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Am replacing rear trailing arms and Watts link. Arms are original and rubber is shot. Watts was rebuilt with poly, which the interweb tells me is not ideal. I have new OEM arms, new Watts links and a new center Watts connecting bracket, all with OEM rubber.
Fell into a research rabbit hole, and found the PB&J mod. Link below. I have drilled all four bushings on the upper arms. Should I drill the bushings on the Watts links too? If I am visualizing how the suspension moves correctly, the axle will rotate as the rear of the car moves down, causing the Watts center mount to be out of plane with the end mounts…. and thinking drilling more flex in the Watts link bushings would help. Am on RB springs, which claims a 1” lower, if that matters.
Just stick with drilling the upper trailing arm bushings, or go drill crazy and put holes in the Watts links bushings too?
I read the web archive of the pb+j mod that someone posted a couple of days ago. I recall the takeaway was that unless you are very lowered and are pushing the car to its limits, then no need to worry about the inherent flaws in the rear geometry.
I think it's great that you got all new rubber bushing arms and watts links, I'd put them on and enjoy!
I replaced all of the links a couple of years back and that alone makes a huge difference in the feel on the road. I even went overboard and installed the Mazdatrix double-shear Watts Link Pivot and it seems to work - I haven't damaged anything under there. For a road car that's driven in a spirited manner, new OEM is all that's really needed. Track cars at the limits of adhesion when cornering might benefit from drilling the upper link bushings, but anything more is just wasting factory rubber bushing life, if you ask me.
The OEM links I installed all at once are the LAST ones the car should ever need. The originals lasted almost 250k miles and nearly 40 years!
My vote is for all new OEM rubber without modifications. The key is tighten everything with the suspension loaded making sure all links have settled rolling or bouncing it done preferably on a 4 post type lift if not jack stands under the axle.
The rear suspension gremlins are way overrated. One only needs to watch the old motorweeks about the 1st gen to see how the OEM rear end reacts in real world situations and it handled its business when put up against an independent rear, Rack&Pinion 944.
A lot of the rear end issues are exaggerated by the slow aging steering box with my rack kit anytime it steps out you can lean into it or put it to bed instantly just due to the instant response of rack and pinion steering.
Here's what I did to eliminate bind in the rear suspension...
I used to make watts pivots for my 8.8 axle conversions from scratch, the bracket welded to the axle tube instead of the center section. The parallel plates were made from 3/16" thick, center bolt was a 3/4"x2" shoulder bolt...
I used to make my double shear watts bellcranks from scratch as well. 1/8" thick ears welded to a short section of pipe. Machined a hard plastic bushing from Delrin for the center pivot, it rotated on a center sleeve that was slightly longer which allowed free bellcrank rotation after the bolt was tightened....
It used rod ends instead of rubber bushings, same parts that I used to install the FB watts on my FC solid axle conversions...
I used this same setup on my personal car. I was in a near head-on crash that destroyed the rearend housing, bent the axle/tube and spun the tube in the housing. All the watts parts survived the crash with no damage, re-used it all with the new rear...
I use a torque-arm to control pinion angle, which allowed me to completely eliminate the stock upper links. This also allowed me to use PTFE lined rod ends on the lower links without causing rear suspension bind.
