Bad Synchro

[hbladman]

I have an 84 911. Just had a new clutch and Porsche short shift kit. This has exposed a
Weak 3rd gear synchro. Is there any transmission fluid that might help mask the bad synchro? I would like to put off a trans rebuild for a while. The car has 56,000 miles.
Thanks

[john walker's workshop]

Sawdust/banana/molassas mix maybe. Other than that, no.

[Matt Monson]

Upshifting at a higher RPM and rev-matching on the way down. Make the synchro do less work by getting the shaft speeds closer to each other when you select the gear.

[porschedude996]

No firsthand experience, but some say Swepco 201 works best.

[pampadori]

Have been living with a bad 2nd gear for a couple years now. With my current life situation, if I decide to do an engine out to repair the transmission, it'll be down for months. Way too many other things that eat up my very limited free time right now.
So I live with double clutching every single shift from 1st to 2nd. Down shifts from 3 to 2 I merely have to make sure the revs are where they will need to be when I notch it into 2nd. Sometimes I push the clutch in and let it out and then in again to be really kind on the down shifts . By doing these minor things, you basically don't even need a synchronized 2nd gear.
I have gone back and forth between swepco and Lucas Oils 75w90 and couldn't tell much difference at all.

[porschedude996]

Originally Posted by pampadori

Have been living with a bad 2nd gear for a couple years now. With my current life situation, if I decide to do an engine out to repair the transmission, it'll be down for months. Way too many other things that eat up my very limited free time right now.
So I live with double clutching every single shift from 1st to 2nd. Down shifts from 3 to 2 I merely have to make sure the revs are where they will need to be when I notch it into 2nd. Sometimes I push the clutch in and let it out and then in again to be really kind on the down shifts . By doing these minor things, you basically don't even need a synchronized 2nd gear.
I have gone back and forth between swepco and Lucas Oils 75w90 and couldn't tell much difference at all.

What, no truck air horn? Just poking fun. I am 1/64” away from a trans overhaul.

[yelcab1]

Double clutch will help until it does not go into gear at all, then it comes apart.

[porschedude996]

Originally Posted by yelcab1

Double clutch will help until it does not go into gear at all, then it comes apart.

Explosive “Apart” ?

[isby]

I’m in the same boat, with 130K mikes on my 915. I double clutch going from 1st to 2nd when the car is cold. Without double clutching, the gears will grind. Once it’s warmed up, I find that it goes into 2nd pretty smoothly without double clutching. I’m planning to open it up next year and expect to do 1st and 2nd synchros, sliders and dogteeth, at a minimum.

[porschedude996]

Originally Posted by isby

I’m in the same boat, with 130K mikes on my 915. I double clutch going from 1st to 2nd when the car is cold. Without double clutching, the gears will grind. Once it’s warmed up, I find that it goes into 2nd pretty smoothly without double clutching. I’m planning to open it up next year and expect to do 1st and 2nd synchros, sliders and dogteeth, at a minimum.

Bearings as needed? Or just change all of them?

[isby]

My plan is to do bearings as needed.

[kevingross]

Originally Posted by isby

My plan is to do bearings as needed.

Good luck with that. The problem is that it is pretty much impossible to inspect many of the bearing races without destructively disassembling the bearing. But if you're doing the work yourself, and willing to go back in there in a couple years when the bearing(s) really start to fail, you can take that chance.

[isby]

Yep - I get it. Willing to take that chance, esp. since car sees very light mileage.

[ahoch]

Swepco didn't do anything discernably different for me. Rev match and double clutch helps... a little.

['78 SC]

Originally Posted by kevingross

Good luck with that. The problem is that it is pretty much impossible to inspect many of the bearing races without destructively disassembling the bearing. But if you're doing the work yourself, and willing to go back in there in a couple years when the bearing(s) really start to fail, you can take that chance.

When I rebuilt my 915 I took the disassembled transmission to a friend who owned a shop and (years ago) raced IMSA. He guided me through which components to replace, which included the expected wear items but also two specific bearings on the pinion shaft (999-052-043-00 cylindrical roller bearing and 999-110-146-01 four-point bearing). Per Kevin's point, he didn't attempt to inspect these and I don't remember why he singled these out, but he knew the transmission had been club raced and would continue to be used on track. So, maybe it was a preemptive measure, given the high loading on these bearings. I also installed the Wevo one-piece bearing retainer plate.

[kevingross]

Originally Posted by '78 SC

When I rebuilt my 915 I took the disassembled transmission to a friend who owned a shop and (years ago) raced IMSA. He guided me through which components to replace, which included the expected wear items but also two specific bearings on the pinion shaft (999-052-043-00 cylindrical roller bearing and 999-110-146-01 four-point bearing). Per Kevin's point, he didn't attempt to inspect these and I don't remember why he singled these out, but he knew the transmission had been club raced and would continue to be used on track. So, maybe it was a preemptive measure, given the high loading on these bearings. I also installed the Wevo one-piece bearing retainer plate.

The perspective is different when you're a shop owner servicing a customer's transmission (or engine, or ...). If I (as one such shop owner) press you to replace the iffy bearings, you'll grumble until your first lap on-track. If I don't, and the transmission has to come back out, you'll hate me forever! Cheers,

[pmax]

Originally Posted by hbladman

I have an 84 911. Just had a new clutch and Porsche short shift kit. This has exposed a
Weak 3rd gear synchro. Is there any transmission fluid that might help mask the bad synchro? I would like to put off a trans rebuild for a while. The car has 56,000 miles.
Thanks

The 915 will shift when it wants to. Part of the fun and charm.

You might want to reconsider that short shift kit.

[Antomero]

Originally Posted by pmax

The 915 will shift when it wants to. Part of the fun and charm.

You might want to reconsider that short shift kit.

Not true! I had my 915 gearbox rebuilt by Peter Dawe. It shifts amazing in every gear at any rpm you decide to shift. A properly sorted 915 gearbox is bliss when functioning correctly. Much better and more involving than a G50. IMO

[john walker's workshop]

Not a fan of short shifters. Increased effort up top and speeds up the shift down below. Basically a teeter totter with the fulcrum moved. Tends to speed up the shift sleeve over the syncro ring faster than it was designed to do and wear the parts prematurely. My 2 cents.

[Matt Monson]

I’ve only ever fitted the factory optional short shifter. I figure if it’s good enough for Porsche, it must be good. Otherwise I tend to agree with John.