I have an 89 with a bone stock 350 (880 block) that I swapped a T56 into with a lot of help from this site. The trans came from a 95 and included a Spec Stage 3+ (?) clutch and flywheel. Also have the Tick adjustable master and new slave. Problem is, a ton of vibration in the car, especially in 1st and reverse. Good engagement/disengagement but a done of shake. The flywheel did come with the bolt-on weight from Spec which I did not install originally, but I have read the TSB about the weighted flywheel for 87+. Everything was torqued to spec on install and flywheel was resurfaced before install. I'm thinking the bolt-on weight is my issue, but I am hoping for a little reassurance before I re-install the trans for the 3rd time on the garage floor (fork issue...) Thanks.

 

The 1-pc rear main seal 350, while internally balanced, requires a slight unbalance on the flywheel. So yes, if the flywheel mfr says it needs the weight, install it.

 

Thanks Sofa, I guess I was up in the air because the manufacturer gives you the option to install or not. I bought the pieces used so wasn't sure if I HAD to install. My guess is the flywheel is used for multiple applications, hence the option.

 

Some aftermarket cranks for 1-pc RMS are set up for neutral balanced flywheels. Stock bottom ends require the counterweight. I guess that's their way of making their FW as universal as they can.