71 Bonnet (Hood) Rattle

[RRChris]

I have a 71 satellite and have been chasing a knock / rattle coming from the front. For a while I was convinced it was the front end. But everything has been replaced - the front end is tight.
The back if the bonnet (hood) seems to move around a bit and this is when the noise occurs. When the bonnet is shut the back sits even with the fenders. When it is open the hinges feel tight. When closing it near the end of travel some unevenness can be felt.
Is it possible that in the closed position, with the hinge geometry and different spring tension, that the hinge assembly can display some looseness causing a rattle / knock that can be heard in the passenger compartment?

 

[RussT Plymouths]

Are all the hood bumpers and hood wedges installed?

Mopar B Body 71 Charger Coronet Satellite Body Bumper Set with Hood Wedges BBK6W

Detroit Muscle Technologies, LLC Mopar restoration gaskets

www.detroitmuscletechnologies.com

MD2601 - 1970-74 Mopar B/E-Body Spring Hood Wedges

Replacement spring loaded hood wedges for 1971-74 B-Body and 1970-74 E-Body Mopar models. Hood wedges mount on each side of the hood to help keep the hood aligned. Sold as a pair.

www.classicindustries.com

Service Manuals – MyMopar

mymopar.com

Download a copy of the 1971 Plymouth Body FSM and read the sheet metal section, it will show where the bumpers and wedges are installed.

 

[RRChris]

Are all the hood bumpers and hood wedges installed?

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http://[URL]https://mymopar.com/service-manuals/

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Download a copy of the 1971 Plymouth Body FSM and read the sheet metal section, it will show where the bumpers and wedges are installed.

Yes, all are installed.

 

[moparmarks]

Could be the torsion bars. I've had cars including a 72 RR that the t-bars chattered up a storm. The hex ends were worn just enough that they would more in the lower control arms. Changed the bars and the noise went away. If they didn't fit fairly tight when going in that could be the problem.

 

[RRChris]

Could be the torsion bars. I've had cars including a 72 RR that the t-bars chattered up a storm. The hex ends were worn just enough that they would more in the lower control arms. Changed the bars and the noise went away. If they didn't fit fairly tight when going in that could be the problem.

The thought had crossed my mind. However, the torsion bar didn't feel particularly loose. If I remember correctly it had to be helped in.
Also, my son says he could feel the knock on the bottom of the cowl panel - immediately above the evaporator / heater box. This would suggest not the torsion bar mounts.
Took out wiper mechanism, as this is the only thing in the cowl area, no change.
Heater box is tight. ?????

 

[Robert Schaad]

I have a 71 satellite and have been chasing a knock / rattle coming from the front. For a while I was convinced it was the front end. But everything has been replaced - the front end is tight.
The back if the bonnet (hood) seems to move around a bit and this is when the noise occurs. When the bonnet is shut the back sits even with the fenders. When it is open the hinges feel tight. When closing it near the end of travel some unevenness can be felt.
Is it possible that in the closed position, with the hinge geometry and different spring tension, that the hinge assembly can display some looseness causing a rattle / knock that can be heard in the passenger compartment?

I have asked an older body man. He says that many times the Hood become loose from the under frame. This means the sealer between the top and bottom of the hood falls off this causing the hood to vibrate causing noise. Solution is to put new sealer between the hood and hood frame.

 

[RRChris]

I have asked an older body man. He says that many times the Hood become loose from the under frame. This means the sealer between the top and bottom of the hood falls off this causing the hood to vibrate causing noise. Solution is to put new sealer between the hood and hood frame.

Sorry mate, I have only just seen your reply. Appreciate the feedback. Will have a look at this.

 

[RRChris]

I have asked an older body man. He says that many times the Hood become loose from the under frame. This means the sealer between the top and bottom of the hood falls off this causing the hood to vibrate causing noise. Solution is to put new sealer between the hood and hood frame.


So, yes the sealer between the hood skin and frame had let go. I cleaned out what I could and re-did the whole hood with polyurethane body sealer. Unfortunately, the knock / clunk is still there. Although, I believe the NVH has improved!!
Thanks for the tip though, I appreciate the feedback on something I has not thought to consider.