Rear end "sway" at highway speed

[John H.]

Re: Rear end "sway" at highway speed

The rear stance of the car is about 1" to 1 1/4" higher than spec., but I understand from previous posts that the rear will settle as the new rubber spring bushings compress over time.

Roger -

Glad you're getting it sorted out! I noted in the photos that your spring appears to have two main (lower) leaves - the bottom one is square at the ends, and the next one up is configured as the original lower leaf was, with the corners cut off at a 45* angle. How many cambered (curved) leaves does that spring have?

[William C.]

Re: Rear end "sway" at highway speed

What shape is the parking brake in? While the trailing arms are off, is a great time to bring the parking brake components up to snuff. If you chaek the total cost, sending the whole training arm assemblies to someone like Bair's that does a lot of these rebuilds might not be a large investment, also I don't see you referencing greasing the bearings in the trailing arms, to properly do that job requires disassembly, and if they fail on the road you will have a MAJOR problem. Also make sure your mechanic orients the snap rings correctly when installing "NEW" snap rings in the rear gearset. The sharp edge should face inboard to keep them from coming off the shaft.

[Roger P.]

Re: Rear end "sway" at highway speed

Roger -

Glad you're getting it sorted out! I noted in the photos that your spring appears to have two main (lower) leaves - the bottom one is square at the ends, and the next one up is configured as the original lower leaf was, with the corners cut off at a 45* angle. How many cambered (curved) leaves does that spring have?

John:
I am definitely learning something new about my car all the time. You have a very sharp eye catching the extra spring leaf (you must be eating your carrots) ! I crawled under the car and counted eight (8) curved leaves plus the two (2) main leaves for a total of ten (10). A previous owner had spacers installed in the front springs, so I can only assume that the car was sagging at some point and the "fix" was to install spacers in the front and an additional main leaf in the rear. Not only are the corners not chamfered on an angle, but it now makes sense why the rubber bushing cup grommets/flanges wouldn't fit in the hole on each end of the bottom spring (the grommets had to be cut off because the holes are smaller than the original main leaf). Obviously, the bottom spring leaf was not made for a '65 Corvette. I don't know if it's worth removing the bottom leaf now as the car might lower too much, and I'm concerned about messing up the (expensive) alignment. Do you think the car will settle down one inch over the next year?

Thank you,
Roger (50141)

[Gene M.]

Re: Rear end "sway" at highway speed

Should settle car out before the alignment. Sounds as if the leaf spring donuts are real stiff.

Your camber and toe in will change if the car settles around an inch. That is a lot. Camber will become very negative and toe in will increase as a result of so much camber. Because the spindle position will be farther from center of the car, it moves relative to the trail arm bushing position which is fixed.

[Roger P.]

Re: Rear end "sway" at highway speed

Bill:
My rear suspension restoration project is now finished (read my post above from yesterday). I had both trailing arms rebuilt with all new parts and bearings - including the emergency brake components. The project was relatively expensive, but I am very happy with the car's performance (and the peace of mind).

Gene:
Based on what I read in the archives, and from what experienced NCRS members suggested, I used rubber leaf spring bushings (vs. polyurethane) for a softer ride. None of the bolts and nuts were torqued until the car was put back on the ground, "shaked, rattled, and rolled", and driven a few miles. I didn't read anything about not getting the car aligned until it settled more than that. However, I did read that the car will naturally settle over time as the rubber bushings slowly flatten; with initial settlement over the first 1,000 miles or so. Even with settlement over time, I can't imagine that the car will settle more than half an inch as the rubber bushings must be designed to handle the load. The stance of the car looks right to my "critical" eye, so I don't think it's worth buying longer leaf spring bushing bolts and then getting the rear aligned again. I was advised to use the shorter bolts and non-adjustable strut rods as that was how GM engineers designed the car ("Zora and his boys knew what they were doing"). Furthermore, it doesn't seem possible that the alignment would change too much since every car's ride height is always changing based on the weight of the driver, passenger, and cargo, and the amount of fuel in the tank. If this were the case, then the alignment shop would want to pre-load the car with "anticipated weight" prior to aligning the wheels. I am curious if John H. or Duke have an opinion on this topic.

Thanks for your input,
Roger (50141)

[Terry M.]

[John H.]

Re: Rear end "sway" at highway speed

I crawled under the car and counted eight (8) curved leaves plus the two (2) main leaves for a total of ten (10). Obviously, the bottom spring leaf was not made for a '65 Corvette. I don't know if it's worth removing the bottom leaf now as the car might lower too much, and I'm concerned about messing up the (expensive) alignment. Do you think the car will settle down one inch over the next year?

Thank you,
Roger (50141)

Roger -

Can't say how much (if any) the existing aftermarket replacement spring will settle, as it hasn't been touched; I wouldn't expect it to behave any differently than it did before. With ten cambered leaves (instead of six), and two main leaves (instead of one), that's probably why it sits high in the rear, and the spring rate is probably significantly higher than the original spring.

If the stance doesn't change and you find the ride stiff in the rear, you might consider replacing the spring with a more correct replacement as a future project.

[Roger P.]

Re: Rear end "sway" at highway speed

John:
My understanding was that the original springs had a total of 9 leaves. My spring has a total of 10 - which I believe is due to the additional "incorrect" main leaf that was added to the original spring by a previous owner. I assume that the additional 1" to 1 1/4" ride height is due to this extra main leaf. The rear suspension provides a nice ride, so I will give the car a chance to settle a little on its own. If necessary, I can replace the 6" leaf spring bushing bolts with 8" bolts to lower the height a bit. Everything else is good, so I will leave things alone for now and enjoy the ride!

Thanks again,
Roger (50141)

[Gerard F.]

Re: Rear end "sway" at highway speed

John:
My understanding was that the original springs had a total of 9 leaves. My spring has a total of 10 - which I believe is due to the additional "incorrect" main leaf that was added to the original spring by a previous owner. I assume that the additional 1" to 1 1/4" ride height is due to this extra main leaf. The rear suspension provides a nice ride, so I will give the car a chance to settle a little on its own. If necessary, I can replace the 6" leaf spring bushing bolts with 8" bolts to lower the height a bit. Everything else is good, so I will leave things alone for now and enjoy the ride!

Thanks again,
Roger (50141)

Roger,

While you enjoy your ride, be careful about doing any quick turns or winding roads at speed. The extra stiffness in the rear could give you some oversteer without compensating it in the front with a heavier stabilizer bar.

Take a look at this recent thread:

https://www.forums.ncrs.org/showthread.php?p=461741&uid=2117

To compound matters, as the rear settles it will increase the negative camber on the rear wheels, giving you that jerky effect on slight turns. Although the camber is not a big deal to adjust, you should keep it straight up and down, or less than 0.5 degree negative.

Excess negative camber is rough on the new rear wheel bearings, as well as adds to your oversteer and instability.

If it were my car, I'd have the mechanic take out that tenth leaf and go back to the stock setup. But it's your car.

[Timothy B.]

Re: Rear end "sway" at highway speed

Roger,

I agree with Jerry and John, get that extra leaf out of there and see how the car sits. Adjusting camber is easy and you can do it with a short level in the garage.

Looks like you have a very nice car, I wanted to suggest you make sure the bolts at the spindle flange and half shaft are grade eight with the correct shoulders and install the french locks and skip the lock washers.

Is this car a big block??

[Joe C.]

Re: Rear end "sway" at highway speed

Leave it alone.
The extra rear roll stiffness will cause a tendency to understeer ("plow"), not oversteer.
This will make a forgiving chassis even more forgiving.
With the extra leaf the spring ain't gonna settle! Ass end will be sitting high fer years to come.
Use the longer link bolts and drive the car..................unless you intend to show it NCRS.
I can safely assume that the way you'll be driving yer Corvette, you'll never come close to reaching the limit of adhesion............especially since the car is a nicely balanced smallblock with easily manageable torque. Further, if you leave the ass end slightly higher than stock, it will upset the weight balance of the car with more forward bias which will further induce "plowing" , so it is important for you to lower the rear back to where it belongs with longer links.

[Duke W.]

Re: Rear end "sway" at highway speed

You're dead wrong, Joe. Increasing rear roll stiffness will reduce understeer, which will increase the tendency to oversteer. We don't know if this spring actuallly has a higher rate than OE, but it probably does.

Look at the nearby thread where the OP is considering replacing the base 9-leaf spring with the HD 7-leaf spring that has about double the rate as the base spring.

The change in handling was discussed including rear world experience. You need to get Puhn's book and read it.

Duke

[Joe C.]

Re: Rear end "sway" at highway speed

You're dead wrong, Joe. Increasing rear roll stiffness will reduce understeer, which will increase the tendency to oversteer. We don't know if this spring actuallly has a higher rate than OE, but it probably does.

Look at the nearby thread where the OP is considering replacing the base 9-leaf spring with the HD 7-leaf spring that has about double the rate as the base spring.

The change in handling was discussed including rear world experience. You need to get Puhn's book and read it.

Duke

You are both absolutely right.

Please disregard the second and third sentence of my above post, and change the last sentence to read: "Further, if you leave the ass end slightly higher than stock, it will upset the weight balance of the car with more forward bias which will induce understeer ("plowing") , so it is important for you not to lower the rear back to where it belongs with longer links.

BTW: In Jerry's reference thread ( https://www.forums.ncrs.org/showthre...61741&uid=2117 ), how can it be that in post number three, you answered your own question, and then ended up talking to yourself?

Furthermore, what do you mean by "rear world experience"? Don't you know that this website is rated "G".

[Roger P.]

Re: Rear end "sway" at highway speed

Jerry, Timothy, Joe, and Duke,
I appreciate all of your input and suggestions. Of course, I am now more confused than before, but that might simply be a lingering affect from New Years Eve festivities . To answer Timothy's question, my car has a small block and therefore doesn't have a rear sway bar nor heavy-duty front sway bar. Again, I don't know why the extra main leaf was added to the spring in the past. If John H. didn't catch it in my photos, I never would have realized this very minor modification. However, the car has settled about 3/8" since the spare tire was installed the other day (it wasn't reinstalled until the alignment was done and final torquing was finished). Now the car is only about 3/4" higher in the rear than spec. I don't race my car nor drive very aggressively, so I don't think that there will be any problem with performance or steering. Although it shouldn't be difficult to remove the extra main leaf, I don't want to mess with things because 1) the car handles very well; 2) it still might settle a little over time; and 3) I don't want to screw up the alignment. If you don't agree with my "wait and see" approach, please let me know.

Thank you,
Roger (50141)

[Gerard F.]

Re: Rear end "sway" at highway speed

Jerry, Timothy, Joe, and Duke,
I appreciate all of your input and suggestions. Of course, I am now more confused than before, but that might simply be a lingering affect from New Years Eve festivities . To answer Timothy's question, my car has a small block and therefore doesn't have a rear sway bar nor heavy-duty front sway bar. Again, I don't know why the extra main leaf was added to the spring in the past. If John H. didn't catch it in my photos, I never would have realized this very minor modification. However, the car has settled about 3/8" since the spare tire was installed the other day (it wasn't reinstalled until the alignment was done and final torquing was finished). Now the car is only about 3/4" higher in the rear than spec. I don't race my car nor drive very aggressively, so I don't think that there will be any problem with performance or steering. Although it shouldn't be difficult to remove the extra main leaf, I don't want to mess with things because 1) the car handles very well; 2) it still might settle a little over time; and 3) I don't want to screw up the alignment. If you don't agree with my "wait and see" approach, please let me know.

Thank you,
Roger (50141)

Roger,

You are probably OK with the "wait and see" approach. You have come a long way with the trailing arms.

If you ever notice that jerky turning movement on a winding road then it's time to take the extra rear leaf out. There is nothing like bringing it back to the original setup, take your time. You even have the M.E.s arguing, but the C.E.'s know the best. Only kidding

Have fun, maybe I'll see you at Kissimmee in a couple or three weeks.