Conical Lock Flange Nuts aka Jet Nuts for one piece bearing retainer?

[Jonny042]

It would seem as though people are highly concerned with the strength and locking potential of this location deep inside the 915 transmission.

Some even go as far as to use steel threaded inserts so they can eliminate the studs and use locking wire on high strength capscrews...... not sure if I'm willing to (or need to) go that far.

I was, however, considering using the fancy nuts in the thread title. Short of going down in the basement and finding my Carrol Smith book on the subject, I thought I'd ask for opinions.

When I took the transmission apart it had silver zinc plated 12mm reduced hex nuts, class 10.9, and similarly plated lock washers. They were pretty goddamn tight, so somebody was serious on their install, but I do know the trans was apart at least once and the last guy to put it together liked to use a LOT of torque. Like, if some is good, more must be better, kind of tight.

I was thinking about using hardened, class 10, reduced wrench size (10mm) nuts:



Would these be an improvement over the regular nuts with lock washers?

[Trackrash]

The torque spec there, IIRC, is 18lbs/ft. Not sure how you get a torque wrench on some of them. That is basically tight as heck.

My one piece retainer came with instructions to use blue locktite and there isn't room for lock washers.

I doubt there will be room for the flange on your one piece retainer, but you will have to check.

['78 SC]

Originally Posted by Trackrash

The torque spec there, IIRC, is 18lbs/ft. Not sure how you get a torque wrench on some of them. That is basically tight as heck.
...

I used a crowsfoot to get at the difficult nuts. Not great, but worked well enough to check torque.

The offset created by the crowsfoot will affect the torque reading. Keep the wrench jaws at right angles to the wrench or do the math to correct the reading.

[Jonny042]

Originally Posted by Trackrash

The torque spec there, IIRC, is 18lbs/ft. Not sure how you get a torque wrench on some of them. That is basically tight as heck.

My one piece retainer came with instructions to use blue locktite and there isn't room for lock washers.

I doubt there will be room for the flange on your one piece retainer, but you will have to check.

Good point, I'll check clearance on the retainer today.

[KTL]

Hey Jonny,

When I bought my one piece retainers from CMS, they came with the jet nut style nuts. So you should be fine using them

I suspect Roger and the guys will also look at the stud holes when they inspect your diff housing case section. Those studs occasionally have stripped threads in a few of the holes. When I serviced a local guy’s 915 with my friend Mark around 15 years ago, we found a coupe of the nuts wouldn’t tighten. Luckily Mark had a Time Sert kit on hand to repair them

[Jonny042]

Thanks, Kevin,

I already have my billet retainer, I would have bought a CMS retainer (along with the machining and side cover) had I known I was going to be shipping my cases off there.

Not enough clearance for a 13mm wrench so Metric Jetnuts it is. The OD of the jetnut flange is slightly smaller than the flat washer pictured below under the normal size 13mm wrench flats on that 8mm nut.

[KTL]

Ok sounds good. If you're looking for a quick source of jet nuts, Pegasus racing can set you up. I love Belmetric but sometimes their shipping is a bit slow. However, you've got PLENTY of other tasks on the to-do list if you had to wait a few days for your jet nuts to arrive?

Keep up the stellar work!!!

[Jonny042]

Originally Posted by KTL

Ok sounds good. If you're looking for a quick source of jet nuts, Pegasus racing can set you up. I love Belmetric but sometimes their shipping is a bit slow. However, you've got PLENTY of other tasks on the to-do list if you had to wait a few days for your jet nuts to arrive?

Keep up the stellar work!!!

Thanks as always Kevin! I do, indeed, have plenty to keep me busy. For the past 1/2 hour I've been filling a (virtual) shopping cart with nuts and bolts and washers.

When I was racing I was a regular Pegasus customer, and since they are close(ish) to me stuff usually arrived the next day. I expect my Belmetric order will arrive well before the transmission cases are back from Arizona.

I've got two different styles of nuts on their way - the ones I pictured and the MS21042 spec jet nuts. Will report back on what I decide. I also ordered some slightly longer studs in case the stockers aren't long enough.

[Mahler9th]

I have used jet nuts and blue Loctite-- no issues.

I have also used cap head screws, blue Loctite and safety wire, which I prefer. But my application is racing.. a pretty torquey 3.6 - 3.8 liter engine.

The latter approach was suggested by a friend that is a Porsche transmission and racing expert. His company sells lots of shifter and tranny parts, and he has high level pro racing experience.

Probably overkill, but it is not expensive nor difficult to do.

I wouldn't bother with either approach for a street car with a 915, with more typical engine power and torque. But it cannot hurt.

[Trackrash]

The instructions that came with my Tarett retainer said to use blue loctite. The factory used split lock washers under the nuts and there isn't room for them with the thicker Tarett unit.