Mad beyond all comprehension

[CVA59]

I swapped out my old 6 lug for a 86 5 lug rear end. Seems simple enough right? Not a chance! My dad and i both have been fighting this POS all day and still cannot get it lined back up. These sorry trailing arms are apparently all out of whack. I know when i took the original rear out the left popped/jumped (like it unsprung itself). I assume the original was bound up all these years. PROBLEM is now: When we get the rear centered side to side it is out of plum with the front end. When we get it plum with the front it is out on the side to side. This is all being done with the springs and everything still installed. All i did was remove the rear end, clean the saddles and re-install the 86 rear. Now, He and i both have been building cars, fabrication, modifying and retrofitting stuff like this our entire life. We have tried every thing possible and since there are no adjustments on this stock rear we are totally lost. I am mad beyond description right now and my patience is totally gone. Plus the fact that it is 5 million degrees outside doesn't help. So, how do i overcome the impossible here?????

[jbon64]

did you check side to side front to back measurments on the original rear ? it's possible that the rear was a bit out of align from the factory to begin with . factory specs in the 60's i assume were pretty lenient to begin with , and probably more so for a truck . another thing to maybe check would be to see if one of the trailing arms are bent .

from one carrier vet to another (cv43) i'm sure you'll track it down

[lakeroadster]

I would think keeping it square should be your first priority, otherwise it will dog track.

And as far as not being centered, how far off is it?

[low79fx]

Has truck ever been in an accident,is frame square? Things you probably thought of already I guess. Good Luck!!

[raycow]

If the replacement rear is an 86, I assume you had to weld on the trailing arm mounts? If so, they might be out of position. How about comparing them on the two rears?

Ray

[CVA59]

We cannot find any evidence of an accident on this truck. I have not welded the axle perches in place yet. Everything is put together and snugged up so we can move it and adjust as needed. The left side is 3/8" further to the rear than the right side. There is no adjusting the u bolts or perches. I have tried to spread and move the trailing arms with no luck. Something is really out of whack on this truck from the factory i believe. As far as i can see the trailing arms appear to be straight or straight as they ever were, LOL.

[protrash64]

I would offer that center is relative to the hite the rear is currently sitting. Is it hanging on jackstands? The panhard centers the rear and it will swing right to left depending on the hite of the axle to the frame.

I had to make at least 3-4 adjustments to my aftermarket panhard to keep my tires from rubbing on my air suspension. 3/8's is about the total movement IIRC. It would hit one side if up and the other if down; I had to find the sweet spot.

[CVA59]

currently all the weight of the truck is sitting on the trailing arms. I blocked the truck under the trailing arms just forward of the u bolts.

[Captainfab]

Have you looked at the trailing arm crossmember to look for signs of movement? A slight bit of movement at the crossmember when extended out the distance of the trailing arm will add up to a fair amount. As already mentioned, I wouldn't be surprised if what you are experiencing was within factory tollerances. It almost sounds like adjustable trailing arms and panhard bar would be the best way to achieve a perfect alignment of the rear end. Yep I know....there's more $$$$

[CVA59]

LOL, thanks Fab. I will try it again tomorrow and see how it looks after some rest. Maybe i will see something i didn't before.

[protrash64]

I really dont think you have an issue if you cant find any damage/loose parts. I'd bolt it together and take it for a spin and see how it rides. The only way to keep the rear absolutely centered would be to install a Watts Link.

[chevy_mike]

I did the same swap using a '73 rear end. One thing you need to do (in my opinion) is to remove the springs. You don't want any affect they could have influancing things. Also, you never said what panhard bar you are using. If stock, you'll have to fab a mount but do that after the rear end is centered. I used an ECE adjustable bar, which connects the axle side to the trailing arm/axle mounting point.

With the frame up on jackstands, put the axle approx where it will be. Rotate the arms up and loosely put the replacement saddles (I am assuming you are using replacement ones and not cut off your old ones, that will make it difficult to get correct measurements) and u-bolts in place. With the arms in a natural "at rest" position, measure from the backing place to the u-bolt. Check both sides. You want this measurement to be the same WITHOUT trying to pull the arms over. You want them to stay in a natural at rest location and get the axle centered. Once centered, set your pinion angle (I used the same angle as the stock rear end). Now you can double check all your measurements/angles and once correct, tack your saddles.

Pull your rear end out and burn those saddles in. As a side note, I had also replaced the front bushings in the arms so they would not have 40 years of slop in them. This helped to keep the arms in the correct plane. Setup your panhard bar AT ride height and you should be good. Springs are the last thing to go back on.

You can check my '68 build for pictures showing what I did. Good luck.

[CVA59]

Thanks Mike, I will remove the springs and try it again just as you have described. Those springs may very be what is preventing me from getting the measurements i need.

[raycow]

Have you taken any diagonal measurements on the frame to see if it is out of square?

Ray

[CVA59]

Yes, the frame is pretty much true.

[CVA59]

Originally Posted by chevy_mike

I did the same swap using a '73 rear end. One thing you need to do (in my opinion) is to remove the springs. You don't want any affect they could have influancing things. Also, you never said what panhard bar you are using. If stock, you'll have to fab a mount but do that after the rear end is centered. I used an ECE adjustable bar, which connects the axle side to the trailing arm/axle mounting point.

With the frame up on jackstands, put the axle approx where it will be. Rotate the arms up and loosely put the replacement saddles (I am assuming you are using replacement ones and not cut off your old ones, that will make it difficult to get correct measurements) and u-bolts in place. With the arms in a natural "at rest" position, measure from the backing place to the u-bolt. Check both sides. You want this measurement to be the same WITHOUT trying to pull the arms over. You want them to stay in a natural at rest location and get the axle centered. Once centered, set your pinion angle (I used the same angle as the stock rear end). Now you can double check all your measurements/angles and once correct, tack your saddles.

Pull your rear end out and burn those saddles in. As a side note, I had also replaced the front bushings in the arms so they would not have 40 years of slop in them. This helped to keep the arms in the correct plane. Setup your panhard bar AT ride height and you should be good. Springs are the last thing to go back on.

You can check my '68 build for pictures showing what I did. Good luck.

Thanks a million Mike. Doing it as you described work perfectly. LOL, In all my years and the many cars i have built this is a first. I had no idea how finicky this rear suspension is to setup perfectly. It is a simple design but i see now that things have to be assembled in just the right order. It is all right on the mark except the pinion angle. I have jacked around and lost the original pinion angle. Does anyone know what it is?? Thanks again to everyone for your input.

[protrash64]

It should be similar to the output shaft on the trans. I say similar because I have seen it written as 'the same as the trans' while others have described the angle as being slightly less(down) because the pinion 'climbs' the ring and causes twist under acceleration and load, therefore adding in the extra degree or so needed to be 'the same'.

Hope this helps, some anyway.

[Captainfab]

I can get that angle for you tomorrow Zack.

[chevy_mike]

Glad to help. It's just a big puzzle and has to be pieced together in the right order.

I did mine long enough ago I can't recall what the angle was. I basically took my old rear end, set the axle pads to be level (with a angle finder) one once they were level, I checked the pinion angle. Then when I setup the new rear end, I just got the pad at zero and set the pinion to the same as I measured. Cake!

[chevy_mike]

Originally Posted by protrash64

It should be similar to the output shaft on the trans. I say similar because I have seen it written as 'the same as the trans' while others have described the angle as being slightly less(down) because the pinion 'climbs' the ring and causes twist under acceleration and load, therefore adding in the extra degree or so needed to be 'the same'.

Hope this helps, some anyway.

That's actully more true with leaf spring rears since the spring will wrap up under acceleration. With trailing arms, you don't get the pinion rotation as the axle is hard mounted to the trailing arms and cannot rotate. This is one reason trailing arms setups hook so well and handle so good (it's what NASCAR uses still). You don't get the loading/unloading as you play with the gas pedal.

[CVA59]

Originally Posted by Captainfab

I can get that angle for you tomorrow Zack.

Thanks Fab.
Zack

[Captainfab]

OK here's what I came up with. With the trailing arm mounts level, the pinion is up 14 degrees.