Stuff EFI - I can't use any more power :(
Turbo Mini Forums

Got my mini out and razzed it up and down the road a few times last night, and guess what - The clutch is slipping YET AGAIN!
In May 04 it had a new flywheel, backplate (to make sure the friction surfaces were nice and new), diaphram/cover (incase this had weakened - unlikely however), friction disc - along with my well documented tweaks to increase the clamping load and it's now slipping again.

I recall it was starting to slip just before I put it to bed in october '04, but it was apparant last night (maybe because I had two other peeps int he car with me (meaning the resistance to the clutch was greater as the car couldn't accelerate like it normally would?)
Dropping to 13psi and flicking high boost (16psi) at 4500 ish rpm it'll not slip, but at full boost it slips and doesn't recover :(

I'm going to swap out the friction disc again, but this is the LAST time...
Instead of concentrating on putting EFI back on it, I'm going to crack on and design a new flywheel and clutch assembly instead (no more diaphrams) - especially as I've located a 'cash in hand' waterjet cutter locally to make light work of the complex ring-gear machining...

Aiming for a minimum of a 280lb ft rating - which should hold torque right down to the rivets on the friction plate and provide plenty of bump-load safety factor in there.

One thing that is interesting - No One else apart from Jimster experiences clutch slip I believe? Those T2's and mapped ignition really do make big curlywurly* figures...





*TM speak for lb ft...

Interesting,

How do you set up the pressure plate? With the diaphram spring level?

I'm yet to try my clutch since I have modifed my backplate. My mini will be on the road in around a week, so we will see then! Although I guess my car dave is around 80kgs (maybe more) lighter than yours, this may help my clutch to hold together. Are you not going for a Double grey?

Team Racing

I used to get plenty of slip after a poor emergency start, it also never recovered.

This was with an AP rally plate and grey diaphram, swoped to a sintered paddle plate and all is well. You have more power than me I know, but my slicks and LSD don't help.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I have tried a rally plate and a sintered plate, no luck, it still slips. I also run a LSD, but on road tyres. Wil, do you know what your old car weighed?

Team Racing

Going off what jimster said - and what AP say about the torque capacity of sintered vs organic, I'm not faffing about with this stuff anymore. I'm really not keen on a sintered for a road car - I know it's well bearable, but my mini is more road car than racecar, and i want it to remain that way.

I am surprised that AP claim their ceramic plates don't have a higher torque rating than organic, certinly Jimster found this to be the case - but they do recover after a torque spike - organic plates will only recover after something like a 25% drop in torque (from what I undserstand of the different materials in a dynamic slip).

End of the day, the fact is that the diameter of the friction area needs to increase, or the pressure applied to it. The former is not the problem, as some of these aftermarket clutch packs available are only a slightly larger diameter... So more clamping load it is!
Double / triple Grey? No thanks: I want to be able to stage on the strip, or sit in stop/start traffic with my foot on the clutch pedal without worrying about my thrust washers... The belville spring in the mini diaphram just doesn't lend itself to creating the required clamping force, with a light release force, like conventional clutch covers do...

Edited by turbodave16v on 8th Jun, 2005.

I spoke to AP, and I told them about my problems, as the time I was running a rally plate, they told me there is no advantage me changing to a sintered plate, if the rally one slips, then so will the sintered.

Team Racing

apologies if this sounds like a stupid question, could you alter the surface roughness of the flywheel to increase friction as an alternative to increasing clamping force to increase friction, or would this see the friction plate wearing to rapidly??

You've answered your own question.

By 'roughing' the surface of the flywheel / backplate, you're actually not using friction to hold the much softer clutch lining but a mechanical lock - which as you say would lead to rapid wear under dynamic slip (ie in the exact situation for what a clutch is to designed) hence not a great idea.

it strikes me that AP are telling you whatever comes to mind at the time ,
oncw at autosport i had a chat with one of there me on the stand about reducing inertia in the clutch assembly , i asked about the possibility of having an inline 7.25" sintered disk mounted to the mini centre , he told me there would be no difference in inertia from a normal mini padde plate, and if i wanted to reduce inertia i could remove 3 pads and adjacent metal, as the remaining 3 pads were more than capable of handling the kind of power i had as long as it was locked up before full torque was made.
they were not interested in doing a couple of one offs ,so i did it myself, Now the difference in weight of the two in percentage terms is substantial ,i did not have a new paddle to weigh so cannot tell exactly, but the weight around the outer is clearly and quite obviously much less than the paddle plate,
so if a slolid organic plate will slip as he told me how would he expect a paddle to work with only half the friction area , it would appear to my he was with hindsight talking shite on both points in question. the only way i remedied any signs of slip was by upping the diaphram strength.
i would be interested to know how you will use a modern cover to pull the backplate up dave , if thats what you are thinking of,

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

thanks dave, be interested to hear any developments just in case i ever get near 'slip' point with a motor packed with plenty of curlywurly's!!

Carl - friction is dimensionless - ie no units. hence, it makes no difference what area there is - as basically the remaining area has twice the load exerted onto it. All it'll do is wear out in half the time. I'm still surprised that the co-eff of friction on the ceramics is purported to not be much higher than the organic...

Daft question !!!!

why don't they put grooves in the flywheel like they do on disc brakes

Metro turbo weekend driver,Mini turbo in the making again!

because it would chew the plate up very quickly id say

Grooves in disks are nothing to do with friction, all they'll do is reduce the friction area if you think about it.

Jim, my car weighed about 629kgs with me in it.

4.2diff might have something to do with it.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I think it's because on a disc brake you actually want it to work dynamically - on a clutch it's a little different. You also have a large - and full - friction area on a clutch setup, different to a disc brake that has one large and one very small friction area.

If you think about the AP rally plates, they actually have 'pads' moulded into the friction lining - this must have a similar effect however - but is (i suspect) primarilly to allow somewhere for the dust that is scrubbed off the lining to escape, rather than rolling under the lining (which will reduce the clamping torque again)...

I dont get slip on my grey/rally in the racer

the road car doesn't slip... it wheel spins soon as you get to a reasonable curley wurly figure!

Alex

AlexF

I've told you before, get rid of the 145R10s..

Even in 3rd and 4th? thought thats where you'd get most chance of slippage?

Must be a lively to drive

I reckon its that slime green engine paint............LOL

Only other idea I had some time ago when I had some thrust washers go on me, was to think about whether the thrust washers could be improved, or added to. I wondered about modifying the crank "lip" behind the primary gear and the end main cap to allow an extra thrust washer in there to take the axial forces from a double grey.
Never got much past that stage of thought TBH.

not 145s got 165s and all the wheels pointing in different directions!

LOL!

3rd is funny or is that useless on high boost.

If I keep it to 10psi the only wheel spin when hitting a bump in 3rd :o)

Alex

AlexF

looking forward to seeing this in action!

Team Racing

I wont be impressive Jim...

I was out playing last night... Off the line its very hard to pull away fast!

So I expect a 16 second 1/4 time hehehe


Alex

AlexF

we are all in the same boat mate, the job of lots of banana's FWD

Team Racing

just a thought, but i remember reading somewhere that the yellow mini's with the black stripe (can't remember who built them now!), like the swiftune mk1 had titanium flywheels with a twin plate clutch,

I've never used a twin/multi plate clutch and have heard of disengagement problems, but could this be a possible route?