What's wrong with my 1976 spider?

[1976spiderman]

I have a small problem that won't go away, my car will jerk back and forth when I drive above 40mph. I fixed the pillow block and bearing from the drive shaft, it was worn out, I installed 2 new ujoints,and a new flex coupling to the tranny.installed new gear oil in the rearend and tranny.but the problem still is there. Any ideas from anyone? Have a good day!! Tim C

[velozi]

Could it be fuel related? Pump can not keep up with amount of gas needed so jerks?

Just a guess.

[maytag]

I think we need more info on "jerks back and forth". Steady throttle? accelerating? all gears?

[1976spiderman]

Thanks for your input! The car shifts fine 1st gear through 5th, it only happens when I start to get to about 40 mph, I also replaced the lower reaction rods,the bushings were really bad, I have a feeling it's in the differential? Or maybe my rear tires are not balanced properly? Thanks everyone!! I also had my carb rebuilt by a pro, don't think it's that, but it could be fuel related. I have to check fuel pressure next.

[majicwrench]

See Maytags post above. Don't bother checking fuel pressure yet. Diff not causing issue. Tires would vibrate. See maytags post above.
Keith

[narfire]

Jerks back and forth is same as side to side? Not front/back.
A shimmy you notice in the steering wheel? How are the front ball joints? and tie rods,center link?, yes tire balance out of whack can cause a vibration. Wide tires on a road or your lane with a pronounce crown can kind of shoot you side to side a bit.

[dmwhiteoak]

May even consider a loose wire , maybe on the coil. At one time I had a similar problem and it turned out to be a weak connection on the power wire to the coil. But only at above 40 mph, probely fuel related.

[TX82FIAT]

"jerks back and forth" is different than a vibration. would you use the phrase "the car bucks a little" or would you describe as vibration. Does the problem go away at speeds above the 40 MPH or is it more consistent in a certain RPM range. Tires will absolutley cause a wobble/vibrtation/jerking type of feel depending on how bad the tires or even one tire is.

[maytag]

this is a lot like playing charades at a party where the guy giving the clues went to the john!

[narfire]

this is a lot like playing charades at a party where the guy giving the clues went to the john!

Phfftttt No kidding

[DocGraphics]

Panhard bushings???

[1976spiderman]

Thanks for all the replys!! This site is really cool! I have not had time to try some of the suggestions hope fully this weekend. Will get back soon hopefully with some good news!! Thanks again!! Tim C

[1976spiderman]

Good day everyone! Finally figured out what was wrong with my spider! Thankyou every one who replied!! The problem was fuel related, it turns out who ever owned the car before me had the fuel lines reversed the return went to the feed side of the carb and the feed was where the return should of been.was very happy that's all it was! Found out also that they took out the mechanical fuel pump and had replaced with an electric one. Was able to enjoy the car finally!! Thanks again for everyone's help!! Have a super day : ) Tim C

[fiat218]

Good day everyone! Finally figured out what was wrong with my spider! Thankyou every one who replied!! The problem was fuel related, it turns out who ever owned the car before me had the fuel lines reversed the return went to the feed side of the carb and the feed was where the return should of been.was very happy that's all it was! Found out also that they took out the mechanical fuel pump and had replaced with an electric one. Was able to enjoy the car finally!! Thanks again for everyone's help!! Have a super day : ) Tim C