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The Vibration Dampener

by Bart McNeil

Gimme a vibe...
The 1956 Jeep Model CJ-3B Parts List contains some seldom noticed lines. And even if noticed, this one is still somewhat of a mystery: "vibration dampener." A thing which dampens vibrations. What thing, and what vibrations? And why do they need to be damp?

(Editor's note: I have to admit that when Bart first said he was writing an article about the "vibration dampener" I didn't realize what he was talking about. I assumed it must be something in the suspension or steering. But once again Bart has combed through old Willys publications, Jeep history books, and the web, to assemble a history of an overlooked original Jeep detail. -- Derek Redmond)

A vibration dampener couldn't be simpler; just a block of wood bolted to the body to hold the spare tire in slight compression to avoid the bounce and wobble (vibration) of the spare when driving over rough roads or terrain. Apparently Willys was more concerned with vibration of the spare tire than most of its customers; vibration dampeners were available starting in 1949, and may have been standard equipment on the CJ-3B, but most of us have never seen one, or noticed it even if we did see one. I have poured over my Jeep books and have only found a few published photos showing a vibration dampener, and two of those photos show only a small portion of the dampener. On the internet I've found a few more.

Click the detail photos below to see the full photos from which they are taken.
 

CJ-1Upon receiving my copy of Fred Coldwell's 2001 book, Preproduction Civilian Jeeps, the first thing I noticed in the cover photo was that in front of the bare spare tire rim two small blocks of wood were installed. This pre-production 1944 CJ-1 had to be the earliest version of the civilian Jeep on which vibration dampeners are found. They can be seen in the 3 o'clock and 5 o'clock position relative to the empty rim. Another photo shows a third dampener behind the spare mount in the 9 o'clock position.
 

CJ-3AAlthough vibration dampeners could be installed on CJ-2As I have found no published photos where they are visible. A vibration dampener does appear on Jim Marski's 1950 CJ-3A with Auburn Jeep-a-Trench and blade, pictured in Jim Allen's Jeep. This workhorse would certainly need some sort of dampener because of its heavy off-road use and quaking machinery. It can barely be seen between the spare and the sheet metal and is located in line with the curve of the tire.
 

Parts List
From Willys Motors Jeep Model CJ-3B Parts List (1956).

The question remains, why didn't Willys install the vibration dampeners on all its civilian Jeeps? The answer is in the parts list line, which reads "Use with 6.00 x 16 tires." Shortly after the introduction of the CJ-2A, buyers could opt for another size rim and tire, and to install the vibration dampener would be a committment the owner might not want to make. The wider 7.00 x 15" tire needs a much thinner vibration dampener. In fact Reed Cary points out that in a 1949 Parts List (CJ-2A and CJ-3A) two were offered: "671157 DAMPENER, vibration, spare wheel (use with 6.00-16 tires)" and "671158 DAMPENER, vibration, spare wheel (use with 7.00-15 tires)."

Reed's own CJ-3A with 7.00 x 15" tires doesn't use a dampener and the tire wall touches the body. We cannot visually determine the width of the dampener on Marski's 3A but it is almost certainly a thin one. It seems that Willys itself had mixed feelings on the need for a dampener with 7.00 x 15" tires. Both the 1956 CJ-3B Parts List and the 1962 Master Parts List show only the standard part number 671157 vibration dampener, used with 6.00" tires.

Drawing But indeed when the units were first introduced for the CJ-3A in 1949, there were two sizes. Service Bulletin 49-24 (70K JPEG) tells dealers, "Where vehicles are used in rough territory, it is suggested that you interest your owners in the installation of this vibration dampener. (...) This installation can also be made on the Model CJ-2A in the same manner, using the same dimensions. The installation of this dampener will materially lengthen the life of the spare tire mounting."

Bill Norris scanned the drawing (left) from the Service Bulletin, showing the size of the wood blocks, and the drawing showing the location of the mounting bolt holes (30K JPEG).
 

CJ-3AIn The Jeep in Sweden, by Stig Edqvist, there are two CJ-3As pictured with vibration dampeners. In this example the 3A was brand new (recently assembled after import) and had never been used. The photo is quite sharp, so that under close scrutiny the vibration dampener can be seen to be the thinner version for use with a 7.00" tire.
 

CJ-3BDerek Redmond's 1959 3B was running with 6.00 x 16" tires when he bought it. This is a detail from a photo which I studied for an hour (for another purpose) before I noticed the vibration dampener, held by only one screw and dangling from the body.

Tim Henderson sent a closeup of the original vibration dampener on his 1956 CJ-3B.
 

CJ-3BLawrence Wade is preserving his father's 1955 CJ-3B. Lawrence's vibration dampener appears to be simply a piece of hard wood 3/4 x 2" by about 5" in length, just visible in this photo. But there is something interesting about the way his father installed this vibration dampener for his optional 15" rims and 7:00 x 15" tires.
 

CJ-3BNormally one would need at most a very thin vibration dampener when using 7.00 x 15" tires, as the 1949 Parts List suggests, but Lawrence's father installed a 3/4-inch block. (See a close photo by Rus Curtis of the vibration dampener from above, 60K JPEG.) Once the vibration dampener was installed he had to fabricate a spacer to fit between the body and the spare tire mount to make it work effectively. The spacer appears to be 3/4-inch pieces of plywood between the spare tire mount and the body. Lawrence describes his father as a perfectionist who went to great efforts to get things to fit. At some point he also cut off the upper right hand corner of the vibration dampener so as not to interfere with the original canvas top.
 

Tire sizeAt first it may seem unnecessary for Mr. Wade to have installed the dampener and spacer between body and spare mount, but let's examine the situation from a different perspective. We have seen that if we change the tire size from 6.00 x 16" to 7.00 x 15" the tire wall moves toward the body sheet metal and touches it (or almost touches it).

The same effect is taking place on all the other installed tires and the right rear tire wall is moving 1/2-inch toward the spare tire just as the spare is moving 1/2-inch toward the right rear tire. A potentially dangerous situation. Under normal day-to-day driving there may be no problem, but under strain which one might encounter in an emergency situation (or severe off-road usage) the spare and right rear tires could rub against each other causing a blow out. Robert (Bert) Baker, a long-time Jeep owner, has experienced this with 7.00 x 15" tires during off-road driving. According to Bert the largest safe tire offered as a standard tire for CJ's was the 6.70 x 15" (or 16"), slightly narrower than the 7.00" tire. So Wade's father outsmarted us. It was most likely a safety issue that caused him to move the tire out by 3/4-inch. To do this he needed both the spacer and the vibration dampener.

A larger tire would create an even greater problem; on my own 3B (used on a farm to plow snow) the previous owner installed 7.50 x 15" truck tires. That may explain why the owner removed the spare mount from the side and installed it on the tailgate.
 

CJ-2APaul Provencher describes his problems caused by the lack of a vibration dampener back in the 1970's: "The side-mounted spare on my CJ-2A was a source of great frustration for me. The original spare would not stay tight against the body. I wedged something in between the body and the tire. My right rear tire rubbed the spare in off-road situations so much that I finally removed the spare and mount and stored the spare inside the Jeep." (Photo by Paul M. Provencher. All Rights Reserved. Used with permission of 4x4icon.com.)
 

CJ-5Joe Caprio's restored 1958 CJ-5 shows a vibration dampener to the right of the empty rim. This was the first example we had seen of the dampener turned 90 degrees, pointing away from the spare tire mount. This change in orientation may be to accommodate either 15" or 16" rims and tires.
 

CJ-5Here's another CJ-5 which appears to retain the original dampener. Keith Ross photographed this example in 2008 in Lake City, Colorado (180K JPEG).
 

CJ-5In Patrick R. Foster's The Story of Jeep there is a factory photo of a 1966 testing of various Jeep vehicles. A CJ-5 is decked out for a safari outside Toledo. A careful examination of the photo reveals a vibration dampener. While not a clear image there is certainly a vibration dampener installed pointing in the 2:30 o'clock position.
 
Most of the Jeeps seen here were used, or were meant to be used, off road or under severe conditions. Jim Marski's 3A speaks for itself. The Swedish 3A with its Monroe lift is ready for farm work. Lawrence Wade's 3B spent a few early years as the only work vehicle on a small poultry operation. Joe Caprio's CJ-5 pushed a plow, and the factory CJ-5 seems to be preparing for an adventure in the roadless wilderness of Ohio. A standard vibration dampener couldn't have cost more than a few cents to manufacture and might have been supplied to the dealer uninstalled with the caution that it is to be installed for hard use and only with the proper size rims and tires. Considering that it is in every parts list as standard equipment, yet can be found on only a few CJs even when 6.00 x 16" tires were the norm, it just might be the case that owners simply didn't want two more holes in their brand new Jeeps.

I hope this article explains why your CJ has a vibration dampener, or has holes where one used to be. Or perhaps it explains why your CJ has never had one.


Thanks to author Bart McNeil, who also credits the participants in the CJ-3B Bulletin Board and the CJ-2A Message Board. Robert (Bert) Baker was especially helpful with his first-hand knowledge of severe off-road driving in relation to tire sizes. Lawrence Wade spent considerable time probing and reporting on his system. Reed Cary, Bill Oakes and others generously quoted information from parts lists, owner's manuals, and offered personal experiences which put the whole thing together. -- Derek Redmond


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Last updated 1 August 2008 by Derek Redmond redmond@cj3b.info
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