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Total driveline slack-can you help?


RebekahsZ

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I'm looking for some folks to help me learn about total driveline slack.  I'm looking at the impact that the driveline gets when I drop the clutch at the drag strip with a manual transmission and I'm trying to get an idea of what is "normal" and expected.  Total driveline slack includes total backlash within the transmission, driveshaft, diff, and axles.  I am not trying to measure differential backlash.  I don't want to have a big discussion or a critique of who's car is better or worse.  I just want to collect some info from you and your car.

 

Will a couple of guys try to repeat my experiment and post up your results?

 

To copy my setup (so we are comparing apples to apples), put a jack under your left seatbelt pocket just in front of the rear wheel.  Jack the wheel just enough off the ground to be able to turn it by hand.  Put the transmission in gear, release the parking brake.  Rotate the tire by hand clockwise until it stops.  Use tape to mark from the center of the hub, straight down to the floor and put a little strip in line with that on the floor.  Now, rotate the tire firmly counter clockwise until the tire stops rotating.  Shoot a cell phone photo that is roughly the same scale as the photo I post of mine (mine is the Weld Draglite).  I will enlarge and print your photo and use a protractor to measure degrees of total driveline slack.

 

Thanks!

post-5903-0-05142500-1398995065_thumb.jpg

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  • 2 weeks later...

Just a set of rebuilt axles and a parenting schedule that leaves no time for drag racing. I did buy a set of more narrow slicks to try to get a little bit of slippage back into the launch. And a plan to start with low tire pressure instead of high pressure to try to get more sidewall wrinkle. I hope to start working on another 3.54 CLSD diff and will try to mix and match shims better to achieve less R&P backlash. Then will swap them and keep the car in service. After i do so i will re-measure. Interestingly, when I was rebuilding the CV axles I did find that there are a couple of degrees of lash/slack in the CVs. I flip the star-fruit shaped inner race of the hub-side CV to put the ball bearings on un-worn races, and shortening of the axles puts the balls on un-worn races in the outer CV housing. Even still, there is some lash in the CVs, at least a couple degrees per CV joint. I think, Phantom, that you run u-joint axles(?). If so, that may be a place where my total slack exceeds yours. Unfortunately, I really only got useable photos and video from one other forum member. He has CV axles and his slack was similar to mine. If I had gotten useable photos from anyone else, I would have posted them. I was glad to get your video and I could see that you had less slack, but it was too quick to analyze anymore than that.

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Sorry about the video. It started and ended quicker than I thought it did. Somehow I got it started before i got the camera set instead of after and I though I'd gotten at least 3 back-firths instead of one. An AV guy I ain't. Yes, you're correct that I have U-joints instead of CV's.

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