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Interesting explanation of importance of driveshaft phasing
- Thread starter Reworked LMTV
- Start date
- 10,457
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- Camp Wood/LC, TX
FMTVs are phased wrong all the time.
Check your Driveshaft phasing on FMTVs!!
Sure enough got a new unit in and look at the front ds! I see this again and again! I guess they forget to mention this in 91B school!!!
www.steelsoldiers.com
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Don't "eye" the drive shaft phasing. Take off an put on flat table.
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Driveline angles are a function of trigonometry. You cannot change the math.
Drive Line Service
Universal Joint Database, Driveline Parts Catalog, Ag PTO Specialists
www.drive-lines.com
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On FMTVs the slip joint spines are so course that you can eyeball the driveshaft and tell if it’s off.
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iPhone method? Not trying to be rude but have you ever taken one apart and clocked it correctly on a FMTV. With the big splines you would know it is off trust me I had to do mine while under the truck and just taking off the U joint from the axle. No problem seeing if it was off a spline. Mine was out of phase and runs so nice now. Good thing I had only run it maybe 75 miles before correcting.
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spankybear
Well-known member
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- WA
I love learning new stuff! On my truck the front shaft looks good but the rear one is off. I'll want to get that one balanced.
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Uh YAH, I just took them all off and got them balanced ! I have taken them off once before.
Can you not see the video above? Never mind. Do it your way...
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https://www.steelmantools.com/diagn...se-vibration-diagnostic-device-kit-60635.html
Had the original version. It died. New version out.
www.picoauto.com
You can make your own sensors (arduino accelerometer and optical sensor used with say a generator) and connect to an old oscilloscope (cheap)
www.picoauto.com
Had the original version. It died. New version out.
Noise, vibration and balancing
The award winning Pico NVH kit help you fix unwanted vibrations and knocking quickly and efficiently
www.picoauto.com
Noise, vibration and balancing
The award winning Pico NVH kit help you fix unwanted vibrations and knocking quickly and efficiently
www.picoauto.com
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Looks like cool stuff but I do not need any of it. In my case my drive shaft was balanced but some moron dropped my front drive shaft on the 1088. He pulled apart the slip shaft joint and did not mark it, then put it back together three splines off. Now in my case I had a growl when I came off full throttle to half throttle. Full throttle or off throttle no growl. As said checked my phase rotated it and as said with the size of the splines you can tell if it was off by one spline. I have run all my hubs and they are now shimmed correct and also check my axle bearings / races. Yea the truck was built by the lowest bidder and mine is 23 years old so I do not expect it to ride / sound like my SL500. I am not going to do a gear change in three axles as I do not need to go any faster the 50 mph in this toy. Do the hubs gears growl a little bit I believe they do at higher speeds but since I know mine have been serviced I do not worry about it. Hope you figure your out.
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Just for smitts and giggles I decided to put on new U joints on my MTV front propeller shaft. Here is why with the splines as big as they are being one tooth off you would have to be a blind man not to see it. One pic of big splines one pic in phase and as said one spline off. I do not need a iPhone to get it right on this type of propeller shaft. High tech tools low tech truck. Main thing is if you are going to pull the slip joint apart mark both half's with a mark that will not wipe off. This is because we could put the slip joint back together 180* from the way it was balanced but still in phase. I believe you took you propeller shaft out and had it balanced but I do not think you pulled the slip joint apart and put it back together because you to would have seen how much just one tooth will change the phase. Was wondering have you serviced you hub's checking all parts and shimming the gears? As said hope you find your noise or find it is just how they are.
Attachments
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Fair enough. I can see it. I engrave mine driveshafts.
There is definitely more than one way to identify issues. More recently I have seen the time savings, and money savings of using a scope or OTC/SPX smoker. High tech tools help narrow down issues faster. For example, failing fuel pump? I don't part pull, I scope the power leads and look for flat portions of the of the wave form, indicating pending armature failure. Are the elbows / junction s of my M1088 leaking? Looked fine. Smoke test said otherwise. Rectifier or regulator failing causing lights to flicker or weak batteries? Scope will tell you. Which cylinder is bad? Pull the valve train cover or just scope the pressure waves of the exhaust? I can back probe the wiring on a 3126 or C7 and see the injectors firing, look at the amp ramp and may even see the pintle opening.
Do you mean set the lash on the gears? No, not yet. I have a set of 3.07's going in. Will see what the does. Probably with do the seals.
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Why they did not key the shaft with one bigger spline I will never know. Guess that is what we get from the lowest bidder. Heck the propeller shaft on my M37 is keyed. Yea repacking the inner bearings and setting up the lash is not a bad job. On my rears I capped off the hubs and removed the CTIS seals and now I have full oil floating bearings on my rears inside and out just no CTIS system on the truck. I also changed out my wheels to combat and new tires. I just have to keep my axle filled up to the fill plug. This truck is just my toy to take to the mud pit that is all. Yep sometimes we need high tech tools makes the job and sometimes just the right simple tool.
coachgeo
Well-known member
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with your own photo of in and out of phase by one spline..... think you've answered your own questions..... key not needed... out of phase is obvious even if out by only one spline
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Well I did not know if it was 180* out from when it was balanced but learned something by removing it today. So looking at the shaft now that it is out my front was never balanced. So I took it to Ocala to the drive line shop and dropped it off. My data tag has the D stamp and the rears have weights on them so I am guessing they balanced the rears but not the front. I do not know and we will see how out of balance it was. He said since it was not balanced then it did not matter how I clocked the correct phase one way or 180* the other. I will make sure to stamp both ends when I get it back so the next person does not have to think too much if they pull the slip joint apart for some stupid reason.
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This part doesn't make sense. Maybe you misunderstood him? That is exactly why the phasing is so critical, and 180° is the worst case.
Even if it hadn't been balanced, it could easily be mostly in balance assembled correctly, and terribly out of balance 180° out of phase. Think about it... if you lay the driveshaft on the table, and the left half is "off balance" 1oz to one side, and the right side of the shaft is 1oz the other way, the whole shaft is in balance. If you clock it 180°, you're 2oz off in one direction... very bad news.
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OK see what you are saying and that makes cents. I told them how I found it out of phase and I just clocked it three splines one way to get it looking like it was in phase. Maybe as you said I did not hear him right but no matter what they should get it right. Another thing as said my data plate has the D stamp but only my intermediate shaft has what looks like a weight on it. The rear most shaft does not. Wonder if I should pull the shaft and have it checked. Dang toys but just got it pulled out of moth balls and tagged so I guess a little money spent now is a good thing.
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