Rear end swap list.....let's make one

[JoelOkie]

Yeah, I'm just talking about changing a rear end where you have to set the spring hardware up to match what came out. It's worked great on all the ones I have done without ever having had a problem. I don't have any experience with any of the other situations, or issues, as I have never encountered any of those thus far. Joel

[Don Coatney]

I believe this is what Tim is talking about.

And if you are doing a driveshaft here is how to do it.

[JoelOkie]

Makes sense, and easy to ascertain.

[Plymouthy Adams]

I have found that the 4" magnetic angle meter is one of the best tools to have in the shop...not only are they excellent for setting the engine and rear gear it was most needed while fabricating the angle when making my AC transistion plate, a must for when I measured my front exhast pipe for the compound angles and short runs between needed bends..I was able to make these measurements and take to the shop without the car and the man bent the pipe per my specs and it was dead on..

of four vehicles I have bought in the past where the PO set the engine and rear gear in place, phasing was a problem in all and required me to go in and massage the set up..the fourth..bought it just for the 360 engine..could care less of the mounting as the body is going deep six soon enough..one of the three was also mangled on the clutch throw-out that the overthrow of his linkage set up broke the pressure plate..these are just a few of the many problems one encounters when buying an in-works project..they can at times get to be a bit more involved that one would like to deal with..multiplied when you ask up front how an item was done and they tell you only what you want to hear..not the truth..discovery later is often the case and sad part is if you had the truth you could have fixed it neat and quick without all the other work you have since done having to be un-done to get back to the root..yes I rant..but with good cause..

Edited August 1, 2010 by Tim Adams

[JoelOkie]

Certainly wise to check things out, especially when someone else has been doing things with the vehicle, in light of assumption being the mother of all screwups.

I have seen magnetic camber gauges that look like they would be pretty handy, and are inexpensive. Don't know what range they have. Levels and squares come natural to me, having had to often figure out various cuts for roof rafters, ect., but a lot of the time it takes 3 hands to hold everything where you want it. Joel

[Dan Babb]

This has been a good thread. I'll be searching for a new rear in the next month or so.

If you're starting from scratch - with a whole new drivetrain - please tell me if this is correct.

Make sure the frame is level. Since most garage floors have a slight angle, this is important, right? (where's the best part on the frame to attach an angle gauge?)

Install engine and transmission. Try to get the tranny installed with just a couple degree down ange (tailshaft pointing to the ground). I'm guessing that up or down angle doesn't matter. As long as you make the rear pinion the opposite, right?

For this example, let's assume it's 3 degrees down.

The pinion angle of the rear end should then be at around 3 degrees up. How much will the driveshaft move when you put it under power? In a parked position, should the pinion be set a bit less than you need so under power when it moves, it will get to the correct angle?

Make sure the ends of the driveshaft are in phase when you install it.

If there are any corrections, please copy the whole proceedure and edit. That way, we'll have one complete correct proceedure for others to use in the future.

[Plymouthy Adams]

generally you will find pinion angles in the 5 degree up range so setting the engine/trans will require 5 degree down..they do not appear on the same plane..you can go with other angles but just ensure the phasing is correct..should you have to stay in the 3 degree for clearance reason on the engine/trans..you can use shims (angle inserts) on the rear axle to offset and get back in phase without rewelding components..axle shims can be had in various offsets..can be combined but be careful that putting the car subject to lots of high torque starts (burnouts) could cause some shifting..if you do this..just take care to keep an eye on the rear assembly, shims and u-bolts..

[Young Ed]

So Tim. My long term project I'm working on is a 40 plymouth pickup with a flathead and a 5spd. The engine itself will be mounted as from the factory. Am I correct that having a significantly longer transmission will not change the angle for the rear end?

[Plymouthy Adams]

correct Ed as it is just a continuation of a straight line..

[Young Ed]

correct Ed as it is just a continuation of a straight line..

So was mopar aware of this angle business in the 40s becomes my question. If this was already common industry practice I should be able to copy the angle of the factory diff and be good to go. Now if I could just luck upon a rear end at the u-pull......

[Plymouthy Adams]

phasing of u-joint was a known fact since their discovery..would be pretty sure of stating the ancient Egyptians used these when building the pyramids but as rust would have taken its toll we do not have examples of them to draw too..hey..everyone else has a theory, why not me?

in all seriousness if you just read up on the methods to ensure proper phasing..you can't go wrong...one prime example of the early Mopars and extreme phasing application..look no further than the route van...Dodge Dakota had this in a lesser degree..many a car engine is offset to the rear both in height and left to right positioning..as long as all are on a parallel line on every plane do not exceed the mechanical limits of the angle, they will work without binding and serve you long time...

you want to keep in mind that the ideal is level at load..that way your degree of error will stay withing the tolerable range +/- as your rear chassis flexes under load and road conditions...static load is also critical on the drive shaft length so the spline will on compression not bottom out and also on the other extreme not pull out of the drive spline during normal flexing....

ALSO as an added note..this phasing of u-joints is just as important to do correctly when setting up steering when converting to R&P setups..the extreme angles needed in doing this job can only be obtained in phasing the joints else you can easily get a binding and "snap" feeling when these mechanical limits are overdriven..

Edited August 2, 2010 by Tim Adams

[Dave72dt]

clarification

This has been a good thread. I'll be searching for a new rear in the next month or so.

If you're starting from scratch - with a whole new drivetrain - please tell me if this is correct.

Make sure the frame is level. Since most garage floors have a slight angle, this is important, right? (where's the best part on the frame to attach an angle gauge?) Frame level side to side, also the ride height of the frame needs to be set at both ends, front and rear. I use a 4' level at several places.

Install engine and transmission. Try to get the tranny installed with just a couple degree down ange (tailshaft pointing to the ground)Level side to side and forward rea on the carb mounting surface on the intake manifold. Most intakes will have a couple degrees built in so the engine drops at the rear I'm guessing that up or down angle doesn't matter.Down only as most diffs are lower than the trans, pointing it up will increase the working angle As long as you make the rear pinion the opposite, right?

For this example, let's assume it's 3 degrees down.

The pinion angle of the rear end should then be at around 3 degrees up. How much will the driveshaft move when you put it under power? In a parked position, should the pinion be set a bit less than you need so under power when it moves, it will get to the correct angle? I think they should be the same angle. Deceleration under load will increase the load angle also. Unless you're running a race vehicle, preloading the pinion angle isn't that important.

Make sure the ends of the driveshaft are in phase when you install it.

when it is built. It'll onl;y go one way when instaslled.

If there are any corrections, please copy the whole proceedure and edit. That way, we'll have one complete correct proceedure for others to use in the future.

Edited August 2, 2010 by Dave72dt

[Young Ed]

Make sure the ends of the driveshaft are in phase when you install it.

when it is built. It'll onl;y go one way whenb instaslled.

Thats not always true. The driveshaft in my 46 pickup could be installed out of phase. The front ujoint is before the slip joint so if you dont install the shaft into the slip joint in the proper orientation its out of phase.

[Dave72dt]

Make sure the ends of the driveshaft are in phase when you install it.

when it is built. It'll onl;y go one way whenb instaslled.

Thats not always true. The driveshaft in my 46 pickup could be installed out of phase. The front ujoint is before the slip joint so if you dont install the shaft into the slip joint in the proper orientation its out of phase.

In a setup like that or in a 2- piece driveshaft, yes phasing it when installing is required.

[Plymouthy Adams]

folks get this point clear..the engine/tranny is not a straight line to the differential...the height of tranny as compared to the differential is not on the same level..it is being parallel that is critical..as I have tried to state and clearly identified by the pictures Don posted to emphasize "phasing"..correct phasing is only achieved following these rules...complimentary angles..

[Tony_Urwin]

Same rule applies when an engine is installed to the right of center (like Mother Mopar did in the 60's and 70's) the engine is still parallel to the frame rails, not angled back to the pinion yoke.

The critical point is that the angles are the same at both ends of the driveshaft, whether up-and-down, or side-to-side.

Pretty common mistake that hotrodders make with their engine swaps.

[Dave72dt]

So Tim. My long term project I'm working on is a 40 plymouth pickup with a flathead and a 5spd. The engine itself will be mounted as from the factory. Am I correct that having a significantly longer transmission will not change the angle for the rear end?

It won't change the pinion angle. It will however increase the working angle of the ujoints.

[Plymouthy Adams]

how will that increase the working angle..I await your explanation..

[Dave72dt]

The parrallel lines remain constant so the vertical distance between them is the same, regardless of the length.The length of the driveshaft becomes shorter so the angle to connect the two parallel lines increases.

[Plymouthy Adams]

no..the angle of the parallel lines remain constant...only the length of the shaft changes..this will give you the appearance of as sharper angle but it is yet the same

Edited August 2, 2010 by Tim Adams

[Dave72dt]

Well then, let's draw a picture. Start with two parallel lines. Mark a spot on the upper line to designate where the transmission ujoint is. Mark a spot on the bottom line to respresent where the diff ujoint is. Now draw a line between those two points. That will represent the driveshaft. With a longer transmision, the transmission ujoint spot will move along the upper parallel line towards the diff so mark a new spot on the upper line. The differential hasn't changed it's location so it's ujoint will be in the same place as before. Now draw a line between the new upper line mark and the mark on the bottom line that represents the ujoint for the differential. That will represent the new, shorter driveshaft and should show that the angles have changed and gotton sharper. It has to. Simple geometry.

[Plymouthy Adams]

OK I now see what you are doing...so to first assure Ed that the answer I gave him is correct...the transmision/engine combo at x degree and add a longer tailshaft will not change the angles..it is just shortening the distance....BUT....to do as I think you are saying is to move the engine and tansmission closer to the differential along a level line..then the working angle will change as you have now positioned one higher than the other...is this what you were referring to?...I was not moving components within his chassis..

I was under the impression that you were within the establised lines of the original configuration in Eds question..one needs to limit the working angle of the driveshaft not to exceed 7 degrees if at all possible..thus staying within the mechanical limits of the u-joint as mentioned earlier..granted thay can operate at a higher angle for brief periods but they do limit the servicable life of the units..constant velocity joints is yet another method to address excess angles safely

Edited August 2, 2010 by Tim Adams

[Dave72dt]

No, he was talking about a transmision with a longer tailshaft and not changing the engine mounts or position. That will move the front u joint closer to the differential. I have no idea how much longer the transmision he's planning on using is than the original but it most likely will not create such an angle that he will encounter problems.

[Plymouthy Adams]

I was just out in the shop, my 51 wagon is on the lift and fully in the air..when I installed the 3.9 V6 with 4 speed auto I have three degrees down bubble on the engine/tranny centerline and three degrees up bubble on the transferred Dakota pinion centerline...now as these are parallel and the distance is now fixed by the mounts...we then look at the angle between the two points that will represent the driveshaft..I have 3.5 degrees and well within the 7 degrees most builder call for and be referred to as high performance..and I have sufficient angles as the suspension flexes in either direction..

now with the engine tranny fixed at 3 degrees down stationary on the chassis, any extra length of the tailshaft is a direct extension of your imaginary line through the engine tranny combo..and the same angle of the drivshaft though it will now be shorter..that is the beauty of parallel lines...

[Dave72dt]

I think we're both talking about the same thing but describing it differently. Engine trans angle as it relates to the pinion angle and seperately, the u joint working angle that changes as you move one point of flex ( u joint )horizintally along the parallel line established by the engine trans angle.

We've either confused everyone more or made sure in our own minds we're right. Always a topic that garners a lot of interest and questions and is equally difficult to describe.