1980 hops at slow speed.
Thread Starter
Instructor
Joined: Sep 2013
Posts: 175
Likes: 3
From: Palmyra NY
1980 hops at slow speed.
Five weeks ago I had the wheels balanced and all new shocks installed. Front end is in excellent shape. Did a test drive and no issues. I drove car today again for a car show. The car has been sitting for five weeks. I now notice that at slow speeds the car seems to hop up and down. Cruising at forty to fifty it is nice and smooth. What could have changed? What should I check? If weather is nice tomorrow I will do another test drive. Thanks. Don
Melting Slicks
Joined: May 2002
Posts: 2,431
Likes: 52
From: Florida
What speed does this occur? Barely creeping at 0.5 mph would likely be posi clutches in need of additive, bad prop. shaft u-joints binding, wheel/wheels installed incorrectly, bulge on tire/tires (aka slipped belt). Let us know what you find.
jim
jim
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Might be an out-of-round tire or wheel. You can jack up each wheel and hand-rotate them to see if tire O.D. or edge of wheel rim could have significant runout. Not uncommon to get a tire that is dimensionally bad.
Also, you don't need 35 psi in your tires. Best all-around performance and ride will be around 30 psi.
Also, you don't need 35 psi in your tires. Best all-around performance and ride will be around 30 psi.
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Thread Starter
Instructor
Joined: Sep 2013
Posts: 175
Likes: 3
From: Palmyra NY
Okay. Here is what I found. This is odd. Before I had the wheels balanced, 30 to 35 mph was pretty smooth except for a slight vibration. Now the car jumps up and down like popcorn. I inspected each wheel and noticed that 3 out of the 4 wheels the weights are moved over 2 inches. I can see where the old weights used to be. Doesn't this seem a bid extreme? I also noticed my left front tire has a slight bulge on the sidewall showing outwards. Not sure if this is also the problem. Comments?
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Sitting for weeks is tough on old tires. Might be time for a new set.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Five weeks ago I had the wheels balanced and all new shocks installed. Front end is in excellent shape. Did a test drive and no issues. I drove car today again for a car show. The car has been sitting for five weeks. I now notice that at slow speeds the car seems to hop up and down. Cruising at forty to fifty it is nice and smooth. What could have changed? What should I check? If weather is nice tomorrow I will do another test drive. Thanks. Don
You say it runs smooth at 40-50, but bounces at 30mph... Once it has smoothed out at 40-50 and you slow down, does it start bouncing again? If it does smooth out after slowing down, it means the tire has probably flat spotted from sitting. And yes even radials can temporarily flat spot if they sit too long.
Having said that and considering the bulge you've observed, and the unknown age of the tires, I would suggest you first try to determine how old they are. Look for the stamped (molded) DOT number on the side wall (it may be on the inside of the tire) first and post it here.
http://www.tirerack.com/tires/tirete....jsp?techid=11
Just a hint, if the last digits are 4 numbers it is a post 2000 tire, three digits means it is a pre-2000 tire.
Good luck... GUSTO
Last edited by GUSTO14; Aug 21, 2016 at 11:14 PM.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
Likes: 1,174
From: Southlake, TX
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
Shortly after that I replaced them with GS-D3's as the rubber had gotten so hard they just "skated" like they were on ice at the slightest application of throttle.
Good luck... GUSTO
Heel & Toe
Joined: Feb 2015
Posts: 21
Likes: 4
Yeah I'm gonna go with the tires.. Had the issue with some older tires. Not so much flat spotted as had become out of round and the radial belting was starting to rupture... (I know I should have changed them sooner .. my bad)
Advanced
Joined: Mar 2014
Posts: 76
Likes: 2
Could be a universal joint. I know when my joints were fucked it was pretty bumpy. if you wanna know how out of round the tire is, jack it up, rotate the front tires by hand with a ruler under it and watch how it gets closer/farther from it when you hold it still. Posi clutch chattering happens more during cornering. so if you do a tight corner at 15 you can feel it.
Heel & Toe
Joined: Feb 2015
Posts: 21
Likes: 4
Could be a universal joint. I know when my joints were fucked it was pretty bumpy. if you wanna know how out of round the tire is, jack it up, rotate the front tires by hand with a ruler under it and watch how it gets closer/farther from it when you hold it still. Posi clutch chattering happens more during cornering. so if you do a tight corner at 15 you can feel it.
Last edited by AkitaCJ75; Aug 22, 2016 at 06:25 PM.
Thread Starter
Instructor
Joined: Sep 2013
Posts: 175
Likes: 3
From: Palmyra NY
Thanks for your input! It's not U-joints. Had them checked last fall by my mechanic. All super tight. I'm just going to go ahead and buy new tires. I see a slight bulge in my LF tire. Not bad but there's something there. Also, my sidewalls are hard as concrete. I was thinking of going with the Cooper Cobra GT's to keep the cost down. I can get them for under $100.00 ea. Have you heard any horror stories about them?
Heel & Toe
Joined: Feb 2015
Posts: 21
Likes: 4
Thanks for your input! It's not U-joints. Had them checked last fall by my mechanic. All super tight. I'm just going to go ahead and buy new tires. I see a slight bulge in my LF tire. Not bad but there's something there. Also, my sidewalls are hard as concrete. I was thinking of going with the Cooper Cobra GT's to keep the cost down. I can get them for under $100.00 ea. Have you heard any horror stories about them?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Cooper Cobra tires are about the same quality as the BFG T/A radial tires. They cost a little less as there is more demand for the T/A's.
If you have a membership at Sam's Club, you can buy 235R60-15 BFG T/A's from them at reasonable prices. Also, their lifetime balance and rotate plan is very good and very reasonable. You may have to order on-line and have sent to your local store.
Bulging sidewalls are NOT a good thing. Best not do much highway driving until you get them changed. Blowouts at speed are NOT good on a fiberglass Corvette.
If you have a membership at Sam's Club, you can buy 235R60-15 BFG T/A's from them at reasonable prices. Also, their lifetime balance and rotate plan is very good and very reasonable. You may have to order on-line and have sent to your local store.
Bulging sidewalls are NOT a good thing. Best not do much highway driving until you get them changed. Blowouts at speed are NOT good on a fiberglass Corvette.