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why unibody???

sharq

sharq

NAXJA Forum User
Location
Tampa Bay
i was just wondering why D-C decided to go with the unibody style body/frame. what are the advantages to utilizing this type of construction? is it cheaper to manufacture this way? or was there some other reason for it. has anyone else ever thought about this or do one of you know? again, just wondering/daydreaming here...
 
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The XJ is an AMC design not DCX. There are many benifits to uniframe (stiffness, saves weight, etc) The search function is your friend there has been a LOT of talk about this topic.
 
tigerShark said:
i was just wondering why D-C decided to go with the unibody style body/frame. what are the advantages to utilizing this type of construction? is it cheaper to manufacture this way? or was there some other reason for it. has anyone else ever thought about this or do one of you know? again, just wondering/daydreaming here...
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I'd say the weight savings were the #1 issue. The XJ was designed at the tail end of the 70's... during the second OPEC oil fiasco.

Remember, the original 4 cylinder XJ had, what?, 90hp? The V6 was a screamer with 110....

Den
 
I wonder too if the unibody, and the subsequent low weight and lower center of gravity, are responsible for the XJ being a relatively safe vehicle on the highway, unlike certain other notorious small SUV's.
 
I wonder too if the unibody, and the subsequent low weight and lower center of gravity, are responsible for the XJ being a relatively safe vehicle on the highway, unlike certain other notorious small SUV's.
Click to expand...

The truck is just probably an all around better design to begin with, plus Dad was telling me that when he read "High and Mighty" that for some reason, with their archaic (sp?) suspensions, the Cherokee and Grand Cherokee's had the lowest roll over rating in stock form.
 
I'm also wondering if the French Connection (pun intended) with the XJ has something to do with the unibody. Renault was contributing to the overall design, and Jeep wanted a small utility that was marketable to people in places (like Europe) where full sized trucks aren't common passenger vehicles.
 
Al, in a way you're on to something there. The Renault folks already had experience designing and building uniframe/unibody French cars, but if I remember correctly the uniframe XJ was going to be the first 4x4 uni.

The uniframe allowed designers to make a 4x4 weighing in at between 3,057 lbs - 3,386 lbs which is considerable since the Wrangler is a few hundred pounds heavier yet has a much shorter wheelbase. (FYI, a 2005 TJ Sport weighs 3,539 lbs).

Most importantly to a struggling non-Big Three company though is what Tom already mentioned - it's cheaper.
 
There use to be an excellent wright up by Ed Stevens about the design of the xj on this site. As I recall, the xj unit body has more torsional strenth than a full size Chevy pick-up truck frame.
 
Don't forget, also, that AMC had been building unibodies for years and years; I don't know if they were the first, or the only, US manufacturer to do so, but they certainly were ahead of the big 3, and it was one of their big sales pitches in the 50's. So even though the Willys and Kaiser heritage Jeeps had frames, a new AMC design might logically have been a unibody anyway.
 
Matthew Currie said:
Don't forget, also, that AMC had been building unibodies for years and years; I don't know if they were the first, or the only, US manufacturer to do so, but they certainly were ahead of the big 3, and it was one of their big sales pitches in the 50's. So even though the Willys and Kaiser heritage Jeeps had frames, a new AMC design might logically have been a unibody anyway.
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Matthew is correct. The XJ is an AMC design. AMC had not designed or built a car with a frame in since sometime in the mid-1950's. Unibody's were considered "standard engineering practice" for AMC.

Please also remember that an XJ is NOT a big vehicle as SUV's and trucks go, so construction methods used on larger vehicles (body on frame) are not necessarily cost-effective nor weight-efficient on smaller vehicles. For it's size, the XJ is a pretty light and stiff structure.
 
AMC tested it out with the AMC Eagle, which came out in '80. Basically a Concord/Hornet/Gremlin modded to a 4x4 with SOA rear axle and Caddy front wheel drive spindles. (compare the lower arms to a Caddy and you'll see what I mean) Actually, it could be further back, like the Olds Toronado design they used. Wonder if it was part of the engine buy back package when GM sold them the "obsolete" V6 that AMC turned around and fixed. (came back as the 231 V6 and then the 2.8L that was used in XJs after GM messed them up again)
 
WB9YZU said:
The answer to the question posed in the Title is "Why Not" :D
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As XJ's get older (and become more "classic"), I might wish that I could buy a replacement tub like the wrangler guys can. Unibodies might not be so fun when you want to do a ground up restoration. But alas, the XJ wouldn't be what it is if it were not a uni-body.

frame.jpg

btw, that ain't me ;) It's from a site that details a 23 year build!: http://aregularguy.info/jeep/
 
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unibodies are lighter weight, which means greater power to weight ratio, better fuel efficenty, they also are cheaper to make however they are not as rigid as a traditional body on frame design. you will often hear people that offroad there jeeps complaining that they bent there uni body which is due to either rolling over hitting stuff or "flexing" which eventually weakens the frame and you have hatch and door alignment issues a good way to avoid warping the frame is to install some uni-body stiffeners
 
Wow, what a load of horse shit...
"Unibodies", and "body on frame" are just groups of vehicles. A unibody can be stronger than a frame, and many are. People love to make body on frame vehicles out to be ungodly strong... thats just not the case. Unibodies are USUALLY weaker, because most cars are unibodies... ie, light duty. Most full size trucks are body on frame, so they get the reputation as work horses.
Theyre not all created equal... and making blanket statements about them is as dumb as saying 'all black people are great at basketball'.

The one, undeniable advantage to body on frame construction, is you can pull EVERYTHING apart for restoration....
 
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