Monday, July 2, 2018

Sound Proofing The Cab Of An R-Series Mack.

I started with the roof and the back of the cab. The vinyl covered cardboard panels were held on by self-tapping screws so came off with out any trouble. The problems came when trying to find the screw holes after they had been covered with the butyl rubber backed aluminium foil.

A visit from Mocha the Cat. Absolutely no help whatsoever. 

Some of the floor had been done with a bitumen based insulation. But most was bare metal, including the fire wall which just had a thin foam and cardboard sandwich to stop the noise.

Dynamat is the name of the sound insulation sheets that come in 12 inch by 24 inch sheets. I used 36 sheets on the cab; two packs of 18 sheets that came from Summit Racing of Arlington, Texas. Not a hard job to do. Cut to size, peel the back off the sticky black butyl rubber then run over it with a roller to get out all the air bubbles. Make sure everything is clean, dry and dust free. Also work in the warm, the product is a lot more flexible on a hot day. 

The original floor covering was rubber mats and had worn badly in places. Replacements are available but I went for carpeting, to also help with noise suppression and to add a little luxury.   

I went for a short-pile rubber-backed 36 inch wide carpet. It's suitable for both indoor and outdoor use and sold by the foot at most home improvement superstores. Both floor and firewall were done using the old mats and panels as patterns while a piece of carpet trim finishes off at the doorstep. 

I used a fabric underlay on the floor and finished off with a full width heavy-duty rubber mat. Just two pedals to cut round. I did away with the  foot-operated siren and air-horn switches. All too often my left foot was going for a non-existent clutch pedal as the truck came to a halt and I was blasting the air-horns by mistake.

The cab is now a lot more user friendly with the new supportive seats and the quieter interior, although with the lack of air-conditioning, there is a lot of wind noise with the windows open on hot days. To be honest; it is still a basic truck  cab that was designed in the 1960's, so it is never going to be like a motorhome or modern truck that is comfortable for a long day's driving but I think that driving days of over thre hours will be few and far between.

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