Flex Disks?
 

My 81SD has been clunking when it downshifts, as it does when approaching a stop. Some threads point to the flex disks as the source here.
Is there a reliable way to check them, or will they just need to be replaced? I have climbed under the car and twisted and have yanked on them. Nothing noticable there. Should there be?

I think when it clunks on a downshift like that it means your vacuum going to the tranny at idle isn't enough. Check that first. I would think it would LEAD to a flex disc failure, not be from one. If they show any cracking replace the flex discs, otherwise I believe they are fine.

Btw- 20" to 0" is ideal anything much lower than 15" at idle will create a downshift clunk, therefore 15" to 2" or so should be liveable.

Don't replace anything without first doing the four P's; Push, Pull, Pry and Prod. If you get under and start examining, you can find what is loose in the drive train.

Good luck,

Don't be afraid.
 

Go ahead and jam a big screwdriver in between the driving and driven bolts on those flex disks and give 'em a good pry. If those disks are mealy, you'll see cracks appear around the bolts when you do some prying.

Sometimes, the cracked disks aren't apparent at rest.

Take a close look at the center support too.


Later,
R Leo

Good plan. I will get under the car and give it the 'Four P's', as well as checking the vacuum again. I am betting something went south there. Seems it started to clunk all at once.

Also, check your vacuum lines - a disconnected or fractured one can play with your shifts. The plastic vacuum lines can get very britttle with age so take it easy.

Old Dies,

Flex disk are good up until a point that you can see the cords within the rubber. Even then they will go thousands of miles before they fail completely. They do not cause "clunks" until they fail completely. The clunks are probably caused by your transmission not shifting properly.

P E H