Donut "Savers"????

[LFFR]

1) Has anyone running donut "savers" actually had a donut failure?
2) Did the "savers" save anything???
3) Who supplied the "savers" you were using?

I had a donut let go at Hallett, this past weekend. The "savers" didn't save anything.

The donuts were the reinforced style and had less than 10 weekends on them. The donuts were shimmed to prevent preload stresses.

I'll post photos after I get the car in the garage and after the post mortem.

The savers weren't Taylor or WM.

John Mihalich, Jr.
Lotus 61

[Roland V. Johnson]

The do-nut savers help to keep the do-nut from failing in the first place. I use a combination of the Wayne Mitchel (and when I can I put one end in either the axle or gearbox.)

[gardnerl]

I had a donut let go last year at VIR on my Lotus 51. Axle took out brake line and caused a lot of damage to the frame. I have added the donut saver that Taylor supplies. Hope they do the trick.

[Robert J. Alder]

Maybe it's a Lotus thing? Just kidding.

[bob darcey]

LFFR: Still curious to hear your report on what actually happened. It seems to me that the "sandwich style" donut savers SHOULD keep the halfshaft centered with a broken donut, but won't do squat if the bolts start breaking--in fact, they may not even stay with the car! Thinking about how this would transpire, it seems that bolts breaking are the first step.

I like the "non-sandwich" type (centering pin welded or screwed to the halfshaft, retaining tube welded to the output axle star) on my Lola--the donuts and/or bolts can disintegrate and the shaft still stays centered. Downside is that the shocks and upper links have to be disconnected and the corner pulled away from the car to get the shafts off the Hewland.

Nonetheless, that short a time period for a set of donuts is rediculous. Either you've got something really catywhompus (which I doubt), or the donut saver broke and actually caused the carnage, or the modern day donuts are garbage.

[LFFR]

Dar,

The car isn't out of the trailer yet.

Steiny was over this past weekend. We were checking old donuts, still in the garage, at my place. The attached photo was the side that didn't fail, in 2001, also at Hallett. We had screwdrivers in the bolt holes, bending the donuts looking for rubber cracks when this pair of leaves went "pinkt". And we didn't have THAT much force on the screwdriver.

Steiny has four new reinforced donuts, in Lotus packaging, that he is going over, in Park City. We think that we may have two possible failure mechanisms. We need to get more measurements and photos before we go public.

John Mihalich, Jr.
Lotus 61

[lotus69ca]

John
I was talking to Peter Denty about this 2 weeks ago and they have the same problem. Someone in the business checked it out and found that they were being made in the Phillipines from old tires. We did not discuss who was sourcing / selling them . He recommends that you always use donut savers
Hope the car was not too badly hurt

John Lindsay

[LFFR]

I turned a Metalastik coupling product sheet. The link is below.

http://f1.grp.yahoofs.com/v1/0BoZR8m...s/rotoflex.pdf

John Mihalich, Jr.
Lotus 61

[DanW]

John,

Did you notice the distinct difference between bolt inserts in your donuts and and the photo on the Rotoflex spec sheet? That is what I was referring to in my note to you.

I am concerned the inserts made from bent sheet steel like the ones in your photo are not as strong as the machined ones and may collapse when the bolts are torqued.

Regards,
Dan Wise

[LFFR]

after all.

Was looking over the Lotus today and found a crack indication on the ear of the weld star. The plating hid the full extent of the crack. Only when I put the pin in the hole did the full extent of the crack show. It was full wall.

This shaft is the sister to the shaft/donut that let go in 2007. Both shafts were new in 2002. The sister shaft is also missing the end of one of the ears.

Has anyone else found cracks in the ears of the weld stars???

What if the failure mode starts with the weld star and then ultimately overloads the donut to failure????

Any experiences/information/observations would be appreciated.

John Mihalich, Jr.
Lotus 61/FF/28

[R. Pare]

I just finished up making a batch of tripods for a customer in France for an old Elva. The mechanic had somehow switched the shafts from side to side one time and upon inspection after the race they found that the shaft had twisted - very obvious as the splines that weren't all the way into the gear were twisted!

Basicly, the old stock Hewland tripods are dead soft - tensile strength is only around 90 kpsi - and to give a decent press fit to the bolts the they went for about a 3 thou interferance fit, which stresses the hell out of the material around the hole. Add to that years of running stresses, and it is easy to see why it finally cracked.

Also, if that is chrome plating (not nickle), you might also have hydrogen embrittlement.