Soundproofing a Diesel

[79vette]

Has anyone used this product from LMC?
Https://www.lmctruck.com/1973-91-che...nsulation-kits

I have a lot of engine noise in my M1009, and cannot drive on the highway without hearing protection. I don't need a Lexus, but I would like to at least be able to talk to a passenger without screaming...

So far I have used Dynamat/Peel n Seal (didn't have enough dynamat to finish the bed and they seem like the same thing to me) and 0.315" closed cell foam to cover the floors and firewall. I have not put down mass loaded vinyl yet, but my floormats are .375" heavy industrial rubber and at least 1lb/sqft and I imagine they would work similarly. The foam really seems to help with heat, but the truck is still unusably loud.

I haven't soundproofed the doors yet, and I need new vent window weatherstrips. But other than that I have no idea what else to do to make this quieter. This truck has way more soundproofing than my gas K5 and my C30, and it's still unbearably loud. Did everyone just wear earplugs when the 6.2 was in production, or is there something I am missing? Is there any kind of sound insulation I can put on the engine side of the firewall or on the bottom side of the transmission tunnel?

I built this to be a camping rig to access remote canyons and mountains, but none of my climbing partners will ride in it because it's so miserably loud. I daily drive an 88 one ton square body and a 79 Corvette with side pipes, and even with hundreds of $ in insulation and days of work the M1009 is still WAY louder than either of my other vehicles, which just have the stock 40+ year old interiors...

[burnin oil]

I think that your best bet will be yanking everything under the dash then spraying a product like lizard skin. After that reinstall everything.

You may want to check the injection timing as a few degrees can work wonders on load noises and a little free power. You may try moving the mufflers further back also and see if that helps. Honestly almost every diesel before the common rail stuff was loud. 6.2s were known for being loud with low power however you shouldn't need ear plugs.

[79vette]

Loud is fine, but this is well above the pain threshold. It's pleasant at idle, but at highway speed the engine and road noise is for sure louder than a 4.5" angle grinder cutting steel.

Do you know what the civilian diesels had from the factory? The military trucks didn't have an interior, but surely the civilian ones had some soundproofing?

Unfortunately lizard skin or other spray on products aren't an option at this point. The Dynamat adhesive is way too strong to ever be removed. I think the only way to get it off would be to grind it off with a wire wheel...

[burnin oil]

I just stripped the interior of an 86 K30 with a 350. It had that wool looking jute material covered by rubber matting. I don't think that it was any different than my 77 blazer.

Have you soundproofed under the hood yet? If not that would probably help alot. For a quick test you could probably just hook a blanket to the hood. Lock the truck in 1st get up to about 25mph. That should give you an idea of the sound deadening.

Edit this in. An angle grinder is about twice as loud as I would expect that truck to be. I barely remember the chevy trucks from my military time. We had a few rolling around but hummers had replaced them. Even the soft top models were quiter than what you described.

[79vette]

I haven't done the hood yet, but I think it will help a lot. Do you just have the factory fiberglass blanket? I'm trying to find the most effective sound proofing that will survive the temperature under the hood.

I am looking at the LMC product linked in the first post. It's spendy at $180, but being plastic faced I expect it would last much longer than the factory blanket.

The truck is loud but OK around town (40mph and under, 1600rpm). On the highway I run 80 mph at 2200 rpm (0.73 overdrive gear) and that's where it gets real loud.

[Dead Parrot]

Stock exhaust system?
Make sure the fan clutch isn't locked up. A fan spinning at 2200+ is a noisy beast.
My M1008 still has the 4.56 gears and seems quieter then what you are describing. It is still pretty much as issued to the military as far as sound abatement.

[79vette]

Originally Posted by Dead Parrot

Stock exhaust system?
Make sure the fan clutch isn't locked up. A fan spinning at 2200+ is a noisy beast.
My M1008 still has the 4.56 gears and seems quieter then what you are describing. It is still pretty much as issued to the military as far as sound abatement.

Good call on the fan clutch. I'll double check.

Exhaust is stock now with new stock-type mufflers, but will be going to a turbo in a few months

[burnin oil]

No good idea on the hood insulation. I run a 7k RPM 400sb under my 72s hood. My old dodge had that factory felt stuff under the hood and it did a decent job on the Cummins engine noise but nothing for the 75PSI twin turbos. Alot of guys cut the dynamat stuff and fill around the hood support structure. I never tried it. With my toys I gave up on sound control. Believe it or not a turbo will quiet the exhaust down a good amount but then you gain the whistle. Most of my diesels have a 4" glass pack for a muffler and they are quiet enough that the engine makes most of the racket. I can comfortably carry a conversation while the truck is loaded.

[kwmech]

My dad has an '83 that is pretty well sound proofed from the factory. Pretty heavy padding on the firewall. You can hear the engine for sure but it is not unbearable, listening to the radio or talking to somebody is not an issue. I'm sure the military version was stripped down to the basics---comfort be dammed. I've got a Toyota pickup I'm restoring at the moment that was kind of tinny driving down the road and I have it stripped out getting ready for the Killmat 80mil that I have on order along with a new carpet kit. We'll see how that works out before I do the same thing to my Suburban

[burnin oil]

Kw, for your dads truck are you talking about the grey wool looking material with a cardboard like material over it? That is the juke material. Same thing under the carpet but no cardboard backing.

[79vette]

Is all this insulation inside the truck? Or does anyone have additional soundproofing on the engine side of the firewall?

For the fan clutch, I can move the fan back and forth with the engine off. But if I give it a good push it will only go about 1/4 of a turn before stopping. Should it spin freely (like 1 complete revolution or more) when the engine has been running for a couple min but is still cold?

[Ziegelsteinfaust]

What's the word on lizard skin vs dynamat?

I know dynamic can work wonders. Besure to insulate part of the doors, and back of cab to aid in quietness. Plus do flooring of some kind. Sound pads like jute make a big difference.

My 83 C10 has no flooring, and it loud+hot in the cab. Not as bad as yours, but I am planning interior when I get around to painting the floor.

[kwmech]

Originally Posted by burnin oil

Kw, for your dads truck are you talking about the grey wool looking material with a cardboard like material over it? That is the juke material. Same thing under the carpet but no cardboard backing.

Don't what color it is off hand, but it is pretty thick and more of a rubbery hard backing to it. Floor is pretty much like any other truck. But I know the firewall is pretty thick

[farmall]

I have an early 80s Diesel with a substantial engine compartment firewall insulation. I have never seen this on a gasser. Looks like this....

[79vette]

Originally Posted by farmall

I have an early 80s Diesel with a substantial engine compartment firewall insulation. I have never seen this on a gasser. Looks like this....

That looks real nice. Any idea what it is made out of?
I'll probably be puling my motor this fall to do head gaskets/studs and install a turbo, and that would be a great time to install some engine bay soundproofing. I doubt I'll be able to find an original one, but I might be able to make something like it.

[Corts60]

Originally Posted by farmall

I have an early 80s Diesel with a substantial engine compartment firewall insulation. I have never seen this on a gasser. Looks like this....

Awesome! I wonder if that is factory? I’ve never seen that firewall insulation before.

[farmall]

Originally Posted by Corts60

Awesome! I wonder if that is factory? I’ve never seen that firewall insulation before.

Yes its factory.
Mine looks exactly like the one in the pic I googled.
Mine is on a no option C30 Diesel parts truck with no motor. It would be nice to install on my gassers but it is a no AC truck.
It has a hardish plasticky rubbery cover/outer shell that has held up well.
It is at least two piece with the HVAC end by itself. Maybe they made one for the AC trucks as well.
79Vette... The radio in my 2 door HUMMER is useless. Not painfully loud but is up there.

[66gmcguy]

As others have mentioned, the underhood insulation will help out a lot. When I had the 6.2 in my truck, the only insulation I had on the entire truck was the underhood insulation and pieces of firewall insulation. No cab floor insulation at all. With 4.10 gears, 31" tall tires, and no OD, it was definitely noisy but it wasn't unbearable by any means.

[79vette]

Originally Posted by 66gmcguy

As others have mentioned, the underhood insulation will help out a lot. When I had the 6.2 in my truck, the only insulation I had on the entire truck was the underhood insulation and pieces of firewall insulation. No cab floor insulation at all. With 4.10 gears, 31" tall tires, and no OD, it was definitely noisy but it wasn't unbearable by any means.

Did you just have the factory fiberglass insulation? Or did you do any other fancy sound deadening in addition to that (dynamat, etc)?

[66gmcguy]

Originally Posted by 79vette

Did you just have the factory fiberglass insulation? Or did you do any other fancy sound deadening in addition to that (dynamat, etc)?

Yes, just the factory fiberglass insulation on the inside of the cab on the firewall, plus the factory insulation on the engine bay side of the firewall, like the one in the picture a few posts up. Except mine was missing several chunks. I don’t think anybody reproduces that piece that goes in the engine bay unfortunately though.

[79vette]

Originally Posted by 66gmcguy

Yes, just the factory fiberglass insulation on the inside of the cab on the firewall, plus the factory insulation on the engine bay side of the firewall, like the one in the picture a few posts up. Except mine was missing several chunks. I don’t think anybody reproduces that piece that goes in the engine bay unfortunately though.

Yeah, that engine bay piece is what didn't come on the military trucks. It looks quite substantial so I am sure it adds a lot to the soundproofing. I'll have to try to make something like that I suppose...

[bhc41051]

I used the quiet ride kit for the hood. I'm sure it helped a little, but I have a 350 with single exhaust and quiet muffler.
https://www.quietride.com/

[LT7A]

My K20 was originally a diesel and has that mat on the engine side of the firewall. I've not seen it be reproduced, but there's a possibility I suppose of somebody parting out a diesel or finding one at a wrecking yard. I guess the alternative would be to spray something heat resistant like the lizard skin on the firewall. I would put multiple layers of dynamat on the interior side of the firewall. That should do a lot. I wonder about that product from lmc. I think of ABS as being hard plastic. It would reflect some sound but could also operate as somewhat of a membrane like the hood itself. Before spending that money, I would buy a couple of moving blankets from harbor freight at five bucks a piece and tape them to the bottom of the hood and make a quick run. I don't think they would last a long time, but they should hold up long enough to test. If they helped appreciably, then I would get welding blankets which are made to handle heat. I would use a dynamat like product over the whole underside of the hood, and then I would use spray adhesive and attach the welding blanket. But, my truck is a workhorse, function over form, and the diesel is long gone. All that said, it still seems like there is something that is making your engine way louder than it ought to be if it sounds like a grinder cutting metal. I wonder if there are any members who live near you that have the 6.2 diesel. Maybe you could go for a ride and try to hear whether it's engine noise, or exhaust noise, or fan noise or what.

[79vette]

If there's anyone in the SoCal area with a good running 6.2 diesel/SM465 truck, I'd love to hear it. I'll bring a case of beer or beverage of your choice if I can hear your truck run for a couple minutes and have you take me for a short drive...

[79vette]

If there's anyone in the SoCal area with a good running 6.2 diesel/SM465 truck, I'd love to hear it. I'll bring a case of beer or beverage of your choice if I can hear your truck run for a couple minutes and have you take me for a short drive...