Trailing arms for a road car?

[Darwinskeeper]

I'm thinking of upgrading the trailing arms on my little red wagon (and possibly installing new trailing arms on the 72 Skylark once I get that running. My question is what kind of arms should I be using? Both of these cars are (would be) 99% street driven with the possibility of the occasional run down the strip during a test & tune night. I don't want anything radical, just something that might improve handling a bit and possibly provide a better launch for those rare times when I do hit a drag strip. What are my options?

 

[shotgun]

If you access to or can weld, boxing the stock lowers is the best bang for the buck.

Add poly bushings and 95% of wheel hop goes away and the car handles "better".

 

[BMR Sales]

x2 anything with poly bushings on both ends will be a good improvement for a street/strip car. Also if you wanted a little more performance based arm you could go with a poly on the chassis side and a rod end on the suspension side.

 

[Norm Peterson]

I don't believe that you are making nearly enough power to warrant boxing the LCAs, so all you'd be doing is giving water and other road crud places to collect in. If you aren't almost pulling the left front tire off the ground on launch, this mod is of very limited value.

Replacing the bushings in them with something firmer will help if you have a wheel hop issue, but won't be helpful if you don't. Poly LCA bushings in both ends of the LCAs will toss your head side to side more when you enter driveways not straight-on, cross diagonal drainage gutters, or hit bumps with only one of your rear tires. They will also dial out some of the understeer that was designed in to the car, but whether that's a good thing or not depends a lot on your own use of the car.


Norm

 

[shotgun]

Norm, not to argue but discuss.

Have you had all those things happen by just boxing the lowers and putting in Polys?

I did it on my 83 Wagon and loved it with none of what you mention.

Now I would agree that poly only up top is bad ( Upper Control Arms) though.

I leave the tops unboxed and use rubber on one end ( usaully in rear ears).

A guy that rented shop space from me did full polys in a Monte SS. I doubt he installed them correctly ( proper lube, torque bolt with chassis loaded, etc ) but his car would take a turn and stay leaning after he straightened out. The car would eventually settle flat, can you say bind?

Unless we are really stepping up, then they get sperical/heim type ends.

 

[Norm Peterson]

My before/after experience with installing poly bushings in the LCAs was that the head-toss was clearly noticeable. Yes, it cornered slightly flatter, but that does not necessarily mean better (it's how you achieve your flatter cornering that means more than just cornering flatter).

I then proceded to modify the poly to remove some of that roll stiffness and the ride got MUCH better.

I'm not into drag racing, but I did autocross the car for several seasons. That does involve a fairly hard start, since you'd like to cross the 'flying start' timer with as much speed as possible (while still being able to negotiate the first turn). IOW, it's as hard of a launch as you'd likely do on a normal street, but not dragstrip hard since the pavement grip isn't there. Initially I was not getting wheel hop after "modifying the mod", though I was starting to get a little after a couple of seasons.

My point on not boxing the LCAs is strictly from an engineering point of view. Unless you can roll the chassis over far enough from engine torque reaction to put the LCAs at some risk of buckling there isn't any need to strengthen them. My first-cut guess is that you start considering boxed or otherwise more rigid LCAs when you're just before the point where your LF is coming off the ground, after which time all further engine torque reaction is taken rearward and the amount of roll suddenly increases much more rapidly. The OP doesn't have that much power to play with, so there is no real benefit to be had. With 350 - 375-ish HP and torque, 3.73's in the axle and performance street tires I didn't need any LCA help either (though the LCA-mounting for the rear sta-bar probably stabilizes the LCA itself slightly).

The performance downsides of making the rear of the car too stiff in roll relative to the front show up in cornering that's admittedly a good bit harder than the levels that most people commonly drive up to.

The ride quality issue shows up much sooner, though the perception may be that the more stiff-legged ride means that since you know the suspension is doing more work you tend to conclude that it is doing a better job and is therefore actually preferable. The preference is very much an individual thing, but whether it's really better or not is separate.

Binding up the suspension as badly as your shop space renter did for his job suggests very strongly that he does not understand how control arm bolts maintain everything in proper position. It's NOT because the bolts are directly carrying the acceleration and braking forces directly. Shouldn't be, anyway.


FWIW, Maximum Motorsports did a study some years ago that estimated the added amounts of roll stiffness that various control arm bushing combinations produced. IIRC, poly/poly in standard LCAs added about 60 lbs/in to the wheel rate, which is more than what the F41 rear sta-bar adds. Yes, I know they're a Mustang outfit, but the Fox/SN95 Mustang chassis that they worked their study up with has a rear suspension that's remarkably similar to the G-body's. UCA angle and spring mounting location differ a little, but that's about all.


Norm

 

[shotgun]

Thanks for responding.

I think we will have to agree to disagree as I have had nothing but positive results boxing the lowers.

If the OP does not mind a hijack, what are the specs on your car?

I believe my Wagon is similar and would like to do a side by side to see what you have done compared to mine ( similar or different).

I am starting to get into this handling thing after being a drag racer for years.

 

[Norm Peterson]

Chassis
Original F41 car with the braces
Extra nonstandard front crossmember
88A poly body bushings in most locations
Springs - Moog 5660 front (~640 lb/in), 5413 rear (~165 lb/in), not trimmed
Shocks - Bilstein HD, S10 front, G-body rear (IIRC)
Sta-bar, front - 32mm front, poly chassis bracket bushings, poly endlinks (the poly endlink bushings have been modified)
Sta-bar, rear - 22 mm
Control arm bushings, front lower - poly with the LCA bushings trimmed back just shorter than inner sleeve length
Control arm bushings, front upper - poly, unmodified, and they have squeaked since day 1
Control arm bushings, rear lower - poly, modified similar to the front lowers (and then some more)
Control arm bushings, rear upper - OE
Wheels - 15 x 8.5 x -13mm offset on all four corners, some trimming and other clearancing was required
Tires - currently mismatched SZ50 and g-Force Sports in 225/60-15. Nobody makes a street 245/50-15 any more. I cut down one of the SZ50's shortly after they went out of production and had to settle for the BFG's as being the best of the bad lot that remained
Alignment - my own specs

Powertrain
355 w/Accel SuperRam, headers, own-design exhaust system, Tremec 3550, 3.73's, Auburn Pro Series diff, still 26 spline axles.

Other
Trunk-mounted battery
Cloth bucket seats from 1987 Nissan Maxima
Lightweight carpeting
Aftermarket tach and electronic speedometer installed in original locations


There really isn't a whole lot that isn't bolt-on at this point. Pushing it up to the next level of chassis preparation means getting serious, if I decide to do so.

I suspect that there is some difference in how hard you and I normally take corners. If you know anybody who never, ever runs less than hard coming off a stop light when the road ahead is clear - I'm that guy when it comes to cornering. At a somewhat tamer cornering pace than mine, all sorts of modifications that are ill-suited to that sort of thing don't matter (because there isn't enough going on with slip angles, camber, and lateral load transfers for such effects to make much difference).


Norm

 

[MalibuMan1979]

didn't do any scientific study, but i boxed my rear lca, added poly on upper and lower arms, welded some spacers in the sway bar mounts, added a grand national rear sway bar. got rid of the body roll. just for a firmer ride i would suggest it. my classic rode like a boat when i got it. now it corners pretty flat.

 

[shotgun]

It is interesting how similar they are. My goals are a little different, daily driver,tow vehicle,family cruiser
Chassis
Original F41 car with the braces
F41 Braces added: Jounce bars,Radiator X brace,fender to radiator braces and rear class II hitch
Added rad to cowl braces

Extra nonstandard front crossmember
I assume you welded something in? I have the GP crossbrace

88A poly body bushings in most locations
Still stock but they are a planned update, What's 88A?
Now has a mix of poly and aluminum bushings

Springs - Moog 5660 front (~640 lb/in), 5413 rear (~165 lb/in), not trimmed
Springs Moog 5608 front 424#, 5391 rear 143#, neither are trimmed but the fronts need it
One coil has been removed from the front coils
Update, beefier progressive rear spring have been added,unknown manu. they are used

Shocks - Bilstein HD, S10 front, G-body rear (IIRC)
Edelbrock IAS

Sta-bar, front - 32mm front, poly chassis bracket bushings, poly endlinks (the poly endlink bushings have been modified)
36mm Fbody hollow bar also with Poly
end links have been modded to match lowered front end from cutting coil springs

Sta-bar, rear - 22 mm
27mm and playing with a second 22mm,yep running 2!
Update, been running the single 27mm/1" bar, nicer ride

Control arm bushings, front lower - poly with the LCA bushings trimmed back just shorter than inner sleeve length
Control arm bushings, front upper - poly, unmodified, and they have squeaked since day 1
Polygraphite, unmolested and don't squeak
complete front end rebuilt with poly,frame drilled to use 1/2" grade 8 bolts, solid tie rod adjusters

Control arm bushings, rear lower - poly, modified similar to the front lowers (and then some more)
Poly in boxed lowers

Control arm bushings, rear upper - OE
Rubber Camaro at the frame,anti-hop bars are solid with unboxed arms
Anti-hops removed, still rubber on the frame nd of the uca,new poly in the rear ears

Wheels - 15 x 8.5 x -13mm offset on all four corners, some trimming and other clearancing was required
Rallye 15x7, stock offset, 1/4 spacer front , 3/8 spacer rear
15x8 Soft 8s all around, same tires

Tires - currently mismatched SZ50 and g-Force Sports in 225/60-15. Nobody makes a street 245/50-15 any more. I cut down one of the SZ50's shortly after they went out of production and had to settle for the BFG's as being the best of the bad lot that remained
235/60x15 front, 255/60x15 rear, mine all match
Alignment - my own specs
Ditto, actually previous owners

Powertrain
355 w/Accel SuperRam, headers, own-design exhaust system, Tremec 3550, 3.73's, Auburn Pro Series diff, still 26 spline axles.
355 with Edelbrock pkg., TES headers,custom exhaust,Custom T5, 3.73,Eaton LSD, aftermarket axles

Other
Trunk-mounted battery
May do this, tough on a Wagon ,still car has 52/48 weight distribution

Cloth bucket seats from 1987 Nissan Maxima
Cloth worn bench

Lightweight carpeting
Aftermarket tach and electronic speedometer installed in original locations
Monte SS gauge cluster