Shifting a 915 gearbox into first trick

[motorstereo]

So my buddy with a ‘78 911SC taught me a 915
Gearbox “trick” — before shifting into first , “pretend” you’re going to shift into 4th. Don’t actually shift , just touch the four position on the H. Then, it goes into first super easy.

Can anyone explain to a transmission amateur how or why this works?? I wish I’d known this a few years ago.

[JonT]

i'll have to try this- i usually softly blip the throttle and it helps me ease into first either moving or at a stop.

[fanaudical]

I'm not sure why that would work. 1st and 4th aren't on the same shift fork. Maybe getting some drag the on the 4th gear synchros slows something down enough that 1st isn't so notchy?

[stownsen914]

Yep that works. Doesn't matter that 1st and 4th are not grouped together on the shaft, it equilibrates the shaft speeds before engaging 1st and reduces the burden on the 1st gear synchro.

[Ian Comerford]

I was advised that if first was a bit reluctant to try ’touching’ second gear before going into first, so don’t go into second but just approach it so to speak. Not sure of why it seems to work but it does.

[rowingone]

Might be better to adjust your linkage at the coupler between the seats to get into every gear properly.

[PeteKz]

rowing one: Of course, the coupling should be correctly adjusted, but that doesn't affect the operation of the synchros, which is what causes the problem of getting into 1st.

[Schulisco]

If you do not know what kind of gear oil is filled, I recommend to think about changing the gesr oil. The 915 uses the Porsche patended synchronization which requires more drag torque to function the synchros properly. Modern oils like part or full synthetic gear oils does not have that much of drag torque, although Porsche still recommends even modern (part) synthetic oils to be used in the 915. Originally Porsche recommended and filled a simple mineral only based SAE90 GL5 gear oil. Mostly Shell Spirax MB90. On shifting problems like yours I would use such an oil for a test. This is by far cheaper than an overhaul and might cure your problem. If not you know the synchros might worn out...compare the datasheet of the MB90 to others choose a similar equipped oil by yourself. The viscosity values are the important thing...

Thomas

[Matt Monson]

When your car is idling in neutral, the mainshaft is still spinning. When you push the clutch in, there’s still a bit of inertia and it’s spinning for a bit. Selecting another gear, any gear, stops the spinning. I use 2nd.

[kltarga72]

Originally Posted by Matt Monson

When your car is idling in neutral, the mainshaft is still spinning. When you push the clutch in, there’s still a bit of inertia and it’s spinning for a bit. Selecting another gear, any gear, stops the spinning. I use 2nd.

Matt,
Shifting into first gear on the 915-gear box has always been troublesome. When I come to a complete stop, shifting into first gear will go smoothly fifty percent of the time on my 1980 SC. If I have trouble shifting into first, I will double clutch. Can I assume that the shifting coupler is aligned correctly because it works great half the time?
I will try moving into 2nd and 4th gear as suggested.
I purchased my first 1972-T 911 in September 1971 and it wasn't long before I had issues when down shifting into first gear. It also wanted to pop out of first gear when I was hard on the gas pedal. Factory rep that was assigned to the Southeastern district looked at it in New Orleans Porsche dealership, and about all he could do was scratch his head.

[Matt Monson]

Downshifting into 1st on a 915 has always been dodgy at best.

[Duc Hunter]

I agree with the oil recommendation above. I use good old swepco.

I am with others as well on touching any other gear. Touching the other gears synchro's will slow the main shaft down (or stop it) and then it should drop into first. I always try not to go near first gear unless I am stopped. If I'm in a parking lot and need to it's only at a very slow speed. At the ridiculously long lights here in Florida I tend to put the car in neutral while I wait. As I move to first gear I tend to touch the third or second gear synchro to stop the main shaft from spinning first. My G50 car its a non-issue with it's different synchros, and I believe a synchro on first. Love the character of the 915.

[mikedsilva]

Originally Posted by Matt Monson

When your car is idling in neutral, the mainshaft is still spinning. When you push the clutch in, there’s still a bit of inertia and it’s spinning for a bit. Selecting another gear, any gear, stops the spinning. I use 2nd.

This. ^

[Rosco_NZ]

Not dog teeth / sliders …??

[Tinkerer]

I have 4 stop signs while exiting my neighborhood and shift smoothly to 1st while rolling each time. New pinion bushing kit, coupler, reworked transmission have made it better than new apparently LOL

[KRLocke]

I always used 2nd when I had a Carrera years ago. Same with putting in reverse.

[Antomero]

Originally Posted by motorstereo

So my buddy with a ‘78 911SC taught me a 915
Gearbox “trick” — before shifting into first , “pretend” you’re going to shift into 4th. Don’t actually shift , just touch the four position on the H. Then, it goes into first super easy.

Can anyone explain to a transmission amateur how or why this works?? I wish I’d known this a few years ago.

Your gearbox most certainly needs a rebuild.

[kltarga72]

Originally Posted by Antomero

Your gearbox most certainly needs a rebuild.

Maybe Motorstereo's gear box needs a rebuild but as I posted on Monday, I had this problem on My 1972 T that was under one year new from the factory and mileage had to be less than 10,000.

[motorstereo]

Schulisco — I’m using Swepco on the advice of folks on this forum. Antomero, I have no trouble with the trans other than occasional trouble shifting into first, so I’m not sure why I would need to rebuild the box, that seems a bit extreme !

Matt M & Stowsen914, thank you for your explanation!

[ErrorMargin]

Originally Posted by motorstereo

...before shifting into first , “pretend” you’re going to shift into 4th. Don’t actually shift , just touch the four position on the H. Then, it goes into first super easy...

Just to be clear, you are saying that if the car is sitting still with the engine runnings and you push in the clutch, it is hard to go directly into first? And if instead you push in the clutch and, while holding down the clutch you move the gear leaver over to forth without actually going into 4th, and then back over to 1st, the transmission then easily goes into 1st?

There is probably nothing wrong with your transmission.

The issue is almost certainly that your shift coupler bushings are worn or even completely disintegrated.

Since the bushings are worn out in the shift coupler, the momentum you give by going toward 4th and then back to 1st helps the coupler rotate a little more than it does just by going directly to first. This is why your procedure makes it easier.

You can easily check to see if your bushings are worn in 5 minutes with just a phillips screwdriver. This process below is super easy, just 4 screws and then take a look.

If you see that the bushings are bad, you can then decide to DIY replace, or take the car to a shop for them to do the work. You will be amazed at how precise the shifting is after you replace the bushings.

Get in the back seat and lift up the carpet that goes over the central tunnel, you will see an access panel with 4 philips screws, like this:




Remove the screws and lift up the cover, you will see something like this. There may be a rubber cover over the coupler that you have to push back a bit, push it back and you will see this:



Now, take a close look at the coupler, it should look like this:



Notice how in the picture above there is a center shaft with dark grey bushings around it? The above picture shows a coupler with good bushings.

If it looks more like the picture below, then your bushings are shot and need to be replaced. Notice how in the picture below the bushings are just gone and the center shaft is loose:



See the next post for info on replacing the bushings.