shudder at 40-50 mph
 

97 f150 4.6 4r70w tranny. started to shudder at about 45 mph. got bad and parked it. got another tranny. after install still does it. will not do it if I continue to accelerate past the 40-45mph zone. if driving at say 40 mph and try to accelerate gradually (normal driving) it shudders. If I am driving below 40 mph and accelerate more rapidly to say 55mph it does not shudder at all. PLEASE HELP?

RE: shudder at 40-50 mph
 

Does it do it only when on the gas? If so, check u-joints.

If it does it coasting or while on the gas, then you may have lost a weight on your wheel and they need balancing.

If not either of those, park it in a dark garage and rev the engine. You may see spark jump from the plug wires. If so replace the wires.

I'd start there. Eliminate the cheapest things first.

RE: shudder at 40-50 mph
 

It only does it when accelerating but the U-joints seem fine. If I let up on the accelerator the shudder stops. I have not thought about the plugs but I do not have a garage to get it in. I think that I will just change the plugs and the wires. To be honest, the truck could probubly use them either way. Let you know hoe it goes. And thanks for the reply.:D

RE: shudder at 40-50 mph
 

You can just do it at night, too.;)

Let us know how it goes. Good luck.

RE: shudder at 40-50 mph
 

:DBullitt94- I changed the plugs and lo and behold the problem is gone!!!!! The truck has never run better since I have owned it. Thank you so much for your input on this problem. :)

RE: shudder at 40-50 mph
 

No problem. Enjoy the ride!