40 coupe bucking/jerking during deceleration

[Scirica1]

I have a 40 coupe that bucks/jerks when I take my foot off the gas at any speed or gear. Similar to slowing in too high a gear. Complete engine tune up, new plugs, points, wires and checked timing (Mallory distributor). Compression is 130/140, valve lash checked and adjusted (adjustable lifters). Engine runs and idles perfectly, no bucking during acceleration. Checked transmission for excessive play/clearances, seems ok. New bearings and synchro 6000 miles ago, ujoint was perfect. There does not appear to be too much play in the rear (3.25 gear). Removed rear drums to check axle keys, no play and keys are perfect. This started to to happen about 3000 miles ago and has been getting progressly worse. Any one have a solution?

[ronn]

mouse nest in exhaust?

[rotorwrench]

It may not be the engine. You may have some looseness in the motor mounts. Torque tube drives can do things like this if there is mounting deterioration. Under hard acceleration the rear axle and tube push forward a good bit but under deceleration it's the opposite. The rear axle & tube try to pull away from the transmission. Even with no brakes on, the engine is braking unless the clutch is disengaged.

Do you have the engine radius rods snugly in place? How are the mountings & shackles on the rear axle & spring?

Kube may be able to add more if you post on the early V8 side.

[Scirica1]

Engine radius in place and snug, shackles and bushings are good, spring rear and crossmember good, no cracks in frame, 4 new motor mounts.

[Pete]

What cam do you have?

[Jim Brierley]

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Could be carb adjustment, try changing the idle screws a bit. Pete's question about the cam also makes sense.