Mix-n-Match - Del-a-lum & poly?

[tripower]

I'm in the process of putting together new suspension pieces for my 65 GTO and was looking at GW & Hotckis of front upper As. If I go the GW route, the Del-a-lums sound like they may be the way to go. Is this overkill? The car will be used for street duty and possible 1/4 mile blasts. Based on that use, would poly be sufficient?

Next question; If I go the del-a-lum route up front, do you have to stay with GWs rear pieces also equipped with d-a-l bushings or can you go with, say, Hotchkis or E-brock rears utilizing poly bushings? I believe I read on the GW site that the car wouldn't handle correctly mixing and matching del-a-lum and poly front to rear. Is this true?

Thanks in advance for your input.

[Lowend]

you can mix Del-A-Lum and poly... but the problem is that ALL poly bushings WILL coldflow over time (they become sort of an egg shape).
In general you don't want to use a solid type rear bushing in the rear suspension as it will create bind. The control arms need to be able to move in multiple plains of motion to really work properly. Poly won't do that, no will steel or Del-A-Lum.
The best way to do it is with a Spherical bearing, but that is expensive and noisy.
Hotchkis uses a special blend of rubber with flutes cut in it to allow the rotational motion. Its not the best way to do it, but it works better than straight poly

[tripower]

Lowend, I believe GW offers rear control arms with a combo of a spherical bearing on one side and del-a-lum on the other. Would that be closer to the ideal?

[BuddyP]

Wow, ya got me all confused now, at first I thought the last year I've read that the Poly were the way to go, now I hear about the Del-a-lum and how those are the way to go, but now I'm hearing that D-a-L's are not the way to go in the rear???? I had just planned on using the D-a-L's up front and Poly in the rear... I still will probably go this route, after all, I'm not going to be racing the car. It'll be for the street.... how does all this seem to sound??

[MrQuick]

Hey Buddy, remember we are talking A body and your 1st gen, way different animal. But to answer your original question...Yes its ok for the street.

[BuddyP]

oh oops, didn't even pay attention to what type of vehicle LOL.... but thanks for the reply!

[Lowend]

I know what model we are talking about...
The lower control arm on the rear of an A-Body still need to be able to move in 2 plains of motion.
Think about what happens when on side of the rear axel is higher than the other; The lower control arm needs to be able to twist in order to let the motion happen without bind. That is where the spherical bearing comes in.
Tripower, the GW arm you mention would be perfect.

[yody]

there is a ton of info on this, read the thread right below "is this okay for the street" There is a lone cowboy named dennis68, he is out for vengeance against these varmint polyurthane bushings. Don't let him find out that you are using poly in the rear of an a body or else there is going to be a showdown! Do some searches and the rear suspension for A bodies. There is a ton of info. I think Dennis has it scientifically researched beyond a doubt so he would be the one to contact

[Norm Peterson]

Here's what's going on at the rear bushings. There are six degrees of freedom at each end of each LCA, and each has the potential for developing loads. Obviously, rotation of the LCA about the pivot must be left essentially free (as in poly) or be resisted at some predetermined and generally acceptable value (OE bonded rubber), and we can ignore that one at least for this discussion. Then there's lateral force, which we can ignore as well (most of the lateral loads are taken by the converging uppers in a C4L or by the PHB/Watts link in a torque arm or 3-link arrangement).

That leaves fore/aft force, vertical force, torsion about the LCA and lateral bending of the LCA. Again, it's pretty obvious that you want the stiffness against fore/aft forces to be high (otherwise, why use any harder bushing material than OE rubber in the first place?). And you need to have some stiffness against the vertical forces, especially if you run a LCA-mounted rear sta-bar.

It's the torsion and lateral bending directions that can induce large (and unwanted) forces. These are the loads that make it difficult for a cylindrical bushing to be good in all directions, since to keep these loads small you need the bushing to be soft (contrary to what you want for resisting the forces mentioned in the previous paragraph). FWIW, these loads are even worse with Del-A-Lum, so save the use of D-A-L for the front suspension and don't even think about using it out back.

It's probably fortunate that this whole topic is really a range of possible compromises rather than one that has a single absolute answer. The factory picks one point that suits their array of requirements. Drag racers choose another. Performance street driving, autocrossing, and road course running, different points still.

This is an all-or-nothing issue. You can daily-drive on all-poly, at least as long as you drive moderately and with due regard for road conditions. Just the fact that poly is back there won't spit you off the pavement as soon as the road bends a little. But you have to respect where in the spectrum of compromise that it has put you and understand up front that there are some limitations (or drive like a moron and find out the hard way that it will bite back). Actually, in what's one of the more extreme-sounding mismatches, Sam Strano has had success in autocross with poly rear LCA bushings in either a 3rd or 4th gen F-body (for those who may not know him, he's a multi-time SCCA Solo II National Champion). And in all fairness, I doubt that poly rear bushings continue to be his preference. But his solution when running the poly was to treat it like another rear sta-bar that developed its own wheel rate in roll, and then run somewhat less rear roll stiffness from the springs and/or sta-bar such that the total remained about the same. Likely, his shock tuning was slightly different as well.


On edit, this isn't intended to be throwing stones at Dennis, and what's above isn't the whole story on poly bushings (not by a long shot).

Norm

[dennis68]

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I should add that I will conceded the fact that use of poly in the rear arms on a C4L application would probably be OK at best for street driving providing that the driver use the car for it's intended application. The problem I see with that is that most if not all of the guys putting poly in the rear arms instantly think they have a Winston South car and proceed to find the nearest slightly banked freeway on-ramp. They don't have the least bit of information regarding roll steer or snap oversteer, both of which they will find out about soon enough. Since most are not responsible enough to respect the non-linear bind issue ever present with the use of polyurethane in the C4L links I find it easier to be adamant against their use.