911 SC transmission problem

kingbird6 · 08:09 PM

I recently had my transmission synchros and thrust bearings on my new 1982 911SC replaced by a Porsche professional I have known for years. He said the tranny was mint inside with 100K miles and so we only had to replace the 1st and 2nd synchros, new 1st gear dogteeth and a thrust bearing. After we reinstalled the tranny I noticed that occasionally it has a real problen getting into gear depending upon how quickly I shift or what speed the car is going. I'm very reasonable with my driving habits and not forcing it quickly into gear. I installed a factory short shift kit right at the time of rebuild that may be exacerbating the problem but 1st and second gear just feels at times like it hits a brick wall... no grinding, it just won't "sync in." Sometimes if I pull it back to neutral and try it again it goes like butter and feels smooth as silk, again never grinding. I really have to time the first gear downshift as I roll to a stop because if I wait until a complete stop it's a bear to get in gear and if I don't nurse it a bit while rolling it's impossible. I think the linkage adjustment is fine or I wouldn't be shifting fine 85% of the time right ? The clutch cable is new and has been professionally adjusted and it still does this. I don't recall the car doing this prior to the rebuild. The mechanic blames it on the short shift kit. I'm wondering otherwise. Please advise....

Jim Sims · 04-17-2004, 10:34 PM

How long have you been driving it since rebuilding? Have you given the new sychro's time to "get broken in"? If a set of dogteeth were replaced I would have also replaced the mating sliding sleeve (operating sleeve) but these parts are getting rather expensive so I understand the mechanic's hesitation if the 1/2 sliding sleeve looked okay. Do you have the original shifter? Put it back in and see if that helps solve the problem. Jim

TonyG · 11:36 PM

kingbird6

Synchros do not need "time to break in". I've heard that many times before but I totally disagree with that line of reasoning.

The reason why is that I remember driving a new 911SC in 1983 (500 miles on the odo), and yet another brand new 1985 911 Carrera off the dealers lot (my fathers car). Both of these cars shifted like butter.... extremely easy shifting.

If they shift perfect when new, they should shift perfect after a "professional rebuild". If they do not, then there is still something not right in the transmission.

Furthermore, back around 1992 I had a 130k mile 1983 SC that had first gear "let go". I had the tranny removed by a "reputable porsche shop" and they replaced the first/second gear synchros, installed a new first gear "something or other" and a bunch of other new parts to the tune of $2500. When I got the car back it shifted exactly like you described. It wouldn't go into 2nd gear. No grinding, but it just wouldn't go in when shifted even semi quickly. The higher the engine speed, the slower the shift would have to be made.

The shop told me to "break the trans in" and get some miles on it. 30k miles later it shifted exactly the same and the shop that did the work was out of business....

Bottom line: The transmissions shift perfect brand new without being "broken in".

I'd take the car back to whomever did the work.

TonyG

johnsjmc · 04-18-2004, 04:35 AM

Any break in required shouldn,t take more than a half hour of driving.I would re adjust your shift coupler before condeming either the trans or the shifter and examine your trans mounts. The reduced movement of the short shift kit magnifies any misalignment of the coupler and should be suspect as your mechanic says. Have him remove your short shifter and if that doesn,t fix the problem he can redo his trans work while still under warranty.

Jim Sims · 04-18-2004, 05:56 AM

"The transmissions shift perfect brand new without being "broken in". - quoting TonyG

Do you know what the factory did when it assembled the transmissions to make them shift perfectly using all brand new parts? Did they do a "break in" before it was installed in the car? I suspect your rebuild may have also skipped replacing the 1/2 sliding sleeve. The first gear "something or other" was probably the first gear dogteeth (synchro hub) which if warranting replacement may have also excessively worn the 1/2 sliding sleeve. It's cases like this that likely prompt 915 tranmission rebuilds where all the friction parts (dogteeth, synchro rings, brake bands, energizing and anchor blocks and sliding sleeves) in the 1st through 4th gears are replaced as a matter of course to preventing warranty returns. Cheers, Jim

kingbird6 · 04-18-2004, 07:25 AM

Thank you for the valued inputs. I'll try putting the original shifter back and see what that does. The transmission before the replacement of 1st and 2nd synchros, 1st gear dogteeth, and 2 thrust bearings seemed to shift fine if I recall with the exception of 1st and 2nd grinding and enough slop in the gate to have to "hunt" for the gears. Now that I replaced the bushings and couplings with the short shift it is very precise. Engine speed doesn't seem to make much of a difference as to when it "locks up". Maybe the engine and or tranny mounts are the problem.

JP911 · JP911's Garage

Ok, kingbird6, here's the real scoop. The SC is just lashing out at you for not driving it's little brother (the 993) more often. Stiff shifting is just one of the ways in which 911s lash out at there owners.
-Guess who?

TonyG · 04-18-2004, 10:29 AM

Jim Sims

My point is that the rebuild that this "reputable shop" here in Los Angeles did at that time, just didn't shift well. But the shop tried to tell me that the "synchros needed to be broken in". Which is a bunch of BS.

I didn't take the trans apart so I don't know first hand what was wrong. And... this was a long time ago.

But I also had a used '85 Euro Cab about 5 years ago that exibited the same problems KingBird describedd going into 2nd gear. I tried adjusting the linkage, replaced busings, etc... all with no positive effect on the problem. This was on a 63k mile car.

TonyG