downshift 2nd crunch, me or the tranny?

jhelgesen · 03-05-2007, 07:46 AM

At the track all weekend, I was having issues of downshifting into second, and getting a small crunch, usually off a long straight. I was trying to make swift but smooth shifts, but would get a crunch. I was trying to double clutch and heal toe to match the revs, but it didn't help.

When I would pause in shifting, letting it sit in neutral a moment, then ease into second, it would work fine.

So am I doing something wrong, or am I loosing my second gear syncro?

BTW, just did a fluid change before the last event, fresh swepco.

Thanks!

john walker's workshop · 03-05-2007, 08:00 AM

shifting 901 and 915 transmissions is a two step process. you have to give the syncro system a split second to work. slamming gears doesn't work well with friction syncros.

Eagledriver · 03-05-2007, 12:30 PM

You could have a syncro going bad. It could be you or the tranny or both. The thing to do is shift in such a way as to avoid the crunch. Your tranny may last many more years if you can do that.

-Andy

bigchillcar · bigchillcar's Garage

well, i agree with john walker..however, if you haven't altered your driving style, i'd be suspecting the 2nd gear synchro, too. maybe check your tranny fluid level again..just to make sure.

Early_S_Man · 01:49 PM

It has been said that the Porsche-patent synchronizers are extremely sensitive to contamination in the gear oil. When I bought my car I was already aware of this sensitivity in Porsche transaxles.

Consequently, when I found a 'graunchy' 2nd gear synchro in my 915, I immediately changed the gear oil ... using Valvoline SAE 90 gear oil. There was some improvement, so I drove very carefully for the next 500 miles, then changed the gear oil again. Again there was improvement, so I drove carefully for another 500 miles and changed it again. The graunchiness was gone for all intents and purposes! I added some Molycote additive [about 4 oz] to the new Valvoline gear oil, and drove it for another year without any problems whatsoever ... before the next gear oil change and Moly supplement addition.

I have recommended a similar 'quick flush' procedure to many Pelicans over the years, especially important when changing to SWEPCO gear oil for the first time. Valvoline gear oil hasn't been $1.49 per quart for quite some time ... but, if it clears up a synchro problem, I think it is still a valid procedure!

livi · 03-05-2007, 02:48 PM

The 915 is a wonderful piece of enigma. I bought my car at 85k miles. New clutch but gear box untouched. Mostly impossible to engage first gear even at standstill. Very annoying. Easy to crunch if I was too eager.

As per Pelican recommendation I changed to Swepco 201. No discernible difference. At first. Somewhere between 1500 and 2000 miles after the lube change the improvement started gradually. Now, some 6000 miles later it is never a problem engaging first gear and I havn´t crunched it since last summer.

How can that be? OK, so there is a learning curve to my driving style, but still. The difference is like night and day and the funny thing is that it took so long before it started to 'work'.

Any thoughts?

bigchillcar · bigchillcar's Garage

livi: you must have started livin' right, buddy...

Early_S_Man · 03-05-2007, 03:57 PM

Markus,

My take on the gradual improvement ...

There were microscopic bearing and gear wear products that had worked into the complex synchronizer mechanism, and were causing the grinding you noticed. After the change to SWEPCO, the superior additive package slowly worked the wear particles loose [detergent action] and they began to be carried around in suspension in the gear oil, and finally were collected on the drain plug magnet as 'fur or fuzz' we find when we change the oil!

livi · 04:00 PM

Ryan, you figure I am finally hooked up with the legendary 915 spirit!

Warren, that makes sense. Thanks! So maybe it is a prudent idea to change it again soon. To have it all cleaned out.

bigchillcar · bigchillcar's Garage

fur in the tranny is not good, markus..

livi · 03-05-2007, 04:13 PM

I thought maybe it was my red racing clogs that made all the difference.

JTL · JTL's Garage

My 2nd gear started grinding too on downshifts from about 40mph. It didn't do this every time and not at all at lower speed. I attributed it to not having the coupler adjusted correctly after a clutch job. Swepco had been in for about 1 year prior to this. Warren, do you think I should do a flush just in case? In the event of a synchro issue shavings are likely to be seen, right?

jt
-84 targa -95k

Early_S_Man · 03-05-2007, 10:41 PM

jt,

It certainly wouldn't hurt anything but your wallet. And, if it works, you will be very, very happy!

One thing that most people on this board don't seem to be aware of is that when the first 915 transaxle was built in the summer of 1971 ... the recommended change interval for the gear oil was the same as for engine oil ... at 1000 miles, and every 10,000 miles thereafter! Later, for the '75 models the interval was changed to 1000 miles, and every 15,000 miles thereafter!

That intensive schedule may not seem reasonable to many, but I feel the factory engineers knew what they were doing with regards to the 915 ...

randywebb · 03-06-2007, 12:05 PM

for many of us, 10,000 miles is about 5 years... hence the need to figure out the min. drain intervals based on time alone

jhelgesen · 03-06-2007, 12:31 PM

Okay, I'll check the fluid level next and try another event. Work on slowing my shifting down. See what she does then.

Thanks!

bigchillcar · bigchillcar's Garage

unless you've recently begun shifting faster and can correlate that to the crunch, i wouldn't think it was a technique problem.

dd74 · 03-06-2007, 04:04 PM

Quote:

Originally posted by Early_S_Man
It has been said that the Porsche-patent synchronizers are extremely sensitive to contamination in the gear oil. When I bought my car I was already aware of this sensitivity in Porsche transaxles.

Consequently, when I found a 'graunchy' 2nd gear synchro in my 915, I immediately changed the gear oil ... using Valvoline SAE 90 gear oil. There was some improvement, so I drove very carefully for the next 500 miles, then changed the gear oil again. Again there was improvement, so I drove carefully for another 500 miles and changed it again. The graunchiness was gone for all intents and purposes! I added some Molycote additive [about 4 oz] to the new Valvoline gear oil, and drove it for another year without any problems whatsoever ... before the next gear oil change and Moly supplement addition.

I have recommended a similar 'quick flush' procedure to many Pelicans over the years, especially important when changing to SWEPCO gear oil for the first time. Valvoline gear oil hasn't been $1.49 per quart for quite some time ... but, if it clears up a synchro problem, I think it is still a valid procedure!

Very interesting procedure, Warren. How fast do you now shift your transmission since flushing the gearbox? Were you able to increase your shift speed from first to second?

Early_S_Man · 03-06-2007, 08:48 PM

Quote:

Originally posted by dd74
Very interesting procedure, Warren. How fast do you now shift your transmission since flushing the gearbox? Were you able to increase your shift speed from first to second?

I don't know that it speeded up my shift so much as it allowed shifting without 'hesitancy' ... that somewhat tentative technique that was waiting for a crunch to happen each time. A very pleasant experience -- when it ISN'T there!

Jim Garfield · 03-07-2007, 03:26 PM

As usual, a good informative post Warren. After switching to Swepco my shifting got better and better over the course of 2k mi. I will drain and refill it again before the upcoming driving season.

bigchillcar · bigchillcar's Garage

warren...you recommend this procedure for a g50 tranny? no crunch in any gears..sorry guys..

but just wondering about my next change.