Nicking 4th gear

dmarv · 05-16-2006, 11:51 AM

Here's what I've got. On my 1976 911S with a 915 transmision, I'm nicking 4th gear on my down shift from 5th. It doesn't happen everytime, only if the lever is slightly pushed to the right during down shifts. My problem started to occur after I replaced the factory tranny mounts with Wevo mounts. The transmission was rebuilt about 5,000 miles ago with all new sychros. I'm wondering if the stiffer tranny mounts maybe the cause of the problem and I should realign my transmission coupler. The coupler was replaced at the same time the transmission was rebuilt. I don't have any other transmission problems, what do you guys (and gals) think?

herman maire · 05-16-2006, 12:09 PM

man...I have the same problem on my S.

I will say that all the bushings are finished, really finished.
Every other gear works great and I can up shift and down shift as fast as I want
from 1st - 5th but when it comes to down shifting from 5th to 4th I get a insane metalic gear sound and it just does not want to go in. Only if I go into 3rd then back to 4th it goes in supper smooth.

I am thinking that I am rubbing the reverse gear because of my shift linkage being so loose.

I would really like to hear some more info on this. I am 90% sure its my bushings+some adj.

holtjv · 05-16-2006, 02:03 PM

is the lockout from reverse not functioning properly? sounds like it may be the culprit. when you drop it from 5th to neutral does it naturally fall on top of 4th or allow you to slop it into R?

You have officially tapped my knowledge on the subject so maybe just something to ponder on. Jack

dmarv · 05-16-2006, 03:13 PM

Reverse lockout, now why didn't I think of that??? Sounds logical to me. Is there a way to test if it operating properly?

dmarv · 05-16-2006, 04:12 PM

I just looked at the reverse lockout on my shifter. The spring loaded pawl has tension on it, so the spring is not broken. Is the pawl supposed to make contact with the shift lever when coming out of 5th? In looking at my lever, the pawl doesn't touch the lever when coming out of 5th. It goes right past it without coming close to the pawl. Shouldn't the lever hit the pawl when coming out of 5th and the pawl directs the lever toward 4th without allowing the lever to engage reverse? It looks like to me that the pawl on the carrier plate is not moving back enough into the shift pattern of the shift lever to act as a reverse lockout (as it was designed). I can't tell if this is due to a broken component on the lock pawl carrier plate or if there is just too much slop in the shifter and the lever is missing the pawl? I did replace the ball socket bushing on the lever a few years ago.

dentist90 · dentist90's Garage

I originally posted this elsewhere, but your problem sounds like mine:
I have had problem with 5-4 downshift with my 915. There is a reverse lockout cam on shifter housing for 5th gear. When the shift lever is placed in 5th the cam is designed to prevent accidentally pulling the shifter back into R. I have had terrible problems with crunching Reverse while trying to downshift 5-4. It is NOT a good sound. I could barely pull the shifter out of 5th before grinding. I did the most logical thing and repositioned shift rod coupler so that I have to pull shifter farther back (ie toward console) to engage R. This has certainly helped, although 2nd gear is quite close to my thigh. PROBLEM: now the R lockout cam not working! When shifting into 5 the shift lever doesn't go far enough forward to allow cam to click in behind it, thus I can pull the shifter from 5 directly into R (only tried it when stopped!). Should't be able to do this! Admittedly I can now downshift from 5-4 without nicking R if I am focused on it. Still jam reverse once in awhile if I have to downshift quickly, as when an oncoming pickup pulled out to pass someone about 500ft ahead of me (had about 2 secs to get out of the way!)
1st thru 4th are great, into 5th is good too (lots of spring pressure. 5th to 4th still makes me cringe every time. Anyone else have issue with nicking R coming out of 5th?
Porsche factory short shift just installed (replaced older, worn factory ss kit). New cup bushing, rod bushing and shift coupler last year. Shifts firmly, no slop... just too easy to remove synchro teeth on reverse.
I have tried adjusting coupling every which way. I wonder if the 5-R shift fork inside the tranny may not be positioned properly?

holtjv · 05-17-2006, 07:51 AM

Quote:

Originally posted by dmarv
I just looked at the reverse lockout on my shifter. The spring loaded pawl has tension on it, so the spring is not broken. Is the pawl supposed to make contact with the shift lever when coming out of 5th? In looking at my lever, the pawl doesn't touch the lever when coming out of 5th. It goes right past it without coming close to the pawl. Shouldn't the lever hit the pawl when coming out of 5th and the pawl directs the lever toward 4th without allowing the lever to engage reverse? It looks like to me that the pawl on the carrier plate is not moving back enough into the shift pattern of the shift lever to act as a reverse lockout (as it was designed). I can't tell if this is due to a broken component on the lock pawl carrier plate or if there is just too much slop in the shifter and the lever is missing the pawl? I did replace the ball socket bushing on the lever a few years ago.

dmarv, I wish you were in Austin to talk to my mechanic, who sets up all the local club racers' 915s--he is very, very, good and where I got my lockout information during a discussion of the woes of the 915 (which I don't experience, knock on wood). Wish I could help you further--if you run into a wall on this, PM me and I'll ask him to talk to you--very nice guy--but he's currently replacing the tensioners on my 79 and some other stuff so I don't want to derail him! J/k--let me know and I'll get you in touch with him. Jack

jakermc · 05-17-2006, 08:25 AM

I've got the same problem with a WEVO short shifter installed. Reverse lock-out function does not appear to be working properly.

Steveinatlanta · 05-17-2006, 10:23 AM

I have the same problem, haven't dared play with anything behind the seat. Replaced the bushing, went back into it in 3 weeks, grease all gone on bushing. Lots of transmission noise in reverse and a low wine now when in fifth. hope someone chimes in with a response to include:

"Really, there's nothing at all wrong with your transmission".

I think we need to start a thread entitled: "The answer is that there is no answer". No one answer anyway. You just have to have the skill to tweak.

JBO · 05-17-2006, 11:21 AM

I also have the problem on a recently rebuilt 915, and I have to pull the shift out of 5th and then move it far left as if I was going into 2nd, then it won't nick, but then I hold my breath getting it into 4th. Makes me not want to use 5th unless I'm going to be in it for a while. I thought a factory SS kit might fix this since you essentially rebuild the shift housing when installing, but from the posts above it sounds like this may not do it.

Calgary944 · 05-17-2006, 11:29 AM

I was grinding something (probably reverse) for the first month of owning my car. It wasn't until I read something here that suggested to take the 5 to 4 shift nice'n'slow.

Basically I pull out of 5th, let the shifter center to the 3-4 plane, and then pull down to 4th. This is about a .3 to .5 second operation, and takes some concentration while doing it.

holtjv · 05-17-2006, 11:59 AM

does double-clutching help? that, and slow shifting, as calgary944 explained, won't solve the problem of needing to shift quickly at the track or in an avoidance situation. You all might want to ping someone from the local club and see who they use to set up their 915s.

Tyson Schmidt · 05-17-2006, 02:08 PM

If you are nicking reverse when 5-4 downshifting, then the reverse lock-out is not working properly.

The problem comes from having the shift coupler adjusted improperly. If the shift lever is not far enough forward in the housing when 5th is fully engaged, then the lever never makes it past the lock-out.

Installing a short-shifter will only make the problem worse, since the throws are shorter. So you have to set the adjustment so that the neutral gate is slightly forward of the center line between the 5th and reverse resting plates on the toip of the shifter.

If the reverse lock-out is working properly, then you should never move the lever into the neutral gate, wiggle it around, then engage 4th, because then you are defeating the reverse lock-out action. It should be a smooth pull straight back, as the lock-out will guide it right into 4th, so long as it's properly adjusted.

I suggest removing the rubber boot, and watching the lock-out while you do some 4-5 and 5-4 shifts. It will begin to make sense once you see what it's supposed to be doing.

dmarv · 05-17-2006, 02:18 PM

Quote:

Originally posted by dmarv
I just looked at the reverse lockout on my shifter. The spring loaded pawl has tension on it, so the spring is not broken. Is the pawl supposed to make contact with the shift lever when coming out of 5th? In looking at my lever, the pawl doesn't touch the lever when coming out of 5th. It goes right past it without coming close to the pawl. Shouldn't the lever hit the pawl when coming out of 5th and the pawl directs the lever toward 4th without allowing the lever to engage reverse? It looks like to me that the pawl on the carrier plate is not moving back enough into the shift pattern of the shift lever to act as a reverse lockout (as it was designed). I can't tell if this is due to a broken component on the lock pawl carrier plate or if there is just too much slop in the shifter and the lever is missing the pawl? I did replace the ball socket bushing on the lever a few years ago.

I looked at the reverse lockout yesterday and this is what I found. Should I try to adjust the shift coupler?

turborat · turborat's Garage

Here's my .02.

Unless one can see visible damage of the reverse lock-out mechanism, the problem is most likely a misalignment of the shifter linkage. I have found that shifts from 5 to 4 were fine when the box was cool. At temperature the problem got progressively worse. I now get the box nice and warm and and then adjust the shifter linkage. I can now downshift with relative confidence that I will not nick reverse gear once everything is up to temperature.

Tyson Schmidt · 05-17-2006, 02:29 PM

Quote:

Originally posted by dmarv
I looked at the reverse lockout yesterday and this is what I found. Should I try to adjust the shift coupler?

Sorry, I missed that post.

I can'r quite tell from your description, but it definitely sounds like mis-adjustment. You've got the right idea on how it should work. It scould be mis adjustment fore-aft, or even left-right, or both for that matter.

When you shift from 4th to 5th, it should brush the lock-out against it's spring tension, then go past the lock-out, and the triangled piece should pop back to it's resting position. If not, then adjust the lever forward so that it travels far enough past the lock-out to allow it to return.

Then when you pull straight back on the lever, it should hit the lock-out, and be guided right into the 4th shift gate. If not, then adjust the left-right until the 4th gate lines up with where the tip of the lock-out ends, so it becomes a smooth motion.

dmarv · 05-17-2006, 02:39 PM

I'll try to adjust the coupler tonight and let you know what happens. Thanks!

dmarv · 05-17-2006, 03:48 PM

OK, I looked at the reverse lockout again and here is what I found. When shifting into 5th, I do not have to move the lever over to the right enough in the neutral gate to place the tab on the gear shift lever to the right of the tab on the carrier plate. The current adjustment of the coupler allows me to shift into 5th while the tab on the gear shift lever is to the left of the tab on the carrier plate. I do not believe this should happen. I should only be able to shift into 5th when the tab on the lever is positioned to the right of the tab on the lock pawl carrier plate. If I push the lever over to the right (more than I normally do) so that the tab on the lever is to the right of the tab on the carrier plate, the lock pawl operates perfectly and I do not knick reverse. Looks like I need to adjust the coupler!

dentist90 · dentist90's Garage

With being able to engage 5th without interlocking the tabs I'm surprised you can find 1st and 2nd! Don't be afraid to adjust shift rod coupler... it's not rocket surgery (or is it brain science?) I think that part is easier than getting the console off.

dentist90 · dentist90's Garage

Quote:

Originally posted by Tyson Schmidt
If you are nicking reverse when 5-4 downshifting, then the reverse lock-out is not working properly.

The problem comes from having the shift coupler adjusted improperly. If the shift lever is not far enough forward in the housing when 5th is fully engaged, then the lever never makes it past the lock-out.

Installing a short-shifter will only make the problem worse, since the throws are shorter. So you have to set the adjustment so that the neutral gate is slightly forward of the center line between the 5th and reverse resting plates on the toip of the shifter.

If the reverse lock-out is working properly, then you should never move the lever into the neutral gate, wiggle it around, then engage 4th, because then you are defeating the reverse lock-out action. It should be a smooth pull straight back, as the lock-out will guide it right into 4th, so long as it's properly adjusted.

Reverse lockout works great... played with shifter before re-installing. Problem is if I set up 5th so that lockout cam slips in behind shift lever I nick R on the pullback to 4th, even before it reaches neutral plane. Even if I keep pressure to the left (toward 3-4 plane) while shifting out of 5th I get the grind. Shifting while not moving is fine, but the gears aren't spinning then. Frustrating! I had to move my neutral plane just the opposite of what you were suggesting to stay out of trouble, ie move neutral plane closer to R than 5th so I could get shift lever unlocked from the shift tab and over to 4th plane before R shift fork starts to move. I tried it the other way and I couldn't go from 5 -4 at all. Had to stop the car completely before I could get out of 5th without grinding R! Luckily no traffic. Right now It's functional, but only about 1/3 of locking tab is overlapped in 5th and lockout cam doesn't click in. Transmission internal shift distances just don't seem to jive with shifter design, but it is the factory SSKit. R being non-synchronized is pretty obvious as there is immediate clashing if I begin to pull back into R zone... no balking here! 1-4 shifts are a breeze no matter how I have adjusted, just moves the shift knob either closer or farther away.