Ive been trying to naildown a vibration issue i have in my 61 LeSabre. The issue comes on at 70mph and goes away at 80. When i drive in low range at the same rpm (40mph) it definitely doesn’t sound right. If i am in park and take it to that rpm , when I return to idle it runs extremely rough and takes a bit to sort of catch its breath and start idling fine. the issues seem to align with my changing flyid in tbe Dynaflow. Im wondering if the torque Convertor could cause an issue like this? i know my brake booster has a leak because when I apply the brake the rpm increases slightly. Its done this for quite some time before the current issue. Any ideas what could be going on?
If the vibration seems to be in the engine/drivetrain AND you already have a known vacuum loss in the brake system........ Fix that first.......then check the operation of the vacuum/mechanical advance on Distributor..... Do this before tearing into other things.
I spent a little time looking at the issue before work today. I removed all vacuum accessories from carb and blocked each port. (Booster, vac advance, PCV). the issue still persists. I can take the engine to 3000 rpm in park and when it returns to idle it is extremely rough. Low erratic vacuum, lower rpm, etc. after 30-60 seconds of keeping it running by gently goosing the throttle it smooths back to normal. It currently has a lobe sensing pertronix unit in the distributor. Tonight i will swap the points distributor in to see if it fixes the issue. Yesterday i put in a new coil, plugs and wire set. No change. This issue first became apparent after a fluid change in the Dynaflow. I wonder if the torque converter could be tempocreating an erratic “high load” situation after coming off medium rpm. I dont know enough about the transmissions to know if that’s possible
