The vintage racers here in the Northwest have had a few failures of the rear hub on their SWB 911's, which leads to some very ugly outcomes.
Has anyone else in the country heard of this happening?
The weak point seems to be around the radius where the shaft meets the flange.
Standard procedure for us now is to crack check this part each off-season.
Is there anyone making an after-market hub out of modern materials for the SWB racers??
Any suggestions and opinions would be helpful,
Thanks, Steve
We have a number of SWB cars and have never had this problem but they are all quite old now and it wouldn't surprise me to find some with fatigue cracks.
There are two part numbers:
904.331.065.01 which I assume is for use with a Nadella shaft and
901.331.065.07 which I assume is for a Lobro
I guess that they crack where the tip of the arrow is pointing at.
If you Magnaflux a shaft and find it isn't cracked have you tried to have it locally shot peened in the radius as this may help to improve its durability.
Investing in a forging tool to make blanks would reduce piece price but I wouldn't be surprised if a suitable tool were to cost $5000+ and with the cost of the tooling to cut the spline it would be difficult to sell enough to recover costs.
Re-manufacturing by machining from solid would be relativley expensive due the the amount of material that would have to be removed but would avoid any capital outlay.
It may be possible to make them out of a precipitaion hardening steel as this would be a way of avoiding distortion due to heat treatment but they would be expensive. It wouldn't be worth making less than 10 hubs.
It would be fairly easy to model them but I would be worried about lack of demand.
Yes - that is where the separation occurs.
There has to be at least 50 SWB race cars in the US alone and these parts aren't getting any younger.
The problem is you can't buy new hubs (that I've found so far) so you're relying on used parts which you don't know any history. And you're still back to crack-checking every year which is a PITA.
I'm looking into getting them machined to aircraft spec from modern materials, but would need to sell a number of pairs (maybe 10 to 20) to make it cost effective for everyone. I was hoping someone had already taken on this project before I went all-in.
The question is how to get the word out to the racers that need these - whether they know it now or not. Any ideas would be really appreciated.
Steve
Why not go the other way and fab a hub carrier to allow you to use LWB stub axles? Then get the vintage bodies to REQUIRE their use.
1966 911 #304065 Irischgruen
There isn't enough material in the SWB Housing to fit re-machine to fit the later hub/bearing design which could have been one solution.
Re-manufacturing the bearing housing is also quite complex and would be expensive.
Some of the short RSR Arms are using cast steel housings to replace the forged components and I would be concerned about fatigue and impact strength witout doing a certain amount of very costly testing.
A forging die would cost too much money relative to demand and to machine out of solid would cost more than making the flange.
It is possible to shorten the later steel arm to fit a SWB car even with standard wheel arches.
They need shortening in two areas.
The main tube needs shortening and the angle of the eye needs to be modified as the first stage and to put the wheel in the correct longitudinal position and to be able to adjust camber and toe correctly.
The section of tube between the bearing housing and the spring plate mounting also needs shortening to allow a 6" wheel to fit under the wheel arch.
This is one we have just modified and is about to be bead blasted before painting.
The problem is that the 'core' arms are difficult to find and costly to modify.
I think it must be more cost effective to make the hub.
One of the issues is that a billet of a quality material such as S155 large enough to make the hub is around $250 before machining and the amount of metal that needs removing is large.
Again a forging die is too costly so we are planning to friction weld two smaller billets together to make a more cost effective blank. using this technique will save a significant amount of money.
Last edited by chris_seven; 07-19-2012 at 11:41 PM.
Chris - are you planning to make these to sell to needy racers like me?
Steve,
We have two plans which are going forward.
The first is to crack detect, shot peen and totally refurbish some exiting hubs as I think this is a good short term solution and I have about 6 hubs that we have already started preparing.
The second is to prepare the frition welded blanks and I have drawn up the material requirements and will buy the steel next week.
It will take about 2 weeks to have the welding carried out and about another week for the heat treatment.
In the meantime we will draw up the hubs so we can make a short run of parts.
I think we will initially make 10 pairs and see how we go.
I am sure that S155/300M will be the best material - still relatively expensive but great quality.
R all SWB hubs the same; including 's' & the infamous 68 model ?
The PET only shows the above part numbers until the LWB cars in 1969 and the bearings are identical for '65 - '68 so I can't see why there should be any changes.Originally Posted by chris_seven
We have now made a batch of new hubs to suit this application.
We have made them from 4340 and they are currently being heat treated before final machining, splining and grinding on the relevant seal and bearing locations.
I expect them to be completed by the end of the month and will post up the relevant photographs as soon as possible.
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