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Transmission diagnosis

OK My car is nearing completion and had it's thrid road test. New set of problems came along. The transmisson is better since replacing all bushings and both trans mounts. Changed out the sludge from inside. think it used to be oil. Didn't put any high dollar oil in yet just standard 80-90 wieght. Hoping to drain it again soon because I want to gwt as much of that nasty junk out. ANYWAY SHIFTS MUCH BETTER UNTIL I GET TO A STOP LIGHT TAKE IT OUT OF GEAR RELEASE CLUTCH AND IDLE ALONG. WHEN THE LIGHT TURNS GREEN PUSH IN CLUTCH AND REALLY HAVE A HARD TIME GETTING INTO 1ST. KIND OF A CRUNCH AND THEN INTO GEAR. If I leave the clutch in take it out of gear and go to another gear back to first it goes fine. Second don't always select smooth either. Does anybody think the synchros are going out? WHY! Could I get along with different oil?
Old 11-11-2001, 05:14 AM
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Sunchros. Those are typical synchro symptoms.

When you go into another gear, the synchros on that gear slow down the input shaft. Once it's slowed down, you don't need to slow it down again to get into gear. If you leave the clutch in, the input shaft doesn't get spun up to (idle) speed again by the engine.

Leaving the clutch in all the time is reported to put extra wear on the clutch throwout bearing and throwout arm (seems reasonable) as well as the thrust surfaces on the crank's main bearings (not so sure on that). I don't know myself, this is what I've heard.

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Old 11-11-2001, 09:18 AM
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I guess you are right Dave. If I can make sense out of what happened, wasn't doing this until I put in new oil. Now the synchros aren't grabbing and spinning up to speed? Maybe I will get tp take it down the freeway soon so I can see if when the oil is hot the synchros work better. (to bad I didn't save the crude that came out).
Old 11-11-2001, 03:05 PM
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Joe,

My tranny definitely runs smoother once it's warmed up. I've also tried three different tranny oils, each of which seemed to have their own strengths and weaknesses. The Mobile 1 synth didn't let the synchros work well, but shifting was smoothest. Swepco is very popular with members of this site, and I'm running it in my car now. All-around performance is very even. However, it doesn't seem any better in my tranny than the Valvoline 80-90HD I was running previously.

(I may get crucified for saying that . . . )



Search this site for tranny oil strings to read about various options and performance attributes.

Good luck,
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Old 11-11-2001, 03:39 PM
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I had my tranny rebuilt by a porsche race mechanic and he told me that the way the 901 was designed that it doesn't like going into first from a stop...ever...even when new. Mainly due to what was said above...the main shaft spins down and the short movement from neutral into first doesn't allow enought time to get the gears to spin up and so there is a crunch...

The cheapest/easiest and least wear solution is to first shift partially into 2nd or 3rd and then move the shifter into first...after a little practice it becomes second nature and I hardly ever get that nasty crunch...

Hope this helps,

Tony
Old 11-11-2001, 06:55 PM
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I have the exact same problem. I'm glad you brought this up. Although, I purchased a side shifter to improve some of these problems.
Old 11-12-2001, 02:51 AM
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Yeah hope I can get used to shifting into 1st through second. I have some of these little idiosyncrosis with my 928. Some times I have to rock it in first to select reverse after parked. Always granny shift second. Beginning to realize Porsches don't get along well with quick shifting.

74 2.0 Alaska Blue Metallic
78 928 Faded Silver
Old 11-12-2001, 07:07 AM
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i've had similar problems, but its more the tail shift mechanism('72 914), the Mobil 75-90W works really well in the car, i notice a big improvement over the standard dino oils, go really warm the car up on the highway, my shifting seemed to improve as the car warmed up, try double-clutching if i doesn't go into gear right away, the 2nd, 3rd and then into first helps to, sometimes POS tailshift just isn't in the mood so i turn the car off and restart in first(i little embrassing at stop lights)
Old 11-12-2001, 10:17 AM
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