driveshaft balancing

[PatAllen]

FWIW....been working very hard to build a jig to mount various DS. all the aluminimum heads simulate the differential mounts or the transmission mount, within 0,0005" so there is no "mounting" errors. all heads are balanced beyond measurable on my IRD350 (fucking precise awesome vibration analyser from the 80's)

i have some fun to figure out what BMW did long time ago to balance the non-true DS this is very funny the one pictured has 0,030" offset, probably caused by one of the stacked u-joinf off from centered, hence to HUGE balancing weight loool

did try some e28, e36, e60 and of course 2002's DS

apparently the tolerances or minimum acceptable out of balance if higher than i thought, because i can "correct" all of them way more that they are.

i can balance them beyond stupid levels with this JIG. i can actualy measure the head of a tie-wrap on the DS....

i do it just for my E60 right now as the fron DS need rebuild and is not balanced from factory for obscure reasons, probalby  because it is mounted on the motor and that the differential is part of the motor too...but they all (the front DS on XI cars) die prematuraly compared to the rears....go figure.

[steve k.]

Love the fun stuff that you do! 

[PatAllen]

i would SO like to know what was/is the tolerances (max runout/ouces/velocity vibration%) for the OEM balanced driveshafts...

i take this to the "next level" as i am very disapointed of the local DS shops. they are completely clueless or simply refuse to answer. if not, they refuse to balance 2 pieces DS.

if its not a GM or a FURD DS they refuse to touch them....@#$!

[PatAllen]

that POOR E60 front driveshaft, factory unbalanced....look the amount of weight it required to get relatively well balanced (far from good)....joints are bad, transfer case input bearing is sick as well....thumbs up to engineers.

[roadhog0]

Mmmmmm, I love this!

[PaulTWinterton]

Could bad joints cause that issue? I had mine balanced and new ujoints peened in.  The shop welded one  20 mm (ish) washer for balance.

[TobyB]

I too have found the runout on stock shafts to be pretty high-

best with the earlier spin- welded shafts (e21, especially).

 

With the advent of cheap strain gauges, vfd's and fast microcontrollers,

I have been tempted to try this...

 

...because I too found driveshaft shops to be little help with what we do.

 

t

 

[tzei]

Very interesting. What rpm(s) do you use?

[PatAllen]

i use a VFD motor so i can vary the speed from 0 to about 2700 rpm. They seems to pick up a harmonic near 2000rpm and i balance them at this speed.

 

the u joint are not solicitated during balancing because the shaft is aligned and all zeroed,

if they are this bad and there is side play in them then it may cause problem.

 

the reason why the one pictured has such a heavy balancing weight is because the guy who made it at the factory didnt stacked the ujoint centered enough. but i guess (back then) they staked them in in a jig and balanced them after without checking runout.

 

balancing weight for DS is nothing but washers or thin steel plate, spot welded to the shaft.

 

Balance Masters offer a solution, i would like to try some on my machine and try to fool them to see how far they works but they refuse to send me samples, and at 150$ trying things for fun is becoming costly for me, i already invested more than 500$ in my jig, motor, steel, bearings, isolated rubber mounts, VFD drive, plus time to machine on the lathe all the jigs and whats not....i am crazy.

 

http://www.balancemasters.com/driveshafts.html

 

[PatAllen]

balance weights

 

https://www.powertrainindustries.com/story/BW6?catalog_table=supplies_balance_weights

 

can we use plain washers ? hell yes.

[jimk]

The Balance Masters balancers if they are like the ones for wheels (referenced on the Balance Masters page), give a startup imbalance until the assemble begins to wobble off center, the the balancing media finds a home.  This happens every time the shaft/wheel would start up.  A rough road would shift the weight and the wheel would bounce for a time.  It's the same method as the balancing in a washing machine spin assembly.

[PatAllen]

1 hour ago, jimk said:

The Balance Masters balancers if they are like the ones for wheels (referenced on the Balance Masters page), give a startup imbalance until the assemble begins to wobble off center, the the balancing media finds a home.  This happens every time the shaft/wheel would start up.  A rough road would shift the weight and the wheel would bounce for a time.  It's the same method as the balancing in a washing machine spin assembly.

i know what you mean, i would try to avoid having a shift and unbalance every bumps, reason why i want to dynamic balance them to extreme limits and see how they behave in real life

[PatAllen]

some of the DS i am playing with and some holders and adapters i machined myself.

 

the one next to the Xi short one is the one that started it all, 1992 E36 325i that was shaking as hell (almost 13 years ago id say), sent to Driveline specialist in Oregon, to have it later replaced by a "professionnaly rebuilt" by them, which was completely miss balanced, had to balance it on the car (yeah) that led me to almost a lawsuit to them, later to the purchasing of my IRD350 vibration analyser, a 3HP electric motor and my current jig today. lesson learned....$$$$$$$$$

[TobyB]

The 3000 rpm ceiling for balancing was killing me with race car driveshafts, especially with a 4.44 diff-

the driveshaft's spinning 1.2x engine revs, and the engine's turning 7500+...

 

...I just never got everything to spin right, then I messed up the transmission tailshaft, and 

gave up and went back to things I could pull out of parts cars....

 

t

now wants his own.  needs more megahurts.

[PatAllen]

7 hours ago, TobyB said:

The 3000 rpm ceiling for balancing was killing me with race car driveshafts, especially with a 4.44 diff-

the driveshaft's spinning 1.2x engine revs, and the engine's turning 7500+...

 

...I just never got everything to spin right, then I messed up the transmission tailshaft, and 

gave up and went back to things I could pull out of parts cars....

 

t

now wants his own.  needs more megahurts.

maybe if they where balanced down enough they wouldn kill the stuff at higher revs ?

fwiw it is not easy to find high speed motor to do high speed balancing, maybe with a belt reduction or something else.