pale Green oil in hard shifting 915 transmission

[phelix]

My new-to-me 914/6 conversion has a 915 transmission with a Wevo shifter, a Wevo gate shift and a Wevo side shift conversion. It uses Patrick Motorsports’ 914/6 conversion linkage. When I first got the car I found 3rd/4th to sometimes be blocked; it was like hitting a wall trying to engage those gears. I eventually found that, despite going wild with Wevo parts, the person/shop doing the conversion didn’t replace the circular bushing under the shift lever that the shift rod hangs from and it had crumbled to the point where it was floating freely on the rod. I installed a new bushing, adjusted the linkage over several iterations and I now have 5 forward gears and 1 reverse. Phew!

But the car is awkward to shift. (I should add that this is my first time driving a Porsche with a 915 transmission; my previous 911 experience is all with G50 cars.) There seems to be a lot of mechanical friction to overcome when shifting gears. The resistance feels quite linear along the entire path of the shift manoeuvre. It makes smooth driving quite difficult as there’s such a long gap between the start and end of an upshift or downshift as the movement is slow and ponderous. There’s no grinding or clunking; it just feels like a lot of “work”. It’s probably worth pointing out that the odd downshift into first just before coming to a stop has gone very well with the lever almost getting sucked into position.

There are no details on who did the transmission work and exactly what they did other than the transmission was “fully rebuilt”, whatever that means. I’ve read enough threads on the 915 to know that phrase to be less than helpful in context of what can actually be replaced.

The car has done about 1600 miles since the conversion. In the paperwork it shows an oil change at about 1000 miles using a 50/50 blend of Redline MTL-90 and Redline 75-90NS. I had a bit of a eureka moment and thought I had found an issue - the wrong oil.
But when I drained the oil it was a pale green color. So either it was never changed at 1000 miles or the shop installed something different than they put on the paperwork.

The oil that came out was nice and translucent and there were minimal filings on the drain plug’s magnet.

My question is - any thoughts on what transmission oil is pale green? It doesn’t look to be anything from Redline or Swepco. It would be ironic if it was the same as what I put in: Motul 75w-90 Technosynthese. Which also happens to be pale green!

I haven’t driven the car yet since refilling the transmission - hopefully there will be time for that today.

And any other advice and comments on how a 915 shifts for a 915 newbie would be gracefully received.

[Nick Triesch]

The 915 will never ever shift like a 99 mustang GT. It’s hard to believe you went from g50 cars to that 915 with all the add on’s. What does all that stuff really do on an old 915? I have a 915 in my 85 911 and it shifts very well with new clutch and flywheel. Also shift parts are newer . Shop put in new trans fluid. When shifting I pause between shifts, never hurry.

[mikedsilva]

The 915 gets a bad reputation, usually as a result of being banged through the gears and using the wrong fluid.
A well working 915 is enjoyable to use.. no, it won't change like a later model car, but it is allowed to be slower since it's much older!

After rebuilding a few using Peter Zimmermans tutorial, I only use a mineral 80/90 like swepco or Kendall 80w90 (sold right here on Pelican). The more experienced builders tell me that the later mode synthetic fluids are too "slippery"....

[brighton911]

I vote for Kendall 75w90. Also rev matching makes quite a positive difference in a 915 as well, just a quick blip between shifts is all you need.

[Jonny042]

Hopefully this doesn't turn into another oil thread..... but I have to say the Motul Motylgear 75W-90 Technosynthese is a great choice. I changed from the blue goo to the same Motul and noticed an immediate and significant improvement.

Shifting times improved in the 200ms range when I first changed the oil and every other interaction with the transmission became easier and more pleasant at the same time. After a few hundred kilometers the times improved even more, as much as 4/10ths of a second quicker than before.

Originally Posted by Jonny042

Following up on this thread, now that I've had some time to get some miles on this oil. This datalog was from earlier today - the shifting speed got a little better over time.... down to .650-.660 seconds from .980 to well over 1.000 Seconds when I first started logging.

Before (Swepco 201):



And after (Motul Motylgear 75W-90 Technosynthese):

I look forward to hearing how your drive goes today.

More to the point of your original question, I have to say that the 915 synchros with the brake band feels different than the cone type synchros in just about every other gearbox. To me the action feels exactly as you say, a greater amount of effort over a longer portion of the movement of the lever as opposed to a "snick" into gear like a modern box. The sideshift might be adding to this effort in a significant way.

[Cairo94507]

I am not sure what you used to replace the shift bushings, but I recently did a Weltmeister short-shift kit on my 901 side-shifter in my '71 914-6. Within 5 miles the stock plastic shifter bushing disintegrated. Fortunately my mechanic had some brass bushing stock and put it in his lathe and made a perfect brass bushing that fit exactly and will never fail again. Just a thought as shifting a 914 is never easy.

[theiceman]

in a related question, while running a 915 with either Kendal, Swepco or whatever your brand is, should you add any type of friction modifier if you are running a LSD ?

[icarp]

From jonny 042: " Hopefully this doesn't turn into another oil thread..... but I have to say the Motul Motylgear 75W-90 Technosynthese is a great choice. I changed from the blue goo to the same Motul and noticed an immediate and significant improvement."

I have also found this to be true , too good to be true?
Nope It's just better, based on my experience .

Ian

[yelcab1]

I have always had great luck (shifting) with Redline MTL in 915 gearbox, G50 gearbox, 996 gearbox, 997 gearbox, Cayman gearbox, Boxster gearbox. In some instances, as soon as the owner backs out of the garage, he immediately commented how good the shifting was.

[Matt Monson]

Originally Posted by Nick Triesch

The 915 will never ever shift like a 99 mustang GT. It’s hard to believe you went from g50 cars to that 915 with all the add on’s. What does all that stuff really do on an old 915? I have a 915 in my 85 911 and it shifts very well with new clutch and flywheel. Also shift parts are newer . Shop put in new trans fluid. When shifting I pause between shifts, never hurry.

What does all that stuff really do? It converts the gearbox to a 916 for use in a mid engine application in a 914.

Phelix,
It feels mechanical because it is. Nothing to do with oil. Those Wevo 916 conversions are persnickety. You may need to fiddle with the adjustment more. Or worst case the shift rods and forks inside the gearbox might require adjustment.

[Jonny042]

Originally Posted by yelcab1

I have always had great luck (shifting) with Redline MTL in 915 gearbox, G50 gearbox, 996 gearbox, 997 gearbox, Cayman gearbox, Boxster gearbox. In some instances, as soon as the owner backs out of the garage, he immediately commented how good the shifting was.

I'm not surprised that the synchros work well with the MTL. I've used it in FWD applications. It's REALLY thin and not very slippery, much like honda MTL.

BUT!!!!! Yikes on using it in a transaxle that contains a hypoid gear, especially with the less than ideal ring and pinion relationship of the 915 (not sure about the later stuff). It's not recommended for use in applications with a hypoid gear or in rear differentials.

[Matt Monson]

Originally Posted by Jonny042

I'm not surprised that the synchros work well with the MTL. I've used it in FWD applications. It's REALLY thin and not very slippery, much like honda MTL.

BUT!!!!! Yikes on using it in a transaxle that contains a hypoid gear, especially with the less than ideal ring and pinion relationship of the 915 (not sure about the later stuff). It's not recommended for use in applications with a hypoid gear or in rear differentials.

Correct. It doesn’t belong in any Porsche transaxle. Shifting feeling is not a valid way to determine if a gear oil is good for your gearbox or not.

[theiceman]

Originally Posted by yelcab1

I have always had great luck (shifting) with Redline MTL in 915 gearbox, G50 gearbox, 996 gearbox, 997 gearbox, Cayman gearbox, Boxster gearbox. In some instances, as soon as the owner backs out of the garage, he immediately commented how good the shifting was.

Just as a point to note, i have Audis too and the big complaint against this product when replacing stock fluid on those forums is its horrible performance in cold weather ( think 32f and below ), provides very balky shifting. This you may not see in cali, but something to be aware of.

[yelcab1]

Thanks for the document. I will continue to use MTL based on my personal experience until my gearbox throws up.

[Matt Monson]

The consequences of using a GL4 in a transaxle. It won’t be the synchros that you wear out.

[phelix]

Thanks for all of the replies. I had a good look at the oil and it's a lot darker than I thought. Here it is next to fresh Motul



and here it is on a white plate, poured out a fair bit thinner. No signs of any metallic "dust" in suspension but it is a bit murky.



This evening's cocktails and dinner will be unique.

I did get a chance to drive the car, albeit only for about 20 minutes. It does feel like it shifts better but I need to put more miles on the car. I fully accept that the side shift conversion and the internal shift gate are going to add friction that a standard 915 in a 911 won't have. And I as a driver need to get used to the 915 and its idiosyncrasies. Double clutching and the occasional throttle blip on upshifts have helped. I sense that the transmission prefers upshifts at higher rpms and spirited driving in general. I'm fine with that - just wish the rest of the traffic was OK with that too.

And I need to recheck the clutch travel. The previous owner had a PPI done on the car by Black Forest in San Diego; in the paperwork there's a note that the clutch wasn't releasing all of the way and this was resolved by going through a bin of used clutch pedal shafts until one was found that provided the necessary travel.

[Jonny042]

Originally Posted by yelcab1

Thanks for the document. I will continue to use MTL based on my personal experience until my gearbox throws up.

Do what you want to your own car, but I understood from your post that you are putting it in customer cars?

[Matt Monson]

It will shift better with more RPMs. I tell people in street driving the sweet spot is 4000-4500, rpm. Much slower than that and the synchros get a workout.

[Porchdog]

My experience is that my 915 shifts better with Kendall than with Swepco.

Even after 20+ years it takes a few shifts to get used to after driving my other cars.

[gled49]

901’s, 911’s, 915’s & 930’s have axial ring and pinions. Do they have the same requirement as a hypoid diff for oil?