Have a 351w in a race car with a 3 speed toploader. We've fought a vibration all year and it keeps breaking the top left ear on the trans. The vibration feels like it's coming from the center of the car around the flywheel but it's hard to tell. Iys the same flywheel we used b4 with no issues, same clutch ect, and all that looks fine, no stress cracks. Could bad engine mounts be the cause? Any other ideas? Replaced u joints, driveshaft seems straight. Worn out harmonic balancer? But would a worm out harmonic balancer translate to vibration in the middle of the car? We've tried to no avail to fix this issue for months
Bad vibration/ breaking the top left ear on trans
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The bellhousing is and has been tight all year we've checked that. It just seems odd but this vibration started after we had our motor refreshed by a guy. As far as alighnment everything seems fine there too. Trans snout is in the pilot bearing good but not bottoming out. Now motor mounts could be an issue because there's more flex than I feel comfortable with when the crewmember is loose and granny is out, but this doesn't really explain the vibration in the center of the car but might be part of the prob2
I'm gonna replace the pilot bearing, this one has the roller bearings and I can feel the end of the bearing, basically like a washer on each end is slightly higher than the bearing rollers so I think this is some of it too. Any advice on a brass pilot bearing or roller style?
Use a Timken FC65174 roller pilot bearing,
.733” width
How is the clutch plate?
Always use a bonded and riveted clutch disc or a Full bonded clutch disc without a cushioned marcel. A clutch that has the clutch facing bonded to the clutch backing plate without a marcel will not rip off and cause a vibration. I use those in my daily driver. They have a more harsh slow clutch. release but they will stay together with high RPM power shifting whereas a stock clutch disc will come apart.
Is the rear crossmember that holds the rear transmission mount level? I bent one with a floor jack and caused a drive line vibration. I went to an alignment shop and they chained the crossmember to eyelet in-the shop floor and jacked the car up, and straightened the crossmember.
.733” width
How is the clutch plate?
Always use a bonded and riveted clutch disc or a Full bonded clutch disc without a cushioned marcel. A clutch that has the clutch facing bonded to the clutch backing plate without a marcel will not rip off and cause a vibration. I use those in my daily driver. They have a more harsh slow clutch. release but they will stay together with high RPM power shifting whereas a stock clutch disc will come apart.
Is the rear crossmember that holds the rear transmission mount level? I bent one with a floor jack and caused a drive line vibration. I went to an alignment shop and they chained the crossmember to eyelet in-the shop floor and jacked the car up, and straightened the crossmember.
No I don't think he rebalanced it to 50 oz, he just fine a refresh on it, New rings, bearings ect and put everything back together. Clutch kit is a zoom, not sure the part number but everything looks fine. A few hot spots on the bottom of the fly wheel and pressure plate but not bad and no warping. We thought it was the car flexing and trans and motor following suit in the turns but that's out because the last one broke on the straitaway under hot laps he floored it and it started vibrating bad and it never got above 4500 rpm if that. He immediately came in the pits and sure enough another broke tranny eyelet
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How sure are you about the driveshaft being straight, made of strong enough tube, and the yokes being straight??
Driveshaft vibration is the #1 killer of trans cases in the drag race world.
Shaft needs to be straight withing .020" run-out, and of thick enoughh wall tube to prevent it from bowing under power and rpm. Too thin a wall and it will take on a form that looks like a swinging jump rope and vibrate like crazy, if it doesn't outright wad itself up and exit the vehicle.
Total run-out on the shaft needs to be less than .020". Have you checked the driveshaft run-out, while installed in the car?? This can be very telling.
Is the vibration there in nuetral but engine revved....or is it only in gear while unmder power??
Vibration there at speed but trans in nuetral, car coasting??
Output bushing in trans good and tight, and same for the slip yoke fit into the bushing, no noticable slop?
You didn't recently add a solid transmission mount, did you?? These are also trans case killers.
Driveshaft vibration is the #1 killer of trans cases in the drag race world.
Shaft needs to be straight withing .020" run-out, and of thick enoughh wall tube to prevent it from bowing under power and rpm. Too thin a wall and it will take on a form that looks like a swinging jump rope and vibrate like crazy, if it doesn't outright wad itself up and exit the vehicle.
Total run-out on the shaft needs to be less than .020". Have you checked the driveshaft run-out, while installed in the car?? This can be very telling.
Is the vibration there in nuetral but engine revved....or is it only in gear while unmder power??
Vibration there at speed but trans in nuetral, car coasting??
Output bushing in trans good and tight, and same for the slip yoke fit into the bushing, no noticable slop?
You didn't recently add a solid transmission mount, did you?? These are also trans case killers.
Output bushing is brand new, we've jacked the car up and looked at the drive shaft while in gear and it didn't appear to have any wobble. We thought drive shaft or something related initially but our driver keeps saying it feels like it's in the center of the car, who knows. I'd love to have the driveshaft checked but we're trying to rule everything out b4 spending more money. The slip yoke is fully splined, now I'm wondering if it's bottoming out of spline on the output shaft on trans?
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IMO driveshaft work is cheap in the big picture of things.
Do you believe you're making more power than you were before the refreshening?
How are the driveshaft angles?
Be absolutely sure of no chance of bottoming out the trans yoke (how much end play in yoke).
We are making more power but not an insane amount more. Its just bizzare bc this wasn't a problem last year and now this year we cant get a hand full of laps in without breaking a trans housing. Its a bad vibration. Nothing as far as angles has changed. I'm going to reinforce motor mounts because I feel like there's too much front to back and possibly side to side flex. Trans isn't jamming into the back of the crank checked that, no wrecks that would've caused anything either. We've asked everybody and their little brother that races ect and everything we've checked seems ok.
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Eyeball checks of the driveshaft are no where near good enough....if you guys are serious about racing you need to have a magnetic base and dial indicator and check things out.
I'm dead serious.
There are literally dozens of things on a racecar you need a dial indicator to do, and no serious gear head should be without one. You can get a magnetic base and a 1" travel .001" increment dial indicator for less than $25 from Harbor Freight when you combine it with their typical 15-20% off coupon.
https://www.harborfreight.com/multi-position-magnetic-base-with-fine-adjustment-63663.html
https://www.harborfreight.com/1-in-travel-machinists-dial-indicator-63521.html
I'm dead serious.
There are literally dozens of things on a racecar you need a dial indicator to do, and no serious gear head should be without one. You can get a magnetic base and a 1" travel .001" increment dial indicator for less than $25 from Harbor Freight when you combine it with their typical 15-20% off coupon.
https://www.harborfreight.com/multi-position-magnetic-base-with-fine-adjustment-63663.html
https://www.harborfreight.com/1-in-travel-machinists-dial-indicator-63521.html
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1,259 Posts
This is a stock car (roundy round...) ? Did you recently change to solid motor mounts or a transmission mount? Possibly something is wrong with the engine balancing, is the vibration damper new, does it run out? Pretty easy to see with the naked eye.
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