BMW/Titan LSD Viability

[Doctor]

Dear all, prompted by a few friends I was asked to share my experience with the different LSD functions and durability. I don't work in the automotive, I'm self taught - apology for the inaccuracies in advance. All of my Caterham experience has been Duratec based and 250BHP plus. They have had some reasonable torque. Here it goes.

I've bought my first Caterham in 2014 - it was a new CSR chassis with 2.0 Duratec engine from Duratec R500 Superlight. The reason for the change was the revvs of the highly tuned 2.0 and probably me being unlucky with the CSR 2.3 test car - lackluster, not revving, swoopy dash - all the wrong signals. The car came with 7" Sierra diff (as did all CSRs) with Titan LSD based on my previous experience. That had a shape of my friend's 2011 CSR EU4 car with 2.0 175 BHP car delivered with Quaife ATB LSD. Very quickly it became obvious that this is not the way - even when not pushing 100% on the race track the car's behavior was very erratic in the corners - every time the car hit the curb with the inner wheel it virtually stopped - for obvious reasons stemming from the function of the ATB - never locking up fully and transferring only the part og the torque to the outer wheel, never all of it. Once the driveshaft snapped, ATB was done for as not suitable for a track use. The next in line was Tran-X plated LSD marketed by Quaife - a product with a friendly price tag. Working much better than ATB when in one piece we recognized that the while principle was correct, the product was not. After talking to Steve from SPC I now understand why - it was developed to deal with much less power and torque in mind then what we exposed it to in Duratec engined Caterham. So this brings me back to Titan. Again, reasonable product when in one piece, my car was able to disintegrate it within about two years and the rebuild was due. All while using the car enthusiastically on the road and doing anything between 3 and 7 track days per year - mainly organized by the club. Same symptoms as described here many times - sinister sounds, erratic locking and unlocking. Spinning at Brands Hatch left hander (Surtees?) on the dry when putting the power down was the final straw - taking it apart (courtesy of Gave Gemzoe Motorsport in Wakefield) revealed the usual - worn clutch plates, broken both Belleville springs, milled away thrust washers. And I consider myself lucky. Why? If the Belleville spring decides to fracture into small enough pieces (this issue is more of a problem with BMW 168 where the Titan LSD has bigger holes in the LSD casing foe the oil. If a piece of a broken Belleville spring finds its way out of the LSD casing (possible) it can also find its way into the pinion and the crown wheel, the consequences of which could be disastrous....

Now let us have some theory, even though it's all merely a repetition with many people here making a very good valid points (Simon Rogers, Neil (7wonders) and a few other spring to my mind immediately). So what is the meaning of all of these things that determines the behavior of our LSD?

1. Static pre-load: this basically describes the amount of torque that will always be locking the wheels together. Increasing it will improve the responsiveness of the locking effect, but it will also increase the noise and the under steer (by not allowing the clutches to slip when the car is cornering. Pre-load represents the base amount of locking torque built into the LSD system. 

2. Ramp angles: depending on the manufacturer, the lower the angle the less torque from the engine needs to be applied to initiate the locking action above the static pre-load. The current LSD designs usually allow for different setups and the description of the ramp angles usually contains two numbers - the first represents the ramp angle used for locking action under power (the torque applied via the prop shaft) while the second one represents the ramp angle applied when we lift off (coasting, the torque is applied via the driveshafts). Titan has exchangeable pinion rings - the first (usually installed as a default) offers 30/90 (usually active as this is the setting allowed for Caterham Racing) with 45/60 as the second option. The second has 30/60 and 45/45 alternatives. The SPC Tracsport comes with 30/30 or 45/45 options for both Sierra 7" and BMW 168 casings.   

3. Locking capacity of the LSD - usually by varying the clutch arrangement that will determine the friction surface - it will have the similar effect on the response of LSD as ramp angle change but it will also limit the maximum torque transferred to the other wheel. Used if despite the low static pre-load and less progressive ramp angles the diff is still too aggressive - not really applicable to us as our problem is usually the slip. 

So why has Titan so many problems and what are the differences if we compare it with SPC Tracsport? 

I'll try to keep some clear continuity here but the problem is that everything is connected together so one thing changes - everything else changes. The easiest to dissect is probably the pre-load Belleville spring failure. Titan has two of them (40ft.lb), they are much stiffer and bulkier than the one found in Tracsport (20ft.lb),  yet they fail way more often than the single spring in Tracport that is much finer - I hold both in my hand side by side. Neil has described it quite well already - the Belleville spring has a shape of a cone - hence the name coned disc spring. The problem of the Titan LSD is that once under load (locking) it repeatedly squashes the spring completely flat (using 100% of the spring lift) which (together with the increased heat induced by the clutch slip) introduces accelerated metal fatigue and fracture with the loss of pre-load. Now, why does Titan need the double of the Tracsport pre-load? It is because it is trying to compensate (unsuccessfully) for the insufficient area of the friction plates to prevent the slip (wheel spin) under load. What is the evidence for that? That would be our thrust washers nearly completely milled away we see on rebuild and also the worn clutch plates. How do we increase the friction area of the LSD? We increase the number of friction plates and increase the size of them. In order to do that we need to increase the size of the housing. Essentially we need more plate friction area that will prevent wheel slip/spin when torque applied to LSD and that will also  allow us to use less pre-load and that in turn will reduce the noise and also makes the diff more friendly when there is a difference in the wheel revolution (turning). One crucial difference - without going into too much of a detail the Tracsport design is clever enough to prevent the Belleville spring to be completely flattened by the action of the LSD - that is an in-built feature. 

Now this is where I speculate a bit so I could do with a bit of a facts check. Looking at the TitanExpress website it would appear that the LSD service kit for the Titan LSD is the same for Ford Sierra 7" and BMW 168 diffs - implying that the size of the clutch plates is the same which I would consider this a mistake since the Sierra 7" is a much larger housing allowing for a bigger LSD - that is exactly what the Tracsport is. I've seen Tracsport versions for Ford 7" and BMW 168 side by side and the Ford version is bigger - possibly using bigger plates that would give more friction area (I'll check this with Steve). 

Conclusion: I now run 620R SV with Sadev sequential, masses of torque compared to my normally aspirated Duratec and it came with Titan LSD. Incidentally I was forced to drop the diff due to the pinion oil seal failure, so I've decided to go for Tracsport there and then. Steve has been a delight to deal with, showing me all of his secrets (not that would possibly dream to understand them all), patiently answering all of my silly questions. He did the final assembly right in front of my while debating comprehensively about all sorts of topics in life!! An utter professional. My impressions? Awesome. I went for 30/30 ramps, chickened out a bit with the oil and went for 75W-110 LSD spec of Millers Oils Nano thing, and the car is a joy to drive under power out of the corner (due to no "I can't cope" LSD slip and the utterly predictive behavior under power). The result is that the rear of the car now feels much more planted and it simply grips and pulls. the biggest transformation for me, however, came under braking - the car is much less nervous under braking on bumpy surface, and also much less thrown out of composure by a cheeky downshift. This one part simply made me feel way more in control of the car then I've ever felt to be before. 

I'm not forcing any of this on anyone, I was simply asked to put something together. Well, here it is.        

[CheshireCat]

Very Interesting. I may have missed something here but how do you decide on  30/30 vs  45/45 ramps ? 

[Doctor]

The Titan ramp angle was 30 degrees under power and I didn't really want anything less progressive. 

[Doctor]

The Titan ramp angle was 30 degrees under power and I didn't really want anything less progressive. 

[Geoff Brown]

As a point of interest Steve Perks of SPC set 45/45 in my LS unit. Because of a whole host of things weather included a test drive is off the cards for some time to come. Maybe even next spring!! 

[ScottR400D]

Mine too is 45/45 which is a good starting point for a mainly road use with the odd TD, I would think.  

With the extra power The Doctor has and his use, 30/30 may well suit him better, but would be a little too aggressive for me. 

Proof of the pudding etc, I am still very happy with mine, no noise and very good behaviour. Another very enjoyable couple of hours out yesterday though it’s getting a little cold for the ZZRs!

That’s it till spring for me too!

[Grant_7]

My Tracsport was also collected last week (Friday) and also set at 45/45 ramp angles.

Will be driving the car back from Premier Power at some point this week, so will get to test the diff, although the journey is only very short (5 miles) and I don't expect to be able to prove much. Still excited however!

[Geoff Brown]

Having just completed my diff refit I filled it with oil. I know that with the Titan LS unit fitted the oil quantity is about 1.0 when allowed to overflow. Currently I believe CC suggest 0.8L to avoid the output seals leaking.

As the SPC LS unit is slightly larger than the Titan one would expect the quantity to be less but I only managed to fill to approximately 0.6L before overflow.

Can anyone who has gone the SPC path confirm this quantity?

[ScottR400D]

That doesn’t sound right Geoff. I got .8l in with no overflow. It never occurred to me that the different lsd would need consideration because in the past I’ve put 1.2l in to overflow, as used to be the recommendation. 

There should be loads of space.

Some thoughts:

Steve didn’t already fill it did he? Unlikely. 

Is the car level or tilting forward? Not tilting down at the rear. 

Are you sure it’s genuinely at the level hole? Maybe rotate the wheels and try to add some more. Maybe it’s not flowed into the lsd? Just guessing now. 

 

 

[Geoff Brown]

ScottR400D #259 - No Steve did not partially fill. Yes the car is in its usual position for servicing on sticks. Absolutely level.

I am going to rotate the internals some & see if that makes a difference for the sake of the very important 0.2L.

Unfortunately no test drive for a few weeks!

[Dave Hardcastle]

Update on my car. Thanks to Martin Phipps I was able to confirm that a Quaife unit was fitted. So the fact that rear wheels turn in the same direction does not preclude a Quaife being fitted, for any future readers of this thread.

My diff has been with Steve Perks for a week now for a Tracsport to be fitted. Having never removed a diff before it's been an interesting time. Thanks to John Vine for the guide that I found elsewhere on here, took the trepidation out of it.

Keeping my fingers crossed that we have some dry days before the new year so that I can go out and play! 

[ScottR400D]

#260 Hope that works Geoff, there should be loads of space for .8.

Let us know how it goes. 

[Grant_7]

Today I collected my car with new Tracsport diff and managed to make the 5 mile journey home last for 30 miles.

Early days for any impressions of traction advantages, especially with the roads being so greasy, however without a doubt it's a hell of a lot quieter than my previous Titan...and that wasn't too bad (as Titan's go). It is literally silent now and super smooth in running; no clonks or drivetrain backlash at all.

In fact, I now realise how noisy my 6th gear is around 65mph (doesn't do it in 5th at either same road speed or same crank speed - perhaps something to do with it being 1:1 and therefore on a different spindle within the gearbox?).

So early days, but without doubt it is quieter and smoother in operation. Next proper test will be on track, especially out of the hairpin at Mallory Park which I struggled with earlier this year.

[Geoff Brown]

Grant_7 #263 - Thanks for the feedback. Your first impressions are those of others & I am sure as time goes on you will be pleased with the SPC LS unit.

My car was ready for road test just as the weather changed for the worse last week & coupled with recent minor surgery to my go & stop feet it looks like no road test for at least four weeks! To quote my Orthopaedic consultant 'no fooling around under or in your little car for some time' !

But I will report here when I do.

[ScottR400D]

Grant, the 6th gear noise you mention, do you mean the light chatter you get on very light lift off or the general noise on overrun?

My car will give the light chatter at about the speed; as you say same revs in 5th it doesn't do it but it does do it in 5th at lower revs. For me it seems to be a certain combination of rpm and load in different gears that allows it to happen. Steve P reckons its excited by firing pulses not being damped because of the light flywheel. I find it easy to avoid by just avoiding the specific conditions.

I also find 6th noisier than other gears on full overrun, just a general 'geary' sort of noise but definitely more than in the other speeds. At first I thought that was the diff but in 5th there's nothing.

[Grant_7]

Hi ScottR400D,

No, not a light chatter. In fact I don''t have anything like that on my 420R that I've noticed. However from your post:

"I also find 6th noisier than other gears on full overrun, just a general 'geary' sort of noise but definitely more than in the other speeds. At first I thought that was the diff but in 5th there's nothing."

Exactly this! Only happens in 6th around 65mph or so on lift off. All other gears are silent. 

[Geoff Brown]

In a moment of boredom I decided to carry out a PM on my now redundant Titan LS unit (aka door stop).

The pics are of the shims, a thrust washer - the edge of which I could shave with - the 'springs' & the plates sans carbon.

Pretty much what others who contributed to this thread found. But not as bad or catastrophic as some!

[DJ.]

Looks pretty grim!

[Geoff Brown]

Not bad for 7 years & 20000 miles considering the service cycle for a Titan is one race season, annually or 10000 road miles with track days taken into account.

Be assured my damage is quite tame in comparison to others who posted here. 

Pity that CC did not make known this 'weakness' at point of sale or in the Owners Handbook. 

[ScottR400D]

The thing is Geoff, I’d suggest that many of those parts have been like that for quite some time and the LSD just hasn’t been functioning. 

In my case though the plates didn’t show quite so much wear as yours I think that at some point where my LSD was still functioning to some extent one of the springs failed catastrophically, simultaneously meaning the LSD didn’t then function at all and the bits of spring went wandering around in the housing! 

Next, one of the bits managed to find its way into the CWP, bringing things to my attention quite noisily.......

 

 

[DJ.]

I've just seen a video on Facebook where one of four loose bolts from an lsd (make unknown to me) went into the crown wheel during a lap of Brands! It sounded horrible.

[Nigel B]

I think you did well to manage 20,000 miles Geoff. My Titan internals looked very similar after 6,500 miles. Only one of the springs was broken on mine, but otherwise your photos look very familiar!

[Billy.Whizz]

#124 not heard anything back from Mr Mac yet then Geoff ?

[Geoff Brown]

Billy.Whizz #273 -  CC are silent though that could be the nature of the beast? You cannot tell me that those at Dartford & Crawley do not read these pages. They must be aware of what is going on in the Seven community.

With a no reply in mind does any one out there know the CC Macdonald e mail address?

The alternative is a drive by of Dartford & Crawley with my letter wrapped around a house brick?!

[Billy.Whizz]

Geoff I have a 420R on order and have mentioned the apparent problems with the titan diff to the sales team and they seem to know nothing about it. Strange.