Discussion in 'Members Rides' started by nils, Mar 15, 2016.
I was on London Bridge a few weeks before it collapsed.
I didn't even realize that it was not suppose to look like that Keith, had to google it.
The tailshaft saga continued over the last few months, I did I bit of a wright up on the Yahoo syncro forum. Thought I might share it here too.
Well I guess seeing as this is a hot topic that just keeps pooping up in my inbox I will add my experience and things I have learnt trying to sort my vibration in the last year.
But lets start with an opinion first, removing the donut will 100% add extra load to your gearbox bearings and the comment that holdens and such don't have them is rot too. It is true that vehicles with live rear axles don't have them, as they deflect during the up and down movement of the suspension. Most irs vehicles where the gearbox and diff do not move relative to each other have some version of this (called a guibo by the way) and those with 3 piece tailshafts, the center bearing is mounted in rubber. So in the world of higher Syncro gearbox prices do you really want to find out over a few hundred bucks whether it needs to be there?
The reason a solid shaft fixs your vibrations is because you have removed 4 of your wear items. (2 bushes inside, the spindle inside and the rubber donut) I would concider this a bandaid fix because it's cheaper.
So back to what I have learnt, the PTO cheap $30 uni's are 30mm x 70mm and have 12 needle bearings inside them. The specifed uni's at $270-340 are 30mm x 68.9mm and have 24 needle bearings inside. I have 2 of the cheap ones that show play after only 1000km.
The original specification for balancing the shaft was 6000rpm, which in todays terms doesnt mean anything except that it was done to a higher standard than what is seen as the norm. (Most balancing machines only go to 3000) BUT! having said that technology has come a long was since then and it is no longer a requirement to spin that fast as increased accuracy of sensors can simulate what will happen at the higher RPM. So what you are looking for when you see your driveshaft shop is the ISO standard to which they balance.
The standard for automotive shafts is G16, I have had mine done 3 times to this to still have a slight humming under the floor at over 85km. It seems that this is not enough and am currently having mine balanced to G6.3, I will get back to you with whether that is the winner.
With that in mind, if the original shaft was balanced to a higher standard, to think that you could get a good balance with a worn center bush, substandard uni or deteriorated donut is kidding yourself. To have the end cut of the prop shaft, to have an engineering shop remake the 2 bushes, grind the internal shaft round again, ream and reassemble cost me around $320.
The donut can be bought as a meyle product for $40-50 or as a BMW part for $240-650.
On to gearbox mounts, the mounts are trash by this age of the vehicle, they are super soft and aren't holding much (also throwing your tailshaft alignment way out). If you have vibrations that come and go at different speeds start here. The factory spec is 4 degrees included angle front and rear. Like mine you will find they are more like 2.5 and 5 due to the output/input ends sagging due to worn mounts. Even with the tailshaft out new mounts make a very noticible diffence to smoothness, shifting and clutch chatter. They can be found for between $40-60 ea and there are 10 of them, if the plastic spacers are damaged replace them while you are at it . lastly don't forget your engine mounts play on this too, check those.
How specific you want to be with your alignment between the front and rear boxes is up to you. Realistically uni's should get about 1 degree of misalignment without issue, so a quick string line should do the job, concentrate your time on the angles instead.
I currently have the whole shebang laser straight within a few mm and the included angles within 0.1 of each other, A slow building hum is still presesnt. Fingers crossed my new balance sorts that out.
To answer your question, Best I can tell you should not have to be shimming things to get the angles within 1 degree of each other unless the front and rear boxes are not anywhere near co-linear to each other.
The adjustment to which is -
The rear gearbox - the 2 ears attached to the front mounts are slotted to move left and right.
- There is not adjustment at the engine end.
The front gearbox - the rear banana shaped carrier also has slotted holes .
- and at the front, the square shaped bar that the front mount bolts to has a bolt on each end that can be moved left and right between the rails of the front subframe.
Back to shimming, as I mentioned you really should not have to shim..
- your gearbox mounts are worn.
- your engine mounts are worn.
- or you have aftermarket parts that are not true to the original design.
- and lastly if you syncro has impact damage underneath as I found out.
So, speaking of the last point that is why I shimmed mine as I found that the engine carrier bar had been hit very hard on the passenger side.
The original measurements I had were 2.5 degrees included angle at the front and almost 5 at the rear.
By installing new mounts I ended up with 3.2 at the front and 4 at the rear. Which is actually within tolerance, no shimming needed. But remember I was still chasing a vibration.
So after hours of inspecting and measuring I found a small kink in the flange that the engine carrier bar is attached to and a heavy mark in the bar. Which made sense as the exhaust had a hole in it from an altercation with a rock on that side too.
As a result I ended up with 9mm of shims (3x3mm) under the passenger side mount and 3mm under the driveside to net me angles of 3.5 and 3.6 (remember as the 2 angles are opposite each other, buy dropping the engine side you decrease the rear gearbox angle and increase the front diff angle at the same time)
This was supper close as far s angles go but I still had a vibration.
Finally we come back full circle to the tailshaft (propshaft if you like)
As mentioned in my last small book, it was decided that due to the higher speed that VW balanced their shafts there was a good possibility that the specification that most shafts are balanced to was too low (G16) and that a specialized balance was required. After having a chat with the (very interested in my van) fellows at Hardy Spicer in Beresfield they agreed that they could balance my shaft at 6000rpm and recommended to increase the tolerance to a G6.3 spec. G6.3 spec is what is usually used for electric motors, gas turbines, turbo chargers and such.
I picked up the shaft this afternoon with some print outs of the before and after, this is where the cool nerd stuff comes in.
The first printout is of the before condition. As you can see and as Brent mentioned it is not actually spun at 6000rpm, but due to the magic maths compters we come up with the equivilant. The "Planes" mentioned at the bottom is if you look at the shaft from the end while running and pertains to how much weight deflection is found up/down, left/right at 6000rpm at 43mm from center. How many G's that is I have no idea, but as you can see it was almost 7 grams one way and 4.5 grams the other, which to G16 spec is well within tolerance.
It was also mentioned to me (not mentioned on the print out) that at the higher tolerance the straightness of the shaft also becomes tighter and as a result may shaft was straightened a little to be within 0.005'' runout (don't ask me why it is on imperial)
The second printout is post G6.3 spec balance and you can see those numbers are down dramatically, well as dramatic as a few grams can be. Down to only 0.425g and 0.213g
As you can imagine I was eager to rush home and install and no doubt the question is "well did it work?"
Indeed it did! smooth as butter! I finally have a 4WD almost 3 years after purchase my syncro can again stand proud.
As an end note, these tolerances could not be achieved with a worn center bearing. If your center bearing/bush is in question this has to be your first fix, well after the obvious anyways.
And to come back to the really world I chatted to the boys a hardy spicer about building a brand new shaft including a rubber donut. They replied with an expected cost of around $1200
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