Whining of 915 Transmission

[HKZ Bob]

Dear all,
yes this in not an engine project, but I might get some smart answers as well in this forum. I have an 915 transmission which I have removed of my car after an unsuccessful rebuild.
This rebuild was done because the of whining and hard shifting of 5th gear.So all synco rings and bearings were replaced.

The wining noise disappears when the clutch was pressed. So I could double check this when I put the transmission in neutral and turned it with an electric drill. I could clearly here the wining without engine noises.

Which parts are rotating in the transmission when the gear is in neutral?

here some sketches. The yellow marked parts were replaced by new ones. Spend some money in porsche bearings.

Here some pictures what has been replaced



Merry Christmas Bob

[HKZ Bob]

Here some more schematics.

[HKZ Bob]

Sorry 18 looks to be a seal

[Porsche84]

Wow, that was expensive to replace all of those parts. The ring and pinion turn if the car is rolling and the clutch is in. Did you look for wear on the ring and pinion and did you check backlash? Frustrating for sure, looking forward to hearing the cause of the noise.

[HKZ Bob]

Jerry I thought the part 15 input shaft turns when tranny is in neutral and the clutch is in.

The car is not rolling. I seperated the transmission from the car. It makes the noise in neutral gear.

BR
Bob

[Walt Fricke]

When the mainshaft is rotated, 1st, 3d, and 5th gears on the pinion shaft also rotate.

When the pinion shaft is rotated, 2d and 4th gears on the mainshaft also rotate.

All gears but reverse are constant mesh, so gears 1-5 are all locked in (so they can move the car) only when their respective operating sleeves slide into and lock to their shaft their non-fixed gears.

As to isolating noise: Since you seem to have the tranny out and on the bench or stand, I suggest you remove the differential. As you know, that is easy. Then use your drill trick and see if you still have the noise. As suggested, the ring and pinion mesh is a likely source of noise. Often, I fear, when they are adujusted to factory specs.

Yes, with the tranny in neutral, and you turn the input shaft, the pinion shaft itself ought not to turn. Or, if it does due to oil drag and whatnot (and I kind of doubt that, as countervailing drag in the R&P area ought to offset that). So that would suggest the whine is not from the R&P area.

Your diagram indicates wear where the two large bearings in the differential case are. Wear here is, alas, all too common. It allows the outer race to rotate in the case, which leads to more wear, which leads to loss of the absolute parallelism of the two shafts which seems to be critical to long term tranny health.

What did you do to fix this?

Have you also posted this on the 911 forum? That is where the guys who have specialized tranny knowledge read and respond most often. And it is bad form to cross post. Yes, the 911 forum is a little too busy, if such a thing can be said - one day's posts often are more than one screen, and it is harder to keep up. But it is still bad form, as those who have something to say like to save their breath if someone else has already said it. And like to avoid looking foolish if someone has been pretty definitive, and a guy like me has been speculating in the wrong direction.

[Porsche84]

What Walt said! You did not mention replacing the diff bearings. Check those closely, if they are the noise source, it should be pretty obvious.

[HKZ Bob]

Originally Posted by Walt Fricke

When the mainshaft is rotated, 1st, 3d, and 5th What did you do to fix this?

Have you also posted this on the 911 forum?

Walt not me thank you but you are picking on the wrong person. But still danke schoen.

[HKZ Bob]

it is getting warmer and I am starting to take my 915 transmission apart.
So I will post some pictures.

For me it is difficult to determine if I have strong wear or not. I do not have seen a lot of open transmissions.

Here my pictures.

Bearings of the differential.



Differential



5th gear syncro rings

The fivth gear was alrays hard to shift. The syncro ring is new maybe wrong assembled. the lower rod where the for is mounted has a lot of play.

Porsche 915 Transmission 5 speed - YouTube





Are these dog tees badly worn?

I have some axial play in the fork. Is that normal?





Thank forum for your jugdement.

Br
Bob

[chris_seven]

If you are rotating the box with an electric drill do you have much oil in the transmission?

What is your datum for the noise you now have? Have you tried a good transmission for comparison?

If you are rotating the box in neutral then the diff bearings will not really be contributing to the noise.

The input shaft bearing is a potential problem but these are quite tough bearings but they do wear and may be noisy.

In real terms I am am not sure you can learn much from this excercise as 915s do tend to be noisy and if you have one in a competition car with no soundproofing or carpets they can sound dreadful.

[porschetub]

Originally Posted by chris_seven

If you are rotating the box with an electric drill do you have much oil in the transmission?

What is your datum for the noise you now have? Have you tried a good transmission for comparison?

If you are rotating the box in neutral then the diff bearings will not really be contributing to the noise.

The input shaft bearing is a potential problem but these are quite tough bearings but they do wear and may be noisy.

In real terms I am am not sure you can learn much from this excercise as 915s do tend to be noisy and if you have one in a competition car with no soundproofing or carpets they can sound dreadful.

Very true,many people moan about the noise they make even in good condition .

[HKZ Bob]

Forum colleges,

yes but this transmission is not in good condition.

I see wear in my housing

Is this area where the shaft goes through the housing sensitive for wear?.



Here I guess I am missing a dog teeth!!



Is the Syncro Ring in the wrong position?



And this is wear correct?
How much clearance a fork should have?



Thank you folks for looking @ my pictures.

BR
Bob

[HKZ Bob]

Originally Posted by chris_seven

If you are rotating the box with an electric drill do you have much oil in the transmission?

According Spec.

What is your datum for the noise you now have? Have you tried a good transmission for comparison?

I had this transmission im my car 10 years ago. I had spend $1000 on new bearings and Syncro Rings.

I had always whinning in 3 rd & 5th gear. Thats all I remember. Now ten years later I give it a 2nd try or use it as a spare parts unit.

I replaced my transmission with a good one. That`s my datum.
There is a huge difference and I canīt put it into words.

BR
Bob

[Walt Fricke]

The shift rod stuff at #11 is not subject to wear that I know of. No real forces on things there.

That missing tooth on the 5/R slider is not a good sign. Plus in another picture one of the teeth looks to be a whole lot shorter than it should be.

Do you have the transmission in reverse for those pictures?

Given that you have pulled the nose housing, it isn't that hard (if you have suitable tools or substitutes) to pull off 5th. That slider needs to be replaced, I'd say, anyway. Then you can get a better look at the dog teeth on the gear itself. I've sure seen much worse (all rounded nubs), but the gear guys are always looking at a number of the facets of the teeth when pronouncing on their health.

Would be nice to know where the missing tooth went.

The gap between the slider's slot and the shift fork doesn't seem excessive to me. You could measure the fork's width when it comes off, and someone will have a brand new one and can give you a dimension. But play there beyond new only means, I think, that you need more stroke in order to get 5 or R engaged, and the shift mechanism ought to have that reserve stroke. In any case, I'd not see that as a source of your noise, whether it is symptomatic of a problem or not. It is the synchro ring combined with the internal groove of the slider, which keeps a gear engaged, not pressure on the fork. My local transmission guy also says that the teeth help keep things engaged, which of course will be less with wear, same as with the synchro ring.

One of the real tranny gurus (retired, I think, from a career which included rebuilding them, and has a tech article on this site, or its equivalent) seems to read the 911 list more often than the engine building forum.

[911Freak]

Tranny guru Walt mentioned is Pete Zimmerman, Pelican user ID Pete Z (I think)
Here is the link to his 915tranny tutorial and rebuild guide
Porsche Wiki

As far as your pictures, the last few seem to show 5th / Rev? If so, I'm pretty sure your synchro is shot because it has not only shinny spots that indicate the friction surface is worn away, but also looks like a couple of gouges from the missing dog teeth. The missing and/or damaged dog teeth indicate that the entire 5th/Rev assembly needs to be repaired...

I have my 915 tranny apart right (if you need any pics let me know) now doing the repair to the diff and main shaft roller bearings, 4 point bearing and spinning race on the PS, replacing the bearing retainer with the CMS 1 piece retainer etc.

I would suggest asking the moderator to move this thread to e 911 tech forum so you can get e best feedback from Pete and a couple other guys who have performed successful 915 repairs.

Good luck!

[chris_seven]

The datum I was trying to describe was not the 'in car' behaviour but the noise being made when you rotate the transmission with an electric drill/

If it only whines in 3rd and 5th then these gears must be worn but you did say that the box whines in neutral.

The synchro damage is a seperate issue and won't make the box whine in neutral as the synchros won't be operating or trying to match speed.

You could check this by asssembing the shafts without the synchros.

[HKZ Bob]

Walt & Forum,

thank you all for your feedback.
I donīt remember which postion I had when I made the pictures.

Since this unit is a powertrain device I thought it belongs to the engine rebuilder forum.

Currently I have lock up my transmission and ordered a 36mm deep socket.

I will provide more pictures when I have removed the 5th. gear.

BR
Bob

[HKZ Bob]

Hello Forum,

here some more pictures. I see that the 5th gear has wear.
The tooth contact patterrn is not good. Can this cause whinning?

Here some more pictures

1)


2)

3)



BR Bob

[HKZ Bob]

Dear Forum,

now I could loosen the 36mm Nut and before I take the transmission apart I have some questions about the gear settings.

When I am engageing the 2nd gear PIN1 has to be flush with the case?
and what about PIN2?

The other positions would be also nice to know.

Thank you.




BR
bob

[Walt Fricke]

You know, I've never paid any attention to these. I don't think it is necessary, or even useful. I haven't even memorized which shaft is for which pair of gear clusters - that's what I use a good diagram for if need be, or by looking up through the hole covered by that 4 bolt plate with the shift dongle fulcrum fork bolted to it.

You are probably in neutral as far as 1/2 and 3/4 are concerned, because you are in reverse. The detents will usually prevent the other two shafts (pins 1 and 2) from being in any other position, because with the pin 3 shaft in the reverse (or 5th) position, the detents prevent the other two from moving. Which means that if you want to use the trick of locking the tranny into two gears at once to aid in removing or reinstalling the big nuts on the shaft ends, you need to trick things - for instance, if you put 5/R into neutral, and shift into one of the other gears, and then loosen (remove?) the lock bolt on the 5/R fork, you can put it into 5 or R without moving the shaft.

But what does it matter? When you are reassembling things, you set the shifters by a measurement for rotation, and by eye for fore and aft movement, with the intermediate housing removed.

5/R is easy to adjust, as it is staring you in the face like it is now. A shop once got this adjustment a little wrong on a tranny of mine, and in every gear but reverse or 5th it would whine. Turns out that was the two straight cut reverse gears rubbing slightly when in their neutral position. Amazing how far you can get in 5th alone if you put your mind to it, on Interstates.