Strange behaviour after tranny refresh

dsmyth · 06-08-2010, 07:26 PM

I just completed an overhaul of the engine and first and second gear /slider and syncros on the transmission. Every thing works perfectly except the transmission. Always something !!! Oh well. Whats going on is first and second keep appearing and disappearing. Not difficult shifting...just not there,locked out. So far I have checked the adjustment of the coupling (between the back seats..all bushings are new as well) and the clutch adjustment, its spot on. Second is there more often than first but very difficult to find and only available when vehicle is stopped. When they can be found they shift normally however slightly stiffer with new syncros. Any ideas as to where I screwed up? thanks Doug

JJ 911SC · JJ 911SC's Garage

Quote:

Originally Posted by dsmyth

... Second is there more often than first but very difficult to find and only available when vehicle is stopped...

Doug

As you know, definitely not an expert... (free bump).

Mine also does that, I read on this site somewhere, that the 1st should be engage when fully stop... or double clutching when the car is rolling to a stop (work for me).

I'll try to find the post.

Cheers

sc_rufctr · 06-09-2010, 05:12 AM

Was the shift fork on the bottom plate checked when the tranny was refreshed?
They can work loose and move around causing this sort of problem.

Peter Zimmermann · 06-09-2010, 06:55 AM

Doug; Uh, oh. Could you have installed the 1/2 slider backward (symmetrical teeth facing 1st speed, and asymmetrical teeth facing 2nd)? Refresh with my Tutorial...

Grady Clay · 06-09-2010, 11:11 AM

Pete,

They actually work surprisingly well backwards. About a year ago, I disassembled a virgin, unmolested ’82 where the Factory installed the 1-2 slider backwards. I drove it. It worked perfectly from new to the 120K disassembly (for another reason).

That transmission must have been assembled new after ‘beer-thirty’ Stuttgart time.

Best,
Grady

dsmyth · 06-09-2010, 07:25 PM

Thanks guys,I did go over the shift fork attachment and it was tight. I was very careful with the assembly and remember spending time ensuring my slider was facing the right direction. It definitely will require removal and investigation next week when I cool off a bit. I just dont understand how it could come and go? When I say go I mean go, no first and second only when stopped and then even very difficult to locate with a firm pull but no grinding. Then both gears there only when stopped for a few tries then gone again. I guess I am only looking for suggestions of things to look for as it comes apart. Engine runs great though !!! Love the 964cam. Thanks Doug

SP2 · 06-09-2010, 09:30 PM

Could this be a detent problem? Is this a 915? I rebuilt my 915 and John Walker reminded me over and over to get the detents right. I remember there are pictures in Bentley too.

bpu699 · 06-10-2010, 08:30 AM

Quote:

Originally Posted by SP2

Could this be a detent problem? Is this a 915? I rebuilt my 915 and John Walker reminded me over and over to get the detents right. I remember there are pictures in Bentley too.

I couldn't get into reverse with my 930. Turns out the reverse detent was sitting 1mm too deep. I put a tiny washer (spring loop) around it so it didn't go in as deep, and now shifts perfectly. I was scratching my head and had replaced lots of other parts before getting to this...

I am not sure of you can check the detents with the trans in the car... I undid the spring/bolt holding in one of the other detents, and then the dang bit fell into the trans...lots of fishing to get it out.

Of note, the 930 detents look absolutely nothing like the pics in the manuals, bentley, etc...

Peter Zimmermann · 06-10-2010, 11:40 AM

Quote:

Originally Posted by dsmyth

Thanks guys,I did go over the shift fork attachment and it was tight. I was very careful with the assembly and remember spending time ensuring my slider was facing the right direction. It definitely will require removal and investigation next week when I cool off a bit. I just dont understand how it could come and go? When I say go I mean go, no first and second only when stopped and then even very difficult to locate with a firm pull but no grinding. Then both gears there only when stopped for a few tries then gone again. I guess I am only looking for suggestions of things to look for as it comes apart. Engine runs great though !!! Love the 964cam. Thanks Doug

Grady's experience was very interesting, but I did a 915 many years ago that was done by another shop not long before. That trans, if you could get it into gear it might work, it might pop out, and whatever it did was unexpected. Other things were also messed up, so I'm not exactly sure what issues were the fault of the backward slider!

Doug, you can verify the slider installation by draining the trans oil and removing the shift fork plate. Check my Tutorial for pictures.