tooth found on magnet on 915 gear oil change

[zedsn]

Recently got my fairly newly acquired 1977 911S on the road for the first time and sometimes I have to put the clutch pedal all the way to the floor or second gear will grind a little bit before engagement. I decided to do a gear oil change this evening and found a tooth on the drain plug magnet and can someone tell me how bad is this and tell me what trans I have in the car. The trans ID stamp says 915/16 717 3146 and case looks like it has never been split and car has atleast 127,000 miles on the clock.

[Charles Freeborn]

Bad, and no telling until it's apart.

[arbita1]

It's hard to tell but I think it kind of looks like a dogs tooth. Probably have a shot syncro which caused that if that's the case. Not the end of the world. Those parts are going to be replaced anyway. As long as it didn't cause damage to something else.

[Trackrash]

Definitely a dog tooth. Sometimes one will break off and it won't be much of a problem.

Other times it's the tip of the iceberg. There is a chance that, without warning, more of the teeth will break off allowing the synchro ring to break free and wreck havic to your transmissions internals.

Since you don't know the history of the trans and it doesn't shift well, you would be smart to fix it sooner than later.

[Cairo94507]

That would be sufficient for me to pull the transaxle and have it rebuilt before any more damage occurred.

[yelcab1]

There is more of that inside the box. You need to rebuild it. Welcome to 915 ownership.

[MichiganMike]

She lost a tooth, doesn't that mean she is growing older? Time for the adult teeth to come in :-)

[KTL]

When a tooth breaks out of the synchro dog ring, the ring loses a significant amount of it's dimensional stability at that location. So each time you change gears, the ring flexes at that point and it invites more teeth to be snapped off from that void in the ring. It flexes the most when you are changing gears and power to the transmission hasn't been fully disabled. Basically you're changing gears too soon before the clutch has disconnected power from the engine.

I'm guessing 2nd gear grinds for a number of reasons:

-2nd gear synchro assembly (dog ring, synchro friction band, 1st-2nd selector ring) is very worn from years of aggressive 1st-2nd upshifts and 2nd gear downshifts.

-With the missing tooth on the dog ring, the ring is tweaked at that missing tooth location and the surrounding teeth can't smoothly engage the 1st-2nd selector ring.

-When the synchro band is really worn, the dog teeth and selector ring end up doing more than their fair share of making the gear engage smoothly. The synchro band's job is to act like a brake and slow down (or speed up) the speed of the free-spinning gear before the dog ring teeth and selector ring engage the gear. If the braking effect is diminished, then the clashing/grinding of dog ring teeth and selector ring notches is what happens

I wouldn't wait too long to open up that gearbox. If the synchro assembly pulls away from the gear due to the prying effect of the dog ring flex, or the synchro band comes free like Gordon said? Things get ugly really fast inside the transmission.

[OsoMoore]

I had my 1st gear synchro jam two years ago due to someone improperly forcing a shift. I dropped the transmission and opened it up. I had 4 broken 1st gear dog teeth, 3 in a row and then 2 good and then the 4th. After un-jamming 1st, I could shift it by hand on the bench. But the 915 synchro transmission is a feat of carefully balanced forces and sizes.

If you have the time and some tools, you can take it apart yourself and replace 1st and 2nd gear synchros and teeth with minor shop assistance (pressing the dog teeth on and off cost me $20).

But if you drive one that is missing teeth, things are out of balance and can probably get worse. It cost me about 1K in parts for my partial rebuild - see Can't Shift Into First if you want some details of that adventure.

[KTL]

I would suggest to preserve the press fit of the gear hub, cut the old dogs off and heat them up to install them. I know there's the P225 and P226 press fixture tools. But I still think it's better to avoid pressing stuff at ambient temperature when possible.

I have an old toaster oven that was retired to the garage. It's perfect for small parts like dog teeth to heat them up. 250-300F and they drop right on to a gear that has been in the freezer.

[Nick Triesch]

You should put your clutch all the way to the floor anyway when changing gears!

[dfhtrhjn]

^ +1 Let's go back to the first statement there. You don't put the clutch pedal all the way in when you shift? You can't be serious...

One tooth is no big deal as long as the tooth fairy doesn't come anymore. If you start seeing more of them, then you'll need to pull it and get your rebuild on.

[Reiver]

I had this issue on PPI with 2 teeth. The box shifted well and I drove it for 20k miles before a 'freshening'.
On every oil change another tooth (there were about 8 in there) from a PO shifting issue I guess.
You'll know when you need a rebuild, it won't go into that gear at all.
It did not do any other damage btw.
Learn to double clutch and extend the mileage.

[zedsn]

I do put my foot to the floor when shifting but I have to make sure that it is bottomed out when I do second gear most times and have to pay special attention when shifting to second. Have been shifting since I was 16 and am 54 years young now and haven't had to replace a clutch yet I may add.

[DRACO A5OG]

Consciously touch the other gears to help slow or stop the gear before entering. I know annoying but it will save the 915 from any further damage. BTW, I shift like crapola :-( since I was 16 owning a bug.

[Reiver]

Originally Posted by zedsn

I do put my foot to the floor when shifting but I have to make sure that it is bottomed out when I do second gear most times and have to pay special attention when shifting to second. Have been shifting since I was 16 and am 54 years young now and haven't had to replace a clutch yet I may add.

Double clutch into second then....you can bypass the synchro if done properly. I do it as it is fun and makes sense when downshifting at speed.
The 915 can make you a better driver in reality and I enjoy its idiosyncrasies. They are all old now and have certain levels of wear so adapt to the box, it can't adapt to you

[dfhtrhjn]

If your clutch is only fully disengaged when the pedal is bottomed out, then you can tighten the cable a little to guarantee full disengagement. I adjust my clutches to be fully out when the pedal is a few inches from the floor, that way there's no doubt the clutch is at it's full throw when the pedal is down.

Cables stretch with time so it might help you a little.

[zedsn]

As far as the clutch pedal I only have to be concerned with second gear and don't believe it is a cable issue as I already looked into this, I installed a wevo shifter and a wevo coupler hoping the stock items were at fault but they were not as to why I did the gear lube change. This car sat for a couple of years before I got it and sat for 1.5 years before I got it on the road. Learning a lot from this car I might add. Being a 944 turbo and 356 guy this is a new animal to me. I think that I will start to look for a rebuilt box without a core charge and double clutch second and still drive the piss out of it. Thanks for all the input. I appreciate this.

[Matt Monson]

Originally Posted by KTL

I would suggest to preserve the press fit of the gear hub, cut the old dogs off and heat them up to install them. I know there's the P225 and P226 press fixture tools. But I still think it's better to avoid pressing stuff at ambient temperature when possible.

I have an old toaster oven that was retired to the garage. It's perfect for small parts like dog teeth to heat them up. 250-300F and they drop right on to a gear that has been in the freezer.

Yep. After spraying liberally with wd40, freeze the gear and heat the synchro (aka dog) teeth. Without the wd40 the gear will rust the second it starts to heat up and get surface moisture, even here is arid Colorado.

That's the reason all my new gears come delivered in Saran Wrap and slimy. Though we don't use wd40. We oil them.

[gliding_serpent]

Crack that tranny open or it could get a lot more expensive fast!