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garya

Pressure Plate Failure

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Less than a year after putting the new clutch in... started getting a metallic clunking sound when the clutch pedal is depressed.  Came on suddenly during the last runs of an autocross.  This is on the 10:1 compression, 314 cam, dual sidedraft, aluminum flywheel engine.  

 

Picture 1 you can see a metal piece in the bell housing in the scrape marks around the edge. 

Picture 2 shows 2 of the 3 attachment points are gone. 

Picture 3.. it's not supposed to do that!

 

Is this just a result of too many clutch dumps with a higher HP engine, or something I did wrong on install?

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That is a 215mm pressure plate,  the real reason you broke the retention straps were clutch drops on the over-run (i.e. down shift without matching the engine speed when you drop the clutch)  the spring is designed to take the greatest load under tension when you miss-match the revs on a down shift you put those straps under compression.  This can overtime fatigue the strap and break it.  The racing and 228mm pressure plates have a much stronger system of supporting the friction shoe inside the cover.    

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It's actually a Sachs 228mm pressure plate!

 

Preyupy: Great call.  With the 314 cam, I have had to shift into 1st coming out of corners at autocrosses... and usually not very gracefully.  As I look at it closely, I can see how that would put those straps under compression.  

 

Guess I need to work on my heel/toe a bit!  Thanks. 

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We have a number of Vintage Racers that have been using this pressure plate for a number of years without any issues. BUT a couple of drivers had some problems (in car videos and Data Acquisition came to the rescue and showed us what was going on) We switched them either to a Tilton 2 disc racing clutch or a 228 mm F&S racing pressure plate. The other problem with the stock type pressure plates is they don't like much more than 7500 rpm (I have seen some really serious failures, the really serious race engines we turn to 8000+ we always use a 7.25" or 5.5" multi disc racing clutch but they are not suitable for street use)

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Same as Preyupy .... I have seen a couple guys with a flare for the dramatic have issues (among many many successful iterations [and brand is not a deciding factor on this]).  For a potential street setup I did work with ClutchMasters to make a 228mm HD pressure plate.

 

Last year a long time racer and friendly-dude grenaded a 215mm clutch while having fun in the parking lot.  Tore into the passenger side foot well.

 

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Edited by AceAndrew

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Andrew, Over the years I have noticed that Parking lots seem to be really hard on clutches, Guibos and differential spider gears. With collateral damage to Transmissions bell housings and differentials.

Edited by Preyupy

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Holy Crap, Andrew.  That is some carnage (and not much ground clearance). LOL... just realized... the engine must have shifted back and broken the distributor cap... I think I see a rotor riiight there. 

 

Interesting that the BMW CCA runs their autocross in parking lots... I haven't lots a gumbo, but I did blow out spider gears mid-slalom, and now the clutch.  

 

I'm back to that dilemma...do I want a street car, or a race car?  A racing clutch is absolutely no fun in traffic... but I don't want to see that much carnage if I continue my wicked downshift ways.

 

I'm planning on putting in a 292 cam instead of the 314 (I bought the engine 2nd hand) to move the power band down and get back a little torque now that the engine is out.  Should prevent me from having to shift into 1st on autocross courses as much.  I can consciously work on matching revs too... probably good for my times in the long run. 

 

Thanks again for the brilliant info!  

Edited by garya

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Hmmm... I've had trouble with the 215's with the vertical straps, but not with the radial like you have. 

 

I found that hard blips were the worst on it- when your foot's on the clutch, those straps are all

that ties the plate to the cover.  When the engine tachs up and down, you can set up real vibrations

in the plate itself, and then dumping it into the friction disc makes matters no better.  BUT a dump

at least has the advantage of keeping the straps under tension.  The blip is using the straps to

push the plate AND pull on it as the engine accelerates/decelerates.

 

Likewise, a dump INTO the engine (where the wheels are spinning the engine up) pushes the plate the wrong way, too.

 

When your foot's OFF the clutch, the whole thing is a big friction- damped

sandwich.

 

fwiw

 

t

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