Lotus Europa Community
Lotus Europa Forums => Garage => Topic started by: Nockenwelle on Sunday,February 24, 2019, 07:58:56 AM
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As we all know the rear axle/hub construction is not the strongest part of the Europa. Nevertheless I'm planning to keep the original design and just renew all worn parts on my S1.
The problem is I need to check if the stub axle is still up to the job and has not been stressed too much in the past. On my first Europa it happened to me that when I was undoing the big nut securing the stub axle the threaded part just sheared off.
If that would have happened while driving I would have encountered a typical Lotus brake down by loosing one of the rear wheels. That's not something I'm particularly keen on.
Does anybody know if there is a reliable way to check the existing stub axle for weakness? Or is the only way to be sure to replace both stub axles by new ones?
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Would magnafluxing detect cracks where the threads end?
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You can't really check for "weakness" because the material itself isn't going to degrade over time, well, apart from rusting of course !
As SwiftDB4 says, magnetic crack detection is most likely the best way to check for surface cracking. You could use a dye penatrent test kit yourself but that's not as searching as mag. particle. Ultrasonic inspection is also possible but again this is a specialist technique and I'm not sure what else that will give you.
When your first Europa sheared the stub axle nut it was most likely part way through a fatigue failure and you were "lucky" to push it into complete failure during some maintenance. If you took your axles to any NDT (none destructive testing) lab they might even do the test whilst you wait, it's not a big deal.
Brian
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Which may bring up the subject of replacing the original stub axles. I know Richard at Banks was having stub axles made, and was searching for heat treating the axles last I asked about them, which was 3-4 years ago. Are they available now and if so, what is the opinion of them?
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I just checked Richard's site and he has two listed for the TC:
original Lotus shaft - described as a "A genuine Lotus replacement part to original specification." There is no description beyond that. S2 versions are also available. The price is £262.25 each for S2, £273.75 each for TC.
EN24 Billet (modified) - which looks very stout (see picture). As you can see, they also include their own hub. Not being familiar with English steel designations (not that familiar with US designations any more beyond how a few compare relatively in strength), EN24 is pretty strong ~ 130,000+ psi. They are apparently free because there is no price associated with them! :) Obviously, it will require a call to Richard to get details. I presume these are the ones to which Andy referred.
Actually, I am now curious about both the Lotus replacements and Richard's. I might be rash in thinking this, but I would expect that the supply of Hillman Imp (or wherever they came from) has dried up by now and Lotus is having new ones made. That being the case, I would think they would make reasonable improvements such as heat treating - but then I tend to be on the optimistic side!
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Interesting suggestions so far. I will at least get the stub axles cheked by a proffesional.
Is anybody actually using the Banks updated version of the shafts?
And this picture shows what could happen if a drive shaft fails while driving (found here http://www.wreckedexotics.com/accident/4269?c=mo450 (http://www.wreckedexotics.com/accident/4269?c=mo450)):
Mechanical failure of one of the drive shafts caused the driver to lose control in a corner and spin off causing severe rear damage.
(http://www.wreckedexotics.com/images/5/900_o4269.jpg)
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Wow that’s catastrophic failure. :blowup:
I will definitely take heed.
Dakazman
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Yikes! That must have hurt!
There used to be a guy on eBay who had a similar arrangement but I just looked for him and didn't find him so he may have closed up shop. IIRC, the reviews were spotty. A few years ago, a guy here had a problem with his stub axle and it turns out he had the problem with a stub axle he bought from the guy on eBay. Most of the other solutions were modified VW or BMW stub axles. Our own Andy Harwood has developed a twin CV joint setup using VW stub axles. Maybe he can tell us how hard it would be to replace the Lotus half shaft/stub axle assy. with what he did (or is doing).
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The ebay conversion stub axles, the poster here had some issues with, didn't he do some machining on his, that revealed, or caused, the issue? Seems it may have been how the yoke was welded on the stub axle shaft? BDA, thanks for crediting me with developing the VW mod, I can't take credit, That would go to Trimandaran from the yahoo list. His mod is documented with photos on the yahoo group, or knowledge vault. His photos are in the 2474R album. He said he'd had no problems with it, in the 3-4 years of driving, but like most, he's not got many miles on it. His car was for sale last year, I think. Richard Mann was interested in using the VW bits for a conversion, and had purchased some VW bits to experiment with. But, I've not seen that he has been active for a long while. Richard Mann's suspension conversion to his S2, and Trimandaran's conversion are what I've been loosely following. So far, it appears the stock VW Beetle, 68-79 IRS, axles, stub axles, spacers, CVJ's will work, Transaxle output shaft yokes need to be modified for CVJ's. I bought Banks version, which uses a 100mm CVJ, that makes it a given that the clutch lever will need to be modified. There are different options to mount the upper links. My work is at a standstill for now and the near future it appears. HTH
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Is it also true that failure of a perfect stub axle can be brought about by worn bearings/spacer and bearing housing??
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From what I recall, any wear in the rear end can lead to axle failure. Richard Hill from the Yahoo group wrote a detailed analysis of the stresses involved in the rear axle design and it's worth a read if only for another perspective on the problem. It's fairly recent (2017) and he covers most of the theories that have been around.
https://groups.yahoo.com/neo/groups/LOTUSEUROPA/files (https://groups.yahoo.com/neo/groups/LOTUSEUROPA/files)
It's a page or 2 down the list and called "stress analysis" or something like that.
Bottom line is that soft spacers cause problems and that it's not a good design to start with. I'm not entirely convinced that it's a really serious problem although there's no doubt that wear is much worse than on "normal" cars and it should be checked at service intervals. And it's worth bearing in mind that service intervals in the TC Europa manual is 3 months, 6 months for a B service !
IIRC it was Tim Engel who came up with a lifetime of around 15-20k miles and that would tie in with the original owner of my car (who kept a diary from day one) and my experiences over the years.
Brian
Edit to add - the 15-20k refers to wheel bearings and not the driveshafts themselves, a classic example of writing whilst thinking of the problem rather than concentrating on the message.
Once the wheel bearings develop play that's obviously not a good idea for the axle itself.
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I found another evidence of stub axle failure on the net. In the treasure grove of the Europa Central registry I discovered the picture shown below. The axle on my first Europa failed in exactly the same way.
Maybe the rear axle/hub arrangement has to be considered as a 'consumable' like a cambelt or a water pump. They don't last for ever and need to be replaced regularly.
Klaus
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Usually my axles start to wear on the outer bearing journal. Because the axle design was never updated from the original Imp ones part of the journal has splines. There is no need for this as the splines could be shorter there. Even though I loctite everything and use hardened spacers this seems to be my first indication of impending failure. I have never had the threaded part of the axle shear off in the 45 years of Europa ownership, even when I used to SCCA race it with 11" wide slicks.
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I have never had the threaded part of the axle shear off in the 45 years of Europa ownership, even when I used to SCCA race it with 11" wide slicks.
That's the same here (minus the 11" slicks !), although is that tempting fate ?
I haven't bothered to do the detailed analysis that Richard did but from what I have seen in the odd photograph, the failure at the end of the threaded portion is due to fatigue. That implies some load variation and that's most likely due to wear in some components because let's face it, there's enough metal in that threaded portion to cope with twice the weight of the car on a single shaft and you'll struggle to get 2G on a corner.
We can get wear in bearings or possibly fretting on the spacer which allows the nut to become slack. It hasn't actually moved, just what it's holding together has "shrunk" which reduces your 150ft/lbs (or whatever it is). With a lock washer it isn't going to undo, but the service instructions specifically mention checking the rear hub and what will surprise owners of modern cars, that's at 5,000 miles service or 3 monthly interval.
When the cars were new we were used to doing oil changes at 3,000 miles and these were high maintenance cars but these days with annual oil changes, I suspect most of us don't adhere to the instructions in the service manual. Another example - at 40k or 3 years, renew all brake seals, washers, hoses and overhaul the servo unit if fitted. How many of us actually do that ?
So when I see something like a broken hub shaft or a snapped front upright I don't immediately blame Lotus design, I'm more likely to think "there's a lack of maintenance".
Brian
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Is the only check on the rear hub - checking the torque of the nut on the stub axle??
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You should check the shimming of the half-shafts at the same time.
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And also ANY play between the hub carrier and the bearings.
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Personally I have never undone the locking washer and checked the torque on the rear driveshaft nut although I would agree that it sounds as if you should from the wording in the manual and the reference to checking other torque figures.
When I ran the Europa daily I'd have a monthly "Sunday morning session" where I'd look over it, check oil levels and lubricate the trunnions/rear UJs. For the rear hubs I'd just check for play and smooth rotation, heaving on the wheel usually shows up wear before it gets serious. Out of interest my worst ever bearing was showing wear at 4,000 miles although I think there was something wrong, either me when replacing the bearing, buying the wrong specification or maybe just cheap rubbish.
Brian
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Very valuable comments here, highly appreciated :)
I think the reason for the thread failure could indeed be to drive the car with a non-properly torqued stub axle. If the hub is not properly seated on the axle there is an increased bending moment with every revolution of the wheel. As our cars have seen a long time of usage you just don't know the 'stress history' of the part. I will carefully check the part but tend to just buy two new stub axles to be on the safe side.
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The stub axle assembly was lifted from a low-HP car. The reason they break is a lack of a proper radius and, mainly, because it is made of cheese.
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Not good news for my 150HP TC in my Europa..........
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I wonder if having a twin link rear suspension helps the stub axle since the stub axle is no longer part of the suspension (if you get my drift). That should relieve it of the tension and compression normally transmitted to the tranny. On the other hand, the failures don't appear to be related to tension or compression - unless you consider failures from squashing the stock bearing spacer as a cause for failure but then hardened spacers would be the solution for that. Just thinking out loud...
JB, I noticed that you posted a picture of an alternate stub axle arrangement. You've probably already posted about it but could you tell us a little about it here?
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The stub axle was brilliant but the machining of the splines in the yoke were off. I have it at a machine shop right now to correct it (hopefully).
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Was it of your own design or did you purchase it somewhere?
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It was this chap:
http://www.dogrings.com/products.html
He used to offer replacements for the Imp axle set up as used in many 60s single seaters. Not sure he does any more.
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Wayne Mitchell is the owner of Dogrings and lives about an hour away. He has a varied background in engineering, formula race car driver and now a machinist working out of his garage. I have commissioned him to to design and fabricate an updated Europa hub and stub axle. Stay tuned for updates.
If anyone has a need for rear type 47 magnesium uprights, Wayne has a couple of sets left over from his run about 10 years ago. They are a beautiful piece of work
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I was looking though some files and found this design for half-shaft/stub axle/disk brake. I found it on lotus-europa.com. It's an apparently old contribution but it was anonymous. The half-shaft part looks a lot like what Richard is selling. It's not complete as somethings are not designated like materials, splines, or suppliers of bought parts (I think there is one or two), but I thought it might be useful to someone as a starting point.
edit: I originally said I didn't know where it came from but I finally found it on lotus-europa.com.