55.2-59 Rear axle moving left/right

[Iceman_70]

So after 11+years I finally finished the ’56…
Technical inspection is horror here in Belgium, so I now need to wait few months to get approval (or not) for the modifications I did
The license plate I got was only valid for 20days, so I drove it as much as I could . Somewhere on a stop, I noticed the rear axle moved to the left. There was like 1/8 between the tire and the fender, while on the right side almost 2”. There are some marks on the left tire, as if it was rubbing the fender…
Now that the truck is back home, I see I have 3/4 on the left and 1-1/4 on the right, so almost centered again.

My setup is :
Chevy 56 stepside, 12-bolt truck rear end with (I think) original leaf springs but I flipped the axle and the shackle hanger like it is explained here
Wheels are 18x9.5 - 6.75 backspace with 255/55R18
The space between the axle ends and the pads is the same on both sides.

I thought a setup with leaf springs is rigid enough to hold the axle centered. Or do I need to install a panhard bar/sway bar ?
Any advice is welcome !

[dsraven]

nice looking truck.
for starters block the front wheels, fore and aft, and then jack the rear up and place it on stands on the frame, not the axle. release the park brake and then grab each wheel and see if there is movement of the axle laterally in the axle tube (in and out from side to side). a little bit is normal because the axle is held in place, so it can't just pull out, with a "C" clip that fits into a groove on the end of the axle at the middle of the axle housing. you could google it for a better description with pictures. anyway, sometimes the groove or the C clip wears and can cause some movement. the axle butts up against a large pin in the middle of the differential and that is what keeps it from pushing in further than it should. sometimes the end of the axle can wear where it butts up against that pin, or the pin can wear in that area. if you get a lot of in and out play in the axles then it would be worthwhile to take the cover off and check to see what you have for wear inside on those parts.
if the axles have the normal amount of in and out movement then start checking the spring end bushings and pins and spring hanger mounting integrity. do the same check on the shackle pins and bushings. check the axle mount U bolts and plates as well to ensure they are tight and not allowing the axle to move on the springs. if everything is in good shape there should be little side to side movement.
are you using original style frame mounted spring hangers and pins/bushings?

[Iceman_70]

Originally Posted by dsraven

nice looking truck.

Thanks !

Originally Posted by dsraven

for starters block the front wheels, fore and aft, and then jack the rear up and place it on stands on the frame, not the axle. release the park brake and then grab each wheel and see if there is movement of the axle laterally in the axle tube (in and out from side to side). a little bit is normal because the axle is held in place, so it can't just pull out, with a "C" clip that fits into a groove on the end of the axle at the middle of the axle housing. you could google it for a better description with pictures. anyway, sometimes the groove or the C clip wears and can cause some movement. the axle butts up against a large pin in the middle of the differential and that is what keeps it from pushing in further than it should. sometimes the end of the axle can wear where it butts up against that pin, or the pin can wear in that area. if you get a lot of in and out play in the axles then it would be worthwhile to take the cover off and check to see what you have for wear inside on those parts.

C-clips … got it … will check …

Originally Posted by dsraven

if the axles have the normal amount of in and out movement then start checking the spring end bushings and pins and spring hanger mounting integrity. do the same check on the shackle pins and bushings. check the axle mount U bolts and plates as well to ensure they are tight and not allowing the axle to move on the springs. if everything is in good shape there should be little side to side movement.
are you using original style frame mounted spring hangers and pins/bushings?

I replaced almost everything back there : new U-bolts, shackles, bushings, pins, spring eye bolts … The rear-end also got new bearings, seals …

Many thx for your feedback !

[dsraven]

You're welcome.
Just wanna say, still check your axle end play because new bearings doesnt have anything to do with worn C clip grooves, worn C clips or worn axle ends/differential pin. Still worth the test.
Stock frame mounts and spring hanger pins/bushings?
You could install a pan hard bar for better stability but research it first because there are a lot of variables with long or short bars, angled or level bars etc. If set up write the tires may still run as the truck suspension moves because the axle moves side to side as the bar outboard end moves up and down in an arc. Long bar means less arc but still an arc.

[leegreen]

how long are the shackles? Are the two pieces connected with a center piece so they stay square with the pins?

something like this


Not like this

[dsraven]

Shackle volts should have the non threaded part protruding through the outer part, then a flat washer lock washer and nut. Or a flat washer and lock nut. The threaded part shouldn't be what is centering and fitting inside the outer part as it usually is slightly smaller than the shank and also wears out faster. Not a good fit.
Lag, good pics except for that. I know, it's a Google pic for reference. Just thought I would clarify.

[chevyguyase]

Just a thought, when I first got my truck I thought my rear axle was moving, my bed was moving. measure between the tire and the frame and the tire to fender.

[dsraven]

Good point on the body mounting.

[mr48chev]

Leegreen hit the nail right square on the head. The movement is in the shackles.

The factory style shackle pins on the 56 should have tapered ends that seat in the arms so you can't do the welded up version but you could take an accurate measurement with a caliper and cut some heavy wall tubing to length and insert it in the middle over the bolt to stiffen it up. If you didn't replace the shackle bushings and pins when you did the redo they may be worn to the point they are loose and those pins and the rest of the chassis have to be greased every 1000 miles or more often. There is no such thing as greasing an AD or TF truck too often.

[Iceman_70]

I’m definitely gonna check the C-clip play…

I indeed have the shackles like in the picture of mr48chev… I bought a complete set, so it included new bushings and pins, which I obviously installed.
Will investigate how I can make sure the shackles remain square…

Again, thx for all the feedback !!

[mr48chev]

Get a helper (good size one) push on the corner of the box or bumper while you are under the truck to see where it is moving.

[dsraven]

I was gonna suggest that procedure but I figured itwas already done prolly. its what I would have done myself first, see if the body moves on the frame or if it feels like suspension or inner axle stuff. then get a buddy to do the pushing, or a buddy on each side to really work together and get things moving while i lay on the ground behind the truck and see if I detect anything causing the issue. sometimes the old brute strength thing is understated, lol.

[dsraven]

on the shackles, check to see that they are square to each other. use a flat piece of wood or steel and start by placing it on the one side bar so it lays down from one end to the other, then slide it across to meet the other side, they should be parallel to each other. with that done and the center bolt tight, get a dimension between the flat bars and do like mr48 says, cut a length of stout tubing, like DOM tubing, that the bolt will slip through and cut it to that dimension. then remove the bolt and install the tubing between the side bars as you assemble it all with the bolt running through the tubing. it will end up looking like the top pic of the shackle in post 5 except not welded to the side bars and it will have the bolt running through the tubing. a mod to that would be tubing cut slightly shorter with some larger flat washers placed at each end. these can be used like shims and then tack welded in place when done. a larger washer than the tubing may help stability because it makes the effective size of the tubing larger which affects a larger area on the flat bar. you could also make an H shaped part for the center if you think it may help, just ensure it will clear the spring on one end and the mount on the other end when the suspension moves through a full travel swing.

[dsraven]

you may also want to check that the bushings are tight in their mounts. it wasn't uncommon for the pins and bushings to get so worn that the pin wore right through the bushing and started to oblong the mount casting. another point brought up by mr48, you can't grease these old trucks enough. the new bushings may have been pressed into the out of round hole so they have an opprotunity to rock in the mount as they "wear in" to their new mount.
curious, if you are using the stock narrow springs, did you remove any leafs to get your current ride height? if so, and you are seeing lateral axle movement, it could be your springs flexing. they are spring steel but steel doesnt know which way it is supposed to flex so it flexes in all directions, just that it flexes easier in the way you think of first when thinking of vehicle leaf springs. if the spring pack has been altered to be less tall, so less leaves bolted together, then it will be less rigid in all directions, not just up and down.
still, check out the movement by having some strong friends push you vehicle's rear side to side while you watch where the movement is. of course a video camera attached to the underside while you drive some tight curves would do the same thing, more spendy though.
you could attach a sharpy marker to the body or frame so that the felt tip rubs a piece of tape stuck to a tire and then do the body push from both sides and that would give an indication of how much it moves by leaving a mark on the tape. not that you need a dimension, just saying if you want a dimension to keep track of what you did to remedy the problem and what the outcome of that fix was.

first ensure the body is centered on the frame and the body mounts are tight
second check the spring pins and bushings and their frame mounts to ensure all is good, possibly do the shackle mod if you feel it may help, its not gonna hurt anything and is removeable if you find you don't want it
third ensure the spring u bolts are tight and the springs are sitting down nicely on the spring pads. often if there is movement here you will see a mettalic or rusty colored "dust" in the area. remember that the spring pack has a bolt holding it all together and helps locate the springs on the springpad but it is the U bolts that keep the springs located there and they also rely on a good flat smooth surface for the springs to sit down on and be tightened against. also, new U bolts should have been used upon install and they typically require a retorque after a short time of driving. if not retorqued then they will not be working at their intended strength. when a bolt is torqued up it becomes like a spring, it is stretched to it's elastic limit and so keeps things tight. overtorquing makes it go past that limit and may cause breakage, undertorquing can do the opposite and allow the nut to loosen. any fastener supplier will tell you that bolts are made to be used once as when they are torqued they are stretched and don't actually return to their original length. thats more important for stuff like suspension parts because a lot of those are tempered steel
fourth have your buddies help you do a body push/rock while you check visually to see if anything is moving. check the spring pack as well for lateral movement
fifth, if you need to get this far, check that the axle is centered in the frame. use a plumb bob and make marks on the garage floor. mark each side frame ouside edge, each side wheel mounting surface and each side spring center, then get out the tape measure and do your checks and comparisons. adjust as required
sixth, if need be, use a come along or a rope and pulley, whatever, set up from the frame on one side to the axle on the other, and physically pull the axle one way and then the other and see what is causing the movement. when the vehicle is driving and turns a corner there can be quite a bit of sideways forces so using a prybar on suspension parts to simulate that force may not be enough.
seventh, keep us posted on your outcomes
hope something in there helps you find the problem

[iceman4]

Iceman, Looks like we could be kindred spirits LOL. Great looking truck you have, Love the color! Picture of my 57....

[_Ogre]

Lots of good info above. My thoughts are the bed moving, but check everything.

You can't use a panhard bar with leaf springs. The panhard bar moves in an arc as the frame moves on the suspension. Even the longest panhard bar moves in an arc. Leaf springs are designed to move up/down only. Installing both will have them fighting for movement and prematurely wear both out.

Someone will inevitably say that leaf springs move in an arc, yes, that is why the rear shackle is made so.

[Iceman_70]

Originally Posted by iceman4

Iceman, Looks like we could be kindred spirits LOL. Great looking truck you have, Love the color! Picture of my 57....

What a coincidence … Great minds ‘do’ think alike ...

[Iceman_70]

Guys,

Apologies for not responding sooner, but other things came on my way, so this had to wait … In the meantime I heard back from the technical inspection (Belgian DMV) and I have to replace my rear axle… I removed the original leaf spring perches and welded new once on the underside to lower the backend … Seems this is forbidden in Belgium as it’s a cast-iron axle… So I’ve been chasing the internet/used parts sites/etc, and I finally found another 12-bolt truck, which seems to be like the one I have … I still have to see if my axles fit (new rear came with 6x5.5, while I have 5x5 wheels) , but the width and the spline count are ok…

When I opened the diff, I saw something weird mounted on the carrier … searched the web, and it looks like it’s a G80, but then I only find it for 14bolt rear ends …
Does anybody have more info on this ?
Is it good or should I throw it out ?

[1project2many]

Hello,

I'm sorry to hear they're making you replace the axle. Will the Belgium DMV consider information showing your axle is not cast iron? The center of the housing is cast steel, while the tubes are made of mild steel. If you clean the paint off the tubes you will likely be able to see where the ends have been welded on by the manufacturer. I may be able to dig up some technical information from GM or from or an axle rebuilder that will verify this.

You're looking at a Guv-Lock centrifugally actuated positive traction differential (GM Option Code G80). If the axles are turning at significantly different speeds, a spring loaded weight will engage linkage that causes friction clutches to engage, providing traction to both tires. These are not durable positraction differentials and will most likely fail if you are fond of "burning rubber."


Technical stuff begins at 11:07.
https://www.youtube.com/watch?v=EsvWCFi_IPk

[leegreen]

I agree with 1project2many. the axles tubes are welded from factory, to the housing, to the leaf mounting pads and to the brake mounting bosses.

They can be welded.
Obviously your life could depend on weld quality.

Good luck convincing your DMV they are wrong!

The G80 rear axle carrier is common option on all sizes of Chevrolet light trucks. It only locks at relatively low speeds for traction.

The one on the picture scares me, looks like it has had moisture in it.

[mr48chev]

That rear end in post 18 looks like it has been under water.

Here is some info on that locker.

[mr48chev]

As others said, the axle tubes are not cast iron but mild steel as all GM axle tubes except maybe the odd one like the Olds 442 with the aluminum center section. I don't know i that one is steel or aluminum tubes.

Before I tore anything apart I'd go higher up the food chain above that particular inspector. The only real issue should be the quality of the welds and the U bolts being correct for the application. I understand that Belgum and some other European countries are hell on wheels when it comes to chassis mods and welded chassis pieces is an absolute no but that is usually Modified control arms and steering linkage.

In these photos of a 12 bolt truck rear off Ebay you can clearly see that the axle tube slips in the cast housing a ways and see the part line. Can that part line be seen on yours or has it been filled and prettied in a way it no longer is visible?

[Iceman_70]

Thanks for all the great feedback !!

Yeah, the rear end is toast or like we say in Belgium 'choco'. When I removed the axle, the bearings fell apart and the tubes have a lot of mush ...

I just reached out to a professional welder, who also restores oldtimers, to see if he has more info on what is allowed or not... or why they disapprove welding on an axle.

just to clarify the process a little more, the inspector in the local branch checks the vehicle and makes a report/pictures of the modifications. This is being send to a commision of the 'Mobility Department' (part of the Flemish Governement). They then review and judge what is 'safe' or not ...
For example, the IFS/power steering rack/disc brakes/brake booster is accepted if I can show "a certificate from the manufacturer of these parts that shows that these parts are suitable for this type of vehicle"

I also need to go to the official Chevrolet importer in Belgium, to have the VIN corrected on the frame ... as the VIN on the title starts with '3K' and the one on the frame isn't ...
Now, I do understand it all has to be safe for myself and others drivers on the road, but at the same time, they should be happy that I spend all the time and money on restoring one of these classics...

Again thx for the feedback and info. The knowledge and experience that is gathered on this board is huge !!

[mr48chev]

In the GM Heritage center vehicle information kit for 56 Chevrolet they do not show 3K as a model.

They also do not show that the factory ever stamped serial numbers on the frame. I have never seen a complete serial number FACTORY stamped ib abt 47/55.1 frame or 55.2 to 59 frame.

3 K would simply mean that it was for a 3 series truck built in Kansas City to my knowledge. I'm by no means a 55.2 / 59 expert though. I can't even tell you who to go to for exact info. Seth Doulton may know but the frame serial number thing has floated around for years and all of the factory info shows that they never had serial numbers on the frames.

By the photos the serial number should read 3B 56 K --------- if the truck was built in Kansas city Model number, year assembly plant, production number.

https://www.gm.com/content/dam/compa...olet-Truck.pdf

[Iceman_70]

Originally Posted by mr48chev

In the GM Heritage center vehicle information kit for 56 Chevrolet they do not show 3K as a model.

They also do not show that the factory ever stamped serial numbers on the frame. I have never seen a complete serial number FACTORY stamped ib abt 47/55.1 frame or 55.2 to 59 frame.

3 K would simply mean that it was for a 3 series truck built in Kansas City to my knowledge. I'm by no means a 55.2 / 59 expert though. I can't even tell you who to go to for exact info. Seth Doulton may know but the frame serial number thing has floated around for years and all of the factory info shows that they never had serial numbers on the frames.

By the photos the serial number should read 3B 56 K --------- if the truck was built in Kansas city Model number, year assembly plant, production number.

https://www.gm.com/content/dam/compa...olet-Truck.pdf

Apologies ...It seems I've made a mistake... It's 3A instead of 3K.
My vin on the title says 3A56Kxxxxxx, while on the frame I have 56Kxxxxxx...

Thx for the GM heritage link ... very usefull info