PHB and converging 4-link together?

[dennis68]

It has come up a few times and I have researched on my own and only become more confused.

Group A states that running a PHB with a converging 4-link will cause there to be 2 roll centers, the PHB determines RC until bind, then the control arms take over causing snap oversteer....no thank you.

Group B contends there can only be 1 roll center and that while maybe not ideal the PHB will determine the RC. Group B is concerned with bind as well....

My thought is could the bind be overcome by simply running rod ends in all the frame locations?

I think Kenny Brown attempted a "road course" type suspension package similiar to this on the late Mustangs a few years back with little success. I do not beleive he was using bearings in the arms though. Any thoughts?

[wally8]

I think the PHB will have more influence on the roll center but bind would have to be a problem. Adding heims will help but you're trying to control the roll center with two opposing linkages essentially.

Think of it this way: the stock four link wants to control the RC in a certain arc. The PHB wants to control it along a different arc. You can't accommodate both. Ultimately you end up with a bind.

Does that make sense?


Wally

[dennis68]

Yep, just checking my thoughts.

It was brought up by another user on a different B/B. He is fairly intelligent and suggested using the PHB in conjunction with the OE arrangement. I suggested it would bind worse than the converging links alone and he thought not.

[Mean 69]

I'll offer this. On a late model Mustang that I owned (an 89 LX), I temporarily ran a PHB (until I broke it), with the stock quad bind, rubber bushings, flexy control arms and all, and it was a big improvement. On this car, I was running wider tires (275's), and would constanly get tire rub in the rear. The PHB really reduced, possibly eliminated that, that was a far too many brain cells ago to recall. In addition, the car felt FAR more settled than it did without the additional lateral restraint.

Why did I take it off? It broke. Here's the moral of the story. I used a PHB on a quad bind setup that was in and of itself designed to control lateral movement, the PHB "should" have futher eliminated/reduced the lateral movement, but the remaining forces were enough to trash the PHB. Granted, it was a POS BBK unit, they pulled it off of the market, but it does make one wonder how much residual force remains with the quad setup that the PHB couldn't handle. Hmm... BTW, the design for the late Mustang quad link is essentially the same as the early GM setup, save some differences in geometry, etc, that are incidental.

With the quad bind setup, and the addition of an PHB, there will be a battle over the RRCH, and subsequent bind wherever that may occur, but the added control over axle migration (lateral) is a benefit that the PHB will overshadow the downside of bump-bind. Your mileage may vary.

By the way, if you REALLY want to screw things up on an early Chevelle/etc, use poly bushings!!!! I think that would be "bind to the third power?" Better yet, Delrin type bushings on ANY of the control arms will result in big time bind in roll. You might not feel it by the seat of your own pants, but I can assure you, your control arms will feel it, torsionally. Gulp.

Mark

[dennis68]

Yeah, I've known about the poly/Delrin for a long time. Ran into some information that I have passed on to the other "A" body groups (Mark you may remember this) edited for clarity and removed some parts that don't pertain to "A" bodies with OE suspension-Chevlle link (http://www.chevelles.com/forum/ultimatebb.php/topic/7/9117.html)

[Salt Racer]

With big mushy factory rubber bushings in suspension links, PHB probably would have greater effect on defining RC location and roll steer characteristic. Those two aspects alone will be felt as great handling improvement.

Combining PHB with less compliant bushings (delrin, spherical rod ends, jonny joints, poly, etc) would result in massive binding.

If I were forced to try this, I'd try something like replacing LCA bushings with rod ends, add PHB, and let those components define roll axis. Then leave soft bushings on at least one end of each UCAs, and/or perhaps try compressible UCAs (like used on circle track 3-link). This will let you define IC location under acceleration, while reducing roll bind by letting the UCAs change their length.

P.S. to Dennis,
Any word on spindles?

[dennis68]

Order form ready to go.....waiting on $$$$$.