any cures for choppy ride on 83 Nighthawk 650sc?

[Brad]

My 83 Nighthawk with a little over 10,000 miles has a very choppy ride. I have balanced the front tire and had forks rebuilt.I bought the bike this summer after being off a bike for 2 years because of an encounter with a deer. Bike runs and handles great but the constant bouncing is hard on my back The tires are almost new Dunlops. I suspect tires or rear shocks. Any help I can get would be appreciated.

[mollusc]

What do you mean by "choppy"?
Have you checked the steering head bearings?

[Brad]

Choppy as in bouncing, like on a bumpy road. Even on smooth roads it feels like running over a bunch of small bumps. Steering head bearing are fine. Thanks for your interest.

[Larry Fine]

Soundslike an out-of-round tire. Spin each by hand with the bike on the center stand.

[mollusc]

Does it get more pronounced when you use the front brake?  I recently had that problem on my NC700X.  Turned out to be tyre balance.

[timberwolfe]

Warped rotor?

[Brad]

Tires and wheels seem fine as far as out of round. No problem with front brakes. I'm familiar with brake rotor pulse but its not that. Front tire has been balanced but not the back. Back tire has a 1/8"deep flat spot about 6-8" long like someone has slid the tire under hard braking. I'm wondering if rear shocks are not functioning as the should. They are 40 years old, maybe they need a rebuild. Is that possible or will I need to buy replacements. I have rear shocks set on softest setting. Thanks for your help

[Larry Fine]

Back tire has a 1/8"deep flat spot about 6-8" long like someone has slid the tire under hard braking.

That'll do it. That qualifies as out-of-round.

[Bob H]

...Even on smooth roads it feels like running over a bunch of small bumps.

It's not your shocks then.

[Bob H]

Back tire has a 1/8"deep flat spot about 6-8" long like someone has slid the tire under hard braking.

That'll do it. That qualifies as out-of-round.

Out-of-round AND out of balance.
Let's say the rear tire was balanced perfectly when it was installed. Now it has a visible flat spot.
If that looks "like someone has slid the tire under hard braking" that would remove some rubber (assuming it's not a flat spot from being stored)

Even if a tire is perfectly balanced, it will become out of balance during normal wear - to the point they tend to vibrate as they get close to end of life. Happens with cars and motorcycles.

[Brad]

Thank you for the info. Looking for new tires now.

[Gene]

 I have the same problem Brad, on my 85 650 Nighthawk. I think it's probably the rear shocks.

[draser]

Sounds like you guessed right, tires and rear shocks - it would make sense to replace or rebuild (if the shock is rebuildable) the rear shocks. Since you've already done the forks you'll have an "updated" suspension all around. And, of course, shocks are the second most important thing (after tires) for safety and comfort.

[Willie]

Speaking of rebuilding the shocks, does anyone know of a vendor that rebuilds OEM shocks? One of mine is leaking and I don't want to spend the kind of money that new ones go for.

[Bob H]

...does anyone know of a vendor that rebuilds OEM shocks? One of mine is leaking and I don't want to spend the kind of money that new ones go for.

I don't have your model - but would think the 84-86 shocks are not better than the 91-2003 shocks which were made by Showa and are pretty terrible if you push them.

I would not put a single dollar into trying to repair the stock shock.

When I "had enough" and started my journey, I was looking for the cheap China ones... but had already spent $250 on "Progressive" brand shocks that were super harsh. I didn't want to keep throwing money down the drain.

K-tech made a 13" shock that should have fit but they didn't want to sell them to me as unable to confirm fitment (despite me giving them the bushing measurements, etc).

Check out my review of YSS here, https://nighthawkforums.com/index.php?topic=96.0
it was $539 well spent. It may cost you that much to rebuild your old shocks, if they are in fact rebuildable.

Watch the video on that link, the Triumph has same 13" shock length as the late model NH 750, which started my focus on YSS. I don't know the shock length on your 700s

YSS are made in Thailand, their engineer moved over from a large name brand shock company.

This is a copy of Cycle World 1991 review mention of the late model NH rear shocks.
They were considered bad back then, when the suspension standards where no where near what they are now.

They considered the antique "damper rod" front forks excellent compared to the rear shocks.
My main complaint was the lack of rebound adjustment and they just "pogo" bounce right back rather than soak up bumps. The YSS shocks are doing a lot better for me.