omega_rugal Posted January 30, 2021 Share Posted January 30, 2021 what exactly keeps the rear axle centered below the truck? only the leaf springs? Link to comment Share on other sites More sharing options...
AZJeff Posted January 30, 2021 Share Posted January 30, 2021 The leaf springs and the center pins of the springs interfacing with the holes in the spring perches are what centers the axle. Tolerance on the location of the spring mounts from the factory allow the spring mount locations to vary back and forth (side to side) up to 2.25mm during the assembly and welding process of the chassis (based on shop manual information). I don't really know what the tolerance is on the factory welding of the spring perches on the axle, but I would guess it's +/-1mm. As you can see, there is reasonable latitude in the axle centering of the axle under the vehicle. The drive shaft can deal with that, no problem, of course. Link to comment Share on other sites More sharing options...
Eagle Posted January 30, 2021 Share Posted January 30, 2021 40 minutes ago, omega_rugal said: what exactly keeps the rear axle centered below the truck? only the leaf springs? Yep. Just the springs. In the (very) old days, Hudsons had a Panhard rod (a.k.a. track bar) on the rear axle, but I've never seen any other brand that used one on a leaf spring rear suspension. Link to comment Share on other sites More sharing options...
omega_rugal Posted January 30, 2021 Author Share Posted January 30, 2021 how about a watts linkage? there seems to be room for it... Link to comment Share on other sites More sharing options...
AZJeff Posted January 31, 2021 Share Posted January 31, 2021 18 hours ago, omega_rugal said: how about a watts linkage? there seems to be room for it... Why bother? What function would it provide that actually NEEDS to be done? Watts linkages or panhard rods are used often with coil spring suspension, for obvious reasons. Leaf springs don't need them for equally obvious reasons. Link to comment Share on other sites More sharing options...
omega_rugal Posted January 31, 2021 Author Share Posted January 31, 2021 leaf springs tend to twist a little, more as they age 11 minutes ago, AZJeff said: Why bother? What function would it provide that actually NEEDS to be done? keeping the axle centered even if the leaf springs or the busings are worn? preventing these two from excessive twisting? Link to comment Share on other sites More sharing options...
BeatCJ Posted January 31, 2021 Share Posted January 31, 2021 There just isn't much movement possible, and if you get too much, it's pretty simple and affordable to replace the bushings. When you do get wear, it tends to be symmetrical, so it has limited effects on tracking. One of those things, so simple, why make it harder? Link to comment Share on other sites More sharing options...
AZJeff Posted January 31, 2021 Share Posted January 31, 2021 1 hour ago, BeatCJ said: There just isn't much movement possible, and if you get too much, it's pretty simple and affordable to replace the bushings. When you do get wear, it tends to be symmetrical, so it has limited effects on tracking. One of those things, so simple, why make it harder? I agree. Engineers have been designing axles mounted on leaf springs for 75 years+, and with a VERY few exceptions, none of them use any auxiliary hardware to control the lateral position of the axle under the chassis. Worn leaf springs won't increase lateral motion of the axle. They will merely cause chassis sag. Worn bushings possibly could cause the axle to move small amounts laterally, but that's an indicator that bushings need to be replaced. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted January 31, 2021 Share Posted January 31, 2021 23 hours ago, Eagle said: Yep. Just the springs. In the (very) old days, Hudsons had a Panhard rod (a.k.a. track bar) on the rear axle, but I've never seen any other brand that used one on a leaf spring rear suspension. YJs had rear track bars Link to comment Share on other sites More sharing options...
derf Posted January 31, 2021 Share Posted January 31, 2021 25 minutes ago, ghetdjc320 said: YJs had rear track bars So did later full size Jeeps. Around the same time as the YJ. Front leaf springs work fine by themselves but they don't corner as well as a good independent suspension or properly designed coil suspension with a straight axle. A panhard bar helps with that. Link to comment Share on other sites More sharing options...
MiNi Beast Posted February 1, 2021 Share Posted February 1, 2021 leafs suck for off camber situations as well. Link to comment Share on other sites More sharing options...
AZJeff Posted February 1, 2021 Share Posted February 1, 2021 5 hours ago, derf said: So did later full size Jeeps. Around the same time as the YJ. Front leaf springs work fine by themselves but they don't corner as well as a good independent suspension or properly designed coil suspension with a straight axle. A panhard bar helps with that. I thought we were talking about the springs on an MJ, which are in the back. Those axles won’t benefit from a pan hard rod the same way a front axle will. Link to comment Share on other sites More sharing options...
Tex06 Posted February 2, 2021 Share Posted February 2, 2021 If someone was racing their MJ, a panhard would help but a watts linkage is a much better choice as it doesn't pull to one side with the loading/unloading of the rear suspension. For a 4x4 though, any type of bar/linkage will limit suspension travel and many types are susceptible to binding at the extreme ends of travel....something leafs are not prone to. Leaf spring rear suspensions are typically "good enough" suspensions, they do not excel at anything other than being cheap but do a good enough job to work for 99% of the situations a vehicle is likely to encounter. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 2, 2021 Author Share Posted February 2, 2021 ok for the rear axle may not make a difference enoigh but in the front? the only bar that holds the front axle centered pulls to one side only Link to comment Share on other sites More sharing options...
BeatCJ Posted February 3, 2021 Share Posted February 3, 2021 That bar doesn't pull, it maintains the end that is bolted to the front axle a fixed distance from the driver side frame. That's all that it needs to do. While steel isn't a particularly good material in compression, it's strong enough in this application. So it pushes, too. At the limits of travel, the axle moves slightly right or left, but not enough that you can't easily adjust with your steering wheel. Add the control arms controlling front and rear location, and tilt ,the suspension in our Comanches and Cherokees is fairly simple, robust and effective. Link to comment Share on other sites More sharing options...
Eagle Posted February 3, 2021 Share Posted February 3, 2021 2 hours ago, BeatCJ said: While steel isn't a particularly good material in compression, it's strong enough in this application. Huh? Whut? Steel isn't good in compression? Why is that what the frames of skyscrapers are made of? Link to comment Share on other sites More sharing options...
MiNi Beast Posted February 3, 2021 Share Posted February 3, 2021 1 hour ago, Eagle said: Huh? Whut? Steel isn't good in compression? Why is that what the frames of skyscrapers are made of? compressive strength of ductile materials such as mild steel used for most structural purposes is around 250 MPa. Link to comment Share on other sites More sharing options...
Pete M Posted February 3, 2021 Share Posted February 3, 2021 15 hours ago, omega_rugal said: ok for the rear axle may not make a difference enoigh but in the front? the only bar that holds the front axle centered pulls to one side only it both pulls AND pushes. Link to comment Share on other sites More sharing options...
BeatCJ Posted February 3, 2021 Share Posted February 3, 2021 9 hours ago, Eagle said: Huh? Whut? Steel isn't good in compression? Why is that what the frames of skyscrapers are made of? Sorry, brain slipped out of gear. I reworded what I was trying to say several times, and didn't reread it before I hit post. Link to comment Share on other sites More sharing options...
Eagle Posted February 3, 2021 Share Posted February 3, 2021 14 hours ago, MiNi Beast said: compressive strength of ductile materials such as mild steel used for most structural purposes is around 250 MPa. Compare that to the compressive strength of aluminum or brass ... or zamak Link to comment Share on other sites More sharing options...
omega_rugal Posted February 3, 2021 Author Share Posted February 3, 2021 6 hours ago, Pete M said: it both pulls AND pushes. not in a straigth line Link to comment Share on other sites More sharing options...
omega_rugal Posted February 3, 2021 Author Share Posted February 3, 2021 as the axle moves up and down it moves sideways and up Link to comment Share on other sites More sharing options...
MiNi Beast Posted February 3, 2021 Share Posted February 3, 2021 telescoping trac bar ftw. Link to comment Share on other sites More sharing options...
Pete M Posted February 4, 2021 Share Posted February 4, 2021 6 hours ago, omega_rugal said: as the axle moves up and down it moves sideways and up it does indeed move in an arc. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 4, 2021 Author Share Posted February 4, 2021 1 hour ago, Pete M said: it does indeed move in an arc. it shouldnt Link to comment Share on other sites More sharing options...
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