The Stovebolt Site Forums The Shop Area Driveline Chevy AD Rear Axle Placement

Got the rear springs hung and the rear axle (a Blazer axle) mocked up. Isn't this too far forward? I don't know because I've never seen a bare AD frame and axles but it seems so.

Please advise!

Rear Axle

Still got the old housing? Measure from the center of the axle to the hole that the bolt in the center of the springs fits into. That will give you the offset you need to get the new axle close to the wheel well.If you ever do this kind of project again I use a plumb bob to mark the frame then pull the housing out. Line up the new one with a reference in place. Saves time.

Steve, Never had a housing to begin with.

The wheel base for the half ton was something like 116". I take it your front axle is still attached?

You can see the bump stops mounted to the frame and they show your rear end is not mounted right. The original rear end had spring pads that were not centered on the rear end, they also had a bushing in them that allows the rear end to pivot as the rear end moves up and down. This is needed because of the torque tube. Your best bet is to measure the wheelbase as truckernix suggested. This will get your rear end in the correct place.

When measuring wheelbase, what do you measure from and to what?

wheel center to wheel center

Bill

Wheel base is the best way. Two things to keep in mind. One, you must be the same left and right or you won't track straight. Two, keep in mind the anchor that was part of the torque tube system you will need that to control spring wind up under load. A good reference might be the center of the king pin. It won't move the spindles will. If you can, use the carpenters trick and measure the diagonals. Left front to right rear and the same for the other side. This will show any minor adjustments. Good luck and show us what you have done.

When I got the frame the rear axle wasn't really attached and was from a 50's car.

The front axle is in place.

So I measure 116" from the center of the front wheel to the rear?

Is it possible I put the springs on backwards?

Not sure what spring anchor is or if you still need it? (assuming Blazer rear end means you are going open drive shaft) Also I believe your rear end will "rotate" rearward when weight is applied. The shackles will possibly swing, about the hangers, to the rear a little under load of the vehicle sitting on it's tires. (not positive about that). The wheel base is what you are looking to measure, as stated, under load, because you did not bob and mark. (Those are not two guys.) If the perch/spring locating pin is NOT in the center of eye to eye, you CAN put them on backwards.

I am not sure what the spring anchor is.

There was nothing to mark in the first place.

If the bump stop is any indication of correct location, it would take a lot of load to move the axle that far backward.

This might be helpful. At least you can see that the pin is offset.
http://www.truckspring.com/products/GM-Pickup-Replacement-Leaf-Spring--(8-Leaves--Rear)__22-195.aspx
And you get some measurements that might be helpful.

Now why did the link come out that way? Just copy and paste into your browser. It should work.

I don't know what spring anchor is either but we will both learn from steve-H. I should have said "because you were unable to bob and mark". Not your fault. Straighten your spindles and measure each side. NOW use a plumb bob to mark each side of frame, then use bob again on each side to align center of axle tube.

That does help. The pin is offset. Perhaps I hung the springs backwards and the long side goes towards the front.

I'll ask again to be certain - I'm measure from the front spindle/kingpin back 116"?

If the king pin is not canted and is on the same vertical Centerline as the spindle, yes, either one. If they say AD is 116" then that's the number. Another reference point is on page 129, 1953 truck specifications. Gives a dimension from rear of frame rail to Center Line of rear axle of 34 x/x, can't read it. Someone may have original copy. By subtracting the other two, looks like 34 7/8". you don't have to be dead nuts on it, just Gov'ment close. 34.875 +/- .125 is close enough.

Well that's a relief, because nothing on this thing is dead nuts. It is as budget build as it gets.

I have the original manual at the shop - I'll check it out tonight or tomorrow.

From the pic it looks like you are doing above a budget build. Nice work, clean. I think the anchor is the bushing they speak of that is part of the old spring to axle tube, torque tube method. I think maybe you are abandoning that? and going to just Ubolts? Blazer style? Rear disc? and you are asking about shocks on another thread, you're going hog wild! Not sure what shock mounting you brought over with the axle. Anyway there are plenty of aftermarket ways to install shock mounts. You are at a slight disadvantage without welder but bolt on is no big deal. Search the net for 47-55 shock mounts and rear-end swaps and universal shock brackets... there will be guys on here that have done close to what you are doing. You look like you have a whole lot of work to do in a whole lot of areas.

Thanks man. It is clean but nothing fancy. All the money is spent (mostly), now it's just assembly and figuring things out.

NO torque tube. Blazer rear end w/ disc brakes (got it for free). No shock setup on either the truck or the axle. I do have a welder, though, so...

I was thinking of just welding shock bolts onto the spring pads for the bottom then running a bar across the frame rails with 2 more shock bolts going through it. Those universal shock brackets are both pricey and I want to move/keep the shocks on the inside for clearence sake.

Edit: I just realized something else: does the stock rear axle go on top or under the springs?

Here is a shock mount I did long ago, the hose clamp is just to hold it while welding. It's being welded on near bottom of tube.
Shock Mount1
Mount2
I don't know many specific answers about AD. I'm a TF guy but the fab stuff I like. What did the blazer have for shock mounts on axle? Your welding mounts idea sound doable. You need a shock to use while mocking or you will make a mistake and bind it somewhere when you buy some and try to mount.

I don't recall any shock mounts on the Blazer axle. I ground off the spring pads and maybe they were attached to that but I don't recall.

What did you use for axle spring seats on the new axle? ClassicParts carries weld on axle seats (perches) that have two holes to choose from that the leaf spring bolt head fits in. One hole is in the center of the seat and the other is off-center. I used the off-centered hole and everything lined up perfectly. The off-center hole accounts for the off-set rubber-mounted axle attachment of the torque tube setup. If your current axle spring seats lack the off-centered hole, you can drill a hole in it to match the hole location in the ones sold by Classic parts. If you go to their site, they have a good picture of the holes.
Carl

I got seats from Northern Tool - trailer seats for 5k loads (just in case ). They do have offset holes on each side but I think I am too far off to make up for it with that.

Jr. we are all waiting for you to measure, will you hurry up?

Haha, it won't be til later tonight or tomorrow. I don't live by the garage. :/

I measured it. The axle right now is 112" inches from the front kingpin. It's off about precisely the difference in the length of the spring from the spring pin.

So I have the springs hung backwards which really pisses me off, because I payed such close attention to replacing the shackle bushings exactly as they came out of the springs. Now, to reverse the springs, I have to bang out those bushings again and put them in opposite ends of the packs.

can't you just turn them around and mock up to be sure first?

The shackle bushings are smooth bored on one side and threaded on the other. I hate the shackle set up - had I the money I'd get the TCI complete spring it or something just be be rid of the original shackle setup.

Edit: I may try to find some poly bushings this time around and use them in place of stock brass bushings.

I am out of this loop. Bushings are rubber, they have sleeves in them made of metal with a bolt passing thru with a nut. That's what I would switch to if you could, but I guess you have to use the AD stuff, which I am unfamiliar with.

At this point I am thinking a bushing is a bushing - the poly with the metal lining is likely an upgrade, considering it's standard on many vehicles that use shackles. So if I can find the in the correct dimensions I am going to use them.

I would reconsider using the factory type bushings for your springs and shackles. The originals lasted for many years. Save your money for other parts.

My concern with the shackles is that they are held on and in place with the center bolt and nothing else. That and the fact that it's always metal on metal. They certainly did last a long time but having taken apart the truck and having had to replace all the shackles and the bushings - there really is no way that poly bushings like those used in off road equipment is not the way to go.

They have grease fittings and if properly greased they will last forever.

Well that's true as well. Here's hoping I don't damage the spring side bushings banging them back out again.

Can anyone say for certain whether the axle sat above or below the springs in a stock AD?

Above. You can use a piece of threaded rod and a socket and press things in and out. It shouldn't take a hammer to do it.

They had to be hammered in so I am guessing they'll have to be hammered out.

Axle set above springs on 3100.

Well I didn't hurry but last night I tied the axle to the springs so I could put the wheels on and roll the thing around easier. I used the 34.87" from rear frame as the guide but this is way off.

http://i.imgur.com/bsW4BTr.jpg

I used the measurement from the rear only because it was easier to be precise than to do it from the front but once on even a rough measurement from the front shows it's off by about 3" from 116".

BUT, here's another pic from the internet. The line marked is a plumb line marking of the original axle.

http://i.imgur.com/FBub9cM.jpg

This mark is almost precisely where mine is/34.78 from rear frame rail.

This pic is from someone who used a TCI spring and shock setup on their rear:

http://i.imgur.com/K0awx5w.jpg

This is where it would look like if it were 116" from the center of the front kingpin. This is also what I think is correct. My driveshaft is from a Van and is a well used junkyard find and happens to be precisely correct for a T5 swap into an AD and the only way it works is if the rear axle is in the position as pictured in the last pic.

Second pic is a bit forward from stock. It might be centered in the fender though. There is a bit of offset to the fender on the AD truck. I don't know why but it is the way they came. Any way, if you have the housing square to the frame you should be OK. You are not working on a "restoration" at this stage of the game. So a little bit of visual change won't hurt. Make certain the housing is centered right to left and square to the front axle and you should be good to go. Now you must get the pinion angle right so have fun.