1977 280Z Rear Susp.

[Guest Skelly]

First Post. We're in the process of building an LS1 conversion but have a basic question about the rear suspension. I just purchased the 280z and drove it a few miles prior to pulling the engine. In checking it out, there was a fairly loud "clanky" ,metal on metal, sound in the rear when under torque load. Looking at the set up. the rear sway bar seems to be grinding against the head of the two bolts connecting the rear control arms. All other components seem fine, so i'm wondering the the sway bar might have been installed aftermarket and / or is the wrong fit item. No other components appear loose and the pinion set up seems fine. Any thoughts? Thanks

[datsunlover]

The bolts that are being 'ground' by the sway bar.. are you talking about the rear most bolts? (close to the diff) If so, sounds to me like someone has put on a rear bar from/for an earlier Z, say a 240. I tried using a 240z rear sway bar (aftermarket, not sure of make) on my 75 280z and had.. bad things happen. My guess is it's not the right bar for your 280, or it's instaled compleatly wrong. I'd say remove it and run without a rear bar..

[Dan Juday]

I had the same thoughts, 240 bar.

Loosing the rear bar is good advice. With the LS1 traction in corners will be even worse using a rear sway bar.

[buZy]

Why would traction be worse with the LS1?

Or any V8 for that matter? I dont see the theroy here. Are you saying I should loose the 280 rear bar in my 240? It seems to work very well but I never tried disconnecting it. Could someday please chime in on this. Thanks.

[datsunlover]

I'm not an expert, but from what I've read and worked out in my mind, it makes sence. Figure an LS1 (or any mild V8.. or heck, probly a higly moded L6) is going to put down WAY more torque to the wheels than stock. In a corner, the sway bar is trying to 'level' the car, therefore not allowing the rear suspension to compress as much as it could. This disturbs weight transfer to the rear of the car, and insted of 'working' the suspension, it works the tires. IE; it spins them. However.. if this is wrong, someone please correct me..

[JMortensen]

You're right datsunlover. More rear roll bar means more inside tire spin. That's one of the reasons that racers run as soft as they can with tiny or no swaybars in the rain. Less traction requires less roll resistance. This is also why John Coffey and Dan Baldwin went smaller or got rid of their rear sway bars when they had inside tire spin on their cars.

 

Datsunlover, do you still have any pics of your old swaybar? Might help Skelly to see them. It was barely on the car, and caused him all sorts of hassle. If yours is like that you should be able to fix it so that is mounted correctly. It sounds to me like you need spacers between the uprights and the bushings to pull the bar back away from the uprights. That's pretty common for the rear mounted bars from what I can tell.

 

ScumDog, I wouldn't take off your rear bar unless your having real trouble with one wheel peel. If you're not the handling benefits far outweigh the traction losses IMO (course I don't have a V8). Of course, with a LSD you'd be set either way...

[Guest Skelly]

Thanks for the input. We hope to have the Z back together in 3-4 weeks. Sounds like pulling the rear bar off may be the best solution. I'm betting it is the wrong bar for the car. Most of the photos of available repalcement 77 bars I can find show a "z" bend on both ends of the bar. This bar is just a simple "u".

[datsunlover]

Well yes, a lot of my 'theory' on this is from my personal expireance in my 280. I have some pics somewhere.. I'll see if I can post them up.. does your bar look like that?

 

 

With the bar on the back, there were improvments in body roll during lane change or winding roads 'spirited driving' for sure.. Unfortunatly, the design of the 280z uprights are slightly difrent than the 240z, causing clearance issues. In my case, a long hard righ hand turn pushed the bar enough that it hit the drive shaft and rode on it for some time.. killing the boot, and damaging the shaft.

 

After I took it off, I actualy liked the handeling better to tell you the truth.. A bit more 'roll' in the rear, but the thing would squat down and take off much better, and sudden application of throttle coming out of turns felt very smooth and in control. With the bar on, it wanted to kick the rear out a lot more, and felt... twitchy. I should point out, I was only running a basicaly stock drivetrain; L28 with SU carbs and slightly better (no cat or proper muffler) then a stock exhast. I can imagine what an extra 100 or so horse would do..

[dsommer]

jmortensen,

 

So you're saying run a sway bar if you are running an LSD?

[JMortensen]

So you're saying run a sway bar if you are running an LSD?

Not quite that simple. I'm saying that the more limited your slip is, the more rear roll stiffness you can run without lighting up the inside tire. Both Coffey and Baldwin have LSD, Coffey runs a Quaife and Baldwin a clutch type with ~10 lbs breakaway, and they both had to cut back on the rear bar to stop spinning the inside rear. I've heard from numerous sources now that Quaifes will tend to spin the inside rear on long sweepers and tight autox courses, and John himself has described how he needed to add preload (like shimming a clutch LSD) to keep this from happening. Dan seems to have the same problem I did with my 300ZX diff, and the clutch type guru Gordon Glasgow has had with a brand new Nismo diff. Despite the advertised 45 lbs for the stock and 75 lbs for the Nismo, they seem to be shipped with ~10 lbs breakaway.

 

All of this heavily depends on how you like the car to handle as well. If you don't like understeer, you'll probably want a rear bar. If you don't like oversteer, you'll want to run without one. Both ways can be made to handle, it just depends on the rest of the setup and the driver which is faster in the end. FWIW--I ended up with just about exactly the setup that John has been advocating for years. He then changed his setup and I think he removed the rear bar completely and was saying how he could put the power down a lot earlier. Not sure if that was a driver comfort issue or just a faster setup in his car or if it made up for the slippy Quaife or what, but it was a pretty big change from what he had previously been saying and it seemed to work for him.

[cygnusx1]

Random Thoughts.

 

Ignoring squat and dive, the whole point is to keep the car flat in a turn so to keep the contact patch as flat as possible to the pavement and to keep tire loads as evenly distributed as possible. This can be done by swaybar, springs, and even tire pressures. Negative camber is a proactive measure that assures that the loaded tires roll with the body and become as flat as possible in a turn.

 

I understand that running no rear sway bar will give you better corner exit traction because both rear tires will be loaded more evenly without the rear bar pulling up on the inside rear control arm. But if you run a large front bar and no rear bar the car will push in an off-power, lateral load situation or during corner entry. It is the RATIO of front bar to rear bar that gives you a desired behavior.

 

On the other hand, roll resistance can be controlled by stiffer spring rates rather than a swaybar. In this case the ratio of front to rear spring stiffness dictates the cars lateral handling behavior.

 

Some seem to favor springs and others seem to favor swaybar. I dont have much track experience but I really like the way my Z stays flat in the turns. I have no means to put in negative camber right now so the alternative is to keep the car as flat as possible. I run pretty stiff springs from Tokico and run pretty heavy swaybars front and rear. The car handles very well and pushes a tiny bit on corner entry which is the "safe" thing to do on the street. Yeah it rides a bit rough but most people who ride in it seem to feel it is acceptable for the street. I would imagine that if I just eliminate my rear swaybar to install the CV shafts, the handling would get really strange unless I change other parameters to compensate.

 

Onwards...

[flibuoy]

My first 240 swap I had (came w/car) the rear bar in, drove a few months and decided too "twitchy", took bar out, much more benign street driving particularly in rain. This car (260) I have left stock rear bar in with loose older rubber bushings and front bar with poly bushings set snug. I'll compare the 3 combinations soon I hope and let list know my opinion on latest.

 

Oh, if you recognize the name it is because my LT1 was giving me fits with no starts...well....this morning I fired it....gotta hook up hoses, bleed clutch and go to paint/exhaust shops....whew a LONG process...learne dmore than I wanted to! John

[Savage42]

Some seem to favor springs and others seem to favor swaybar. I dont have much track experience but I really like the way my Z stays flat in the turns. I have no means to put in negative camber right now so the alternative is to keep the car as flat as possible. I run pretty stiff springs from Tokico and run pretty heavy swaybars front and rear. The car handles very well and pushes a tiny bit on corner entry which is the "safe" thing to do on the street. Yeah it rides a bit rough but most people who ride in it seem to feel it is acceptable for the street. I would imagine that if I just eliminate my rear swaybar to install the CV shafts' date=' the handling would get really strange unless I change other parameters to compensate.[/quote']

I've always liked sway bars and not too stiff of a spring. Heavy springs are great for a smooth track, but often kill you on the street or autocross where the lot isn't always perfectly smooth. I tend to run -1.5 to -2 degrees of camber up front and found that running rubber endlink bushings on the front bar gets rid of some understeer and gives you better turn-in on sharp corners at an autocross. Of course, setup depends solely on your focus of what you want the car to do. With the diversity on these forums from street to strip to track.....each setup is quite a bit different. Hope that helps a little. Also, I'd never run anything but a LSD and prefer the clutch type. I put an LSD in my 510 back in '91, before most even did it on their street cars. Times have changed, as we all want more performance!!