Close to where I live, there is a perfectly paved 4-lane road with 6 "S" curves. Everytime I drive on it, I love to take the curves as fast as I can. There is a BIG question I have....Whenever I take the curves around 60 mph (35-40 mph is considered a safe speed), I notice the car sort of "hops" a little. It stays the course (hugs the lane) but it just (for lack of better words) "hops" during the critical part of the curves.

Now, whenever I drive my wifes BMW Z3 or my Honda Civic Si, on the same stretch of road, the cars handle as smooth as silk.

As far as the suspension on the Vette...(all within the past 7 months) all new Bilstein HD shocks in the 4 corners, complete front end bushing replacement, and new tires (R235x15x60). The only thing that I haven't replaced is the rear spring. But from all indications, the spring seems to be in very good condition.

Why do the "hops" occur? Can it be fixed? How? OR is that an inherent trait for a 1975? Any help will be appreciated!!!

 

what tire pressure are you running?

 

Several possible areas of concern come to mind: differential problems with the posi-trac unit; half-shaft U-joint problems; trailing arm bushing problems; strut rod bushings worn out. I'm sure there are other possibilities, but those come to mind. The 'hopping' sounds more like binding U-joints or T/A bushings worn out to me; but with no info about your car's condition on rear end components, that's my best guess.

 

30 lbs

 

I'm glad you brought up T/A bushings. I had them replaced about 18 mos ago. What do you mean by "binding U-joints"? How would you check them to see if they were binding?

 

Since you said the road is perfectly paved, I would guess that you are having unwanted/excessive rear end movement since you said everything has been replaced in the front end. Now keep in mind that all cars especially from that era have a ton of movement built into the basic suspension design which is not true today, even on the most basic transportation vehicles. So what do I mean?

I decided a few years ago that the best way to increase the effectiveness of the suspension on my 78 was to eliminate "unwanted" suspension deflection wherever possible. Now I don't really think that your issue is coming from the front end but I relate my experiences as a reference in the front. My front suspension is 100% OEM design BUT I have done everything to eliminate unwanted deflections: Poly upper and lower control arm bushnings, poly sway bar mouinting and end link bushings on the OEM stock 1 1/8 inch front sway bar, new rag joint, poly upper bushings on the Bilstein HD shocks, and about 2 weeks ago a custom blue printed rebuild of the OEM steering box. I run 550 springs, 1 inch lower than stock. I run 255/45/17 ZR tires-less sidewall than the stock 255/60/15 S rated which have MUCH stiffer sidewalls. The ride is very tolerable.

In back-your issue-I would guess is unwanted rear suspension movement, as others have stated. I have a 360 monospring with poly mounting cushions. If you are running a steel spring, besides being 40 LBS heavier, the steel spring is MUCH slower reacting to the yaw of the vehicle. I also have Bilstein Sports in the rear, which are 30% stiffer than the Bilstein HD's in the front. I have a 3/4 inch OEM type rear sway bar with poly mounting bushings. Most importantly, to control unwanted rear end movement (camber changes), I have adjustable competition strut rods (much stronger than the OEM ones) with Heim joint ends (zero bushing deflection, no bushings) which dramatically reduces rear end movement-the ride is still quite good. I have not changed my trailing arm bushings yet but will soon (65,000 miles on the car). 255/50/17 ZR's in the rear!

I would bet my car would race through that section of road with astonishing speed compared to a stock OEM suspended vette-all while using the OEM suspension. I would look carefully in the rear for areas to eliminate rear suspension movement.

Hope this helps!

 

THANKS JB78L-82! What you explained was VERY helpful. Everything in the rear is OEM....I'm contemplating replace the steel lateral spring with a fiberglass mono-spring. Probably do that in the Spring (no pun intended). So what I have to do, is not push it as hard as I would like in the curves until I stiffen the rear suspension or anything related to the suspension. I'm also planning to replace the OEM steering with a direct-fit rack & pinion system....small steps, small steps.

Again Thanks! for your help!

 

Take a look at my other comments on the other thread on the front page of this forum about steering issues:

power steering too quick-This is the thread!

 

You mentioned that the road in that area is smooth. That being the case, your suspension should not be "hopping"...regardless of the system design...unless there is a damaged/broken/binding component somewhere. You need to be looking for a worn out bushing, a U-joint that is binding {that means that there is a 'tight' spot in the joint which will cause a lurch in motion whenever it binds up}, or other intermittant condition which could cause that symptom. I would tend to look into components that have movement, rather than cushioned items, just for that reason--like the U-joints and differential clutch. If I were to 'guess' at one of those [based on your symptoms], I would guess the differential clutch. You might check your fluid level in the rear gear and add a tube of Posi-trac fluid to see if that helps it.

 

I agree that your suggestions could also be the problem BUT I would think that binding U joints or differential issues would show up more on very low speed turning of the vehicle through tight radius turns such as a 90 degree turn left or right from a stop light/stop sign, not so much on a road described by the OP. Just my 2 cents!