Engine Shakes

[jesseb24524]

Ive done many upgrandes to my 72 360 engine however it still shakes when idle isnt set high. And shakes terribly when im in drive with foot on the brake(shakes the cab). Engine runs as smooth as my wifes hyundai when the idle is set high or im pressing on the gas. Any suggestions?

[JMcTurnan]

Maybe the mounts rubber has worn off. Also out of time? Carb problems? How much does it shake?

[70_F100]

Sounds very much like you have a vacuum leak.

At idle, the additional air fed to the engine through the leak would lean-out the air-fuel mix.

Above idle, the small amount of additional air wouldn't be noticeable, as relative to the air flow through the carb, the amount of air introduced through the source of a vacuum leak would be insignificant.

When accelerating, additional fuel is introduced into the intake, and again the small amount of air attributable to a vacuum leak would be insignificant.

[jesseb24524]

It shakes much more when in gear than it does at idle but I have had the carb rebuilt and timing set recently

[JMcTurnan]

Sounds almost like a vacuum leak, get a vacuum gauge and tell me what it reads.

[fordman]

it is a vacuum leak. i had that happen to a truck i reaently got. it ended up being a vacuum leak.

[JMcTurnan]

Does it go into gear though? If it does it leaves out the autmoatic transmission vacuum modulator. Check for any pil slightly dripping out of the front intake.

[70_F100]

Just because a modulator is bad, it will NOT affect the engagement of the transmission. The modulator controls shift points and shift harshness.

What does "pil slightly dripping out of the front intake" have to do with a vacuum leak????

[JMcTurnan]

If it slightly leaks down there, then when you put it in gear your truck seems to shake. Mine did. I wasn't saying it was bad, but maybe a small leak. From intake tree to down there. If he has automatic tranny.

[JMcTurnan]

Do you have rough times shifting?
+

[fordman]

to find a vacuum leak spray some carb cleaner around when the engine is running. when the engine changes pitches you found the leak.

[jesseb24524]

yeah it is automatic it goes into gear and can sometimes shift hard

[70_F100]

Check the short vacuum line going into the modulator to see if it's either disconnected or cracked.

That's a possibility, but if it only shifts hard "sometimes," there's a good probability that it's not the problem.

It sounds like you've more than likely got a vacuum leak, as I said before.

Do what fordman suggested. Get some spray carburetor cleaner and spray it around the base of the carb and on your vacuum lines. You don't need to overdo it, just a little bit will reveal a leak.

Other thoughts: Have you adjusted the idle mixture? How about the timing? What is your point dwell set at? Have you done a complete tune-up (points, condenser, cap, rotor, wires)????

Something else comes to mind. Disconnect the vacuum line to your brake booster (assuming you have power brakes) and plug that line. Put it in drive with your foot on the brake. Does it still vibrate? Bad booster.

[fordman]

thats what mine was i had to read it before i coudl remember. mine had a bad leaky brake booster.

[jesseb24524]

changed plugs, wires, cap, rotor, electronic ignition, rebuilt carb, fuel filter, fuel pump, air cleaner, pcv, coil. yes it does have power brakes