Thread: REC mighty bang at lock up

Out of nowhere mighty bang around 85km/h running up to freeway speed. Like a brick got thrown up underneath front. Momentary interruption to driveline and then continues to run perfectly. Has repeated several times in same conditions and also once less severely on strong acceleration around 60 km/h.
Methinks is torque converter lock up clutch. All other shifts smooth and at correct speed.
So disturbing have been driving in 3rd on freeway.
89 RRC with 4HP22 and nice clean Transmax fluid.

Is it a 3.9 or late 3.5 with a Borg Warner transfer case?
If so it could be the rear output shaft splines on the BW worn so much they are slipping.
Alternatively the chain could be so worn it is slipping a tooth.
The rear output shaft is easy to fix and relatively cheap but the chain is a bigger job.

Regards Philip A