Drilled Metric Nuts (M8 x 1.25)

[James Michael]

Hi there,
The studs on my differential that attach the lay gear "Spider" to the differential sheared off when I was in New Orleans.
I got a new spider and studs and reinstalled eveything but after race when I checked, the nuts (and studs) were already loosening to the point where I could rotate the nut by hand. I had torqued them to 25 ft-lbs. I used anti-sieze to get a good preload on the bolt. Any ideas to prevent this from happening?

I was thinking I could torque the nuts then lock wire them so was wondering where I can find drilled M8 x 1.25 nuts? Spruce aircraft have drilled nuts but they are only english. The nuts that came with the kit are the the smaller sized jetnuts which look almost impossible to drill so purchasing a pre-drilled nut would be better.

Thanks for any advice. I could use some special locktight but I think lock wiring the nuts would be better. I had this same problem with my header bolts but lock wiring seems to do the trick.

[Craig Henry]

Something is likely wrong. A "jetnut" has a built in interference fit by design. You would need a wrench to get in on and off... especially if new.

[BeerBudgetRacing]

Can you use a second nut as a jamb nut? Maybe a flange nut upside-down and drill through the flange for your wire?

[Fred Michael]

Sounds like the stud installation is your problem if they are loose.

[S Lathrop]

How much damage was there on the mating surfaces and how much damage was there to the holes and threads for the studs.

What kind of diff do you have?

[ghickman]

This sort of sounds like a Williams chain drive diff. The drive flange is bolted to the output shaft on the drive side rather than held by a splined shaft such as the Taylor.

[James Michael]

I was told that it is a Wavetrak differential. The spider that the lay gear bolts to is bolted into the side of the differential using 6 studs and a locating pin. The spider is lined up with the pin and the 6 studs and located. Then they have a drilled steel plate that sits over the studs, then you put the nuts on top of the steel plate. The piece that bolts to the CV joint sits inside of this and is splined to the output shaft from the diff. There is a clip that retains this part from coming off the spline.

When these studs sheared the 1st time, some had already departed the scene. I think 4 broke inside the diff. (Sadly I don't think I ever had checked these for tightness before this happened). I removed these and it did not appear any damage had occurred to the threads. To get the studs in, there is a small allen head hole at the end of the stud that I used to tighten the studs, then the spider goes on, then the steel plate, and then you put on the final nuts. This happened at New Orleans, but I repaired it and raced Hallett (3 sessions) but when I checked today, as I said they were all loose. Yes the jam nuts could be rotated by hand - maybe they had backed off that much already to the point when you can rotate them?
Spruce sells drilled nut in English so I would think I could find someone who sells drilled nut in metric. I could try the double nut setup but there are only a few threads beyond the nut so not much room to play with.
Thanks for any feedback.

[Jnovak]

Not a williams, I have one and it is not like that.

[S Lathrop]

James:

Do I understand correctly that this is not the first time this unit has faild?

I think, at a minimum you need to talk with who ever made your diff. Or you need to seriously think about changing it for one that you can get serviced.

[Pop Chevy]

I would not have used antiseize on the threads, Locktite also acts as a thread lube then hardens. Better choice.

[Ivinsea]

James,
I believe the studs you are referring to are these (recessed inside the sprocket):



This is a notorious weak spot on the Quaife diff due to the bolt circle being too small. Some guys remove the CV joint and tighten the studs/jet nuts EVERY session.

Wayne used to sell a kit with 6 studs and jet nuts and the plate.

We have had the studs or nuts work loose on both cars and have broken off a few studs.

What seems to work best is to remove the old studs and get the threads in the hole really clean, then use Loctite red on the new studs and let it dry overnight. Then use Loctite blue on the jet nuts. Then use anti-tamper paint on the nuts. I think once one nut works loose, the other are soon to loosen up too.

Some guys don't like to use the red on the studs as it would be a real pain if the stud broke.

[James Michael]

Yea, I think locktite would have been a better choice but I am weary about assuming locktite will keep them from lossening. Yea I could go buy another differential but this is costly and I have a race in a month I would prefer not to spend 5K and rip my entire car apart.
I think drilled nuts is my best choice for now, I just need to find a supplier.
Yes talking to people at the track, some of the P1/P2 cars have had this same thing happen where the studs fail in shear. It is not the best design. Those studs have to take all the torque and they are spaced fairly close together:
Since T=F x d the smaller the d, the bigger the force and threads in shear is not good design practice anyway. Actually I was told the friction at clamp up actually transmits a majority of the torque (like a clutch) not the shear in the bolt but if you lose clamp up, then the frictional force goes down so now the bolts are acting in shear which makes the situation worse until the bolts fail. I had this happen to me on a flywheel where the bolts failed in shear (same thing where the bolts started to loosen).
In any case, I think if I lock wire the nuts, they can not loosen (at least not much), so this may be all I need. I've had the car since 2007, and the bolts failed now so it has been awhile.
James

[James Michael]

Thanks Invinsia - yes this is exactly what I have. I can try the locktite method but as you say, if they do loosen and fail, you're going to have a rough time getting them out. When I got them out the 1st time, there was no locktight as far as I could tell so they came out pretty easily. I think lockwire would work better. I think there are speciality houses that make drilled nuts (spruce aircraft, 877-477-7823 and corned drill nuts, phone is 800-566-4565). I am going to call these guys and see if I can get a metric drilled nut.
James

[glenn cooper]

Pretty common deal on Stohr sports racers and F1000's using that dif.
I'd be tempted to speak with one of the bigger prep shops, and when I say "tempted"...

[S Lathrop]

James;

Years ago I had trouble with the splined VW hubs as used on FV and FSV when we started racing the FSV on ovals.

My solution and it worked very well was to assemble the hub with a structural epoxy, adhesive. This will take heat to disassemble. But in your case, I would try to assemble the studs with a structural epoxy adhesive. But to make it possible to get the studs out, I would use parting wax or soap on the stud and then coat the stud with epoxy. Given that you most likely have compromised the threads, this is a very doable repair.

[Fast Finn]

We have had good luck with using red loctite on studs and Heico lock washers under nuts.

Hannu

[Revs2-12k]

James,

Please keep us posted on the M8 Nut & Stud safety wired solution, it's pretty tight in there, but probably worth the effort.

I experienced this problem at Mosport a few years ago. Scary what could happen there. Thankfully Critter had the kit from Nate at Autotech and we were able to remove the sheared off studs from the diff.

If you cannot remove or the threads are damaged, the diff can be rotated 180 degrees giving you fresh mounting holes. See Pic. That is probably an unpleasant job at the track.

I've since kept a set of new stud and jetnuts as spares & have kept a diligent eye on them ever since with Red Lockite, Proper Torque and Orange Inspection Lacquer. Since then, my sprocket carrier has lightly loosened a few times, but nothing that cannot be remedied between sessions.

I have not tried Heico washers, will probably install them next time I have it apart. They may help the nuts from bottoming out the stud threads. I also think a stiffer/harder/thicker donut/backing plate may also be the answer. When you look at an old one, you can see depressions where the 6-Jetnuts compressed the steel.

[Jnovak]

I am surprised that they still build these the same way. we broke the first 2 that we installed. Quaiffe knows about this but they still have not fixed it. what a JOKE.

[S Lathrop]

There is a fix for this problem but it would require that new CV Joint drive flanges be made and the diff itself would have to be machined.

You could machine a step of 1/8 or 3/16 deep with the edge of the step exactly aligned with the center line of the bolt circle. Have studs that with an unthreaded portion just slightly longer than the step. This way you can double the area of the stud that is subjected to the shear loading. And you can do this in the existing space.

The other alternative would be to machine the matting surface of the drive flange and the diff with dogs to interlock. This is how I get away with aluminum spindles and CV joint drive flanges and never have a failure.

My bet is that you can modify these diffs in this manner.

[James Michael]

Well,
I could not find a supplier who had drilled M8 x 1.25 nuts so I just did it myself.
Took a few tries but I got them drilled. Broke a few of my 1/16" drills in the process but got 6 drilled nuts (4 holes-2 wires for each nut). Installed studs with red locktite, put nuts on to 30 ft-lbs (4 nylon and 2 of the deformed type), then lockwired them all together. I did look very closely and it sure does not look like I damaged the threads of the differential when removing the broken studs from before.

Their was enough room but some of the lockwire is close to the splined part that attaches to the CV but since they all rotate together, I don't think fretting should be an issue even if they touch a bit but at least now they are not touching.

It's not pretty but it should work. I can get a wrench in there to check tightness if needed but with the lockwire, the nuts and studs should not loosen. I'll give a report after the next race if anyone is interested.
James