"Mushy" transmission behavior?

[RS Motorsport]

At Carolina Motorsports Park this past weekend we encountered an unusual (at least from our experience) behaviour from the transmission.

As a prelude, with Kevin (of Comprent MS) we tore down the transmission for inspection after the Friday Test day. It showed no signs of pitting, bending, wear, etc. So, I was pretty pleased.

Saturday morning practice (8AM fairly cool high 70's) transmission was great - predictible and crisp. When entering hot pits on down shifting the shifter felt 'mushy' as if there was something pushing back on the shifter without a positive response of downshift.

In qualifying the symptom returned on track during up and down shifting.

In the race (it's now hot - high 80's low 90's ambient) around lap 11 the shifting progressively became more and more difficult until ultimately the only gears I felt 'safe' using were 3-4 with 5th being impossible to get into. The tranny allowed shifting 4-3-2-1 into the pit after the event.

This basically repeated itself on Sunday in the same way. When it's cool it seems to be okay, but hot it's not happy.

The car has 27 sessions over 6 days. We reused the fluid on the inspection Saturday.

Obviously, I am going to go into again prior to the next event, but was seeking any input others may have on this type of situation.

Thanks in advance,

Jeff

[imported_Ian7]

"mushiness" at the shift lever could be stretch/compression of a failing cable inside the sheath (had this twice on a FRenault), but doesn't fully jive with the cool/hot differences in behavior.

[SCOTTY81]

You might want to try putting some fire sleeve on the cable where it comes close to the exhaust.

[RS Motorsport]

Scotty - I need more power!!

okay, sorry for that.

But, you have nailed the problem. After extensive communication with some very helpful and knowledgeable racers we have (we think) identified the cause of this issue.

The shifter cable in these cars is somewhat suseptible to heat. Specifically, if it gets hot the core can degrade and cause shifting 'sluggishness' (yeah, I made that word up).

Anyway, the fix is a different cable (available from Comprent Motorsports) and a real deal heat sheild sleeve (also available from Comprent).

We have one on order for each of our cars.

Will update as updates are available, but feel that this is a knowledgebase item for all owners.

Jeff
RS Motorsport