strange shifting issue
 

So, the wife and I went to Roebling road raceway this past weekend for a track day, we drive an 86 911 (915 trans). My wife runs white group (solo) and I run advanced solo. She was the first run of the day and about 3 or 4 laps in, she comes in and said the transmission would not downshift to 4th from 5th at the end of the straight. thinking she was crazy I took the car out in my run group and sure enough after 3 or 4 laps the car would not downshift to 4th or 3rd, the shifter does release from 5th, but trying to go into 4th it's like the shifter is jammed, cant move it in any direction. when the car slows to a crawl, most times you're able to shift in every gear. The next lap around the same thing happens. I am able to upshift with no issues. When she went back out after the car had sat a little while the shifting was fine for 3 or 4 laps then would get stuck again on downshifts. The car shifts great on the street with no bindingand no getting stuck. Definitely seems to be a heat related issue.
History on the car: transmission rebuilt about 3 years ago. new mounts (4yrs old), wevo coupler, rebuilt shifter with factory ss kit, new shift bushings, trans fluid changed 2 months ago. (believe its swepco 201)
After the shifter base was rebuilt a few months ago we had an issue of 5th getting caught on the lock out tabs but shifting was fine. Took it back to the mechanic for an adjustment and now it doesn't get caught on the tab but gets stuck in the neutral plane. Sorry to be so long winded but very hard to describe.
Thanks in advance for any advice on what the issue could be.
Steve
I know you're all concerned we had to sit out for the weekend, but no worries luckily we brought out the bmw also.:D

I wasn't able to get my coupling adjusted just right after rebuilding my shifter and replacing the coupler with the Wevo coupler. I got it real close and had a mechanic fine tune it for me. I think the adjustment is more difficult with the short shifter and I also, had a gated shifter. Sounds like you might have other problems.

I'm pretty sure it's not an adjustment issue as I get all gears driving on the street and for the first few laps. Could it be low on trans fluid causing the sticking issue? Steve

Anyone?

Still sounds like coupler adjustment, just one that is only exacerbated enough by heat. When it won't go into 4th, what will it do? Third? Back into 5th? Is it only 5th to 4th? Is it hung up on the reverse lockout tab? Any grinding? Is this during hard braking or lateral G forces or full load? How are your transmission mounts?

Happens under hard braking while downshifting from 5th to 4th. When it happens the gear level doesn't move in any direction( right, left, front, or back). Almost feels like it gets stuck between gates. When the car slows to about 50mph the gears engage again. I'll check mounts but they are only a few years old with limited miles ( mostly track). How to tell if the mounts are no good? Thanks Steve

Shifter.
 

Shifter bushings, or perhaps the de-tent.

Gerry

[QUOTE=86 911 Targa;9727825]Shifter bushings, or perhaps the de-tent.

Gerry[/QUOTE

All bushings are new ( less then 2 months old). What is de-tent?

Targa, the link seems to pertain to 996 trans not 915? Maybe I'm missing something!?

Shifter.
 

Porsche 911 Shifting Improvements | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article
^^^^^
Sorry-My bad.

Deleted earlier post.

I'll try to post some pics of the shifter assy.

I'm leaning towards a thermal issue at the coupler.

Gerry

+1 for loose motor/transmission mounts

Great!! I'll check both motor and trans mounts. How long do they usually last? I replaced both in 2013. The car has a few track miles and are oem rubber. How can you tell if they are past their prime? Thanks in advance Steve

In hopes to fix my shifting issue I'm going to order rebel racing motor n trans mounts. Question is, stiffer bushings at the trans or vice versa? Really hope this will fix the issue but the old ones still seem to be in decent shape.. Thanks in advance Steve

Based on your observation that hard braking induces the problem, I'd check engine mounts as well.

Plan is to replace both, engine and transmission mounts. I would like to know , do I put the stiffer bushings at the trans or stiffer bushings at the engine?
Steve

my 2cts..., use regular mounts.
regular mounts, due to their larger mass of rubber, are more pardonable.
and since they'll be new, they will be stiff enough to do the job well.

beeing a lover of partsporn, I couldn't resist to get myself those nice alloy framed wevo mounts quite some miles ago.
First nice effect was, that the hwole engine/trans unit was sitting more stiffer holding it all in position.
downside to that: stupid as I was, I did not readjust the coupler and the clutch cable.
so all the wear of my trans was suddenly omnipotent.
all of that finally lead to a trans rebuild.