each end, going towards each other.

[john f]

Take a close look at the threads in the nut.

john f

[Ted Idlof]

Still no answer.

After looking at all your suggestions plus magnafluxing the shaft and sending pictures and having discussions with Scotty at Taylor and Telo at WorldSpeed, I could not find anything amiss. So I buttoned it back up, went out on track for an hour spread over 4 sessions.

Only missed one shift but it was in the heat of battle and totally operator error. For the other 500+ shifts, the box felt perfect; like 'buttah'.

Opened it back up and carefully checked the torque; back to normal.

Now I know what you're thinking: "he originally 1) had a couple of shots of Patron, 2) just got confused about which nut was left hand and actually tightened it to 236, 3) got frustrated, 4) went in for dinner, 5) had a few beers and a another senior moment, forgetting what he had previously done, 6) came back out and loosened it the right way. But I can assure you none of that happened as I am a left brained Dilbert with checklists and notes, complete with "twenty seven eight-by-ten colour glossy pictures with circles and arrows and a paragraph on the back of each one" keeping me from doing something stupid.

So the mystery persists.

[SCOTTY81]

And I might add Ted the detailed pictures and notes where well appreciated on this end.......
I am glad to here it is back to normal......

scotty