The Stovebolt Site Forums The Shop Area Driveline Setting Rear Axle Pinion Angle

I am in process of replacing my original HO52 rear axle with a Chevy 14-bolt.

I have the axle loosely in place with the new spring perches, U-bolts, and plates from Ruff Stuff and the next step is to set the pinion angle and weld the spring perches in place. Everything I read says to set the pinion angle at ride height which makes a lot of sense but my truck doesn't have anything mounted to the frame except the bare cab so clearly not the ride height it will be when fully assembled. I also do not have a driveshaft yet (pending final axle installation and measurements) so I can not install it and measure it's angle.

Most of the information I have found says the engine/transmission angle and the pinion angle should be within 1 degree of each other and the engine/transmission should be angled down 2-3 degrees. When I set up my engine and transmission mounts I aimed for 3 degrees and believe I am pretty close to that. If the pinoin angle should be the same then I should be aiming for 3 degrees but I also read that for leaf srpings the angle should be 5-7 degrees leading to some confusion.

I do have a 2 post lift but the lift points being on the frame makes the ride height issue that much worse.

Any recommendation regarding setting the pinion angle would be appreciated.

Ideally you need full weight of the truck setting on the ground in ready to drive mode, if you can't wait for that, use straps and pull the frame and axles together as much as you think you need to. I would tighten the u-bolt as is and wait for the weight to be applied. You also need the driveshaft, the measurements for u-joint working angles measure off the driveshaft. Long driveshafts will have different setting angles then a short driveshaft.

Measure from transmission output shaft or engine oil pan and the driveshaft, you want 1-3 degrees difference, then measure from driveshaft to the pinion, you are again looking for 1-3 degrees difference. As long as both of these are equal or really close and you have more then zero and not to much more over 3, the u-joints will be happy.

Just remember, as you drive, the angles are always changing, so being dead on equal is not really needed. You are just setting a starting point where in most driving situations, the angles will still be close enough to each other that everything works as it should.

You do not need to add extra angle down just for leaf springs, that is for racing proposes only. The idea is under hard loads ( launch ) the spring warp and will throw the u-joints out range without the extra added in.

You can set the angles with ( trans pointed down, pinion up ), ( trans down pinion down ), ( trans sideways, pinion sideways ) really anyway you want, as long as both angle equal each other. Looking down from the top or looking from the side, doesn't matter, one view looks flat, one has angle. Or you can split the difference and have both sideways and up & down angles but still not going over 3 degrees combined.

U-joints speed up and slow down as they rotate with angles applied to the input and output shafts, less angle, less speed variations. Get really crazy with the angles and speed variation is extreme. As long as both ends have equal angles, the speed variation is canceled out and vibrations will be at a minimum. With zero angle, the needle bearings in the caps do not rotate which leads to short life spans.

Where did you get the information that the V8 engine/transmission should be angled down 2-3 degrees in a '49/'50 3600?
Was it explained why it would be better than being level? The inline six is set level as far as I can tell.

That’s a good video, Bill. Can anyone offer a suggestion on the easiest way to “phase” the driveshaft?

I remember trying to get it reasonably close, but with play in the rear and only so many splines up front…it seemed impractical to get it dead nuts.

I’ve never measured the angle, but my inline six is definitely NOT level.

My 216 doesn't set level. If you eyeball the carburetor mounting flange in relationship to the top of the head, it's pretty easy to tell that there's an angle between the two that lets the carb set level. But the crankshaft is definitely down in the rear.

I don't know what angle my engine sits at but it's not level. I noted in some Chevrolet manual or other not to shim the front motor mount between the mount and the frame. That statement assumes changing the engine angle was a common enough practice. Last time I pulled the engine on mine I found assorted front-end shim embedded in the grease on the cross member.There were marks worn in the frame where the shims had been. Rather than shim the engine when I last had to deal with U-joints, I shimmed the auxiliary trans to get the u-joint angles I needed. Spicer publishes a booklet detailing how to accommodate tandem axles, auxiliary transmissions, pumps, winches, power take offs, etc. I got mine free from the driveline shop I deal with. Lots of shimming going on. If the OP doesn't get the pinion set exactly right when all is loaded, said and done, there are tapered shims to the rescue. I have several left from some project or other and they are marked 3 degrees. They are intended to go between an axle and spring perch. These are also used to set caster on beam front axles.

I need to get out my angle finder to see if I need to get my eyes checked. I'd say it's a 50/50 proposition.

I'm voting on getting your eyes checked, Carl.

Here's a couple pics to help out. The engine is sitting basically level on a cart. The angle gauge reads about 4 degrees.

In order for a driveshaft to be in phase, the cups on both ends of the driveshaft itself should be lined up. If there isn't a keyed position on the driveshaft splines, then keep trying. If you've tried every position, then either the yoke or the spline end has been welded on incorrectly.

Thanks for all the information, especially the video (it's great).

I am not sure where I heard that the engine/transmission should be angled down to the rear about 3 degrees but I believe I have found the information to be consistent with any build information I have reviewed. It is not unique to our vintage of trucks or SBC engine installations.

Thanks Joe H for the clarification regarding the need (or lack of) for additional angle with leaf springs. I am certainly not building a drag car and don't plan on any full power launch attempts so I will plan to get my pinion angle as close to the engine/transmission angle as I can.

I think if I put the chassis up on the lift and place jack stands under the rear axle I can lower the lift to put the chassis weight on the axle and then using a come along pull the chassis down to approximate spring loads at "normal" ride height. I do not have a good feel for how much the springs deflect under normal loads but something will be closer than nothing.

Kevin, I think the phasing is really a function of the drive shaft construction assuming that the two ends are welded in place to the tube. If you have a telescoping drive shaft that has the front and back connected by a spline or multiple in-line drive shafts with a spline connection then phasing comes into play. I am anticipating a single drive shaft when I get that far and do not anticipate needing to deal with phasing concerns.

JW51 When I build a driveshaft I put the tranny yoke in a 3jaw chuck,put a machinists level on the u-joint hole set the other yoke the same way,tack it 3 places. Run the shaft if the yokes are wobbleing cut the tacks adjust with hammer. once it's welded is probably in balance too.On a racer can balance with a strobe light wheel balancer and hose clamps ! That's kinda crude though.

To help me estimate the amount of deflection of the springs to simulate normal ride height I am wonding if anyone can provide the frame height difference between an unloaded (tires just barely touching the ground) and normal with the vehicle weight for a 3600 with standard (not overload) leaf springs? I can guess but any means to confirm that I am close would be appreciated.

JW51 There is a lot of science in pinion angle,good thing I didn't know this over the years, have always eyeballed it from a creeper !! After about a dump truck load of driveshafts put thru my 8 foot Fay and Scott lathe,mine,theirs,neighbors they all worked. There is even one in my winch truck that has a schedule 40 coupling in it has hauled big loads since 82.

Look up the shipping weight of a new truck bed for your year and model, that will tell you how much weight to add. If you are really a numbers guy, look up the build information sheet at the GM Heritage Center and see what the deflection rate of the rear springs are. Deflection rate is how much weight it takes to compress the springs 1". Use the spring rate with the shipping weight, and you should get a pretty close number to compress the springs. Hard woods are heavier then softer woods, so add or subtract depending on the bed wood you use. My '37 has red oak, I think the wood weighs as much or more then the steel did.

GM Heritage Archive - 1950 Chevrolet Truck Data

Look though the link above, it has all the spec's you need including frame height.

For what it may (or may not) be worth, I'm not one of the "forget about the compensating 1 degree" folks. I learned long ago (over 50 years, sadly) what can happen if a driveshaft runs at the wrong orientation and it was a costly lesson. The heavier the load and the better the traction/lower the gears, the more certain it is you'll get axle wrap on takeoff. Just my 2 cents.

Joe H, thanks for the link. I have seen that book somewhere before (probably here) but need to remember that it exists. As typically happens the book dimensions for the 3600 are with differnet size tires than I have but I think there are enough dimensions that I can calculate the numbers for my configuration.

fixite7, thanks for the eyeball insight. I do not have a nice digital protractor like the videos like to use, just a carpenter's protractor and a bubble level but I would like to believe I can get within one degree.

Jon G, thanks for the insight regarding axle wrap, a heavy load start probably puts a lot of torque load into the equation given that there will not be any wheel spin.

I tried my trick of putting the chassis on the lift with jack stands under the rear axle to load it. Unfortunately moving the front of the truck up/down changes the chassis angle so fine tuning the setup may be a bigger challenge than I was hoping. I did measure about a 1 degree change from totally unloaded to chassis weight loaded rear springs. Without doing the math suggested by Joe H I suspect that adding the rest of the truck metal and wood bed will probably move it another degree or two. If that holds true I think I will add 2 degrees to the engine/transmission (currently reading 2 rather than 3 degrees) for a pinion angle of 4 degrees.

I also made a rough initial measurement for my drive shaft and from the tail of the NV3500 to the U-joint on the rear axle it is roughly 62 3/4" long and runs downhill at a 10 degree angle.

That link gives dimensions to the bottom of the pumpkin and the top of the frame at full load, so by subtracting the two, you could get the distance from top of frame to bottom of pumpkin and use ratchet straps to compress the suspension to that distance.

I tried to use the measurements but could not come up with a result that made much sense so I just use rachet straps and pulled the chassis down tothe rear axle as much as I could. The pinion angles I measured were 4 degrees and 2 degrees depending on if the springs were drawn down or left with chassis weight only.

I welded the perches in place and completed the initial axle installation.

I still need to determine what the lower shock mounting brackets will be. One of the 14-bolts may be usable but the other is on the rear side of the axle so it needs to be replaced.

Cleaning and painting the axle and related parts is on the long term to-do list as well as changing the fluid (really all of the fluids) and sealing the rear cover and axle shafts.

While you are at it, putting shocks on opposite sides of axle, like on your used axle, helps with damping axle wrap, since building upper brackets from scratch.

Ed

I don't think I can put one of the shocks on the back side of the axle. The location for the upper mount on the frame and the shock iteself would likely interfer with my fuel tank. The space available for the fuel tank behind the axle and between the frame rails on the 3600 is pretty limited (much less than the 3100).

The frame on a 3600 is narrower than a 3100, so could you move the shock mounts to the outside of the frame? I know that the mounts on the front are inside the frame, but don't know why. Or for that matter why the ones on a 3100 are outside the frame. The lower mount is pretty close to the tire (not that it's going to go anywhere.)

Of course, you'd have to move the lower shock mounts too.

[on edit] Just looked at your previous pics showing the frame and springs. Not much room between frame and springs for shocks.
But maybe there's enough room to squeeze the shocks in there.

The little room that I have outboard of the fuel tank is going to be consumed by the exhaust.

At the moment I am planning to use the original upper shock mounts on both sides and relocate/fabricate lower shock mounts on the 14-bolt axle to correspond to those upper mount locations. I am hoping but not really expecting the driver's side 14-bolt axle lower bracket to work such that I only need to change the passenger side but that is probably a pipe dream. I plan to measure the location of the original HO52 axle shock mounts relative to the spring perches to determine the desired side to side location. I am hoping to be able to use standard rear shocks rather than something unique but that is the subject of a different thread to be created if/when I am looking for guidance from the experts here.

235 mounting angle? With the engine sitting level on the ground just look at the intake manifold. It shows the approximate correct angle that the front of the engine has to come up to.
No hotchkiss drive engines sit level when installed.

WICruiser On the old eyeball method ideally you want the shaft straight in there...then they say oh u-joint rollers will "wear into a pocket" Crap I'm from that school where if you lose a roller in the dust,cut a piece of baling wire to fill the gap !! If the u-joints are binding you'll feel it or it will cry out to you. One of mine popped the other day gave it a shhot of corn head grease shut right up !! My winch truck came to me with driveshaft misalignment,cut a block of wood to put the center u-joint in the right place has run that way since 82. Not rocket science.

fixite7, thanks I think I have the angle set pretty close but will not really know how the u-joints "feel" until I get a drive shaft.

Moving on to other aspects of the conversion like getting brake lines in place - even with the brakes spaced out they are really close to the springs making getting the brake lines bent so that they can be connected to the wheel cylinders looks to be challenging.