1st gear down shifting issue

tomtom911 · 06-01-2015, 03:12 PM

I have an issue down shifting into first gear. To get the car into 1st gear while driving I have to do one of the following, I have to either double clutch it while in neutral then go to first. OR once in neutral I Push the shifter all the way to the right, back a forth sideways one or two times.

I cannot down shift into 1st unless the car is stopped, get the grinding noise. any ideas or reasons for this??

rusnak · 06-01-2015, 03:15 PM

You are not supposed to shift into 1rst unless the car is stopped. Too much stress on the synchro.

dentist90 · dentist90's Garage

1st has a synchro so that it can be engaged while moving (slowly). I had similar problem, could not go into 1st while coming to a stop, or entering my driveway, without a crunch unless I matched revs before selecting 1st. Synchro ring is no doubt worn, allowing dog teeth to collide before shaft speeds match. Since I rebuilt my tranny and replaced these components no problem selecting 1st at 10mph. Until the rebuild the best you can do is blip the throttle in neutral before trying to go into 1st (double clutch and rev match) or come to a complete stop.

sugarwood · sugarwood's Garage

Quote:

Originally Posted by rusnak

You are not supposed to shift into 1rst unless the car is stopped. Too much stress on the synchro.

I am able to shift into 1st while still moving 10mph with no trouble at all.
Is this damaging?

Arne2 · Arne2's Garage

My 915 was rebuilt about 25k ago, and I have no trouble getting into 1st while moving at any reasonable (slow) speed. I agree that it is likely that your car has a worn synchro on 1st gear.

Arne2 · Arne2's Garage

Quote:

Originally Posted by sugarwood

I am able to shift into 1st while still moving 10mph with no trouble at all.
Is this damaging?

Not if you don't abuse it. Don't try to force it or try to shift into 1st too fast.

In a 915, another possible issue is that the OP may have oil that is too slippery. The Porsche-type synchros in the 915 transmission require some friction to operate properly. Many modern gear oils lack the amount of internal drag necessary. The two that are most commonly noted are non-synth Swepco and non-synth Kendall. Many people feel that the Kendall gives the best shift quality for street use, and I found that to be the case personally. After changing my car to Kendall, the shift quality was noticeably improved, particularly in the synchro operation.

For the OP, if you have a pre-'87 car it might be worth an oil change before deciding you need a rebuild.

rusnak · 06-01-2015, 03:51 PM

Quote:

Originally Posted by sugarwood

I am able to shift into 1st while still moving 10mph with no trouble at all.
Is this damaging?

I wouldn't do it. I would use second or neutral. I seem to recall Peter Zimmermann saying that shifting into 1rst while moving was hard on the synchro.

Reiver · 06-01-2015, 04:15 PM

Just double clutch it...no reason for a quick shift into 1st gear that I can think of.
Matter of fact mine shifts great using the synchro's but I'd rather double clutch...more fun.

tomtom911 · 06-03-2015, 04:06 AM

Thanks for the replies. This is my first 911 and surprised to hear some say that shifting in the 1st from a slow speed is not advised. Never heard that before. At what point does someone decide to replace the synchro. Can someone explain the Dentists comment about matching revs. What does that mean and how to do that.

ManniB · 06-03-2015, 06:58 AM

https://www.youtube.com/watch?v=Z9HVkGSa694

Just an example of many videos about "doble clutching" on youtube.

- Manfred

midnight911 · midnight911's Garage

Someone help me elaborate. i think i learned that the stock 915 has asymmetric dog gear or synchro making it difficult to come down from higher gears. 2nd and higher gears have symmetric shape or structure allowing both up shift and downshift easier. Autox cars get these symmetric 1st gear so that you can now use 1st gear while at speed or load as well as while the car on halt.
internetz is allowing me post poser info...doh...

911pcars · 06-03-2015, 11:26 AM

Quote:

Originally Posted by Reiver

Just double clutch it...no reason for a quick shift into 1st gear that I can think of.
Matter of fact mine shifts great using the synchro's but I'd rather double clutch...more fun.

+1
Learning to double-clutch a 915 is required.
Speed matching with a throttle blip is NOT double-clutching
915 synchros do not last long. For evidence, see posts and numerous threads on "can't downshift".

Redundantly,
Sherwood