The Stovebolt Site Forums The Shop Area Driveline Pinion Angle Chevy 12 Bolt Swap

I swapped a chevy 12 bolt rear91969) into my 1950 3600. The rear axle angle is 12 degrees up. Has anyone experienced this amount of angle before? Can shims fix 12 degrees or must perches be modified? Based on the rear driveshaft, i think if i can get rear axle to about 0 degree, that would give me about 3-4 degree pinion angle, in the end. Any thoughts, experiences?

What's the angle of the transmission output shaft? 12 degrees up is a lot to compensate for, probably more than shims can manage. There's an article in the Tech Tips section that deals with U joint angles and such, and since it's part of a Dana/Spicer tech bulletin, it's definitely more than just hearsay.

http://www.stovebolt.com/techtips/driveline/setup/index.html

For some reason the links in the tech tip are not working, but you might be able to look up the Spicer articles mentioned on the web. Good luck!
Jerry

Sorry we haven't gotten the links fixed.
Here they are.

Info

12 degrees up compared to what? The only pinion angle you need to be concerned with is pinion to driveshaft. The other angle is driveshaft to tailshaft of transmission.

Also, is the full weight of the truck setting on the springs?

Welcome to the Bolt!
This part of your post indicates to me that you need to do some homework on how to set up your drivetrain.
The first thing you need to measure is the angle in degrees away from parallel to the ground of the crankshaft/transmission output shaft. Once you have this measurement, you will need to match this angle with the rear end pinion angle, within a degree or two. In other words, the crankshaft/transmission output shaft and the pinion shaft should be very nearly parallel to each other. If this is not done, you will eat u-joints like I eat Halloween candy/pumpkin pie/Christmas cookies/Easter jelly beans (I can go on, but you get the picture).
Carl

This basic info is in the previously linked tech tip and more detail in the Manuals described, correct links for those provided in my post above.

Greg, the Spicer links would not open for me, is my computer?

No, the links in tech tip are probably broken, we're working to fix them
In the meantime this should do it, quoted from thread about the issue I linked to earlier
Does this work?

Hi,

I guess i will ask the question another way. Has anyone done a 12 bolt ( or any axle) swap into a AD 3600? If so, what pinion angle did you end up with or decide on based on welding spring perches or shims? And how has it been working out.

Thanks
Rob

As stated above, pinion and transmission output shaft should be near parallel in loaded condition, easy to measure and setup. That is all that matters. Most transmission/engine combinations are inclined about 3 degrees down at the rear, so, if the pinion is about that to start with, you are on the right track.

Ed

The "frame checking instruction" for the 3600 in the factory assembly manual shows the crankshaft at 3 degrees, 42 minutes, 9 seconds. How good is your level? I used a magnetic slope indicator which isn't very accurate, but since the angle changes with loading and going over bumps in the road, I thought it sufficient.

The U-joints don't care what angle from the ground, they care that the front joint is bent the same as the rear joint, within a degree or less. This helps the shaft run smooth and u-joints last longer.

So again measure your actual situation with truck loaded as it usually is, and weld spring perches to suit, make transmission and pinion parallel. (For more details and exceptions read the manual)

I'll be following this thread.

I am doing an axle swap in my '50 3600. I went with a 10 bolt 8.5 ring gear rear end out of a ZR2 Chevy Blazer because it's 63 inches wide wms-to-wms.

I'm going to weld up my spring perches so they match the stock axle perch/pinion angle (haven't measured the trans or perch angles yet) and when the truck is ready to drive I'll re-measure when it's loaded and use shims to get it right. I plan on lowering the rear about 2.5 inches, so I already know I'll have to shim it a little to get it right...

If you want an easy explanation of driveshaft angles and WHY you need to get it right, check out this Youtube video:

Pinion angle explained

It's better if you already have to weld perches on to weld them at the correct angle, not to weld them and plan to use shims.
Assemble the axle with perches in the truck, not welded, adjust angle and everything the way you want it and just tac weld the perches in. Remove axle, check that perch angle to pinion is the same each side, cut them loose and match best average if necessary. Weld them and reinstall in the truck, should be perfect and require no shims with this method.

Totally agree with Grigg, do not weld them first. Finish up the assembly with the axle floating in the perches and get the weight on the ground in ready to drive position.

Loosen the rear u-bolts and adjust the pinion angle to match the transmission angle. Thats all that matters ! Tack weld in place, remove axle and finish welding.

Stacking shims is risky if the center bolts in the springs use a short head. Then you end up with nothing to locate the axle to the spring perches because the shims are taking up all the room.

Go to Harbor Freight and purchase one of these, http://www.harborfreight.com/dial-gauge-angle-finder-34214.html
Its cheap and easy to use and the only tool you need to set up a driveline.

You can get a lever and angle app for your smart phone, use it to check angles between/while reading the instructions on the same screen.

It's amazing how accurate that smart phone angle app is- I used it to set up an IRS rear end one time and it was dead on when I got the car to the alignment shop!

I guess there are no short cuts here. I was hoping to get at least ONE THING FINISHED on the truck, rather than have a million things half finished...

My axle OD is 2.62" at the perch location, and my rear springs are 2" wide (the axle tubes on this rear end change diameter back and forth from the diff to the axle flange). Off the shelf perches will not be a perfect fit (2.5" or 3" tube OD perches). I was contemplating how to build my own, but am concerned about getting everything centered/equal/straight if I do make them.

The centering hole and the axle cut out one each side has to be perfect in every dimension & angular relationship in order to get the axle lined up perfectly with the frame. I don't know that I possess the equipment to build perfect perches on my own. On the internet I've seen some simple ones that guys have whacked out that apparently work, but the idea of having my rear axle out of alignment bothers me a great deal.

Do I just make the best ones that I can and then use a tape measure from the axle ends to the front of the frame to get the alignment right prior to welding them in? What are the chances of my frame even being straight? Small to none, I would bet. Maybe it's all a wash in the end? It's not a race car after all, but I will be driving this truck on the freeway.

Any ideas?

Buy the perches for 2.5" axle tube and modify slightly to fit your larger tubes.
I recently did same for my 14 bolt with 3-5/8" tubes and purchased 3.5" perches (1/8" difference, I might have actual measurements off). When I get a chance I can link a picture or two, until then look in my photo link below and folder with axle stuff.
You can do a nice enough job with a paper template and an angle grinder or file, it's not much material to remove.

Ok I will answer your question. Before you do any welding or cutting off rear spring perches do this. Put the truck on the ground with the tires on. Get an angle finder atch above or below the rear of whatever transmission you have and determine the downward angle. Say its 8 degrees down. Next measure the angle on the nose of the rear, you say its about 12 degrees up. What you want to achieve is the front and rear angles to be within 2 degrees with each other. Or 8 down and 10 up, so that would get you within 2. You don't want them parallel. So rear 2 degree shims above or below your leaf springs, if that is what you have would do the trick, that would bring the nose of the rear down just a bit. THen tack weld the axel . Ps make sure the rear is square sitting on or under the springs.

Grigg- your perch modification is really nice- and I can see that you had some really nice equipment at your disposal to to it the right way...this is exactly what I am concerned about- not having that kind of equipment to get the arch for the axle perfectly matched on both sides, and perfectly aligned with the perch center hole. If I have to enlarge an "off the shelf" perch with a grinder or file, the centering hole won't be exactly centered in relation to the axle cut-outs...

52pu- The perches on my new axle have already been removed. I'll be putting perches on top of the new axle because it's a 3/4 ton truck. It is my understanding that the transmission output shaft thrust line and the differential pinion line need to be parallel. I'm going to fit everything up after I get the engine/trans/cab and bed back on the frame, so that the suspension is loaded properly and then set it up and tack weld. As for the axle being "square sitting on or under the springs"- that is what I am concerned about- creating hinky perches and NOT having things be square...

Draw out the difference in diameters with a compas on a piece of paper, it's not much difference and well within what you can do with a file or grinder to a scribe line, quite accurately. No milling machine necessary.
The perches wrap around the tube well less than 1/2 way. Even at half way around your 1/8" difference in diameter is 1/16" on either side front and back. No need to take any material off the center of spring perch, so adjust radius tapering from less than 1/16" front and back to nothing at the center. You can cut out a piece of card stock same as axle tube diameter or setup compas and scribe or trace or swing the desired radius on store bought perches. Lay it out so same amount is removed front and back of the arches and alignment is nothing to worry about.

I think you'll find that easier than making perches from scratch yourself, and cheaper than having something special made to your drawing.
Trust in your ability or ability to learn and give it a try.

Swapping any axle to any truck does not change what Carl said.(and others) You just swap it in and do what is necessary to obtain equal and opposite angles at 3-4 deg.(parallel). That's how you "swap"/replace an axle. Simple as that. Not to be rude, but this question should have been asked before you swapped it in and got 12 deg. The swap is usually done by cutting off the old perches and welding on the new ones at the proper angle.
My suggestion is don't do what I used to do when I was younger. Don't chase this all over the yard with "fixes", just redo it.

NorCal, listen to Grigg. You are overthinking this. Grind, dremmel, sand, whatever to get perch to fit nice on the tube diameter. We are only talking 1/16 radius difference. So take off a 1/16 off of the perch radius. Do this WITHOUT bed installed. It's much easier to mock it up. It's all 85% self locating. Forget all that "loaded" stuff. Has nothing to do with it. Make the off-the-shelf perches fit the tube while spring pin is in hole, axle rotated to achieve pinion angle, axle centered on frame and wheel bases within 1/8 of each other. Tack them on while springs are on them. Use the weight of the frame/springs or.... clamps, magnets, hose clamps, vice grips...whatever will hold it all while tacking.
Make sure you grind to good clean metal all around the tube area and clean the perches before you tack. Make sure you have a clean metal place near both perches for the ground clamp. Always make sure the jaw of the ground clamp with the cable attached, is on the best ground spot.
I would then sit down and stare at it and think about it for awhile. Measure all one more time. Go back and forth from one perch to the other so as not to heat the tube and melt a seal or heat damage a bearing. The tranny tail and the pinion yoke ARE to be parallel and 3-4 deg. If it was possible to hook up the drive shaft, that would be a real good check of X, Y and Z axes and pinion angle before final weld.
When you are done, touch up the paint and move on. No shims.
P.S. What does this mean? "the centering hole won't be exactly centered in relation to the axle cut-outs..."

"Lowering the rear"? You are on your own there.
I apologize for too much detail if you are experienced already. It may be useful for other users "down the road".

I really appreciate all the input here, especially since I hijacked this thread....

bartamos, by "centering hole won't be exactly centered in relation to the axle cut-outs"- I mean that I am (or was) concerned that when I re-radius a perch that I will move the radius to one side and the center hole in the top for the spring pin will no longer be right at the center of the top of the radius (one side of the axle will end up further forward in the chassis than the other).

Grigg- yes, I tend to overthink everything I am doing, especially when I am doing it for the first time... I've done a few restorations and a fair amount of garage fabricating with crude tools (no vertical mill or lathe), but have never messed with the suspension geometry by cutting and re-welding anything before. I see what you are saying- I'm going to give it a go as soon as I get my frame blasted.
Thanks guys,

Dave

Dave, I wouldn't give to much thought about be off a little. Look at the front suspension and how may joints there are that can move, then add in all the rear joints that move. Assuming every one of them was dead on tight, then you might worry about the 1/16" you are grinding out of the perch, but since we all know the spring pins and bushings are loose, whats a 1/16" really going to do?

Lots of folks drill new locating holes in the perches to center the tires in the fenders, most do it by eye and still get down the road OK.

Pinion angle changes with suspension movement, thats why you need to have full weight of empty truck on the axles. The pinion angle needs to stay in the working limits of the u-joint when full loaded or full extended.

Understood Dave. You will be fine. Grigg didn't say you are overthinking, I did. BTW: The loading, as it pertains to pinion angle, is referring to torque load/axle rotation during acceleration and braking and bumps. Not the load in the back of a pick up. Most of the chatter is about high HP cars and pounding thru the gears while accelerating as fast as possible. A Chevy motor is designed at 4 deg down at tranny with carb level. So your pinion yoke should be 4 up. (All things normal and stock).

As far as centering hole comment. Look at the assembly this way: The perch is flat up against the spring with pin in hole. Let's pretend perch is welded to spring. (you could actually clamp them) Then the perch radius rests on the tube. The tube/entire diff is free to rotate and slide while aligning and centering. You would have to really screw up the 1/16 radius modification to make a problem. The reworked radius does not have to be perfect. It may land on the tube and have a few gaps here and there. Call them weld gaps.
The truck is supposed to be at ride height when all this is done. I don't think the leaf springs on a 3/4T will move much with the bed on, and if they do, it won't rotate the axle. Up to you. So much easier to work on without. Get two 200 lb guys to stand on frame while tacking.
The off the shelf perch will have a hole right on the center line of radius. If your spring/truck is designed with spring pin to be on center of tube, you are good to go. Keep checking the WB to be near spec.

Thanks guys. I'll post links to pics when I start the process.

Excellent.

To follow up on the earlier discussion of adapting spring perches to fit a little larger diameter axle tube.
Here is the before and after of what I was working with for a 14 bolt axle https://goo.gl/photos/6mnKfuwDs65uqf568
Purchased aftermarket spring perches for an IH Scout because that is what is available for 2" wide springs, unfortunately for 2.75" axle tube. The 14 bolt has 3.375" axle tubes (I had dimensions wrong earlier).

Anyhow that picture illustrates the small amounts of material to remove to adapt smaller diameter perches to a larger diameter axle tube.
I changed it 5/8" and you can imagine 1/8" change would be very slight; short work with a decent half round file.

Of the several aftermarket spring perch choices these are what I choose and they are very sturdy and nicely made, right on dimensions and square, also longer than many perches available including ones sold for trailer axles. Another advantage is they include alternate center bolt holes in top which for an AD truck would allow you to center the rear wheels in the fenders if you so choose.
http://www.ruffstuffspecialties.com/catalog/springperchantiwrap.html

Grigg

I am converting my torque tube drive line to an open drive shaft. I'll be cutting of the spring perches and using a pumpkin from a '56 3100 (3.90) which is a direct bolt-in on the '47. The three-speed on the floor will be replaced by a SM420 transmission.

While researching the pinion angle set-up, I came across this link from the Hot Rod Hotline. It does a nice job of explaining what's going on, how to set-up the pinion angle correctly, and includes some easy to read pictures/graphics.

Grigg- that is comforting to know...

Also a funny thing- that's the same place I ordered my perches from... I'm using an older CJ perch that is 2" wide for a 2.50 axle. I also got my axle shock mounts from them.

Only problem is the perch pin hole is 0.60 and the leafs spring pins on my 3600 are 0.50 diameter. I guess I'll have to sort that out as well..

You could look for different spring bolt with larger head? Or make a little bushing and tack weld it in the perch.

The trouble with articles like the HotRod Hotline one, is it is written by yahoos that are not as careful as us yahoos try to be. To say truck needs to be on level ground is wrong and to start adding shims under transmission mount is wrong. (tilts the carb/float bowl out of level.) Maybe the motor shown is fuel injected. It also says one cause is "Improper phasing", it never mentions it again and does not say what it is. (It's the matching of the Ujoint yoke caps, VERY important!). You can install the slip yoke splines wrong and cause an out of phase condition. Many drive shafts and slip yokes are marked at the factory or shop to insure reinstall.

Albeit the blog is written to fix a vibration, it is not how to set up a motor/differential from scratch or adding/swapping one or the other as in our case here.
Folks are paid to write an article, they read a bunch of web bits and pieces, some of which is wrong and repeated over and over, and they put it all together in their own professional writing words...and it gets all screwed up.
Many articles talk about 3 deg, I don't know where they get that. GM has it's motors/tailshafts at 4 deg down from carb mount surface and we are supposed to parallel that at pinion. Forget 3 deg as a number for leaf spring trucks with stock Chevy motors. If it's a Chevy motor within our era's, and not at 4 deg, it's wrong. This is where level surface comes from. As Grigg said, the ujoint angles don't care about level ground. You are looking to match and be opposite. The level ground IS important when setting up a motor because the carb fuel level needs to be level to ground as we expect most driving done on level roads. It's a baseline for setting a Chevy motor. You set your chassis on level surface and check the intake manifold carb mounting surface for level or same bubble as garage floor. That's where that gets mixed up with pinion angle.

Its been a few days and see the post was hi jacked, but that's cool, if the thread helps others that's ok with me.
For my project, I've since removed original perches (12 degree up) and will re-install rear with new 2.00" perches and then will re-install and get a happy angle, 2 or 3 degree, then tack the perches, remove rear axle, and stagger weld the perches, then re-install.I'll then change out the UJoint on driveshaft for the 12 bolt rear acceptance. Drive Shaft length looks really good so far, but will determine when I re-install axle for tacking the perches.

Not hijacked. Same topic, pinion angle/diff swap. Glad to see you are moving forward. You are redoing it right, good job.

Similarly here on this forum and others not everything posted is correct.
The end user should always consider that and do their own research (beyond the forum) coming to their own understanding and conclusions.
Perhaps best we can do is site sources for hopefully more reliable info to support the opinions and understandings we try to share here.