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Everyone should be aware that running on any dyno is not without its risks, and those risks are solely the owner of the vehicle/engine. About twenty years ago our GTO club did a car show at Universal Technical Institute in Ontario, CA during one of their Saturday open houses. As a reward for showing our cars the school invited us to run our cars on their chassis dyno. Several cars ahead of me went without incident and posted mediocre numbers. I had my '67 GTO I refer to as my Cruiser since it was my go-to car at that time for shows and longer distance events. It was the second run where I asked them to run it up to six grand since the previous pull showed we were not near the horsepower peak. Well, at 5,800 RPM and 129 MPH the driveshaft let go. Driveshaft bowed up and pulled out of the safety loop and quickly broke in half. Front portion exited the car and penetrated all the way through a cement block wall. The rear half stayed attached to the differential and flailed around until the dyno stopped. The thick 3" exhaust pipes were beaten almost flat but they saved the floor and the T400 trans was now in pieces. Very expensive day, but I knew the replacement cost was mine. You play and sometimes you really pay. At least the students cleaned up all the trans fluid and helped push it out on the street so I could call the auto club for the flatbed ride home. The positive thought was it was time to move up to an overdrive trans. I guess positive thought #2 was I could have been out on the street at speed when it came apart and not strapped safely down on the dyno.
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I called him as soon as I got home and he said he didnt notice, he said that it wouldn’t have pulled hard on the dyno slipping (he is right)- the hydro throw out may not have enough airgap- but i am ready to replace it all..

The shop had me sign a release if anything went, so they are clear…..

I’m happy with tuning the clutch thing just sucks….
I just don't know about those hydraulic clutches, I've heard more bad than good. I'm running a PRW 11" steel wheel with a McLeod Super Street Pro with no problems in four years and an easy pedal, think I waited 50 miles to go wot which isn’t right but I still have no issues. Hope everything works out for you after all you've been through, just my 3 cents worth.
 

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Discussion Starter · #23 ·
I just don't know about those hydraulic clutches, I've heard more bad than good. I'm running a PRW 11" steel wheel with a McLeod Super Street Pro with no problems in four years and an easy pedal, think I waited 50 miles to go wot which isn’t right but I still have no issues. Hope everything works out for you after all you've been through, just my 3 cents worth.

Thank you! I have an appointment with the shop to replace the clutch and resurface the flywheel, i hope thsi cures the issues and we move down the road….

I have to admit, thsi wasn’t an issue I’ve been anticipating??
 

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Everyone should be aware that running on any dyno is not without its risks, and those risks are solely the owner of the vehicle/engine. About twenty years ago our GTO club did a car show at Universal Technical Institute in Ontario, CA during one of their Saturday open houses. As a reward for showing our cars the school invited us to run our cars on their chassis dyno. Several cars ahead of me went without incident and posted mediocre numbers. I had my '67 GTO I refer to as my Cruiser since it was my go-to car at that time for shows and longer distance events. It was the second run where I asked them to run it up to six grand since the previous pull showed we were not near the horsepower peak. Well, at 5,800 RPM and 129 MPH the driveshaft let go. Driveshaft bowed up and pulled out of the safety loop and quickly broke in half. Front portion exited the car and penetrated all the way through a cement block wall. The rear half stayed attached to the differential and flailed around until the dyno stopped. The thick 3" exhaust pipes were beaten almost flat but they saved the floor and the T400 trans was now in pieces. Very expensive day, but I knew the replacement cost was mine. You play and sometimes you really pay. At least the students cleaned up all the trans fluid and helped push it out on the street so I could call the auto club for the flatbed ride home. The positive thought was it was time to move up to an overdrive trans. I guess positive thought #2 was I could have been out on the street at speed when it came apart and not strapped safely down on the dyno.
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WOW! So what do you think caused that, rpms to much? Had you ever revved it that high? Do you think it would have done that on the street or does the dyno have a different effect? Did you upgrade any of the parts or were they stock? Did you have the drive shaft loop or did they put that in for safety? At least no one was hurt or killed, there's some scary dyno videos on YouTube.
 

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Hmmm. I ran a ceramic clutch disc and thought the same thing because I never used a ceramic disc.

See the "shiny" on the clutch disc springs? That's what happens when you use the Hays flywheel and the taller headed crank bolts - they hit the springs when you are slipping out the clutch to take off because they sit too high. Gotta use the correct "thin" headed crank bolts.

Don't know if this applies to you, just pointing it out when you stated the whirring noise when slipping the clutch disc - my experience also thinking it was the ceramic disc material sound.
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You do have me thinking on this. I know I used the thin head bolts just for this reason but anything's possible. The pressure plate side on the disk I used is a bit different than the stock style which is what I thought would be contributing to the sound. When I test fitted everything the disk seemed to clear the head bolts (I did check this because I had heard of others having clearance issues. Guess this gives me something else to check out when I get a chance.

Thanks Jim!

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WOW! So what do you think caused that, rpms to much? Had you ever revved it that high? Do you think it would have done that on the street or does the dyno have a different effect? Did you upgrade any of the parts or were they stock? Did you have the drive shaft loop or did they put that in for safety? At least no one was hurt or killed, there's some scary dyno videos on YouTube.
Stock parts on the Cruiser. Driveshaft failure at speed was the culprit, and it was turning the same speed as the engine or 5,800 RPM. Always shifted at 6,000 and would sometimes bump the rev limiter at 6,300 but those were lower gears and driveshaft wasn't spinning that fast. The car ran 102-103 many times in the quarter without problems but the additional speed did it in. The more likely cause of the failure was one of the circlips in the front universal wasn't fully seated and popped out allowing the driveshaft to go off center when the cap moved out some. At that point the whipping started and it quickly failed without time to do anything. Circlip probably ran for years not quite seated but didn't cause problems. Driveshaft loop was installed per NHRA guidelines which mandates it be within 6" of the universal joint. You can see severe scoring on the inside of the loop so it did work for a few seconds, but then the bow of the failing shaft pulled it right out of the loop. Since then I've talked to racers that lost driveshafts at speed and all said the loop didn't do any good. I now toss the stock driveshafts and go aftermarket just for extra security.

After seeing this happen I always cringe when I see guys standing next to a car when it is being run up on a chassis dyno. I now stand way in front or the rear of the car.
 

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Ya no kidding, I would be outside....so the track makes you have a loop on a stock car? The track I want to go to this fall in Byron IL only requires a helmet and foot wear until you hit faster times. What about two loops front and back or wouldn't that work? I have upgraded everything so hopefully I'm good and I've shifted it at 6k a bunch of times, so far so good but that's my biggest fear is wrecking something, plus I can't get traction that's going to effect my time the most but maybe when the drag radials or heated up it will make a difference.
 

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You do have me thinking on this. I know I used the thin head bolts just for this reason but anything's possible. The pressure plate side on the disk I used is a bit different than the stock style which is what I thought would be contributing to the sound. When I test fitted everything the disk seemed to clear the head bolts (I did check this because I had heard of others having clearance issues. Guess this gives me something else to check out when I get a chance.

Thanks Jim!

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Ya, I think I may have mentioned this during your build. Not sure if you can really check it. I was thinking you could have someone push in on the clutch pedal while looking up from underneath through the inspection cover, but I am not sure if you could get the disc moved back far enough from the flywheel to see anything. Not sure if a bore scope could be snaked in from the clutch fork hole while the clutch pedal was depressed.

Not saying you have an issue, but your description of the sound is similar to what I think my ceramic disc sounded like. You might want to email Mcleod and see what they have to say. It could be a "normal" sound, but in my case it wasn't. o_O
 

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Yes you did. And I remember holding the disk to the flywheel, turning it, and it seemed OK. That doesn't mean that it is so a little investigation may be in order. Pretty tight in there for a scope. Good recommendation on reaching out to McLeod. If they say it's normal, I won't worry about it for the time being. If it's not normal, I'm thinking the trans would have to come out to check.
 

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Hmmm. I ran a ceramic clutch disc and thought the same thing because I never used a ceramic disc.

See the "shiny" on the clutch disc springs? That's what happens when you use the Hays flywheel and the taller headed crank bolts - they hit the springs when you are slipping out the clutch to take off because they sit too high. Gotta use the correct "thin" headed crank bolts.

Don't know if this applies to you, just pointing it out when you stated the whirring noise when slipping the clutch disc - my experience also thinking it was the ceramic disc material sound.
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yeah had the same situation.
 

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.so the track makes you have a loop on a stock car? The track I want to go to this fall in Byron IL only requires a helmet and foot wear until you hit faster times.
Stock would be ok. Here's the section from the NHRA 2020 rule book on driveshaft loops:

DRIVELINE
OEM production line all-wheel-drive vehicles permitted.
Driveshaft loop required on all cars running 13.99 (*8.59) or
quicker and utilizing slicks, except vehicles running 11.49 (*7.35)
seconds or slower equipped with street tires. See General
Regulations 2:4.


At one time when I took the slower car to the strip, I'd rob the slicks off the hotter car and therefore needed the loop to get through tech. I think a loop would do good if you snapped a universal off the starting line within a few dozen feet. From what I've seen they are totally worthless at speed..

As far as a rear loop, NHRA is probably more concerned that the driveshaft doesn't break and come up and puncture the fuel tank. If the rear universal broke the driveshaft would probably just slide out of the trans and exit the rear of the car.
 
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