can anyone help with what happened to the pressure plate, in my slant 6 HAMBster, i had been experiencing some clutch slip off the line and decided to replace the plate and when i removed the clutch/pressure plate this is what i found the pressure plate has no evidence of (heat or blueing) and has only 6 passes 1/4 mile and 15 passes 1/8 mile i hope my new ceramic disc setup is ok as the new setup cost$$$$ i will find out on February 20 at Queensland Australia nostalgia drags @willowbank raceway meeting
That very same thing happened to the crooked six on the starting line at tulsa i dont belive the stock cast iron plates will take the abuse. Shawn if you are still onthe board show the young man your pics. Just be glad it did not come apart at the finish line.i have had that happen andi assure you its no fun
I have read that that is a weak link. Also, where the pressure plate cover is undercut to bolt to the flywheel can cause it to come apart. The small bellhousing makes it hard to find and fit a SFI clutch assembly. If you search the www.slantsix.org site you should find some safer alternatives to the stock clutch.
Does the class you run in require you to run a standard trans?If not ive read where they are building 904,s as stong as 727,s and less weight.Also a good converter is hard to beat.Just asking,not finding fault......Good luck..................YG
Did you use a US pressure plate ??? Because they are made to turn in the opposite direction of the Aussie ones, it's somekinda Southern Hemisphere thing.
Hi Fully Six, I knew about the one breaking here in Tulsa, that was Shawn Mcdermot's Crooked Six, before he won at Mokan Hamb drags. That's why I got mine from Mcleod Industries, Steel flywheel,122 teeth, Disk and pressure plate, all three SFI. These motors will turn a lot of rev's, mine went way past 7500 when I missed second gear and broke a timing chain, that chain replacement came from your area through Clifford's. With that kind of pressure plate it could have came apart at both ends, and that's scarry. Joe
I enlarged the picture to look for growth rings where it came apart, no luck. It looks like you just used it too much when it was new. I think you were a very lucky fellow. As said before, You were not the first one. I hope it doesn't happen again.
Mine did the same thing on a test/tune night about two years ago. No reason for it to do so, but it did. I replaced it with a truck tranny and the 10" clutch and pressure plate and have had no more problems. Robert
That's an interesting break. Not a tach break at all, purely axial. Noting that the breaks immediately follow the finger pulls in the direction of rotation suggests possible flexing at the finger pulls against the springs. Some questions occur to me up front. That much plate flex could result from running significantly stronger than stock springs. Are you? The plate appears to've been faced. If so, how much, and how was it supported? Could it've been flexed during machining? Sufficient chattering could hammer it enough to break like that as well. Had you noticed any? And lastly, how do you drive'er? Do you side step the clutch or "feed" it in? The 9" can isn't undercut at the screws like the 10" so that shouldn't be as much a concern.
It looks cast to me and a very porous casting. Casting like that is super weak. Probally could have smacked it one time with a hammer and cracked it. You can see where the fingers put the presure on it and it snapped. I'd say casting flaw of the piece.
I talked to a couple of the clutch Gurus from the Nitro board.. They seem to think that the clutch is engaged to far, Or the wrong throw out bearing...
"cast iron" In the 70's i ran a weber 10" with a schiefer 9" disc, went thru the traps better than 8k every time, never had a prob., 225 .060 over, .045 head, 500 holley. hooker, 4 speed, 4:56, 7" radirs. 3 uhra records.
Were you running a full circle disc or one of the metallic type with separate pucks? If so a hard engagement could break the unsupported area.
There is no metallurgical mystery here other than the cast iron is simply overloaded. As some have pointed out, possibly the springs are stiffer than standard, possibly the disk has been faced and possibly the geometry of the setup is compressing those springs beyond where they would normally get compressed too resulting in higher load per spring. The disk has failed in bending about each of the three points where it pulls against the springs. The holes here are the stress riser. Because they interupt the rear surface of the disk and because there is missing material to share the stress. The surface stress here in the back of the disk around the hole is tensile which is the worst kind of stress for getting a crack to start. But there is no fatigue here. The totally crystalline failure suggests one sudden overload. The bending (tensile) stresses will also be compounded by a puck type clutch that does not support the whole disk over its full face. (i.e. point contact causes higher loads than distributed loads, all else being equal.) Also, cast iron is not the best material in tension, but is very good in compression. Cast iron, by its very nature, often has "defects" of a more significant nature than say steel. But all materials have defects and the designers/manufacturers allow for this. At the end of the day these defects make the overall material not as good as say steel in that application. Remember the thing was designed for moms & pops to commute with. It was never designed for the treatment it received. It's a cool photo none the less as an example of what went wrong. Just my 2 cents worth
I'd say a lead foot caused this shitty cast iron thing to break. If it was a 225 errect six you wouldent have these problems. :~)
OK, after strenuous and repetative testing I believe I have a definitive answer for you (see the "ANRA 20010 Season Opener" thread). I broke one pressure plate identically, under much the same circumstances. Then blew another one immediately following, under like circumstances. The first was slipping badly during my last run last season, but on disassembly and close visual inspection appeared fine. I put it in this year's engine and it fractured (4 pieces, but didn't blow) during my first burnout. This kept it from disengaging at the end of the burnout and I had to stall the engine & car out with the brakes while hitting the kill. The second (even though an inherently weaker design) held up for the burnout but slipped badly on the launch and through first gear. It blew when I pressed the pedal to hit second. I've come to the conclusion that in both cases the excess slipping heated up the pressure plate to a temperature that effected a change in the cast iron of the plate. Not enough to discolor it, as both sets of pieces were still a good color, but enough to make a change at the structural level. Following that change the next application of pedal pressure was sufficient to flex the plate past its new limits. Thus, if it were at near an idle (as in following a burnout) it'd seperate at a low enough speed to avoid any further damage. If it were at around 5000 (as in a shift) it'd easily blow through the clutch can. This is supported by the remains of my pieces. Neither clutch disc was so much as scratched and both were left in place. In the second instance the clutch can and the bell were destroyed and the scatter shield put through its designed paces. These are my present tentative conclusions, barring further discoveries (I haven't finished teardown yet). So far, they look to be holding up.
Dick, I have a question aboput the 10" clutch that you broke. Was this one for the truck application and if so, was it for the small tranny? I'm running the 10" out of a 3/4 ton truck with the same tranny and have been running for three years and I do not see any problems with this set up. The pressure plate that I broke several years ago was the 9 1/4" set up I believe. It was for a car tranny and it broke at 1000 rpm's after a burnout and I had to shut the car down similiar to what you did. I'm fixing to put some power to mine and want to make sure that I do not have this problem if I can possibly get around it. Thanks for your report on this so far, Robert
Robert, the 10" I had was part of a parts buy so I can't be certain. However, my best guess is that it was from a light truck. I do still have the gearbox it came with, would a picture of that give you the info you want? I also ran the 9 1/4" for three years as well prior to its break. I feel the "formula" for the breaks was thus ...... Excess slippage (cause not relevant) weakening the pressure plate "beam strength" in some manner (heat? vibration? other?) so that ..... the next pedal press warps and cracks the now weakened plate, at which time ...... the plate seperates, with damage level depending on revs. No excess slippage> no material change> no break. Increase in horsepower = more possiblity of slippage> more possibility of material change & break upon next pedal press. I see this as a moving scale application. I don't feel that time is as big a factor in these failures as one might first think. It could happen to a new one as easily as an old one. I also feel that the traction problems we had with our original tires was a contributing factor to delaying our pressure plate problem, via delaying the plate slippage. They'd turn loose before the plate slipped much. The Cokers don't.
The 10" pressure plate that I am running is the one that has "fingers" instead of the three or four pieces as the 9" car pressure plate. I am also running the truck tranny which is about 75 pounds heavier than the car. As I have had no problems with it, I'm going to continue to run it and see what happens. Hopefully nothing bad. Thanks, Robert
Sounds like you're describing a diaphragm style? If so, it has a naturally more even pressure loading, and should be safer from that standpoint. Yes, the 10" I had was a three-finger (Borg style) job, similar to the car ones.
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