270r lsd problem

[ScottR400D]

Just been out for a blat in my 2015 R400D. All as normal until, cruising along at about 60, lift off and the diff chattered much louder than it ever has. It's always done it a bit but this was definitely much louder. 

It stopped after a few seconds and went back to normal levels of chatter. 10 minutes later slowing to a stop at some lights there was a distinct 'knock' from the diff as I slowed. Only became distinct at about 20mph and definitely from the diff.

Once on the move again it was as normal until just before I got home when I had a short burst of the loud chatter on lift off, then back to normal. The 'knock' is still there as I slow.

I'm assuming this is the plates problem, diff out, have it rebuilt with sintered plates? 

I have noticed recently that, giving it a boot full in 3rd/4th will get the rear squirming even on decent roads. Same cause? 

[7 wonders of the world]

Scott

If your running a Sierra final drive just cut your losses and get a decent LSD fitted and then you can spend more time driving   

Tracsport LSD is the way to go......... 

[ScottR400D]

It’s the BMW diff. My intention is to remove the diff then do whatever TracSport recommend. 

[ChrisC]

Could also be a driveshaft problem, there is a spring that can break.  Makes a terrible noise when it goes, but is for some reason intermittent.  Had that on a 2011 Sigma car a few years ago, so don't assume diff straight away.

[ScottR400D]

Thanks Chris. Where is this spring?

I’m leaning toward the diff because the noise today was just a louder version of the chatter that’s always been there. 

I’ll prob just strip everything out and check all carefully. 

Do we have a guide as to the order to remove everything, I forget how I built it! 

[ChrisC]

Unfortunately not 100% sure before mine was discovered by Boss Racing.   In think its on one end pushing on the shaft itself, so a simple fix (if you can get the part).

My original post

https://www.lotus7.club/forum/techtalk/road-speed-clonk-what-solved

[ScottR400D]

Chris, I saw the video and posted this in the old thread instead of here. 

Thanks Chris. That’s interesting. The noise in the video is just what I get when rolling to a halt but tge chattering at speed was different. As I said it’s always chattered but this was louder without doubt. 

I’ve jacked it up and the wheels rotate quietly. I notice that turning one causes the other to go the other way, in neutral. I thought it should go the same way but searching seems to suggest:

1)It should go same way.

2)it should go other way. 

3) It shouldn’t move.

4) It doesn’t matter. 

Dies anyone know for a fact?

[7 wonders of the world]

With a plate LSD both wheels should turn in the same direction, depending upon preload there may be a difference in rotational speed ie if the preload is very light.

However if yours are rotating in opposing directions that would indicate no preload allowing it to mimic an open differential.

common causes are broken bellevilles or worn / damaged plates.....

drop one wheel to floor and see if you have any preload

[ScottR400D]

Thinking ahead, can anyone confirm that SPC rebuilds the BMW/Titan diff? I still have the issue with mine that RRT have looked at twice and failed to fix and was thinking of trying Steve.

I'm about to take it out for the 3rd time tomorrow.

[7 wonders of the world]

Scott,

Give Steve a call, make sure you have a hour or two though,

Not sure where you are but if you can pop up and see Steve  

[ScottR400D]

Are you confirming that he does the BMW diff, 7W?

I'm about 3 hours from him but plenty of time.

[ScottR400D]

Are you confirming that he does the BMW diff, 7W?

I'm about 3 hours from him but plenty of time.

[ScottR400D]

Well, I believe I've finally got to the root of the issue and I at last have a functioning car.

My diff was removed for the second time after a full rebuild by Phil at R and R didn't cure a tapping noise that seemed to emanate from the CWP. Phil and Olly did some work on it and it was replaced but still had the tapping noise. Out for a third time and back to R and R more close inspection and it's been assembled again and is waiting to be tested. Phil and Olly have been brilliant, but it seems damage was done when the Titan LSD disintegrated after 8000 miles.

Whilst they were doing that it was suggested that I talk to Steve at SPC, mainly to see if he had any advice to offer about what might be causing the noise because, according to common belief, he doesn't do the SPC LSD for the BMW 168 differential. So I rang Steve to find that he DOES make a version of his diff to suit the BMW! 

In the end I've bitten the bullet and bought a new open diff from CC and had an SPC LSD fitted by Steve. (Did I mention that he DOES make a version of his diff to suit the BMW!)

If you speak to Steve he will tell you with some authority that the Titan LSD is the problem with these diffs, especially when you're putting 200bhp + through it. Apparently, it's not really big enough and the Belleville washers used in it operate between hardly any load to 100% deflection, I.e. flat. They're not designed to do that;they should operate between 15 and 75% full deflection (that's easily verified on line) and so they crack. The more torque they have to handle the sooner they crack. The plate material used in the Titan isn't the best either, again that seems to be commonly acknowledged in the diff industry. 

The SPC diff uses molybdenum plates (like ZF) and bigger and correctly loaded Bellevilles. It has the reputation of being much stronger and quieter and better in operation than the Titan, will easily take the torque of the most powerful 7 and will last a long time. (Fit and forget has been used in its description) 

So what's it like? Well, I've only done a couple of hundred miles so far but I find it silent, clunk free and it's definitely more effective than the Titan. Before, giving the car full throttle in lower gears would often result in 'fishtailing' if the road surface was less than perfect and would often set up a slide coming out of corners. 

Not any more; give it full throttle out of a tight corner and it just rockets off in the direction you're pointing it. So far I haven't broken traction at all, and I've tried. It also seems to turn in easier as if it's not encouraging as much understeer as the Titan. That's hard to define, it just feels better, I have much more confidence in the car.

During this exercise, I've been informed by both CC and RR that the Titan diff does need regular inspection and maintenance and it's not unusual to find them failing at low mileages and causing other damage. I've gathered that regular checking of the preload and changing the oil to inspect for debris is very worthwhile.Steve has recommended, for me too with his diff, the fitting of a magnetic filler plug. I've done that, it should make inspection for debris that much easier.

The downside of all this is the cost. I've spent well over £3.5K sorting this, though I now have a fully rebuilt spare Titan assembly. The SPC LSD is a couple of hundred more than the Titan new, and not necessarily that much more than a full rebuild if the Titan breaks up in use. ( My rebuild was around £900 all in, it won't take many of them to pay back the investment if the SPC is all it's meant to be)

I would strongly recommend anyone who's having to consider having their Titan rebuilt to think about fitting an SPC instead. If it's all its cracked up to be, (and IME, other than longevity which I can't yet attest to, it is) it's the better option, IMO. Especially if they have over 200bhp or their Titan hasn't lasted as they expected it to.

 

[DJ.]

Good to hear you're finally happy with your car, I hope you enjoy many trouble free miles now

Duncan

[ScottR400D]

Thanks Duncan. I’m certainly enjoying it more than I used to.  

At least I know how to remove and replace the diff and most of the back end!  

[Shortshift]

Excellent news - though £3.5k in total is rather eye watering.

Good, also, to have confirmation that Steve at SPC can supply one of hos LSD's for the BMW unit. 

I'll be out to check my (presumed) Titan carbon-plate unit later today...

James

[aerobod - near CYYC]

Peter, is this the BMW 168 LSD unit that SPC fitted to your car? https://racingdiffs.com/collections/all-solution-lsd-unit/products/bmw-high-performance-lsd-unit?variant=33671152894087

[7 wonders of the world]

No, Peter has a Tracsport,

Steve @ SPC has now made a version of his proven Tracsport that fits the BMW final drive, previously it was just made in Sierra format.

 

[Doctor]

Truth to be said, Sierra is a much stronger diff than BMW, and that goes for the SPC as well. 

[ScottR400D]

Doctor, yes you’re right in that the Sierra diff  has a larger CWP and stronger and more capable bearings because they are large taper rollers. The BMW unusually runs ball bearing races presumably for lower drag and lower emissions. 

The SPC LSD for the BMW has slightly smaller internals for packaging reasons but is still a lot more robust than the Titan, not just because it’s bigger  

There’s an argument that the best solution would be the Sierra casing with the SPC LSD but to get that in a car with a BMW fitted requires new driveshafts and propshaft so a pretty expensive change given that the BMW housing, CWP and bearings are not the weak point in the assembly. 

I’m of the opinion that the BMW housing and CWP fitted with the SPC LSD is a good upgrade without necessarily being that expensive, if the Titan needs rebuilding anyway. 

[7 wonders of the world]

Sierra one is also lighter too....

[Doctor]

Bottom line is not to buy a Caterham with BMW diff. 

[ChrisC]

Its funny how the tides turn, if you read old posts on BMW diffs on here its all about how wonderful the BMW diff is after they swapped from Sierra units.

[Doctor]

They are smooth and run fine, just unable to handle higher powered vehicles. 

[ScottR400D]

As far as I’m aware it’s the Titan LSD that can’t handle the higher powered vehicles. 

Why is the Sierra unit any better than the BMW in that respect?