Lost 4th gear at high revs

[bobmga62]

Ran my spitfire for the first time at nhms this weekend..

During the first practice session, shifting into fourth on the main straight started to really tighten up

by the race, on the second lap on I could not shift into fourth at all.. could pull the lever out of third but its just balked up going into fourth..

between races I changed the transmission fluid to what I had on hand some synthetic and a mixture of pennzoil hypoid..

anyhow, the sam happened again at thigh speed.. ironically, as soon as I brought the revs down on the cool off lap, I was able to shift into fourth no problem.

Since this is registered for the street, I took it out today, absolutely no problem...
any suggestions, any experience with this problem before with members..

thanks

r

 

[TomMull]

Interesting issue and a tough one judging from the lack of responses. I don't have anything intelligent to add but will throw out a couple of ideas for discussion. There is a lot to go wrong with the linkage but nothing I can think of that's heat related. Nothing internal either. Is it possible that the problem arises from something becoming temporarily misaligned from hard running and not heat? The 3-4 synchro then comes to mind. Can you tweak it in with double clutch?
Good luck with it. Tom

 

[Andrew Mace]

I don't know if it would matter (and I've no sage advice either way, unfortunately), but is it a three-rail or single-rail gearbox?

 

[tdskip]

This is a total wild guess, but heat/foaming or something like that preventing proper synchro lubrication?

Doesn't seem likely as I type this...

 

[DNK]

I thought that earlier Tom, wasn't sure how it would effect things.

 

[tomshobby]

My TR6 transmission was acting up when warm. This was about three years ago. I changed to Red Line MT90 and it has been fine ever since. https://www.redlineoil.com/product.aspx?pid=46&pcid=7

Might be worth a try at least before any extensive work.

 

[TR3driver]

FWIW, Ken G. (a former Triumph dealer mechanic) wrote some years back about problems with using synthetic oils that were too 'slick' for good synchro operation. Symptoms sounded similar to yours, gearbox worked fine at first but started refusing to go into gear when it got hot. I think that was a 'big' TR gearbox, but the Spitfire box works the same way, so might suffer from the same problem.

I'd give the MT90 a try.

 

[DNK]

Either way sounds like he needs some track time to heat up that box at speed to try different fluids

 

[bobmga62]

i'm inclined to think its a lubrication issue myself....

(back in my early race days, just ran straight 40 weight racing oil.. never had a problem???


will need to schedule in a test day at nhms (only 100 miles) away, cause all other events are 400 miles away...and something about doing Watkins glen without fourth gear would be insane..

thanks for the input guys!!!!

 

[CJD]

I'm thinking clutch. It sounds like it's dragging at high temp/or speed. Could be mechanical or hydraulic.

John

 

[tomshobby]

I did have problems downshifting into 3rd once. It was right after I built my engine. Turned out I did not tighten one of the clutch slave mount bolts. It allowed the plate to flex and when the engine was warm the downshift problem would show up.