Pinion angle shims

I hate to ask but does anyone know what spring shims are needed on the rear springs of a lifted M1009 that has a 23-degree driveshaft angle on the rear. Also, the front driveshaft is a stock size with a 19-degree angle. I fear if the vehicle were to bounce it would extend the front shaft past its limit and break the transfer case or the flange of the transmission. It appears fully extended. I never had to think this way before. Thank you in advance.

cucvrus said:

I fear if the vehicle were to bounce it would extend the front shaft past its limit and break the transfer case or the flange of the transmission. It appears fully extended.

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Your last two pics should be the rear DS, not the front...(?)
Anyway, it needs to be 2" longer at least and that can't be solved by just adding shims.

Also, the difference between pinion angle and TC output should remain within 1-2deg - unless you installed a DS with a CV-joint.

I've lifted Vehicles 4 to 6" inches many times over the years, I've never had a rear drive line come out that far, you have the wrong drive line, that's definitely a no bueno .

Did You move the rear axle back with offset spring pads ?

You're going to have to stretch that rear drive line out, while you're at it put a 1410 yoke on it and get a 1410 yoke for that 14 bolt rear, that will offer you considerably more articulation and strength, in the pic it appears to have a 1310 but I cant tell for sure .

Those degrees shims are readily available all over the Internet I've seen them on fleaBay, 5° should be plenty

Can't see the front drive line but from your description it sounds all right unless it's also stretched out to the max, GM offered two different Front drive lines for those old trucks and I've personally seen three different lengths, there's always people that have that stuff lying around and it'll save you having a new one made because it has a CV in it so it's more expensive .

gringeltaube said:

Your last two pics should be the rear DS, not the front...(?)
Anyway, it needs to be 2" longer at least and that can't be solved by just adding shims.

Also, the difference between pinion angle and TC output should remain within 1-2deg - unless you installed a DS with a CV-joint.

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I know about the rear driveshaft needing to be lengthened. And hindsight I should have never got involved with the lift kit. I am best sticking with stock and basics. Millions of dollars are spent on the stock M1009 design, testing and engineering to toss it aside for what? I want to get the rear axle angle correct so I can get the measurements for another rear driveshaft. The company making the driveshaft does not provide axle shims and I am just asking what shims are needed to correct this angle. After I have the axle corrected, I will measure again for a new driveshaft. Currently it has 1.5" into the tail off the transfer case and stock it had about 3.5". I am doing this at the owner's request and have done everything to the best of my skills. Just lengthening the drive shaft 2" will not fix the problem. I have a set of Summit 4-degree shims that the owner sent me, and I am asking if that would be enough. I need to keep moving forward as I have a lot of work to complete on several vehicles currently and am stuck on this issue. Thank you for your replies. The front driveshaft is new and is at 19 degrees. I just feel it is at the maximum stretch and could cause issues later going down the road or on rough terrain. Thank you.

Valley Rock said:

I've lifted Vehicles 4 to 6" inches many times over the years, I've never had a rear drive line come out that far, you have the wrong drive line, that's definitely a no bueno .

Did You move the rear axle back with offset spring pads ?

You're going to have to stretch that rear drive line out, while you're at it put a 1410 yoke on it and get a 1410 yoke for that 14 bolt rear, that will offer you considerably more articulation and strength, in the pic it appears to have a 1310 but I cant tell for sure .

Those degrees shims are readily available all over the Internet I've seen them on fleaBay, 5° should be plenty

Can't see the front drive line but from your description it sounds all right unless it's also stretched out to the max, GM offered two different Front drive lines for those old trucks and I've personally seen three different lengths, there's always people that have that stuff lying around and it'll save you having a new one made because it has a CV in it so it's more expensive .

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I installed a Rough Country 4" lift kit complete 4 springs, 4 shocks, and the pitman arm. I installed all new extended brake hoses front and rear. I cleaned and painted as I went. Everything was fine till I got to the rear drive shaft. That is the stock M1009 driveshaft with stock rear axle and stock size U joints. I hope that helps clear that up. I have not posted any pictures of the front driveshaft because I need to address the rear at this time. I have 4 degrees as that is what the owner sent me. Can you stack these shims? It had shims on the new springs and placed the spring with the thin part of the shim toward the front. That would be correct in my mind. OK I am going to call a place in the AM.

I used my iPhone and came up with 23 degrees. It is accurate. I use it to set up scaffold all the time. A trick my Wife showed me. It took me a bit to remember. But it came right back once I found the measurements in my utilities Icon.

Don’t stack shims.

I could try to describe how to properly measure the angles to determine the shims you need but there are some excellent instructions on the internet. Here is a good one to start with.
How To Measure Drive Shaft Angles

Something else to keep in mind is the shim type you get. Please don't buy aluminum shims, especially if the holes are slotted. Get steel shims with holes instead of slots and get new centering bolts that are long enough to go through the shims if the ones you have aren't. That way the shims can't go anywhere, and the head of the centering bolt still sits in the spring perch as designed. You would be surprised how many people have had axles move because they didn't know any better.

I measured the axle, and it is currently tilted upward 2 degrees, and I have 8 degrees axle shims coming my way. I want to get past this part. Thank you for all the help.

In all my years of doing this I dont ever recall using 8° shims, but nowadays many of the lift blocks have the angle built in to them, which is the way to go .

This is about the most simple suspension that exists so it's a great platform to learn from .

Leaf springs don't move nearly as much as coil/off road suspensions, so 1.5" of drive line hanging out from the back of Your T-case should be plenty of travel .

Point your pinion up towards/slightly below the T-case output and let the u-joints do their job .

Furthermore its a long box, so driveline angle is not going to be severe especially with only a 4" lift .

cucvrus said:

I measured the axle, and it is currently tilted upward 2 degrees.

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.... meaning it's about correct - if we can assume that the engine/transmission/TC is tilted more or less 2-3 degrees.

I have 8 degrees axle shims coming my way.

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Put them aside; you don't need any shims.

As I wrote in post #2: you want your driveshaft to be lengthened 1.5 - 2 inches, that's all.

Valley Rock said:

Point your pinion up towards/slightly below the T-case output and let the u-joints do their job .

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That's what we do when the driveshaft has a CV-joint at the upper end. Otherwise, better not...(!)

For industrial Cardan type shafts we design in 7° of misalignment. The universal joints need some amount of oscillation in order to support lubrication. With perfect alignment the grease squeezes out from under the needle bearings and if they don't roll they don't pick up any new grease.

87cr250r said:

........ The universal joints need some amount of oscillation in order to support lubrication. With perfect alignment the grease squeezes out from under the needle bearings and if they don't roll they don't pick up any new grease.

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Good point: in a vehicle everything twists and flexes, especially the springs. So, the pinion angle varies constantly, load-depending between driving and coasting. Enough at least to ensure adequate lubrication when running a CV driveshaft.

Correct driveline geometry is most important in a vehicle, to avoid those annoying vibrations/ harmonics.

I am so confused at this point. It was against my better judgement that o got involved in this lift kit massacre. I will prevail and follow the high torque drive shaft companies recommendation.

cucvrus said:

I am so confused at this point. It was against my better judgement that o got involved in this lift kit massacre. I will prevail and follow the high torque drive shaft companies recommendation.

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I have learned over the years, they know what they are talking about, but can be confusing.

I have decided smaller tires and little to no lift take less gearing, get better mileage, and are easier to get in and out of.

So you tell me if that M1009 has a severe angle on the driveshaft. Angled enough that the ujoint caps touch each other.

cucvrus said:

So you tell me if that M1009 has a severe angle on the driveshaft. Angled enough that the ujoint caps touch each other. View attachment 929300

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Put it in D and watch it turn. Practicals always beat theory. Of course if it's that bad, then dropout might still bind it. I would venture to guess that a lot of people with a lot less attention to detail have just shoved these springs under their trucks and been okay. Half the running/driving CUCVs I've seen for sale are stock with 4" lift kits. This would be a good time to assess the owner's budget and let them know you don't guarantee modifications.

It is really difficult to tell looking at pictures if there will be interference when the shaft rotates. It would’ t hurt to take something soft like some sort of putty and stuff it in around both the u-joints and turn the shaft by hand to see if it binds. If there is still some room in there for suspension travel, you can try driving it to find out if it vibrates. If it does vibrate, the difference if the two u-joint angles is too much. You would need to raise or lower the pinion accordingly.

CARC686 said:

Put it in D and watch it turn. Practicals always beat theory. Of course if it's that bad, then dropout might still bind it. I would venture to guess that a lot of people with a lot less attention to detail have just shoved these springs under their trucks and been okay. Half the running/driving CUCVs I've seen for sale are stock with 4" lift kits. This would be a good time to assess the owner's budget and let them know you don't guarantee modifications.

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He does make a good point. If it isn’t going off road, it probably doesn’t matter anyway. I have seen it done that way many times as well. Once or twice I have seen people stranded offroad with jeeps who’s drive shafts fell out for the exact same reason.