All right, I've tried some Saab forums, to no avail, so put on your Smarty Pants Transmission Remote Troubleshooting hat and riddle me this:
Why does my '89 Saab 900's transmission (with hydraulic clutch) shift like E36 M3 when I've just come off the highway and stopped at a light or when I'm in stop/go traffic? Getting into 1st is tough and, on rare occasions, I have to start from 2nd. Doesn't do it when cold; sometimes, it does it when I use reverse.
Some info:
+New disk only about 20k ago
+New slave/pilot bearing/throwout bearing
+New master
+Numerous clutch bleeds (pressurized the reservoir)
+Fresh fluid
+Same gear oil I've been using forever (Redline MTL/MT-90 mix).
+PP and flywheel looked good when I put the new disk in, but??
So, bad pressure plate? Only has 100k and seemed to be in good shape when I did the clutch. Car will move forward on flat pavement if I push the shifter toward, say, 1st gear without depressing the clutch. Clutch line is solid except for ~6 inches of rubber hose; doesn't appear to be bulging or otherwise knackered.
Or maybe God hates Saabs?? Certainly there's been a lot of failure lately...
Input shaft seal leaking a bit of oil on the disc?
New input shaft seal when the disk went in...forgot that one.
Edit: new rear main seal, too...
If you get it into first, is it trying to move the car? I'm trying to eliminate a clutch/bleeding issue vs and internal issue.
If its not acting like the clutch is dragging, you may have some kind of synchro issue. On the highway you're spending a lot of time heating the fluid... which would suggest that it shifts too easily.
Possibly a bent/worn shift fork that changes dimensions when hot?
Classic saab 900 transmissions are built of glass. They also form the oilpan for the engine (the oil is NOT shared between transmission and engine) so the heat of the engine easily heat soaks the transmission. Chances are, the high heat of the engine oil is warming the transmission up to the point where tolerances are closed up enough to cause the problems you describe.
If your car is a turbo, it has an oilcooler.. might want to check to make sure it is functional and not clogged (or bypassed as it is under the car on the driver's side front) if your car is a non-turbo, it does not have an oilcooler.. you might want to pick up an oilfilter housing from a turbo car to install a cooler (I should have a spare in about a month)
I am going to say that you have a broken clutch spring. Has there been any symptoms of juddering or noises? You know more than normal 
EDIT: I had another thought that the pressure plate or TOB might have a broken bit off of them. I realized I had seen something different with a poorly made/sized TOB that was causing weird wear to the pressure plate springs and thus caused damage to one of the clutch springs from bits that had broken off.
My 86 only uses sae 30w in the gearbox, I also ran into problems with synthetic, so straight Dino for mine.
Doesn't 80-90w get thicker hot ?
The symptoms of hard to get into 1st and sometimes reverse are classic of the input shaft being spun. Clutch drag is the #1 cause, but bind with the pilot bearing gets a good #2 cause rating.
You describe it as being only when you come off a highway to a stop, or stop and go traffic. That could well be a red herring, as these are conditions that simply have you using 1st gear, quite a bit.
You mention though that it never does it when cold. OK. that brings in a new variable. What changes here when things are hot?
Transmission fluid is the thing that comes to mind most for me. It thins out quite a bit. Thick oil will hold an input shaft from spinning much, while thin oil will let it spin freely. I've run into this before.
Tranmission fluid for a second time, but this time as the wrong friction modifier. Some transmissions (like certain annoying Toyota boxes) are very sensitive to this, and will have all sorts of problems with the synchros if the oil is of the wrong type.
So, if it were my Saab, I'd be inclined to do a fluid change in the gearbox, and if it weren't stupidly expensive, might even get genuine Saab oil for it.
Powar
Dork
6/6/12 8:05 a.m.
Did you use a Scantech (scamtech) slave? They are notoriously made of crap and hopes and dreams. Maybe it isn't doing its job completely?
If I get it into first, no, the car does not move. Man, I hope it's not internal: I've already had it rebuilt once and the engine has to come out to get at it.
I'll try some fresh fluid. My local Saab indy has been using Red Line MTL in c900 gearboxes forever, but now I'm wondering if I've got too much MT-90 in there. It's kinda tough to get the ratio right because getting all of the old oil out is really hard on these transmissions, which have a somewhat-separate primary gear case. The MTL gets too thin when I drive the car hard so I cut it with MT-90.
I used a Saab slave and Lockheed master (OE). Unless I have a gun to my head, I do not use ScanCrap, which, incidentally, recently went mammaries skyward, but has been resurrected as some other company, the name of which escapes me now. Maybe they will suck less??
It's a Turbo. I'll put my hand on the oil cooler next time I park it after highway driving.
If new fluids ain't it, then I guess I'm going back in with a new PP...
this is where older saab transmissions rule. They had a dipstick.. even on the manuals. I think they are an easy retrofit
mad_machine wrote:
this is where older saab transmissions rule. They had a dipstick.. even on the manuals. I think they are an easy retrofit
Was there a C900 with the dipstick? I thought they were all on 99s (spelled "four speed").
Saab stopped fitting a proper, full-length gearbox dipstick after MY89; they went to a silly shorter one thereafter.
If anyone reading this is considering retrofitting a stubby-dipsticked c900 gearbox with a long earlier dipstick, make sure you use the early -- shorter -- bolts, too. The later aluminum cover is thicker, and its mounting bolts are, too, so if you mix the early, thin steel cover with the later, long bolts, then they will bottom out, crack the case and...ta-da...you need a new transmission.
