Trouble shifting at track RPMs (grinding)
 

Car is all tuned, but still getting frustrated with shifting issues. When I get the RPMs to the top of their range, the tranny will not let me shift from first to second. All I get is a grind until the RPMs drop and allow me to shift. Normal driving and shifting works fine.

I have done some research, and it seems like this is very common on T5s. I was going to invest in a center force dual friction, but most people that have tried that said it does not fix it. So many ideas of why this happens and I'm trying to see if I can solve it without getting a different tranny (z rated or T56).

Some people have suggested that at high RPMs the transmission twists a bit and causes a misalignment condition. Any thoughts on that? Is it possible to brace the tranny more than it is? I have done the modification of installing a bolt through the cross member and floor pan.

Could be the main shaft worn or the bearing on it at the input shaft. Or worn blocker rings.

Worn sycros?

If it's a wear issue you might try a 25 to 50% mix of Lucus oil treatment in it. I've seen that stuff cover a multitude of issues.

That Lucas stuff works great. The T-5 transmission requires the use of Mercon fluid (Ford application) which has since been upgraded to Mercon V since Ford discontinued the use of the old Mercon. I would suggest starting out with a fresh fluid change, & go from there.

I'm kind of a fan of synchromesh in manual gear boxes myself. It's specifically designed to work with bronze and brass syncros and blocking rings and slush box oil is more focused on the clutch packs in autos. I rather like the Amzoil version of it too and it's not much more expensive that the Penzoil dyno oil.

Just an opinion and you know what that's worth!

Thanks for input. I used the recommended ATF with Merc V. Tranny had a fresh rebuild with new gear set. I'm trying to convince myself it's not the internals.

Since it shifts okay except at high rpm it would seem the first to second gear synchro is unable to overcome the inertia of the spinning mass at that speed. First to second is the most likely culprit for overwhelming a synchro since there is the most difference in ratio here of all successive gear speeds, therefore the more inertia to overcome to match (synchronize) engine and transmission speeds.

Things that might cause this would be rpm beyond the design parameters of the transmission, a worn blocker ring, less than optimum lubrication, mechanical wear of the input shaft/bearing as previously suggested here, a partially dragging clutch, or any combination of these.

Since the box was rebuilt, you might want to start by checking for complete clutch release. A small amount of clutch drag might be adequately handled by the synchro at low rpm, but the additional inertia at high rpm could be too much to overcome.