915 transmission - synchro or linkage.

[sref]

Hi folks

so here I am... an absolute newbie and keen and in need to learn on any level...
Just got a "new" 1977 911s Targa (Miss. B) with standard 915 transmission which is a bit reluctant on its 2nd gear.
In standstill all gears enter without troubles but when driving and shifting into 2 (up or down) the gear tends to pops out, or need a slight hand pressure to stay in, grinding can occur but is not always the case. Also from 10 changes 3-4 might go in nice and smooth. What I have noticed is that if one changes gear bellow 1000RPM all goes fine, no troubles...
So what would be your analysis... Tuning of shifting linkage or worn out synchro/dog tooth?

Thank you for sharing your wise know-how.
See you soon guys!

[CCM911]

First and foremost, welcome to the Pelican forum. Now you know that we need a photo of your beautiful new car before we get started. But in this case I will allow an exception, LOL.

If it pops out of gear, worn synchro or dogteeth, or both.

I am so sorry to be the bearer of bad news.

[The cap'n]

That problem can be the first signs of an exploding 2nd gear synchro. IIRC, the issue became bad enough that Porsche made changes to it in the early 80s.

The Cap'n

[Peter Zimmermann]

Drain the trans fluid and inspect the magnet on the drain plug for small metal particles that look like teeth.

[yelcab1]

Nothing good comes after this statement "it pops out of gear "

[craig245t]

I recently bought my first 911 (82 SC targa) here in the UK back in April. I drove it home, 350 miles from the sellers house and was really worried after it jumped out of 1st gear a couple of times when pulling away from junctions.

I hit the web when I got home and found a range of answers.....I started with the cheapest as they were things I wanted to do anyway.

I changed the gearbox oil and the gearbox mounts, I planned to change the engine mounts but they've seized solid. Anyway, it hasn't jumped out of gear since.

My advice, based only on limited experience would be........

1. Change gearbox oil
2. Check/change gearbox and engine mounts (total of 4).....not expensive.
3. Check gear change linkage bushes for wear/play.

Got to be worth doing before committing to major surgery on the box......good luck.

[KTL]

Synchro wear doesn't actually cause gear pop-out directly. Worn synchros will eventually lead to crunching gears (actually it's the male dog ring teeth that clash with the shift sleeve slots to cause crunching) because the synchro has lost its ability to match gear shaft speeds for the teeth to engage the sleeve most easily. Gear crunching as a result of worn synchro bands (and/or shift sleeve) can be reduced almost entirely by slowing down your shift or double-clutching. But ultimately parts need to be replaced to eliminate the crunching.

Gear pop-out can be loss of dog ring teeth. That's why Peter said check the drain plug magnet for lost teeth stuck on there. The loss of those teeth prevents the gear from remaining engaged within the shift sleeve when power is transmitted through the gear. Or the shift fork is out of alignment and the teeth are not fully engaging the shift sleeve.

The exploding synchro saga is typically due to the synchro being forced to do too much work. Usually too worn to do it's job and actually its too much force put on the synchro & gear when coming OUT of gear. That force is caused by yanking on the shifter before the clutch is fully depressed and disconnecting power from the gear stack. Premature yanking (keep it clean, this is a family show.....) makes the big flat retaining clip flex and eventually can come off the gear. Once that clip lets go, serious carnage ensues. The trick to fixing that is converting to 930 retaining system. But that's only directly changeable on 3rd & 4th. 2nd isn't possible w/out modifying the gear.

915 4th gear issues

[Bob Kontak]

These are my thoughts, which are simply a remix of the above.

Do what Peter says first (chunks o' metal).

I think the plugs are 17mm female allen sockets. Buy a 1/2 inch drive allen socket. I remember buying a hefty long handled 17MM wrench at an industrial supply place in Houston in the 90's. Bummer is, over time the 17MM socket holes can get beat up if reused and the 17mm allen socket can be used with an extension (or two) from outside the wheel well (top sealing plug) and you can push against the ratchet to maintain the bite where the fastener meets the tool. YMMV but that's what I found.

If you find chunks of stuff, full stop. Time for a refresh. If no chunks, craig245's comments are a worthy effort especially if you find wear in the parts he is mentioning

Skip adding a short shifter for now as they do beat on synchros a bit more than the long throw shifter.

Given you are in Houston, there are enough Pelicans around that wrench. With an offering of beer and even a modest amount of cash (no 1099's) , you may find your new best friend who will help you pull the engine and split the trans.

Whatever KTL is speaking of regarding beefing stuff up, Matt Monson (member here) can do.

Cost to UPS ship a 915 is around $125 each way. There is also a shop in west Houston, past Katy, that is highly regarded. Folks here will know.

Mayo in Dallas is also an option, but I feel Matt knows more about fussing with the synchros and dog teeth to alleviate any "break in" time for smooth operation right out of the box. Something to do with back-cutting something that does not require the synchros to wear some before smooth operation.

After all this wind, and given I know the same amount as craig245 (i.e., limited experience), this info is worth what you paid for it.

I spent $2,500 for Mayo to do mine. The basic tear down and re-ssembly is favorably cheap (under or at $1K) if you drop the trans off.

[911 envy]

My 74 with 84,000 miles and a stock short shift performs just OK until I downshift from 5th to 4th. Sounds like it’s trying to go into reverse. I’ve seen the lockout in action and it blocks the lever from going into reverse from 5th. Pardon what most will consider a dumb question but is the same synchronizer take care of going into 5th from 4th and then back to 4th? The coupler does not appear to have need bushings but could I just have a coupler adjustment issue?

Thanks for your help.

[mepstein]

Originally Posted by Bob Kontak

These are my thoughts, which are simply a remix of the above.

Do what Peter says first (chunks o' metal).

I think the plugs are 17mm female allen sockets. Buy a 1/2 inch drive allen socket. I remember buying a hefty long handled 17MM wrench at an industrial supply place in Houston in the 90's. Bummer is, over time the 17MM socket holes can get beat up if reused and the 17mm allen socket can be used with an extension (or two) from outside the wheel well (top sealing plug) and you can push against the ratchet to maintain the bite where the fastener meets the tool. YMMV but that's what I found.

If you find chunks of stuff, full stop. Time for a refresh. If no chunks, craig245's comments are a worthy effort especially if you find wear in the parts he is mentioning

Skip adding a short shifter for now as they do beat on synchros a bit more than the long throw shifter.

Given you are in Houston, there are enough Pelicans around that wrench. With an offering of beer and even a modest amount of cash (no 1099's) , you may find your new best friend who will help you pull the engine and split the trans.

Whatever KTL is speaking of regarding beefing stuff up, Matt Monson (member here) can do.

Cost to UPS ship a 915 is around $125 each way. There is also a shop in west Houston, past Katy, that is highly regarded. Folks here will know.

Mayo in Dallas is also an option, but I feel Matt knows more about fussing with the synchros and dog teeth to alleviate any "break in" time for smooth operation right out of the box. Something to do with back-cutting something that does not require the synchros to wear some before smooth operation.

After all this wind, and given I know the same amount as craig245 (i.e., limited experience), this info is worth what you paid for it.

I spent $2,500 for Mayo to do mine. The basic tear down and re-ssembly is favorably cheap (under or at $1K) if you drop the trans off.

Funny, there's a shop in Houston that sends us engines and transmissions to rebuild. They don't have anyone in house that knows the air cooled stuff and they can still make a profit shipping it to us to do the work.

[ErrorMargin]

Originally Posted by yelcab1

Nothing good comes after this statement "it pops out of gear "

I can confirm!

The 915 on my 84 Targa started popping out of first which led to me pulling the engine and transmission from the car. I sent the transmission out for rebuild while I work on refreshing the engine.

https://forums.pelicanparts.com/porsche-911-technical-forum/1153485-pulled-engine-my-84-targa-now-fun-begins.html

[Matt Monson]

Originally Posted by mepstein

Funny, there's a shop in Houston that sends us engines and transmissions to rebuild. They don't have anyone in house that knows the air cooled stuff and they can still make a profit shipping it to us to do the work.

It’s a ten year old thread.

[mepstein]

Originally Posted by Matt Monson

It’s a ten year old thread.

LOL. Right

[JSV798]

Originally Posted by 911 envy

My 74 with 84,000 miles and a stock short shift performs just OK until I downshift from 5th to 4th. Sounds like it’s trying to go into reverse. I’ve seen the lockout in action and it blocks the lever from going into reverse from 5th. Pardon what most will consider a dumb question but is the same synchronizer take care of going into 5th from 4th and then back to 4th? The coupler does not appear to have need bushings but could I just have a coupler adjustment issue?

Thanks for your help.

This is almost certainly incorrect adjustment of the coupler. I've had this problem. The solution is to lengthen the linkage by slacking the bolt under the lid behind the seats and pulling back GENTLY on the gearlever. Before you loosen the bolt put tape on the shaft so that you know where you started from. You are looking to lengthen the shaft by only around 1mm. Tighten bolt and retest. Continue doing this as necessary. DO NOT rotate the shaft or else you will lose sideways adjustment.

Roy

[KTL]

Originally Posted by 911 envy

Pardon what most will consider a dumb question but is the same synchronizer take care of going into 5th from 4th and then back to 4th?
.

Perfectly valid question to ask. No, 5th gear and 4th gear do not have related synchronization

The shared aspect of synchronization is only the sliding engagement sleeve that is shared by “paired” vertical gears. What I mean by “paired” is in relation to the shifter pattern

1 3 5
2 4 R

1st and 2nd share an engagement sleeve
3rd and 4th share an engagement sleeve
5th and reverse share an engagement sleeve

But their actual synchronizer assemblies are separate and operated by the respective side of the sleeve for each gear. So the actual synchro operation for the paired gears is not at all shared. BUT, those paired gears are married from a shifting standpoint. Married in the sense that they both are operated by the same shift fork inside the transmission. Which means the adjustment of the actual gear shift lever itself, in a forward or rearward direction of adjustment, affects both of those gears

[911 envy]

I did what Roy suggested but before I realized I had replies to my question. New to the site and expected I’d get notified about a reply. By lengthening the rod did you mean the distance between the collar bolts and the coupler? Hope so since that’s what I did. But I increased that distance more than an inch just to get the shifter perpendicular. Not sure how I screwed that up because before I touched anything the shifter was perpendicular and the collar bolts were within a half inch of the coupler. But I was finally able to shift into all the gears. I’m probably really screwed but won’t know til I drive the car. I’m in the middle of replacing the alternator.

The explanation on synchronizers from my Frankfort neighbor is a real education. So I’m guessing I could have a 5th to 4th synchronizer problem. Right? I read that I should eliminate some of the simpler steps first such as checking connections and grounds and the shifter and coupler bushings. I’ve ordered a new cable. Did that because my clutch is hard to push to the floor and the cable is adjusted to the very end. Do those to facts tell me anything about the condition of my clutch?

Please be patient with me. I bought this 911 because 55 years ago I owned a 69T. Sold it when duty called. Once you’ve owned a 911 you never forget. I’m trying to test the proposition you’re never to old to learn.

Ron from IN.

[Schulisco]

Originally Posted by 911 envy

My 74 with 84,000 miles and a stock short shift performs just OK until I downshift from 5th to 4th. Sounds like it’s trying to go into reverse. I’ve seen the lockout in action and it blocks the lever from going into reverse from 5th.

Thanks for your help.

Had exactly the same issue. The issue is a misadjusted shifting linkage. The shift lever is adjusted too right and too way in front direction. Make a complete readjustment of your shifting linkage and make sure that all plastic bushings are still ok. If not, replace _all_ bad ones at first (on both shift lever and shift coupler). Then make a basic adjustment like shown in this video:
https://www.youtube.com/watch?v=b3nPONBAaZM

Thomas

[911 envy]

Thank you. I’ll watch the video and start over after I replace my cable.

Thanks again.