Transmission cquestion

[Bob Harriman]

I have been trying for two years to educate myself to help me diagnose my gear grinding in first and reverse without actually pulling the trans out which I know is a difficult if not impossible task. I have a 901/13 with AFMSZ gears. Shifting into first or reverse is quite a bit easier upon startup with colder/ thicker gear oil viscosity. In fact my shifting is much smoother in the winter than the summer. Double clutching seems to fix the issue especially when downshifting. My understanding is that my syncros are crush style which requires more friction than other types of syncros so the syncro can come to the input shaft speed to engage corrctly and/or quicker. Double clutching seems to accomplish this. My 2,3,4 and 5 gear do not have the grinding issue but they also downshift much easier when double clutching. I have checked my clutch cable for stretching, adjustment and the pedal stop and they are all adjusted correctly. I am using Kendall gear oil. My questions are, is this a sign of syncro failure or an input shaft lubricating issue? If syncro failure wouldn't it be difficult to accomplish smooth shifting even when double clutching? Will an input shaft seal create a similar issue due to a failure in lubrication. I have changed my gear oil twice in the last two years with no noticeable change. I'm just looking for a bit of education as to how the syncro actually works when it is apparently moved and needs to come to the proper speed to engage the input shaft. Any guidance and/or recommendation of some literature for explanation would be greatly appreciated. Again, I cannot engage first or reverse without a bad grind unless I touch another gear syncro or upon a cold start. Infact, I have a delay in clutch disengagement when approaching a stop especially when it's much hotter which has scared the shit out of me as it feels sometimes like I'm gonna rear end the car in front of me for a quick second then disengages.

Thanks,

Bob

[gled49]

You could have a main shaft seal leak wetting down the clutch causing release issues. Double clutching was a non syncro approach to shifting without grinding, so if your syncros / shift sleeves / coupling gears are bad, DC will help your shifting. I've never worked on a 901/911 trans that didn't need 1st and 2nd gear work. Gordon

[savaden]

Sounds like a clutch release issue. The splines on the mainshaft could be gunked up or the pilot bearing in the flywheel could be sticking.
SV

[Noah]

I have the same problem in my stock 901 box (911/01, 1970 T). Shifts really nicely when cold. But the warmer the engine/trans get, the worse the shifting and clutch feel become. Gets pretty much impossible to shift into 1st or reverse without a little grinding. And the clutch pedal itself becomes stiff and there is a stiction feeling when depressing it. There are no engine or gearbox leaks in my case, and the cable is adjusted properly and not worn. I figure gearbox wear explains the shifting problems -- but the stiff, sticky clutch feel the warmer the engine/tranny gets is something I don't understand.

[yale]

I have had my 901 transmission rebuilt and I still have the same issue as you guys talk about above. I have tried quite a few different gear oils as well. Swepco was among the worst which surprised me. Since I live in downtown NYC, not being able to get into first smoothly when the gear box is hot can be quite a drag. The old saw about shift into second (or touch second) then first, also seems to loose efficacy when the gear box has been on a good drive and then comes into NYC summer weekend traffic. I have just given up thinking it's anything but the luck of the draw, as in some boxes will do this and some wont. Mine is limited slip by the way as a data point.

[Jon B]

I cannot engage first or reverse without a bad grind...

Any time you grind gears going into reverse, without car in motion, you have a clutch release or pilot bearing issue. There can be many reasons for this, from various adjustments to worn out, damaged, incorrect or missing parts. If you cannot cure the issue with cable adjustment, and are certain your cable and associated pieces are correct and in good condition, then you need to examine your clutch, input shaft and release components, piece by piece. Is your release fork hitting something, limiting its movement? If so, why? Is your release bearing missing its plastic clips (pre-70)? Is your clutch disc the correct type, with correct lining dimensions? Does it have excessive runout, is it damaged or bent? Is it hitting the flywheel bolt heads? Are your flywheel dimensions all within factory specs? Does your transmission shaft have excessive runout or damage? Are the various fork pivot pieces assembled correctly; have they been adjusted for multiple flywheel resurfacings? There can be many possibilities for this situation. At some point, if you cannot solve this yourself, you should employ a very experienced person or professional to identify the problem, and correct it.

Jon B.
Vista, CA

[Bob Harriman]

Thanks Jon. I knew that would actually be the answer. It would be nice to diagnose without dropping the trans but obviously that's impossible. Oh well, I need to change my trans carrier to a 911 style (I have a 69 912). My factory sway bar is too close to the 912 carrier. I've had to shim the bar to get under it which causes it to be too close to the ground for some speed bumps.