jayh007

Installing a one piece drive shaft. I am going to need to adjust the Pinion Angle. I been looking at a few adjustable UCA. Thinking of just going with adjustable poly or trying the UMI roto joint. Anyone have any experience with the roto joint. Car is a occasional weekend driver with 6-7 track days a year. Looking for comments on NVH and durability

06whitegt

I'd go with and adjustable ucl with poly bushings on bothe ends of the ucl if you are using poly on the lcl's. The roto joint has no play in it, so the bushing at the diff end is going to get all the force transmitted to it. I have the roto join ucl and poly bushing on the lcl's. and kinda wish I'd gone poly top and bottom.

Norm Peterson

The forces are the same at the two ends of the UCA. Poly will "give" a little, where the spherical won't (at least not by enough to notice by "eyeballing"). But this difference in deflection does not translate to any difference in the forces.


Norm
structural engineer, retired

Derf00

what about NVH or resilience of the part itself? Usually the adjustment points are the weak point for control arms (U and L both). Also, doesn't the adjustment creep over time where you would have to at least check it every 6 mo to a year? Just like an alignment on a car requires at least checking it once or twice a year?

Sam Strano

I'm a UMI dealer, and used lots of their parts... in fact we are working on a Corvette project right now together. And I drove their Camaro at a Optima even a few weeks ago.

First thing to note is pretty much any upper arm change will result in more noise as the tubular arms act like sound tubes from the differential more so than a stamped arm.

The Poly front bushing will be better at isolating that noise than a Roto-joint, which is functionally a rebuildable spherical bearing/rod-end type deal, though with twice as much race area that means less wear and it can be adjusted where a rod-end cannot.

I'd go with this arm: http://www.stranoparts.com/partdetai...=206&ModelID=5

And I'd also consider this to replace the bushing in the diff, which get BADLY torn up:
http://www.stranoparts.com/partdetai...=206&ModelID=5

Norm Peterson

Poly does a better job of suppressing NVH than sphericals (especially all-metal rod ends), but not as good as the still softer OE rubber.

Poly can creep, however that usually requires heavy loading sustained over some length of time. I'd be more concerned with impact loading such as from a dragstrip launch or intentional wheelspin and wheel hop.

On-car adjustables are somewhat susceptible to losing their adjustment. Apparently there can be enough torque developed across the control arm pivots to gradually loosen the jam nuts at least in a few cases.


FWIW, I've had LCAs with poly at one end and a spherical similar to a Roto-joint at the other for a couple of years, and none of the ends has opened up any play or evidence of cold flow. Brisk street driving and road course track day use is what mine have had to cope with. Every so often I shoot a little grease in each zerk is all I've had to do thus far, and everything is still tight. I had to disconnect one end of one LCA to fix a steering wheel centering error way back in the beginning (mine are not on-car adjustable mainly to avoid any potential loosening problems).


Norm

jayh007

After doing a little more research i going with spherical bearing on the diff and poly up front. I like the idea of the spherical bearing allowing the axle to rotate but to completely free the axle I am going to need to change the poly joints on the lower control arms.

Sam Strano

I have both, and I'm a site sponsor too. And I've got about any type of LCA as well. UMI's with roto-joint at the axle end, Steeda Billet Aluminum with sphericals at the axle side too.