915 Thrust Washer Bearing: Any Ideas ...???

Mahler9th · 01-24-2007, 06:47 PM

I have had several failures in my 915 transmission during the past 18-24 months. This is a transmission in a race car... other cars with similar bhp and torque have not had the problems. Almost every part in the thing has been replaced recently-- less than 10 hours of track time.

3rd, 4th, and 5th are shorter than stock. 8:31 r&P. The 3rd and 4th gears are from Paul Guard. GT TB diff, later aluminum side cover, Wevo bearing retainer plate and Wevo blueprinted main case.

Wevo shifter and coupler.

About 3 hours of track time since the last major failure (R&P and some other parts). I just took the thing apart to check it out and have found that the thrust washer between 2nd and 3rd on the input shaft is damaged. Not yet sure if the pieces damaged anything else. Doesn't look like it.

I have seen this part damaged when other failures have occurred, and I am reaching the conclusion that this area may be the "source of the fire."

Has anyone out there had a similar issue with these thrust washers lasting only a short time?

I have been working with some local experts... we have been examining parts pretty carefully. So far we are stumped.

Some pics of one of the failures below. Not easy to see the damaged washer. Pretty easy to see the other damage.

Walt Fricke · 01-24-2007, 07:34 PM

Are we seeing 3d gear on one shaft hitting (and damaging) 2d gear on the other shaft? Because something is out of whack concerning spacing, like too few or many spacers on one or the other of the shafts?

I am a bit baffled as to how a thrust washer itself can fail. Or even be damaged - knicked on its circumference, maye, by debris, but that ought not to affect its function, should it? But surely it can't compress to allow the shaft to shaft alignment of the constant mesh gears to be off.

If the gears on the pinion shaft were loose or otherwise not forced into the stops over at the pinon end? Bound up so torque didn't fully seat 4th?

I'm guessing.

Walt Fricke

Mahler9th · 01-25-2007, 09:20 AM

The stack ups were correct and there ws no looseness. I don't think other debris could get in there to cause it to fail.

These pictures are from a previous failure, where there was collateral damage to 2nd and 3rd, but I do not tink tehe problem started there.

The different issues over time have all pretty much come after 1 1/2 to 2 days of racing. In each case, this thrust washer has shown signs of damge.

This is the first time I disassembled everything before a major failure occurred, and the only thing I see so far is that the thrust washer is fractured.

I also have a slight suspicion that the dog teeth and third have started to come off of the gear, but I haven't confirmed that yet. If they have started coming off, I will be checking with Paul Guard to see if he has any guesses as to why/how this could happen.

Jim Sims · 01-25-2007, 06:14 PM

In two 1973 5-speed 915's I've rebuilt I found almost all the thrust washers with cracks all around the edge. It looked like a material flaw (lap, billet pipe rolled flat?) in the steel sheet the washers were originally punched from. The washers were not fractured but looked like they could cleave apart parallel to the ground surfaces. These washers were replaced with new parts.

Mahler9th · 01-25-2007, 06:24 PM

I have been using new parts each time, and for these I only buy factory units. I think these thrust washers see some type of load that causes the damage, only in the extreme case (like mne) do they come apart. I am running at the upper end of what these transmissions can handle, but my application is not unlike those of several friends and they have not had the failures

I wonder if one could have these things made out of a different, more robust material...

Hopefully this will get figured out.. trnsmission parts aren't getting any cheaper.

Walt Fricke · 01-26-2007, 12:13 AM

I'd never have believed these could fracture. I have a set I'll have to look at. It is not a part I'd have thought to replace.

Maybe an excuse to buy straight cut gears to reduce thrust loads?

You can tack weld the dog teeth in place. I think some do this routinely, though I don't think it is common (I haven't).

Walt

KTL · 01-26-2007, 05:26 AM

Quote:

Originally posted by Walt Fricke

You can tack weld the dog teeth in place. I think some do this routinely, though I don't think it is common (I haven't).

Walt

Walt is right. Chris Streit (cstreit on Pelican) has had his share of failures in his 915 and a few of them have apparently been the 3rd gear dog teeth coming away from the gear.

Apparently the press fit of the gear and dog teeth gets compromised by R&R'ing the dog teeth too many times. So, the dog teeth ring is then micro welded onto the gear to prevent the separation of the two.

I'd be interested to see a picture of the thrust washer and a description of what loads act on this part. I can't envision how the thrust washer is loaded.

Mahler9th · 01-26-2007, 07:19 AM

Several reknowned experts have told me: do not weld the dog teeth to the gear.

So do not do it! The proper process is apparently "peening."

The people with whom I am in contact cannot be refuted. They are absolute experts.

I will try to post pictures of the failed thrust washer later. I have a few examples.

KTL · 01-26-2007, 08:34 AM

Check with Roger at PowerhausII in Colorado? I think that's who Chris was dealing with.

Good to know. Whatever the case may be with the staking of the dog ring, it's still known for the teeth to come away from the gear.

Walt Fricke · 01-26-2007, 11:55 AM

I learned just this week that Roger is no longer with Powerhaus II. But Stan is, and he is the deep technical expertise at that shop. A call there might lead to a conversation with him. Either this is a problem Stan has seen, or it is something he would certainly be interested in.

I think he showed me a welded on dog tooth ring - a few little tiny TIG spots. But doubtless peening would keep things in place as well, and guys without TIGS could do it.

Checked my "spare" set of spacers. I can see how the 3d gear one might be most prone to trouble, as it is by far the thinnest. Up until now my only concern with these spacers was to be sure to put the right ones in the right places. This set shows a little staining and traces of insignificant wear (which the fingernail can't feel).

The IDs and ODs of all of these look funny - like they were made of two pieces, sort of a wavy circumferential irregular indented small groove in the cylindrical surface made especially visible by stain - but I suppose that is an artifact of the stamping/cutting process.

Your pictures will be interesting to view.

Walt Fricke