Got a BMW diff? - check your bolts

[redlight]

The diff is only part of the story, lets hope CC get this sorted out soon and we will all be confident in knowing are cars are fun to drive again. I am composing the letter to the CEO listing the build progress of my car over the last 3 years.

[pmobbs]

Today, I collected my car from CCs at Dartford. The diff carrier and the brake lines have been replaced. The De Dion tube has been left in place. I was able to have an extended talk with George Campbell (Engineering Development Manager). I found him to be intelligent, thoughtful, measured and helpful. I put two questions to him - 1) Could he guarantee that the new pattern diff carrier would allow the clearance necessary to prevent any further contact between it and the De Dion tube? The brake line in my car had been flattened on the driver's side through impact with the bolt heads on the old style diff carrier (see above for photos). I explained that I was concerned that the new style carrier reportedly only reduces its length at the point responsible for damaging the De Dion by 11mm, and that because on my car the brake line that had been flattened ran across the midline of the tube which is ~50mm in diameter, I could not understand how reducing the carriers length by 11mm could guarantee the tube could pass the carrier without damage. On this matter he responded that CCs priority had to find a fix that dealt with the safety issues involved and that they were confident that the new carrier and revised brake lines rendered the car safe. However, he did not leave me with the impression that the fix they have employed would guarantee the clearance necessary to avoid damage to the tube. He agreed that good engineering principles would suggest the suspension should not under any circumstances by able to contact the De Dion tube. 2) I asked what measures CCs had taken to contact the owners of cars with the same specification as mine (Roadsport 150bhp delivered/manufactured in June 2011)? On this, he said that it was not a simple matter. CCs had concentrated on the engineering solution to the safety issues and that they were still developing a plan of action. I suggested that as a first step they might like to place a notice on the CCs' web site asking owners of suspect cars to inspect their De Dion tubes and diff carriers. I offered the opinion that it would be to CCs advantage to be proactive in this matter and that I was not happy to think that there might be cars on the road with what appears to me to be a potentially dangerous fault.

 

I drove the car home more slowly than I would normally! I noticed that a clonk from the rear had disappeared and that rear end noise had decreased substantially. I guess that may be new diff oil, or my imagination, but I think the new carrier that is reportedly much less likely to flex, was in some part responsible for quietening things down.

 

Where to from here? I have copied two emails that I sent to James Gibson earlier on to the CEO of CCs. In one of those emails, I specifically asked Mr MacDonald to respond concerning communication with the owners of the cars affected by the diff carrier design error. I will now write to him to put to him directly the same questions I put to George Campbell. I have asked George Campbell to inform Graham MacDonald of the detail of our conversation. I am hopeful of a prompt and reassuring response.............

 

I will post pictures of the work done by CCs as soon as I have had a chance to get the car up in the air.

 

Blatchat may be a thorn in CCs' side, and I can understand why they may be aggravated by some of the posts, but at the present time all I can say is God Bless you Blatchat and the Lotus 7 club....****unless I had read the post at the head of this thread, I would have been blissfully unaware of a potentially catastrophic fault****. I wonder how many people are in that unfortunate state at the present time?

[Grubbster]

Fitted more to the dedion today, still if I raise it though it hits a little bit of casting that sticks out before reaching the bolts, so even if mine weren't countersunk I don't think the tube could hit them

 

This is still the case with mine, the brake pipe supplied is modified to put it further back on the dedion, but if my suspension moves into extreme compression I'm sure it will hit the bit of casting that protudes from the back of the diff and therefore wouldn't go high enough to reach the bolt heads (if there were any).

[ParsleyTheLion]

Thanks for the comprehensive update pmobbs.

 

Presumably, this means that the "new" level diff carrier is just a containment action, and perhaps CC are working on a further and proper redesign that robustly gives adequate clearance...

 

Let's hope so...

[pmobbs]

Not sure whether it's a containment response or not but I have yet to be convinced that what has been done is a true 'engineering solution' that will prevent further damage to the De Dion. Frankly, given the reports above and my own experience, I really don't think it's a long term solution. I plan to hold CC to its Quality Assurance statement and they absolutely must deal with the issue of owners who may be unaware they have a potentially dangerous fault. This is surely in the company's best interests.....it can't be long before they read about this problem elsewhere than on Blatchat?

[Alan Reeves]

Thanks very much for the update and our thoughts.

 

I am currently sunning myself in Aus but will be back on the case when home.

 

It is interesting that they find BC a thorn but they just do not respond in a manner that would at least make one feel there is a fix coming for all of us.

 

It is interesting in that after they tightened up mine etc it was quieter ie no clonking...which of course i didnt know was clonking

 

Thanks

[Oily Mick]

Quoting pmobbs: 

they absolutely must deal with the issue of owners who may be unaware they have a potentially dangerous fault. This is surely in the company's best interests.....it can't be long before they read about this problem elsewhere than on Blatchat?

Hope you have more luck than dedion mounts that just let go without warning here

☹️

[redlight]

Thanks pmobbs for your report back. I think that the rest of us need to keep this issue at the top of the Tech Topics list so that CC can see that we are not going away. I have not checked to see what my de dion tube is hitting, bolts or casing, but it is marked. As the marks are on the front edge of the tube I do not think the brake pipe is in danger of being hit. As I had the new lock washers from the start none of the diff bolts are loose. I am looking forward to the email from CC saying they have a fix although I am a bit feed up with the thought of taking the diff out for a 5th time in a car that has done 3000 miles in three years.

Come on CC a fix would be a great Christmas present.

[fondelli]

Interesting thread. If you remove the bolt issue, is an S3 and SV chassis affected the same way ie does the larger SV chassis help the fouling problem?

[Garry7]

In short - no it doesnt. A few of the guys in this thread (with damage) run SV's - myself included. I have a dent in the n/s of the tube but well away from the hard brake line.

 

Garry

[fondelli]

Thanks for this- I have just bought another 7 from south- which I am adding a LSD to, so I need to make sure that whatever is the latest mod is added to the car

[redlight]

Latest from CC. They are working this problem, which is good to know. You need to be on their list to receive communication on progress.

[fondelli]

Mmmm Not much point on collecting until there is a solution?

[ParsleyTheLion]

October edition of Caterham Life is on the CC website. This month's friendly face is George Campbell! Had rather hoped his picture would show him holding a modified diff carrier, but it seems to be a steering wheel ....

[1360rallye]

Just been reading 24th Oct issue of Autocar - they've just collected a new Supersport for a long term test.

I also noticed on p13 a article on the Morgan 3 wheeler which suffered a suspension failure during an Autocar test which " seriously damaged the car and made steering impossible". Morgan are quoted as saying the wishbones are "suitably designed for the intended purpose". The article also says that Morgan has since increased the strength of production wishbones by 20% "to allow a larger safety margin to cover people using their cars for experiences beyond normal road driving conditions" Morgan has said it will supply new lower wishbones free to existing owners who want them - but insist this is not a recall.

 

I wonder if the Autocar Supersport has an update diff cage?

 

I also noted in the CC CEO's blog this month an interest in listening to the views of customers...

 

Andrew

[fondelli]

So, Is the concensus that the new diff carrier is a MK1 solution to stop the brake pipe being crushed? The MK2 solution will therefore aim to stop the diff hitting the de dion tube?

[6speedmanual]

Morgan suspension discussion

here

 

I wonder what the mode of failure was? Bent lower wishbonw around the lower spring/shock mounting point?

 

Small volume producers are in a difficult place on stuations like this. They don't run fleets of test cars up to 150,000 miles to see what fails. However, they should respond quickly and decisively to issues which crop up on customer cars as they are effectively the durability test fleet.

 

Awareness of potential issues spreading through car club chat forums is useful for small volume and also for old/unusual cars which are well outside manufacturer support. But not all owners will be spending their evenings on such anorack passtime. Part of a car companies responsibility is to communicate to the owners of the parc of their vehicles.

 

Peter

[Grubbster]

Quoting fondelli: 

So, Is the concensus that the new diff carrier is a MK1 solution to stop the brake pipe being crushed? The MK2 solution will therefore aim to stop the diff hitting the de dion tube?

 

No, the brake pipe route has been modified to keep it out of the way of the diff. The rear diff carrier bolts no longer stick out (as they are countersunk not hex head) so the diff won't hit them in extreme suspension compression. Even without the modified carrier I think you'd be going some in road use to actually compress the suspension far enough to be a problem (unlikely not impossible!).

 

You can see the revised carrier with countersunk bolts here -

 

[6speedmanual]

Seeing as all 7s manufactured now will get BMW diffs, why the heck don't they redesign the spaceframe so it is a direct fit. The carrier must be a hastily engineered stop-gap.

Not checking for clearance at all extremes of the suspension movement seems rather laspe.

 

Peter

[Z3MCJez]

As Peter says, this has to be the answer in the near future.

 

However, presuming that CC don't want to develop two chassis variants, then I can't see this happening until the race cars are all out of Ford diffs. In 2012 only the Academy and in 2013 the Roadsport too are the only series running BMW diffs. It will be 2015 before Supersport has the BMW and I don't know what the plans are for the R300 / R600.

 

Thus I see the diff carrier as having 3 years of life left yet.

 

Jez

[CB]

"Even without the modified carrier I think you'd be going some in road use to actually compress the suspension far enough to be a problem (unlikely not impossible!)"

 

From my experience with the old carrier I'm not convinced by that to be honest. Take one "not particularly light" driver, corner weight the car, later add a passenger and then drive along a standard British road (i.e. not exactly smooth, with the odd small pothole). End result = more clonking of de-dion against the old carrier than I ever got 1-up on track.

[Grubbster]

Fair enough, happy to be corrected on that - it just looks like a hell of a lot of movement necessary to cause the impact.

[Grubbster]

As for a proper solution I'd rather go back to the sierra diff - just have them built properly with quality parts and position the bushes correctly on the chassis and there isn't a problem It's lighter and the dedion doesn't go near it. I've never had a problem with mine on the other car. The BMW one is a lot bigger and heavier, plus the mountings are all near the front so a lot of weight hanging out behind the mountings which can't be a good thing. On the plus side they are reported to give a bit better traction (less slip) than the sierra type.

[fondelli]

Notwithstanding the fact that the carrier needs a bit of re-design, surely if you want to replace a diff with another type, the first thing you would do is find one that fits in the space available?

[6speedmanual]

Finding an alternative diff is probably not very easy. There is range of options but many are from some 4x4 derivative, there not being so many conventional rwd cars about these days. Also vehicle weights and torque outputs are significantly up since Sierra days, especially with current diesel technology. So currently available diffs will (generally) tend to be heavier.

 

Regarding installation, carrying out full movement clearance check is a definite requirement. It is no good to say it is ok most of the time or it only fouls in extremis. The suspension WILL move throughout its range surprisingly often and not just when fully loaded on humps and bumps.

 

Assembling the installation check car with depressurused shocks and no springs allows the suspension to be jacked/levered to all permutations of bump/rebound/roll/steering lock. Then when at extremes (or when fouls are closest, because the fouls could be at a mid travel position) allowance should be make for bush compression (or failure), engineering build tolerances and flexing of the chassis and suspension parts.

 

Doing this before a vehicle was allowed out on the road/test track was standard practice where I worked in vehicle engineering. When anything in that vehicle area had changed, especially wheel and tyre options were more common, a check was made. Getting it wrong could result in an instant tyre slice-up. Collisions between lumps of metal - diff and carrier, axle, brake pipe are entirely avoidable.

 

If the BMW diff fouls only occurred with fixings loosening and unscrewing, then an immediate fix of getting correct clamping tension and possibly loctiting should be approached. (although the countersinking and brake pipe mods mentioned above suggests there is a problem in the fully tightened state)

 

It might cost a few quid to jump on such a problem as is discussed in this thread but surely better than allowing dissatisfaction and damage/repair claims from a growing number of clients.

 

Peter

 

 

 

Edited by - 6speedmanual on 3 Nov 2012 01:42:58

 

Edited by - 6speedmanual on 3 Nov 2012 01:48:19