Gun Jam

Okay

I have manual brakes, C4 trans that was rebuilt less than a year ago.

Under light braking there is no issue, however with moderate braking a vibration occurs you can feel it in the brake peddle, the seat and hear it.
Here is the kicker when the car comes to a full stop it continues to vibrate at the same frequency and amplitude. It will vibrate until you shift into neutral or let off the brake, it does not vibrate under acceleration only during braking.

The neighbor thinks its a loose flex plate / torque converter I think he is on the right path.

Any other ideas?

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andrewmp6

its the front brakes or wheel bearing or out of blance tire flexplate would shake always i think

Gun Jam

Maybe I didn’t explain it as well as I though I had..........It continues to vibrate after the car comes to a complete stop.

The vibration goes away when I let off brake or shift into neutral.

The car is smooth during normal driving 30 mph to 90+ mph all smooth.

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MidNite27

Brake Booster? I dont know much technical terms but if theres a pump for brake pressure maybe its sticking or something.

dodgestang

If you are running a brake booster I would at it first. Do you notice and change in idle characteristics of the car while it is doing this vibration?

The second thing I owuld check would be the torgue on flywheel and torque coverter...which is a little more work.

Also make sure your rear trans mount is tight.

If it was truly a 'loose' issue after hard braking when the car rocks back to a stop (without letting off brake) I would expect the noise to go away.

Gun Jam

Its manual brakes there is no booster.

It idles fine while it’s making the noise. Shifting into neutral makes it stop letting the car roll a few feet also makes it stop

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fastlane65

I'd be leaning toward the converter - at dead stop it is the only part still moving. It might be loosing the pump and isn't working at very low idle. Is trans fluid low or old? Maybe pull the pan and check the screen, replace the fluid and screen, see if that helps before trying any big dollar stuff.

Gun Jam

Trans fluid is new and full so is screen both replaced less than 1500 miles ago.

I should have switced to a manual trans before rebuilding this c4 [&:]

It probably is the converter (I wonder how long it will last??)

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Gun Jam

I found it!

I turns out the right side motor mount had become weak enough to allow the engine to slump foward enough to allow the water pump output shaft to contact the front of the electric fan. When they touched they would create a vibration. Shifting into neutral or letting the car roll would allow the engine to return to its correct spot.

I replaced rt side MM and now its fine but im also going to try and score another 1/4" of clearance between fan and water pump.

Gun