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Discussion Starter #1
Went for a spin last night after a dull day to put a smile on my face :wroom: . Putting my foot down along a nice straight section of road and changing into 3rd I noticed my revs go wild - backed off and tried again - revs went to 6k with no pull from the engine. Obvious thought was that the clutch is going, although when I dropped of the sport mode and treated her gently for a while it seemed to pull happely again in all gears (No fast changes) with no slip. Is this a clear indication that the clutch is on the way out?

If so does anyone know the best place in the UK/midlands to get one other than BMW - or is it best done by the dealership :confused:

JB
 

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You may want to search this forum using terms (UUC) and (11"). There are many threads about the weak factory clutch.

Cars with strong V8 motors typically come with 10.5" or 11" clutches. For example, a 200 HP Ford Mustang has a 10.5" clutch and a 225 HP Corvette has an 11" clutch.

The stock sized M5 9-5/8" clutch is a joke...a carryover design from BMW's 4 and 6 cylinder cars. It will burn out again and again....labor ain't cheap. The BMW clutch kit should come with wingnuts for quick removal.

Some BMW dealerships are installing the supersized UUC clutch kit at the customer's request. They will not pick up the extra expense for parts, but many are anxious to reduce recurring failures. Some will even cover labor under any remaining warranty. It will require some discussion, since it's not the customary route. An independent foreign service shop will obviously install whatever clutch you want.
 

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Lscman seems to have made the transition from technical expert to advocate for UUC. Smaller diameter clutches require greater clamp pressure to grip under a particular torque loading. Plenty of race cars use clutches in the 5 in. to 7 in. diameter range without slipping. The main issue with the stock BMW M5 clutch is inadequate clamp pressure, in the interests of (1) a light clutch pedal, (2) desire to incorporate the LuK (plastic) self-adjusting feature, (3) desire to use a dual-mass flywheel (also LuK) as has been its practice for about the past 8 or so years, and possibly (4) to provide an upper limit on shock loading transmitted to the drive train. Greg's shifting instructions are needed with the BMW factory set-up, more so with an S2 car. Us old drag racers know that this is not the preferred shifting method for a quick time.

It is abundantly clear that a larger diameter clutch, such as the BMW 850CSi unit that is used by UUC in its M5 clutch kit, will (1) provide significantly increased torque capacity without major increase in clamp pressure, (2) provide much greater wear allowance that may translate to longer service life if driving style features a lot of slipping on start-up from rest, and (3) the combination of larger diameter, greater swept area, and lower clamp pressure makes it MUCH easier to launch the car in a drag race situation. I will also agree that we all would have been better served had BMW seen fit to redesign the M5 flywheel to fit a larger diameter clutch.

However, everything in life is a compromise and the clutch issue is no exception. The trade-off is the UUC large clutch/single mass flywheel vs. original size clutch/increased pedal pressure on the stock (or lightened) dual-mass flywheel using the Sachs Race Engineering clutch. The first provides a soft pedal, the second eliminates all transmission rattle noise. Both provide enough torque capacity for spirited driving of the M5. Pick your poison.

Part of the reason why the idle rattle is more of an issue on the M5 than on cars made 10 years ago (when single-mass flywheels were universally used) is that the Getrag transmission seems to have looser tooth clearances and a low-viscosity lubricant is specified by BMW. Lscman formerly was a strong advocate for using nothing other than the factory fill in these transmissions. Has this changed?

Regards, Dick Roberts
 

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Discussion Starter #4
Thanks for the quick replies and objective advice guys. Great information as usual.

Went for a drive tonight and the car felt fine, but suspect that last night was an early indicator...although speaking to a BMW tech. earlier today - he reckons that M5's are common for splipping the clutch when changing quick into third at high revs - any merit in this?


Anyhow will probably go for a stock clutch for now and see how it goes. Anyone know how many man hours involved?

Cheers
JB
RRoberts said:
Lscman seems to have made the transition from technical expert to advocate for UUC. Smaller diameter clutches require greater clamp pressure to grip under a particular torque loading. Plenty of race cars use clutches in the 5 in. to 7 in. diameter range without slipping. The main issue with the stock BMW M5 clutch is inadequate clamp pressure, in the interests of (1) a light clutch pedal, (2) desire to incorporate the LuK (plastic) self-adjusting feature, (3) desire to use a dual-mass flywheel (also LuK) as has been its practice for about the past 8 or so years, and possibly (4) to provide an upper limit on shock loading transmitted to the drive train. Greg's shifting instructions are needed with the BMW factory set-up, more so with an S2 car. Us old drag racers know that this is not the preferred shifting method for a quick time.

It is abundantly clear that a larger diameter clutch, such as the BMW 850CSi unit that is used by UUC in its M5 clutch kit, will (1) provide significantly increased torque capacity without major increase in clamp pressure, (2) provide much greater wear allowance that may translate to longer service life if driving style features a lot of slipping on start-up from rest, and (3) the combination of larger diameter, greater swept area, and lower clamp pressure makes it MUCH easier to launch the car in a drag race situation. I will also agree that we all would have been better served had BMW seen fit to redesign the M5 flywheel to fit a larger diameter clutch.

However, everything in life is a compromise and the clutch issue is no exception. The trade-off is the UUC large clutch/single mass flywheel vs. original size clutch/increased pedal pressure on the stock (or lightened) dual-mass flywheel using the Sachs Race Engineering clutch. The first provides a soft pedal, the second eliminates all transmission rattle noise. Both provide enough torque capacity for spirited driving of the M5. Pick your poison.

Part of the reason why the idle rattle is more of an issue on the M5 than on cars made 10 years ago (when single-mass flywheels were universally used) is that the Getrag transmission seems to have looser tooth clearances and a low-viscosity lubricant is specified by BMW. Lscman formerly was a strong advocate for using nothing other than the factory fill in these transmissions. Has this changed?

Regards, Dick Roberts
 

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Lscman said:
The BMW clutch kit should come with wingnuts for quick removal.
QUOTE]

LMAO hiha
 

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RRoberts said:
Lscman seems to have made the transition from technical expert to advocate for UUC. Lscman formerly was a strong advocate for using nothing other than the factory fill in these transmissions. Has this changed?
Dick.....since you made unsolicited comments and accusations, I feel compelled to respond to your inquiry.

I was similarly criticized for my preference for Ground Control camber plates over K-Mac offerings. I have strong technical reasons for suggesting that product too. I feel fortunate that I'm able to express my opinion about E39 aftermarket products that are not sold by forum sponsors. Fact is, I have never used the Ground Control plates or suspension parts and I do not have an oversized UUC clutch either. GC's Jay Morris can kiss my tailpipe. I do not feel free to say the same about the forum sponsors...pro or con. I would love to have the GC suspension & UUC 11" clutch on my car, but I simply have other priorities for funds at this moment.

Exactly what does my strong preference for factory-approved Esso/BMW transmission gearbox fluid for use in the Getrag Type 226 have to do with clutches? I heard the similar allegations when I supported the use of Mobil 1 & Amsoil engine oils. I find your sarcastic comments out-of-character. Have I offered insufficent technical reasons why I prefer factory fill that meets Getrag spec? I've already explained this in about 10,000 words.

I am not a proponent of any particular brand of anything. That said, I'm unaware of ANY alternatives to the UUC stage I 11" street kit. Based upon 30 years of automotive experience, I feel an oversized organic street clutch is the optimal solution. You are free to feel differently. Since I became aware of this unique UUC product, I began spreading the word. It is frustrating to hear from folks going thru 2 or 3 undersized clutches in a 3 year old vehicle & I am trying to help.

Fact is, I was one of the first Ford Fox chassis owners to upgrade from a 10" clutch to the latest factory 10.5". I performed this swap in fall of 1985, a whopping 20 YEARS AGO. I redrilled my flywheel to make it fit because I didn't want to pay $120 for the new retrofit flywheel that was freshly released in 1986! This was done after frying a couple high pressure 10" plates from Zoom, Centerforce and other's. All they did was change clutch pedal feel. In fact, Ford SVO Team tried the same thing (elevated pressures on an undersized organic clutch) and came to the same exact conclusions (it is fruitless). Does this scenereio sound the least bit familiar? If you search the archives, you will see I expressed my concerns about the tiny 9-5/8" clutch and no oversized alternative long before UUC released their 11" version. I'm DONE already with experimenting with tiny clutches. It is clear that you are not, and honestly, that's fine. Please tell everyone how many miles you have on your latest 9-5/8" clutch setup. Let them decide if it's a viable solution. Just cut me a break as I am trying to save folks the wasted effort of installing an OEM units, featherweight aluminum flywheels drilled for 9-5/8" clutches & similarly worthless stuff. Someone needs to offer alternatives to folks who are not clutch experts. You repeatedly offer lightweight, compact sports car and racing clutches with aggressive linings and/or no marcel as evidence that a larger clutch is not needed in a 2 ton sedan. I am not interested in disputing your claim or making you look foolish or slanted. I simply stated my preference....hoping other's would too.

Do you know anyone that installed a larger brake system on their car? Realizing that additional line pressure and more aggressive pad compounds are available, why are oversize brakes helpful? My feeling is that clutches and brakes have some similarities. I don't think it's anyone's job to make light of folks who recommend oversize brakes to address a genuine overduty condition.

I applauded your 9-5/8" Sachs aftermarket solution, as I did MIB's solution. When you performed that upgrade some time ago, I thought it was the best alternative out there for a street M5. A higher pressure plate and higher performance non-marcel disk is better than OEM or many other stock-sized soutions, for sure. IMO, it can not compete with a significantly-oversized clutch for the reasons I've outlined. When Centerforce or Evosport or anybody else releases an 11" or 12" organic clutch for E39, I'll spread the word. Hope that's OK with everyone. :cheers:
 

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You two are my favorite tech. guys on the board. I always tune in when either of you contribute.

I have much respect for Lscman and know that he is giving good info. and helping those with questions. However, I do feel he has leaned too hard in advocating the UUC setup. From the mechanical standpoint of the clutch it sounds superb, however it has attributes that may people here should find unacceptable. Those are gear rattle, and lack of energy storage with an overly light flywheel. Even though claims of equivalent moment of inertia, I am skeptical. I absolutely hated the Dinan 7-pound lighter flywheel installation on an S2. UUC's is 13 pounds lighter, I believe.

With this in mind, I don't think the UUC solution should be advocated so readily. I do agree with RRoberts that clamping pressure with an organic disk is a solid solution and that increased clutch diameter is not the only solution as suggested by Lscman.

At this point, I actually consider the Sachs unit with modified slave cylinder to be the configuration that offers the best all-around solution for the M5 at this time.
 

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Lscman said:
Exactly what does my strong preference for factory-approved Esso/BMW transmission gearbox fluid for use in the Getrag Type 226 have to do with clutches?

Please tell everyone how many miles you have on your latest 9-5/8" clutch setup. Let them decide if it's a viable solution. :
The tie between trans fluid and clutch (really flywheel) selection has to do with the recommendation, I believe from UUC, that owners who experience excessive idle rattle with the UUC big clutch & flywheel kit switch to Redline or other heavier fluid. In the old days, we all ran 90 wt. with single-mass flywheels. I have spoken to a few people with the UUC kit, and have heard reports that it "sounds like a diesel" at idle. This may not be the experience of all, but it would seem to happen at least some of the time. I agree with you that we should all stay with the BMW factory fill in this transmission (and change it once in a while).

I now have just about 10,000 miles and a couple of track days on the Sachs clutch and pressure plate, and it is working fine. This is not enough use to establish service life. The original clutch first saw the track at about 6000 miles. I had not noticed slippage on the street with the stock clutch, but immediately experienced severe slippage at the track when attempting hard acceleration out of corners in 3rd and higher gears. The car is a Dinan S2. Examination of the disc showed about .015 in. less thickness than a new disc, with blue discoloration of the pressure plate friction surface but not the flywheel. The slippage I experienced was not wear-induced, but rather insufficient clamping pressure (and not enough clutch diameter, to your point). The Sachs clutch and pressure plate does not slip, even when I bang the shifts. In fact, it is tough to drag-race launch from a standing start because it doesn't like to slip. The disc is a bonded, non-Marcel, solid center design and is way stronger than the stock disc. Engagement is perfectly smooth and chatter-free during normal street start-up from rest. I sometimes get a very slight chatter when backing up (my garage is slightly uphill, and I must back in).

I am not a Sachs salesman, just as you are not selling UUC products. I think Rob Levinson has come up with a nice product that addresses a need within the constraints of using available parts. I would consider using the UUC kit the next time I need to replace a clutch or a flywheel if it was free of idle rattle, although I still have some concerns with aluminum flywheels (even fairly heavy ones) for the street. I have failed a few steel friction surface inserts in my prior years. As well as many aftermarket hot-rod clutches. But I am better behaved now.

My point, and what set me off, was that the present selection of M5 higher-clamp clutch/flywheel combinations are ALL compromises. Idle noise/shorter wear life/increased pedal pressure - you can't have it all right now. Favorable mention of one of these choices without also mentioning the drawbacks is not offering complete advice. Please accept my apology if I offended you with my earlier post.

I'm happy enough with my dual-mass flywheel/Sachs Race Engineering clutch/larger clutch slave cylinder set-up that I won't try something different until it fails, although it is not perfection. But it sure doesn't slip.

Regards, Dick Roberts
 

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RRoberts,

Thanks for clarifying, friend. Indeed, everything has pros and cons. I see potential slippage & subpar lifecycle as the primary concerns. A slight rattle at idle with tranny in neutral and clutch out seems so secondary to me because it is quite infrequent (red light in neutral) and totally manageable (simply push in clutch). Other upgrades like poly control arm bushings, urethane strut mounts or aftermarket mufflers produce unmanageable NVH that can constantly affects occupants while in motion. For whatever reason, folks are not focused on these NVH issues and they almost seem in vogue.

Since personal opinion is invariably flawed & may not coincide with other's objectives, I always try to refer folks to prior threads on the subject containing opinion from first hand UUC owners. Many of these threads contain cautions, links and alternative offerings from Spec, Sachs & OEM clutch owners. Asking folks to search the forum in this fashion would seem proper.

Until somebody finds a way to cram a dual mass and 11" clutch into the M5 bellhousing (ain't happenin'), I personally see no better alternative for folks frying clutches on 2 or 3 year old cars with 30K mi or so. This is by no means normal and tweaking an undersized clutch assy can not address a fundamental flaw. I think these folks need a significantly bigger diameter clutch that absorbs more heat without excessive temps. Engineers (in most car companies) came to this conclusion 20 yrs ago.

Hbramstedt,

I can't state my position much more clearly or simply. I advocate oversize brakes and clutches for better performance under severe duty, independent of manufacturer. It's my understanding that UUC makes the only 11" organic street clutch kit for M5.
 

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Great repartee from Lscman & RRoberts, who by the way are two of my favorite posters! I have now had the UUC Stage III installed for almost 1 month. No more slippage, I can make hard shifts, & the clutch (thus far!) is seemingly "bullet-proof". :M5launch:

I am so happy with it that I would advocate this product without hesitation to anybody that is having slippage problems and finding themselves having to replace the OEM clutch.

I am just so happy to have this readily accessable, great performing option available. You may read my review of the UUC Stage III clutch/Lightweight Flywheel here . I will be updating the review as time/circumstances change.

Robert
 

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Discussion Starter #11
Lo Robert.

Already read the thread - sounds good. If you don't mind me asking can you tell me how much in cost in total and if you have it the man hours associated with the Job.

Cheers JB :cheers:


1badm5 said:
Great repartee from Lscman & RRoberts, who by the way are two of my favorite posters! I have now had the UUC Stage III installed for almost 1 month. No more slippage, I can make hard shifts, & hte clutch (thus far!) is seemingly "bullet-proof". :M5launch:

I am so happy with it that I would advocate this product without hesitation to anybody that is having slippage problems and finding themselves having to replace the OEM clutch.

I am just so happy to have this readily accessable, great performing option available. You may read my review of the UUC Stage III clutch/Lightweight Flywheel here . I will be updating the review as time/circumstances change.

Robert
 

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The UUC Clutch cost $2800 US. with an additional $600 corecharge (refundable) deposit on the flywheel. Go to uucmotorwerks website for details. The cost of install was $495, but included the EVO III SSK w/DSSR & Transmission Mounts install as well as a change-out of transmission fluid & differential fluids (I provided all parts & fluids). So, it's hard for me to say what the labor charge would have been for the clutch/flywheel by itself.

Robert


JB_UK said:
Lo Robert.

Already read the thread - sounds good. If you don't mind me asking can you tell me how much in cost in total and if you have it the man hours associated with the Job.

Cheers JB :cheers:
 

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Great thread – as a new M5 owner I'm thrilled by the quality of the discussion here.

Just one question. If I were to fit a UUC clutch, would my extended warranty cover the drivetrain parts further down the food chain, now that they are exposed to greater forces?

Has anyone, on either side of the Atlantic, tested BMW on this?
 

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Discussion Starter #15
Search the threads relating to clutch upgrades - I'm sure one guy got some info from his dealer that they are covering this under an approved upgrade..BMW know the clutch is 'relatively' weak and from what I can tell the drive train is upto the job of an upgrade. Other threads suggest that the UUC stage 3 6 part clutch package is an excllent choice - although there are alternatives.

Enjoy...
JB
Timray said:
Great thread – as a new M5 owner I'm thrilled by the quality of the discussion here.

Just one question. If I were to fit a UUC clutch, would my extended warranty cover the drivetrain parts further down the food chain, now that they are exposed to greater forces?

Has anyone, on either side of the Atlantic, tested BMW on this?
 
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