dcamick

1984: Last record that I have for a Shock (Koni) replacement....I will still need to try and Identify what I have currently am running. Regardless, a chronic rear Vibration at 65 mph and above, has got me going though a process of elimination.

If I choose to replace my shocks, what are my Options for Best Handling replacements? I have used and like Bilsteins....If my current Installed Shocks are 25+ years old.....they will be replaced, regardless.......If by some chance they original HD shocks, I will plan to have them rebuilt.

Thanks for any help.....as usual.

Dcamick

Vet65te

Doug - How long have you had this imbalance issue on the back end? I know you recently installed new tires, was this vibration problem around even before the new tires?
Any leaks visible from the shocks?
Mike T - Prescott AZ

68hemi

Best shock replacement would be QA-1 adjustable shocks available from Summit for about $170. each.

Factoid

Sorry, Doug, not to hijack but can the original F41 shocks be rebuilt and if so where? How about the F41 rear 7-leaf spring?

So, for my hijack penance I will second Darryl’s comment on the QA1 single adjustable. I have them on my ‘69 with a Vansteel composite spring. Once I got them adjusted they are perfect.



You can see the adjuster just peeking over the strut rod. I started at a setting of 12 and after several round of test/adjust ended up at a 6 for street driving. The lower the number the softer the setting.

dcamick

​​​​​​​Thanks Mark....NP!!! Unfortunately, I believe I do not have Original shocks.....unless they were Koni????? So, it's a mute point...

dcamick

Mike,
Good to hear from you! It's driving me crazy......This Vibration is right in my "Cruising ZONE" LOL!

To answer your question: Yes, the new tires and wheels were going to happen...so I did that first with the same 65-70 MPH high frequency vibration that distorts my rear view mirror!!! It's definitely a vibration behind me.....

NOTE: Clutching to idle @ 65 MPH Vibration remains. So I believe the problem is at or behind the Transmission.......

Drive shaft looks new with balancing weights at each end.... I have an option to index the DS 180 degrees but there are clear reference marks on the U-Joints so I think the drive shaft was installed correctly???????

I have records of replacements of everything including shocks........I'm leaning toward shocks and u-joints (Drive shaft). Trailing arms were rebuilt......Shocks replaced in 1984 (no apparent leaks....maybe they are dry!!!). Receipt found shows a Koni Purchase.. And I confirmed they are currently Koni's... People just do not want to work on this Corvette in my area. A few that I have talked to do not impress me at all!!! So My next step is to replace these seemingly low mileage, old shocks.....I can replace the shocks myself but probably need help with the drive shaft u-Joints. But they look good. I believe taking the drive shaft out and checking u-joints and trans and differential yokes will be the next step! Who Knows! I have put a lot of time into this and its starting to bother me!

Once again, good to hear from you...Happy New Year!

Dcamick

Mike C#2

Koni’s of that vintage have a lifetime warranty to the original purchaser I’m pretty sure.Whatever you go with you may get a brand new set depending on what they require for proof of purchase. Even if you don’t run them, could probably sell them for 30-50 cents on the dollar to help offset cost of new ones or if you run the Konis no cost upgrade.

Lotsacubes

Have Bilstein HDs with my F41. Like them.

68hemi

Have you replaced the trans mount?

silver837

Koni has a restoration service for any shock they make or made.

dcamick

Darryl,

Trans mounts and Motor Motor mounts are New. I can only assume they are correct.

Thanks for your input!
Dcamick

dcamick

Mike,

Interesting, I have the Warranty Pamphlet for those shocks in my records...LOL!

MarkC

I had a similar issue when I bought my car 9 1/2 years ago. The front wheel bearing nut was too loose. As far as shocks go, I changed over to Double Adjustable QA1’s on the rear and I love them. They are pricey but worth the money. BTW, I don’t think the shocks will fix the vibration.

dcamick

Note: It's very Hard for an Old man like me to push down on four corners to check my shocks for rebound......but with this suspension, there is not a lot of downward movement!! Might not be the shocks.

There is some related History for this Corvette in my binder:
A hand written Note:

Over tightening a pinion U-Joint does not make much sense to me! Wouldn't that potentially damage the U-Joint Caps at the Pinion?

Thanks All!
Dcamick

SWCDuke

The natural frequency of the base front suspension corresponds to about 60-65 MPH, but since F-41 has double the spring rates it is much higher and higher still for the rear. I think your problem lies somewhere in the rotating drivetrain components. Have you removed the shocks and just manually tested that they have substantial resisting force to being stroked, especially in rebound?

I suspect something is out of balance or bent. Get the car up on a lift and check the U-joints for excess wear.

Duke

Bluestripe67

Doug, I'm digging deep here. Is the wheel seated flat against the hub? Is the hub flat/smooth? Check the back of the wheel to make sure it's flat. Dennis

dcamick

Duke, Just got out from under the car. All u-joints appear to be in good shape, rotating freely with no sloppiness or noise. I looked at the shocks....will need to take them off to check! all Rear end Brackets, rods and bushing appear to be new......I believe I will have to have the drive shaft removed and the front and rear U-joints replaced as a start..... Thanks Duke!

dcamick

Hey Dennis,

I have had three sets of wheels and tire mounted, I believe correctly. I prechecked the hubs, as always prior to mounting. Thanks for you input, Buddy!

MrTrim

Dcamick,
Have you had your tires balanced on a "Road Force" balancer? All balancers are not created equal. Have had a similar concern and doing a "Road Force" balance eliminated my vibration at 65MPH that I was having. Before, on a regular style balancer, it showed my wheels were balanced within spec. On the "Road Force" balancer the tire shop had to rotate 2 of the tires on the wheels for a correct balance and one tire had to be replaced. Just a thought here.
Chris

dcamick

Duke and All,

I have noticed that when the Corvette is lifted with the wheels in the air, the rear strut rods are hitting the flange on the bracket under the differential. Almost appearing to be very slightly twisted....Not sure if the rod orientation changes or centers when the wheel are on the ground?????? Those rubber bushings appear to be in pretty rough shape....Could that potential Metal to metal contact cause my substantial vibration? I will edit and include a picture....or 5!!! As mentioned, the orientation might change when lowered onto the ground.....