Crazy Suspension

[JoeK]

Okay, so this is a slightly more complicated question than the brake thing. I mean who needs to stop when you can just go around it

Seriously though, on my '68 2000, sometimes the suspension seems to freak out on me. A touch of history first. The PO told me he put comp springs on the front, thereby lowering the car, I think he said 1". He also said something about cutting down the front suspension pads or stops or something. That all sounded good to me.

So I bought the car, I'm driving it home and hit a good sized pothole at 55mph. It felt like the car jumped off the ground! It felt as if I had let go of the steering wheel, or more like the steering wheel let go of the ground. Incidentally, the shifter hit me in knee hard enough to leave a bruise. But the car recovered like nothing had happened. So I've noticed that this continually happens when I hit sizable bumps, especially if I'm turning. Is it possible that this car is so light it's actually launching to some degree? I don't think I've ever driven a car so light, other than go-kart, which almost feel the same when you hit a bump, because you literally have no suspension

I'm thinking I can attribute some of this to the lowering of the car, since the car now seems to have only about 1.5" of downward travel on the front suspension. I've also noticed that the car has what I believe to be the stock sway bar, as it's only about 5/8" diameter

Thoughts? Should I stop driving this car immediatly and take it to my nearest suspension shop?

All insights and opinions welcome. Thanks, Joe

[JoeK]

Well, I may have found the culprit here, but I'm not sure what to do about it. As I look at the front suspension, I see that the front rubber bumpers are cut a little, but maybe not enough. As the car sits, there is less than 1/2 inch of downward travel before the bumper hits. Shouldn't I have more travel?

I'm looking at the Bob Sharp Racing Competiton Prep Manual and it talks about cutting down the bumpers. Right now they look to be about 1 3/4 inches tall and the Bob Sharp manual says to cut them down to 3/4" with a 1/2" nub sticking up for improved street applications. Has anybody had any luck with this type of modification?

Thanks, Joe

[70MTroadster]

Hi,

When I found my 70 1600 Roadster, I had been sitting for 12 years so maybe the springs sagged a little, I don't know, but I had issues similar but not as violent as you are experiencing. My springs, front and back, as far as I can tell, are stock.

I too have the Bob Sharp stuff and went ahead and modified my front and rear bump stops for Improved Street. It sure helped me. Especially on the horrible city roads of Missoula, MT. Hard on them thar kidneys

With a drop of an inch in the front like you have, I can see why you are getting the Go Kart Syndrome. I'd go ahead and cut them down to the Improved Street dimensions if they have not already been done.

Scott

[70MTroadster]

I should proofread my posts....I just read mine and I wrote that "I" had been sitting for 12 years....Hahaha....I guess maybe I sagged?

Anyway, I crack myself up...

Scott

[oilleak]

My car (comp front everything) has just less than 2.5 inches between the stop and it's contact point.
Check the whole front end for loose and worn parts too. sloppy steering gear and idlers can cause issues too.

[70MTroadster]

Brian,

Mine has been off the road for a while but seems like mine is about that with the cut down stops in the front and about 1.5 inches in the rear with cut down stops.

The front end is tighter than heck too.

Are your stops cut or stock?

I defineately plan on getting the new front springs from Mike Young for the front as soon as I have the $$

Scott

[JoeK]

Well, it looks like I'll be tearing into the front end soon. I'll go ahead and cut down my rubber bumpers. When I look at the diagram in the Bob Sharp Manual, I see a nub sticking up for improved street. What I can't tell from the diagram is whether it would look like a nipple sticking up, or would it be 1/4" wide ridge along the top.

As I look at it, it looks like the same bolts that hold the rubber bumper on also hold the A-arm suspension arms together. It seems like this operation would mess up my front alignment, am I right?

And if so, does anybody have a suggestion for an alignment shop in the East Bay, Ca that knows these cars?

[oilleak]

Mine are cut.

the 1/4 inch deal is a strip across the stop

The support for the stop is held on by the bolts the hold the lower ball joint - you can remove them without upsetting anything however, you can remove the stop from the metal support pedastal with out removeing the pedastal. the bump stop has a stud on the bottom that you can get to from underneath going up through the metal support pedastal that it sits on.

[Minh]

Use the the mini single handed hacksaw to cut the stops. I read that somewhere on the forum a while back.

The sway bar upgrade won't hurt, but I think it mayl tighten up a bit more now just thinking about.

If you have the NISMO comp springs they are a quite a bit stiffer than stock.

The springs from Mike Young are in the middle of stock and comp stiffness from what I have read.

[spl310]

I have the early comp springs on my car. They ride hard. The springs from Mike Young have the same spring rating, so they should ride just as hard - just a little shorter...

I would like to find some that are a little more firm than stock, but not as hard as the comp springs - and as short as the Mike Young springs...

[oilleak]

My car (comp front everything) has just less than 2.5 inches between the stop and it's contact point.
Check the whole front end for loose and worn parts too. sloppy steering gear and idlers can cause issues too.

Whoops! I was thinking about the rear suspension travel. Just checked it as I was checking my A are bolts and the front suspension travel from static on my car is 1 and 7/16ths inches, NOT 2.5. Sorry for the confusion.

[JoeK]

Thanks Brian, I was wondering how you could get so much. Even so, I've now cut my stops down to the improved street dimension, which is a total of 1 1/4 inches tall. Now I have 3/4 inch of travel at static. That still seems like a pretty small amount of travel, but it defineatly feels better. I haven't had the chance to take her out on the freeway yet though. I may cut them down more, but first I will probably do some front end tightening up to see what I get from that.

Thanks to all for the help so far

[DatsunBucky]

Don't forget that the suspension travel at the bump stop is less than that at the wheel. I don't have the numbers, but 3/4" at the stop could be 1.25" at the wheel (or something like that).

Also keep in mind that 40 years ago, the technology was such that to make a car handle, it had to ride like a brick. From what I remember, it wasn't until the 240Z came out that car manufacturers found out you could have a compliant suspension and have the car handle well.

[JoeK]

That's a great point Bucky. I was thinking that I only had 3/4" downward travel, but yet driving it feels like she goes further down over bumps and whatnot. I wonder how I could measure that accurately?

So I just got back from a good cruise on the highway, with lots of bumps and potholes, and I'm happy to report no "out of control" issues. Though I do feel a bit of shuddering at high speed, which I am blaming on loose ball joints at this point. When I had the car up in the air to remove and cut the bumper stops, I could rock the rotors back and forth a little, and it looked like I could see a little lower ball joint movement.

Does anybody know of a good suspension guy in this area (bay area). The one thing I've never liked is suspension repairs. I just hate beating on my car parts with a big hammer. Also, are these parts available?

[DatsunBucky]

[thinking cap on]

Let's see... measure from the lower a-arm pivot to the bump stop (a), then measure from the pivot to the center of the wheel contact patch(b). Just for grins and ease of arithmetic, let's say (a) measures six inches and (b) measures nine inches. I might be wrong here, but the way I see it, (b) is one-and-a-half times (a), so wheel movement would be 1.5 times the movement at the stop, or bump stop movement would be 2/3 the travel at the wheel.

[/thinking cap off] Hey, NASCAR IS NEAT! (oops, better put cap back on)

This makes sense in my mind, but I just pulled the numbers out of the air. I'm sure they're different than this, but the logic sounds OK.

BTW, I've almost got all the paint stripped off the Roadster. The hood and part of the front fascia are all that's left. Next time I'll work overtime or whatever to pay someone else to strip it.