So why cant you use the Sachs HD pressure plate with an LTW flywheel???

[JaredM3]

Well I broke the straps on my stock pressure plate the other day...Im looking for a setup that will take a little more abuse...

My disk is fine, so I am just looking for a pressure plate...Whats the story of not being able to use the HD pressure plate with the LTW flywheel?

Specs: UUC stage 1 alum flywheel = uses stock PP and M5 disk(sprung hub) to "reduce chatter" lol

I was thinking of just having a clutch shop beef up a stock PP but can the ltw flywheel not take the increased clamping load?

[JaredM3]

Nobody knows... Ill have to stop by Turner tomorrow on my way to Maine and ask them whats up...

[savage217]

Wrong section thats why. For technical questions go to the track section.

[Rob Levinson]

First, analyze why the straps broke.

Are you reverse-loading the engine? Remember... brakes for braking, engine for accelerating. Don't downshift to slow down the car. That's the #1 reason why straps break, and the tell-tale is a strap that is buckled or bent.

Consider a UUC complete clutch... we over-build the straps specifically to make them more tolerant of hard use/abuse:



More details:

http://www.uucmotorwerks.com/performance_clutches/

[Hova]

First, analyze why the straps broke.

Are you reverse-loading the engine? Remember... brakes for braking, engine for accelerating. Don't downshift to slow down the car. That's the #1 reason why straps break, and the tell-tale is a strap that is buckled or bent.

Consider a UUC complete clutch... we over-build the straps specifically to make them more tolerant of hard use/abuse:



More details:

http://www.uucmotorwerks.com/performance_clutches/

as long as i rev match, i use my engine to brake/slow my car down everyone in a while, i don't see any harm being done besides wearing my clutch down.

[Rob Levinson]

as long as i rev match, i use my engine to brake/slow my car down everyone in a while, i don't see any harm being done besides wearing my clutch down.

Reverse-loading means instead of putting power through the clutch rotationally one way, from engine to wheels, you're putting it from wheels to engine. That's engine braking, and doing that significantly is a very bad thing.

Has nothing to do with rev-matching at all. It has to do with force going through the clutch backwards.

It's easy to explain this with the picture I posted earlier:



The drive straps connect the pressure plate (the disk that presses against the clutch disk) to the cover (in the pic, the black pat).

See how they go diagonally, riveted/bolted to the plate on the left and the cover on the right?

The direction of rotation of the engine results in a tension, or pulling force applied to those straps. They are very strong in tension.

When you reverse-load the engine, the power is going the other way (no, direction does not reverse, but resistance is another form of power) and the straps are put in compression. When compressed, the spring steel straps will snap. Usually the failure point is at the riveted ends, but it can break at any point. That is why I said in my initial post that the tell-tale for a reverse-loading clutch failure is a buckled/bent strap or bent with breakage.

Looks like this:



Broken looks like this, note the wave in the strap which should be straight:



That one was nasty, as bits of broken strap bounced all around the transmission bellhousing. In some cases, the strap can break at one end, whip out like a knife blade, and carve a perfect line around the bellhousing as the engine spins. I've seen transmissions cut in half from that.

After observing this phenomenon in the US, I have conferred with my contacts at Sachs in Germany several times who have corroborated the failure and confirmed the cause/effect relationship.

- Rob

[Hova]

Reverse-loading means instead of putting power through the clutch rotationally one way, from engine to wheels, you're putting it from wheels to engine. That's engine braking, and doing that significantly is a very bad thing.

Has nothing to do with rev-matching at all. It has to do with force going through the clutch backwards.

It's easy to explain this with the picture I posted earlier:



The drive straps connect the pressure plate (the disk that presses against the clutch disk) to the cover (in the pic, the black pat).

See how they go diagonally, riveted/bolted to the plate on the left and the cover on the right?

The direction of rotation of the engine results in a tension, or pulling force applied to those straps. They are very strong in tension.

When you reverse-load the engine, the power is going the other way (no, direction does not reverse, but resistance is another form of power) and the straps are put in compression. When compressed, the spring steel straps will snap. Usually the failure point is at the riveted ends, but it can break at any point. That is why I said in my initial post that the tell-tale for a reverse-loading clutch failure is a buckled/bent strap or bent with breakage.

Looks like this:



Broken looks like this, note the wave in the strap which should be straight:



That one was nasty, as bits of broken strap bounced all around the transmission bellhousing. In some cases, the strap can break at one end, whip out like a knife blade, and carve a perfect line around the bellhousing as the engine spins. I've seen transmissions cut in half from that.

After observing this phenomenon in the US, I have conferred with my contacts at Sachs in Germany several times who have corroborated the failure and confirmed the cause/effect relationship.

- Rob

im looking at my OEM pressure plat on my desk right now, and i never noticed that until you pointed it out. I now see what you mean, the reverse loading of the pressure plate. Yeah i cant imagine much load being put on that without it bending/snapping.

thanks Rob

[bmxcm]

wow, this is something I never knew about. maybe I should change my habits considering this is the way I slow down 90% of the time. although I've been driving that way on my daily beater for the past 60k some odd miles, on an already 180k clutch (original for all i know) with no ill affects.

so what am I supposed to stop downshifting all together!?! not sure what to think...

[Rob Levinson]

wow, this is something I never knew about. maybe I should change my habits considering this is the way I slow down 90% of the time. although I've been driving that way on my daily beater for the past 60k some odd miles, on an already 180k clutch (original for all i know) with no ill affects.

so what am I supposed to stop downshifting all together!?! not sure what to think...

The big damage as above happens mostly in track use, especially with sticky track tires. Speeds and forces are much greater.

Nevertheless, it's just not a good idea even for street use. There's no point... do the math on this; is it better to wear out a $2000 transmission and do a $1000 clutch replacement job, or use a pair of $79 brake pads? Do whatever you can afford. ;-)

- Rob

[GotBHP?]

The big damage as above happens mostly in track use, especially with sticky track tires. Speeds and forces are much greater.

Nevertheless, it's just not a good idea even for street use. There's no point... do the math on this; is it better to wear out a $2000 transmission and do a $1000 clutch replacement job, or use a pair of $79 brake pads? Do whatever you can afford. ;-)

- Rob

Well do you proportion the brake bias on your BBK's to account for 0 engine braking? Doubt it, considering how important engine braking is to braking stability and performance.

The largest loads (that would cause them to buckle) those straps will see is when you don't rev match going into a lower gear. I do agree that he should examine how they failed, whether in tension or due to buckling.

[Rob Levinson]

Well do you proportion the brake bias on your BBK's to account for 0 engine braking? Doubt it, considering how important engine braking is to braking stability and performance.

What you're saying is the exact opposite of what happens! If you want to de-stabilize the car, engine brake... congrats, now you've got a significantly greater amount of rear braking without any way to modulate it at all.

Ever see a guy, for "no reason", spin his car in a braking zone? That's engine braking, locking up the rear wheels. ABS won't help you there.

The largest loads (that would cause them to buckle) those straps will see is when you don't rev match going into a lower gear.

Usually that's just going to cook your clutch. The force doesn't get put into the clutch completely until full engagement... and then it's reverse-loading as explained above.

- Rob

[Hova]

Usually that's just going to cook your clutch. The force doesn't get put into the clutch completely until full engagement... and then it's reverse-loading as explained above.

- Rob

so if i downshift, but rev match, and do so within 100rpm... i am buckling my pressure plate straps? and i shouldnt do this?

[Rob Levinson]

so if i downshift, but rev match, and do so within 100rpm... i am buckling my pressure plate straps? and i shouldnt do this?

For clarification, let me give you the strap-buckling scenario...

Near the end of track main straight, 120+mph. Downshift 5th-3rd, release clutch. Revs jump to near redline due to required engine speed to match road speed through gearing. The shockload goes from full throttle (power in normal direction) to maximum tire grip-created power back through drivetrain. Instant strap damage.

We are not discussing reasonable downshifting. Downshifting at most street-driven speeds (sub-insane) with regular street tires (not R-compound track tires) is much less likely to cause the damage. Engine braking on the street is more just bad technique than anything else to worry about. Bad technique on the street becomes ingrained behavior that is hard to shake on the track. Practice good "track technique" in your street driving at normal speeds, your track driving will improve.

- Rob

[GotBHP?]

What you're saying is the exact opposite of what happens! If you want to de-stabilize the car, engine brake... congrats, now you've got a significantly greater amount of rear braking without any way to modulate it at all.

Ever see a guy, for "no reason", spin his car in a braking zone? That's engine braking, locking up the rear wheels. ABS won't help you there.

*ALL* factory cars with manual transmissions, racecars (successful ones), F1 cars etc. factor in engine braking into front and rear brake bias. I've worked on it on FSAE cars, my friend in F1 sees it, my Prof's that worked in Champ Car for years did it. Until recently you could adjust engine braking in F1 as a part of adjusting brake bias and stability during braking.

Ask your engineer who designs your own brake kits. I don't mean to bash him or anything, but if he knows his stuff he will agree with me.

Don't tell people to not use engine braking, its part of driving (sorry for the double neg).

[Hova]

For clarification, let me give you the strap-buckling scenario...

Near the end of track main straight, 120+mph. Downshift 5th-3rd, release clutch. Revs jump to near redline due to required engine speed to match road speed through gearing. The shockload goes from full throttle (power in normal direction) to maximum tire grip-created power back through drivetrain. Instant strap damage.

We are not discussing reasonable downshifting. Downshifting at most street-driven speeds (sub-insane) with regular street tires (not R-compound track tires) is much less likely to cause the damage. Engine braking on the street is more just bad technique than anything else to worry about. Bad technique on the street becomes ingrained behavior that is hard to shake on the track. Practice good "track technique" in your street driving at normal speeds, your track driving will improve.

- Rob

thanks for the clarification.

[Veedubbvr6]

so if these were bent or busted, what would be the initial result in drivability? Loud noises? tons of chattering and possible warpage, etc? I'm curious because I always use engine braking when I'm driving on the streets...not that I'm going from 140 in 5th to suddenly slowing down and throwing it in 3rd at 120 or something.. I usually do it when it'd be about 3k in the lower gear..(make sense?) But I'm wondering if I may've already caused slight damage by doing this...what would be the noticeable difference right off the bat?


...and for the record, I'm not talking about the M but rather the GTi...I have a feeling my clutch setup is about done-fer...at least my flywheel anyway.

[Rob Levinson]

*ALL* factory cars with manual transmissions, racecars (successful ones), F1 cars etc. factor in engine braking into front and rear brake bias. I've worked on it on FSAE cars, my friend in F1 sees it, my Prof's that worked in Champ Car for years did it. Until recently you could adjust engine braking in F1 as a part of adjusting brake bias and stability during braking.

Ask your engineer who designs your own brake kits. I don't mean to bash him or anything, but if he knows his stuff he will agree with me.

Don't tell people to not use engine braking, its part of driving (sorry for the double neg).

I really think you're mixing several concepts here that are not congruent.

Just so you're aware of how any aftermarket BBK development works, it all starts with a baseline of the brake torque at each axle of the OE system, a simple calculation derived from several factors including brake line pressure, rotor swept area (pad height), rotor diameter, overall piston area, pad friction coefficient, and about a half-dozen other secodary factors. Bias itself is a simple ratio comparing front brake torque to rear brake torque. As OE brake systems, especially in BMWs, have near-ideal bias as originally designed, a good aftermarket BBK is designed to match that ratio.

Honestly, I'm not sure where you're figuring engine braking into the design or operation of the service brakes, especially as engine braking itself is a radically variable dynamic variable... from zero (none) to 100% (mechanically locking the rear wheels through excessive engine/wheel speed delta).

Take this to the next step to see why I think you're mixing some concepts; you refer to manual transmission cars being designed with engine braking in mind as to how their regular brakes are configured. So... with any model BMW being equipped with the exact same brakes whether automatic or manual, that concept sort of evaporates, yes?

There are various ways to configure dynamic bias controls deliberately in advanced racing classes, some mechanical, some electronic, and some driver-actuated. As a matter of fact, ABS itself is a form of bias control. However, beyond ABS, a street-driven BMW or one configured for Stock or Prepared BMW Club Racing (or similar) rules does not use any of that.

If you're talking about F1, they're not using engine braking as primary vehicle braking; minor throttle changes will shift weight bias, and those drivers are at the level where such fine control is worthwhile. Their adjustments in actual brake bias are also further chassis controls that they change depending on vehicle attitude in a corner. Again, this is a whole other level of driving that is not applicable to the types of cars that likely anyone reading this thread is driving.

When we're talking about extreme engine braking that damages drive straps and causes instability, of course we should tell people not to do that. You wouldn't tell someone to deliberately go and break drive straps or lock up their rear wheels, would you?

- Rob

[Rob Levinson]

so if these were bent or busted, what would be the initial result in drivability? Loud noises? tons of chattering and possible warpage, etc? I'm curious because I always use engine braking when I'm driving on the streets...not that I'm going from 140 in 5th to suddenly slowing down and throwing it in 3rd at 120 or something.. I usually do it when it'd be about 3k in the lower gear..(make sense?) But I'm wondering if I may've already caused slight damage by doing this...what would be the noticeable difference right off the bat?


...and for the record, I'm not talking about the M but rather the GTi...I have a feeling my clutch setup is about done-fer...at least my flywheel anyway.

A slightly tweaked drive strap may show no symptoms at all, or the clutch may feel just a little "weird" with different problems including an altered engagement response or change in pedal effort.

A broken drive strap may result in less clamping force, exaggerated oddities in clutch engagement feel, or a rattling noise like a piece of loose metal (because there may be a piece of loose metal rattling around!).

The worst case is a strap that has broken at one end and then pivots out on the other rivet, which then acts like a blade spinning around the bellhousing, as I mentioned earlier. Damage looks like this:



Worse cases will cut all the way through, destroying the transmission.

- Rob

[Veedubbvr6]

Crazy! Thanks for the clarification buddy.

[GotBHP?]

I really think you're mixing several concepts here that are not congruent.

Just so you're aware of how any aftermarket BBK development works, it all starts with a baseline of the brake torque at each axle of the OE system, a simple calculation derived from several factors including brake line pressure, rotor swept area (pad height), rotor diameter, overall piston area, pad friction coefficient, and about a half-dozen other secodary factors. Bias itself is a simple ratio comparing front brake torque to rear brake torque. As OE brake systems, especially in BMWs, have near-ideal bias as originally designed, a good aftermarket BBK is designed to match that ratio.

Honestly, I'm not sure where you're figuring engine braking into the design or operation of the service brakes, especially as engine braking itself is a radically variable dynamic variable... from zero (none) to 100% (mechanically locking the rear wheels through excessive engine/wheel speed delta).

Take this to the next step to see why I think you're mixing some concepts; you refer to manual transmission cars being designed with engine braking in mind as to how their regular brakes are configured. So... with any model BMW being equipped with the exact same brakes whether automatic or manual, that concept sort of evaporates, yes?

There are various ways to configure dynamic bias controls deliberately in advanced racing classes, some mechanical, some electronic, and some driver-actuated. As a matter of fact, ABS itself is a form of bias control. However, beyond ABS, a street-driven BMW or one configured for Stock or Prepared BMW Club Racing (or similar) rules does not use any of that.

If you're talking about F1, they're not using engine braking as primary vehicle braking; minor throttle changes will shift weight bias, and those drivers are at the level where such fine control is worthwhile. Their adjustments in actual brake bias are also further chassis controls that they change depending on vehicle attitude in a corner. Again, this is a whole other level of driving that is not applicable to the types of cars that likely anyone reading this thread is driving.

When we're talking about extreme engine braking that damages drive straps and causes instability, of course we should tell people not to do that. You wouldn't tell someone to deliberately go and break drive straps or lock up their rear wheels, would you?

- Rob

Man-o-man you like making long posts for a relatively simple issue, and I'm pretty sure you missed my point... or I have missed your original point, my bad.

You say to not use engine braking (or at least that is what I gathered from what you are saying). I only say engine braking is an important factor in the calculation of overall brake bias (or, effective braking torque at each axle if you would like). Perhaps there was no disagreement to begin with, but so long as you agree with my point here I think we are on the same page.

If you base your aftermarket brake systems off the OEM setup, you probably are already factoring in engine braking, without having to do any of the complicated dynamic simulations that have already been done.

I only mention manual transmission cars because I honestly have no idea which automatic transmission cars remain in gear while decelerating, which ones do not, and which ones do a combination.

As for F1, they used to be able to use the engine ECU to make minor throttle adjustments during braking. This may slightly effect weight balance front and rear, but it was mainly used to change the braking torque at the rear wheels actively, because active brake bias control is not allowed.

[Rob Levinson]

Man-o-man you like making long posts for a relatively simple issue, and I'm pretty sure you missed my point... or I have missed your original point, my bad.

LOL! Sometimes simple answers can be worse than useless... at least with detail, you get more focus.

I only say engine braking is an important factor in the calculation of overall brake bias (or, effective braking torque at each axle if you would like). Perhaps there was no disagreement to begin with, but so long as you agree with my point here I think we are on the same page.

I am disagreeing with that.

To repeat part of my earlier post, "I'm not sure where you're figuring engine braking into the design or operation of the service brakes, especially as engine braking itself is a radically variable dynamic variable... from zero (none) to 100% (mechanically locking the rear wheels through excessive engine/wheel speed delta)."

- Rob

[Chester]

So those "straps" are the only thing holding the inner assembly of the pressure plate to the outer housing? And it's able to center the inner mass when revving the engine, engaging/disengaging the engine?

Are there not 10 pins fixed to the pressure plate housing that float the friction surface and splines the throwout bearings pushes against? Wouldn't these pins be what really transfers the engine twist to the pressure plate housing which is bolted to the flywheel? Wouldn't these pins also center the inner assembly and keep it nice and aligned? Do you really think those straps serve any other purpose than to push the friction surface to the clutch disc/flywheel?

The pressure plate in the picture is a Sachs E34M5 HD unit. Sorry for the blurry pictures.

[Rob Levinson]

So those "straps" are the only thing holding the inner assembly of the pressure plate to the outer housing? And it's able to center the inner mass when revving the engine, engaging/disengaging the engine?

Are there not 10 pins fixed to the pressure plate housing that float the friction surface and splines the throwout bearings pushes against? Wouldn't these pins be what really transfers the engine twist to the pressure plate housing which is bolted to the flywheel? Wouldn't these pins also center the inner assembly and keep it nice and aligned? Do you really think those straps serve any other purpose than to push the friction surface to the clutch disc/flywheel?

The pressure plate in the picture is a Sachs E34M5 HD unit. Sorry for the blurry pictures.

Was there a bulk sale on emoticons? Sheesh!

The plate component itself is not connected by those pins... those pins are floating the plate as you can see in those pics, through the finger release springs. They are only rigidly connected to the cover, not the plate.

When there is that much errant force going backwards through the system, that plate does all sorts of dancing around, and those pins are just keeping the plate in the general vicinity of where it's supposed to be, not preventing it from tweaking the drive straps. This is why those finger springs are often also slightly tweaked when the drivestraps buckle.

But hey, if you want to argue with Sachs engineers, Babelfish will let you convert all of those emoticons to German.

- Rob