Great S Type 1999
Accelerating between 55 & 65mph, there is a judder, at 80mph no problem.
Any answers?
Chris

 

Might be a coil.

 

+1 on an intermitient misfiring coil(s). Hook up a COP (Coil On Plug) tester and look at each coil at idle (warm engine) - the offending coil(s) will stick out!

 

or an out of balance/out of round tiyre (new international spelling) or a torque converter.

I think we need more info.

 

i'll go with mikey and suggest an unbalanced wheel

 

where do i find a COP tester? i've recently replace 2 coils and wonder if i have others going, so far no CEL. the others threw a code so it was easy to find those.

thanks!

 

Reading very carefully what you said in the opening.

I would be a little suspect of the transmission fluid. If it has not been changed/serviced in its life, shuddering as you describe is common.

I also agree with all the other suggestions so far.

 

I reckon AutoZone or the like probably sell COP testers or get one online.

 

ChrisNorris, can you tell us if you suspect engine vs chassis? Do you feel it with depressing gas pedal or is chassis shaking. Coils, fuel vs tires, etc.?

 

Search "COP tester" on www.amazon.com - about $85 - $95