915 advice

[ARCSinAK]

GREETINGS & HAPPY NEAR YEAR-

I HAVE A 1980SC WITH 107K ON THE CLOCK, THE 1ST GEAR SCINCROS ARE SHOWING THERE AGE, I WOULD LIKE TO BE ABLE TO EASE INTO 1ST AT 15 MPH CURRENTLY I HAVE TO BE DAM NEAR DEAD NUTS STOPPED AND USE A LITTLE FINESSE ...DOES IT MAKE MORE SENSE TO SEARCH FOR A USED REBUILT TRANS OR JUST DIVE INTO A FULL RE-BUILD. I HAVENOTICED A FEW 915'S FOR SALE ON THE USED 911 PARTS BOARDS FOR UNDER TWO GRAND, WHO OWNS SAY FREASH RE-BUILD ON ALL GEARS???JUST CURIOUS WHAT YOU VETERANS THINK, I AM MECHANICALLY INCLINED AND HAVE PONDERED READING WYANES 101 PROJECTS BOOK AND GOING FOR IT....HARD TO FIND A EXPERIENCED 911 MECHANIC ON KAUAI. YOUR THOUGHTS ARE WELCOME.

REGARDS-

JS

[mack6820]

According to other threads. Your not supposed to shift into 1st unless your at a dead stop. Sounds to me like your shifter just needs adjusted. Does it grind?

[john walker's workshop]

1st and 2nd can be repaired without a complete disassemble. engine and trans out, remove trans end cover, remove the 5th and reverse stuff under it, remove the side plate (4 nuts), remove the center housing, remove the two roller bearings on the shafts and slide off 1st gearremove the fork nut and tap off the fork and shift sleeve, then slide off 2nd gear. general items that should be replaced are the syncro ring(s), shift sleeve, brake bands and for longevity, both 1st and 2nd pressed on dog tooth rings, because they tend to shed teeth when they're old. there are a few minor additional details, like detent position and centering the shift sleeve, but if you go there, we'll help.

[kidrock]

I don't know of too many cars, much less a Porsche, that will downshift into 1st at 15mph

[tcar]

My P-car mechanic says the same thing: don't shift into first while the car is moving, the secret to longer lived SYNCHROS.

[80-911SC]

why would you want to shift down into first, your corners over there that tight and slow that you need first. first as i know is mainly to get the rolling mass moving . my SC has 167k and does about the same but i only run in first from a stop or will driving thru a parking lot.

sorry if not a help but doesn't sound like that odd of an issue to not be able to do something most people don't and say you shouldn't do ...............

[Christien]

If you're mechanically inclined you can DIY a 915 rebuild. It's not that hard, and there's lots of info here about it. Even if you replace every last thing (not likely necessary) it'll still run you cheaper than a replacement rebuilt tranny.

But like everyone has said, if your only issue is downshifting to 1st, a rebuild isn't necessary. I've never driven a 915 that downshifts to first at anything more than a slow roll. 1st gear on a 915 isn't a driving gear, it's an acceleration-from-stop gear.

[Matt Monson]

I agree with the others about downshifting into 1st. But if you have your heart set on downshifting to 1st on a roll, the best thing you can do is put symmetrical dogteeth on 1st gear, use a 2nd gear synchro and get a matching symmetrical slider (930.302.411.00) for 1-2.

[revmax]

I posted this link on another 915 thread the other day... Pete Zimmermann (The Used 911 Story author) has a tutorial going on regarding the 915 gearbox. Great reading for the gearbox minded. I think there's more to come.

Porsche Wiki (beta)

[ARCSinAK]

I appreciate all of your thoughts and advice.....I feel there are many times that is advantageous to be able to shift into first at slow speed, I have read about the 915 traits but have also heard of many people saying when there new they easily shift into 1st at 15 mph and under. As I am sure you know the tach mirrors your road speed in second gear....On a tight slow hairpin or a stop sign that you would like to roll this means you have a long wait if you are in second for the sweet spot 3400+ on a stock 3.0 sc....On kauai there are a number of super tight turns where if you are in second your not in the power band and waiting, where as if you could slide into 1st and be at 3-5 grand upon exit of the turn you wouldbe able to carry and maintain a greater average speed.

ALOHA

JS

[Peter Zimmermann]

Contrary to what some say, downshifting into first just before the car stops rolling is GOOD, and will extend the life of 1st gear synchro by many thousands of miles. However, JS, what you're searching for is a performance shift, something radically different from a longevity shift. To use the car the way that you want, it should be considered a "pay to play" choice, and frequent 1st gear repairs might become the norm.

DO NOT give up your virgin/almost virgin transmission in favor of an unknown! If you do anything at all, find a core transmission, buy it outright, and repair it. Your 107K mile trans will need the rear pinion shaft bearing repair, read about it in my Tutorial - http://porsche.wikidot.com/forum:start - along with the other sections offered so far. You will also need to replace the 1/2 synchros, 1/2 slider, etc., but because of the low mileage your bearings are probably OK.

After repairs are done you will have to develop the "touch" needed to downshift at 15 mph, with luck you have already learned how to do it. But you can't forget that your transmission was not designed to do what you're asking it to do, so all bets are off regarding life expectancy!

[Gunter]

Go for it, JS.

Take the engine/transmission out and fix it.

Then you can enjoy the" Ballett of the head to toe dance" you describe in one of your earlier threads:

Ever man should own a porsche

You can also ship the 915 to JW and have it rebuild professionally.

Either way, once fixed, you can enjoy sliding into 1st and "be at 3-5 grand" coming out of the hairpins. Oh, that sweet spot.

[911pcars]

I routinely downshift into first when necessary, otherwise it's like taking off in 2nd gear. The gearbox slips into 1st with no effort when done correctly and with little to no wear to the synchro assy.

Go to the archives and search on the key word, "double-clutch". It's a skill everyone with a Porsche should master to increase the service life of the gearbox. One caveat, there's a wrong way and a correct way to double-clutch. Don't take the easy way out. That's equivalent to business as usual.

Some people claim that's what synchros are for. Correct. But it's still a wear item.

Hope this helps,
Sherwood

[Flieger]

Just get a 2,7 RS spec motor behind a 901 AFMSX gearbox with a 7:31 final drive. I can start in second if I want to. Of course, it does cruise at 4000rpm on the highway.

[ARCSinAK]

Thanks again to all for your input, I appreciate your time and knowledge. Mr. Zimmermin I stayed up late into the night at the firehouse reading your tutorial, must say it was well planned and written. Gunter, I will contact JW, but it might make more sense to buy a "core" which I assume is a used 915 case and replace all the gears ect. By the time I remove my 915 crate it send it to the mainland and pay freight both ways my guess is it would be more dough and I would be out of a Porsche for a month plus.

Hope you having a great day, aloha.

JS

[yelcab1]

Originally Posted by ARCSinAK

Thanks again to all for your input, I appreciate your time and knowledge. Mr. Zimmermin I stayed up late into the night at the firehouse reading your tutorial, must say it was well planned and written. Gunter, I will contact JW, but it might make more sense to buy a "core" which I assume is a used 915 case and replace all the gears ect. By the time I remove my 915 crate it send it to the mainland and pay freight both ways my guess is it would be more dough and I would be out of a Porsche for a month plus.

Hope you having a great day, aloha.

JS

Fix it dude. Some of us will even lend you the tools to do it. I can shift into 1st but I don't think I can do that at 15mph. maybe 5-10, but not 15. And, I do pay to play.

[Gunter]

JS:

Suggestion: Do the 1st/2nd refurbish yourself as suggested by JW and others.

Or, negotiate buying a used 915 in the lower 48 and have it shipped directly to JW for a rebuild.
That way you can still drive until the rebuild 915 arrives.
Contact JW and discuss this, who knows, he may have a lead on a 915.
You can be assured that he'll be honest and dilligent in doing a rebuild.

BTW: Gears are very seldom replaced, but the rest like sliders, syncros, dogteeth...............and regardless if you do it yourself or have it done, the cost of the parts is a shocker.

I also suggest that you decide what else you want to do with upgrades to the engine before you take it out to deal with the 915.
Convert to SS 3.2 ??
ALU Sport clutch ??
If you have the money, you can add ~40 horses by using 98mm P/C's, 964 cams, SSI's, exchange the Lambda CIS to an earlier non-Lambda CIS with larger intake runners.

Maybe do it all at once?

[ARCSinAK]

Thanks Doctor-

I have always had a thing for HP.....Hard to drop 15K on my ride at the moment...but sure will at some point. Do you feel a custom 3.2 with those options is a better set up than a stock 3.6 conversion?

Regards-
JS
JS

[Gunter]

Conversion to 3.6 involves a lot more than you think.

The half-shafts and CV's on an '80 are the small type before the size-increase in 1986.

Plus, the 915 was not designed for the power of a 3.6. Some people will howl about this because they installed a 3.6 with a 915.
For everyone howling, I can point to a few busted 915's with 3.6 liters.

You'd need to upgrade the brakes and the suspension as well with a 3.6.

It's always nice to dream. But, for about $6k, a DIY conversion to a SS 3.2 will give a noticeable HP increase and an engine that loves the 4-6 RPM range.

And all with the same 915, CV's, brakes and suspension.

[ARCSinAK]

Thanks Gunter-

All the Canadians I have met are stand up people.

Regards-

JS