Knocking under car during deceleration

[Fleetwood Meadow]

My ‘51 Meadowbrook has started making a knocking sound under the car when I decelerate. It’s not all the time. It happens more randomly. It sounds like it’s in the middle of the car but it isn’t always when I’m hitting the brake. Sometimes I am just letting the car slow down on its own and it starts knocking. Where should I be looking for issues? It doesn’t sound like the clinking of a broken brake component but I haven’t taken them apart yet to rule it out. It’s not when the car is speeding up. 

[keiser31]

Check the tightness of your drive shaft. Check your exhaust pipe system, too.

Edited December 31, 2018 by keiser31 (see edit history)

[FLYER15015]

Could be your "U" joints unloading.

I had that same "knocking" sound while coasting in an '02 Ram van and it was an out of balance drive shaft.

Got her rebalanced and new universals and the issue went away.

 

 

 

Mike in Colorado

[Spinneyhill]

Yes, roll under there and give the universals a good wiggle around, looking for movement. If there is a centre bearing, look at that too. Another thing is to look for the exhaust knocking on something on overrun. The engine will tilt differently when driven from the back, possibly bringing the pipe against something.

 

If it is the exhaust, move it. Then have a good look at the engine mounts; they might be a bit puffed too, allowing the engine to rock too much, hence the knocking of pipe on something.

[Fleetwood Meadow]

I checked the u-joints. They are fine. The drive shaft doesn’t wiggle at all. I took the end of the exhaust and jiggled it and it moved the entire system up to the header. I also could recreate the sound of the banging. The gasket has blown out at the header pipe. So I will have to put another one in and then tighten the pipe again. 

[Spinneyhill]

1 hour ago, Meadowfleet said:

The gasket has blown out at the header pipe.

Might mean the engine mounts are allowing too much movement = rocking of the engine.

[FLYER15015]

Also add more hangers to the system, particularly @ both ends of the muffler and at the rear bumper area.

The "rocking" pipe wore out your gasket, but then you knew that............