Could It Be The Rear End???
02-28-2017, 08:35 PM
#21
Melting Slicks
C2 Hot Cam Guy,
Go to the "search this forum" archive application at the upper right side of the home page.
Type in: Vibration at high speed. Then, scroll down to the post by 1965 Nassau for more info.
That thread even has a great pic of it by John Z.
Gary
Last edited by Gary's '66; 02-28-2017 at 08:38 PM.
02-28-2017, 08:40 PM
#22
Race Director
Member Since: Apr 2015
Location: Fresno California
Posts: 17,505
Received 3,443 Likes
on
2,113 Posts
Yeah, Jack . . . who was that BONEHEAD??? . . . oh, wait . . . never mind!!! 
Thanks to everybody that has responded so far . . .
YES - I have moved the rear tires to the front - no affect
YES - the rear snubber is brand new
YES - I had the tires radial forced balanced - no affect
I think GTOguy may be on to part of the issue - that it's driveshaft related . . .but, im my specific case that my diveshaft is simply too short!
Let me explain. When it came time to shorten my stock driveshaft while engineering the installation of my G-Force Street 5 speed, either I took the wrong measurement, or the shop cut it too short (my shaft is too short? . . . the story of my life!). As currently installed there is slightly over an inch ( + 1/16th) of my transmission yoke (this application uses a stock Muncie yoke) protruding from the tailshaft of my transmission. My new theory is that too much of the yoke is exposed and that may be allowing the yoke to wobble ever so slightly! I'm thinking the driveshaft needs to be lengthened by @ 1/2" to work properly. Can you all concur with my latest assumptions? Thanks as always for the input!
Tom
Thanks to everybody that has responded so far . . .
YES - I have moved the rear tires to the front - no affect
YES - the rear snubber is brand new
YES - I had the tires radial forced balanced - no affect
I think GTOguy may be on to part of the issue - that it's driveshaft related . . .but, im my specific case that my diveshaft is simply too short!
Let me explain. When it came time to shorten my stock driveshaft while engineering the installation of my G-Force Street 5 speed, either I took the wrong measurement, or the shop cut it too short (my shaft is too short? . . . the story of my life!). As currently installed there is slightly over an inch ( + 1/16th) of my transmission yoke (this application uses a stock Muncie yoke) protruding from the tailshaft of my transmission. My new theory is that too much of the yoke is exposed and that may be allowing the yoke to wobble ever so slightly! I'm thinking the driveshaft needs to be lengthened by @ 1/2" to work properly. Can you all concur with my latest assumptions? Thanks as always for the input!
Tom
02-28-2017, 08:49 PM
#23
Team Owner
It would have to be excessively short and that would be instantly apparent on the yoke shaft in wear or damage! On the stroke the u-joint could be like a flapping butterfly fluttering away! The play just by sliding the driveshaft fore and aft would be noticeable!
Last edited by TCracingCA; 02-28-2017 at 08:50 PM.
02-28-2017, 10:10 PM
#24
Melting Slicks
Thread Starter
Member Since: Apr 2002
Location: Ellicott City Maryland
Posts: 2,881
Received 1,962 Likes
on
664 Posts
How much of the input shaft is inside the tailhousing? Photo? Not having enough slip-yoke inside the trans supported by the output shaft and rear bushing could indeed cause a vibration issue. When your shaft is hanging out in the breeze with little support, bad things are bound to happen!
02-28-2017, 11:31 PM
#25
Instructor
Here's a vibration app that works using your phone. Costs about $400 but could isolate your source.
http://vibratesoftware.com/
Mac
http://vibratesoftware.com/
Mac
04-20-2023, 10:00 AM
#26
2nd Gear
Member Since: Sep 2022
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
Tires and wheels need to be checked for axial and lateral run-0ut as well as being in balance. Axle flanges need to be checked for run-out as well. How was the front yoke in the driveshaft? If saddle-worn, it'll cause vibration at higher speeds. Have run into almost zero rear end issues that resulted in vibration. You could always hear a bad one long before failure. Vibration always seems to be driveshaft angle/trueness, excessive run-out on the axle flanges and wheels/tires, etc. (external stuff) Keep us posted!
I recently took my half shafts to Sacramento Driveline. Both required balancing. I mentioned that I heard they are not balanced from the factory and was told that's very possible but that doesn't mean they don't require balancing. I also learned that one shaft unbalanced can cause a vibration...and two (even slightly) unbalanced shafts spinning on each side of the differential will counteract with each other and increase the already unbalanced condition. My vibration was not serious and started at about 3500rpm. I'll have things back together in a couple of weeks and report back.
04-20-2023, 10:26 AM
#27
Tether Man
Member Since: Dec 2004
Location: Pittsburgh, South Hills
Posts: 4,537
Received 2,014 Likes
on
1,039 Posts
2023 C2 of the Year Finalist - Modified
2022 C2 of the Year Finalist - Unmodified
2019 C1 of Year Finalist (appearance mods)
I recently took my half shafts to Sacramento Driveline. Both required balancing. I mentioned that I heard they are not balanced from the factory and was told that's very possible but that doesn't mean they don't require balancing. I also learned that one shaft unbalanced can cause a vibration...and two (even slightly) unbalanced shafts spinning on each side of the differential will counteract with each other and increase the already unbalanced condition. My vibration was not serious and started at about 3500rpm. I'll have things back together in a couple of weeks and report back.
There are a lot of us that will want to know, me included but this post is 4+ years old and Tom probably has either figured it out or parts are falling off his Corvette!!!
Your points are well taken, however! I am very interested in what you find out...