How loose is loose? (rear suspension)

M

Marcus Miller

New member
Several people have told me a trick to running the stock watts link and trailing arms is to leave the lower arms loose, and use a lock nuts to keep them from backing off.
My question is how loose is loose? Rock the car on the ground so they clank loose? loose they can be deflected with the rear on jackstands? Upper arms also or only the lowers?
Safe?

thanks!
Marcus
 
Hi Marcus, I think you've got it switched around. Bottoms should be in good shape, tops should be crappy. I just replaced the bottoms with urethane bushings to get them more stiff. Left the uppers alone with the crappy rubber that was in them.

Good luck!
 
I can see how that makes sense. Thanks for correcting that! (Picturing my rear end falling out...)


Marcus

[This message has been edited by Marcus Miller (edited August 30, 2004).]
 
Its a bit of a sketchy technique.

A major issue with the stock watts link is the alignment issues that arise when the car is lowered.
The lower it is the worse it gets. There is sgnifican binding as the axle roll top side forward as the body is lowered around it. Take the springs out sometime and jack it through its motions. Watch how the angle of the pivot on the axle gets out of allignment witht the angle of the pivots on the chassis.

The second problem is the trailing links, and their issues that they will have when the car is lowered. IF there is good upper axle location then the upper links can be loose. As in eliminated....but keep 'em in the car, not legal to remove. Use a very soft bushing material. But using the stock watts link for longitudinal location is pushing things. A lot.

Better solutions include a non stock watts link, (Rod ends to handle 3D rotations), the elimination of the Watts link and replacement with a panhard rod, and the addition of a traction control link that can do the job of upper axle longitudinal location allowing the use of super soft upper link bushings.

Also, bear in mind that whatever is done at the back affects roll centers, transfer rates and so on, and can create unintended consequences with changes that have benn made to the front suspension.

------------------
Jake Gulick
CarriageHouse Motorsports
ITA 57 RX-7
New England Region
[email protected]
 
Take it from Jake - he's the last winner of a NARRC race. Congratulations, Jake!!!

------------------
Dave Youngren
NER ITA RX7 #61
 
Marcus,

That's a Pro7 trick! Basically you want the nuts tight enough to create resistance while turning the bolt. The bolt shouldn't turn freely. I would say a light to medium drag will work for what you are after. We used to do all the links. Makes a huge difference. What year is your chassis?

Eric
 
Hard lessons learned about loose rear ends, stock watts links, and panhard bars.
Here is what I've seen from my competitors and my own car--school of hard knocks.

Loose trailing arm bushings work nice, but all the mounting holes will get pounded into ovals. Happens faster with a panhard bar.

Stock watts link--will break if run loose.
It will also hit a rib on the pumpkin at low ride heights--the pumpkin rib must be trimmed back. The stock watts link with cylindrical rubber bushings will try to resist axle wind up--and contribute to binding.

And if you're wondering, I now run a tri-link and panhard bar. Rear end is as solid as it's ever been. Now if I can only get the front to work as well!

Tak
# 29 ITA SFR SCCA
 
Originally posted by wlfpkrcn:
Marcus,

That's a Pro7 trick! Basically you want the nuts tight enough to create resistance while turning the bolt. The bolt shouldn't turn freely. I would say a light to medium drag will work for what you are after. We used to do all the links. Makes a huge difference. What year is your chassis?

Eric
Click to expand...

You got it! The car is still in Pro7 trim for now, the ITA conversion will come along slowly, and might end up being a new chassis..

The current cahssis is an 85. That leads to the next logical question, should I modify the lower trailing arm mounting points to em,ulate the earlier cars? (I know this is not ITA legal, and would be used only when run as a pro7)


Thanks!
Marcus
 
Marcus definetly change the mounting points up 19mm. I tried for a while to get the push out of my car. I moved the mounting points up and I was dialing push into my car. My Chassis was a 85 as well. The other proble I ran into was corner weighting. The 81-82 chassis's always came out better than the later ones.

Hope this helps,
Eric
 
Eric, that helps a ton. It was exactly what I was looking to learn.
What else should know about running the thing in pro7 trim? How low?
Marcus
 
Marcus,

"What else should know about running the thing in pro7 trim?"

I don't know where to start. What area's do you have questions on? I'll answer whatever question you have. I'm not sure how to give you a "generic" answer, and give you the info that would help you.

"how low?"
Approx 3/4" rake. I usually started there and corner weighted. The rear you can't change except cutting one coil off the RR spring.
 
Actually, I don't have that many more, questions
smile.gif
I think I ahve most of them figgured out. I'm sure there is a bunch I tihnk I know, but I really don't know, that I really should know.


Marcus


[This message has been edited by Marcus Miller (edited September 02, 2004).]
 
I cancelled out of it yesterday, for a short course (no turn 7) in a mixed 3/4 run group, and my last SCCA school the first wekend of October, I thoguht it best to not tempt fate.
Are you going to be there?
I may come by and hang out (its like ~20 mintes from my brother's house...)
 
I will probably be going out Sunday at some point. My brother is racing his BMW. I have to get out at some and rough him up a little bit. I'm about 20 minutes away as well so I might be able to skip out on honey do's for a couple hours.

Eric
 
Great! I am still undecided for the weekend. If I make it out, I'll find you guys. If I don't see you, good luck to your brother!

Marcus
 
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