Syncro driveshaft runout?

[stormforge]

Does anyone have a good idea what sort of maximum runout I should be seeing at various points along the syncro driveshaft? Is there an official spec?

Here's a test indicator on the front flange of the shaft. I'm seeing something like +/- 0.009" from one extreme to the other -- so under 20 thousandths full indicator movement. This doesn't seem like a whole lot to me?

Driveshaft vibration is giving me fits since I replaced my engine mounts. The angles look great, the u-joints are fresh and shimmed to about 0.002" of axial play... I can't figure out what's going on...

Thanks!
-Bill
'89 Syncro

[MsTaboo]

I don't have any runout data for you but unless your driveshaft is a really cheap knockoff it shouldn't matter.
The driveshaft is centered on the transaxle and diff by the machined recess on the ends. The outside edge may not be perfect since it doesn't matter.
Vibration can come from a bunch of different reasons but if the driveshaft setup was vibration free before you did work then most likely the problem is alignment.

Sorry if the following is redundant.

The one alignment usually overlooked is whether the whole drivetrain is inline.
Visualize the layout from above (plan view), the transaxle, shaft, and front diff all need to be in a straight line.
The easiest way to check this is with a basic construction laser. Set it up with a vertical beam and put it on the floor under the van. Check that the case seams on the diff and transaxle are in alignment. If not then it's easy to loosen either the engine/transaxle mounts and shift or the front diff mounts.
Since you changed your engine mounts it's most likely the engine/transaxle is out of line.

If this alignment is good and you still have vibrations then the next to check are the angles between the diff/shaft/transaxle.
The easiest way to check those are with a laser pointer tool setup. These are easy to make if you have access to a lathe but not so much if you don't.
G.W. used to sell/rent a laser alignment tool but unfortunately they no longer offer.
These are the ones I use, basic construction laser and the G.W. kit.

To use kit;
Van needs to be level side to side. Rotate laser/puck until a dot is formed, mark card.
Repeat from the other side, and check the dots.
Shift transaxle or diff until the dots are on the centerline and just a few degrees below level. Keep repeating until dots fall in the same place from either direction.

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Currently:
'90 Syncro Westy 3 knob w/Zetec

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[stormforge]

Thanks for the reply! Yeah, the flange recesses do ensure that the shaft runout isn't going to be too bad -- but, I could have screwed up the u-joint replacement or something like that which the runout test would catch.

I have my own homemade laser alignment tool which has always worked well for me in the past. After I replaced the ancient, collapsed engine mounts the rear of the engine was raised by almost 0.5". This pitched the nose of the transmission down to about -4.5 degrees. My correction for this was to trim a little bit off the steel inserts on the transmission mounts to lift up the front of the transmission. Now my angles match at about -3.5 degrees in both directions (the image below is work in progress...) and my side-to-side alignment is dead on.

So, I'm stumped as to the vibration at about 45 MPH... I rebuilt this driveshaft about 2 years ago but I pulled it apart and measured everything and snugged up some of the shims for the u-joints since there was some play. Still no good... Everything was fine until I replaced the engine mounts.

The runout is actually greatest (+/- 0.010") at the front end of the shaft. The center and rear of the shaft are closer to +/- 0.004" -- which is probably fine. I'm not sure about +/- 0.010"? Maybe that's a lot? I can try to remove some of that with a different set of shims for the corresponding u-joint.

Or maybe I need to go back and double-check the new engine mounts for the third time...?

Thanks!
-Bill
'89 Syncro

[MsTaboo]

Have you had the driveshaft balanced at a shop?
_________________
Currently:
'90 Syncro Westy 3 knob w/Zetec

The information age has morphed into the age of disinformation and willful ignorance. Agnotology!
Help the fight against Truth Decay.
Defend democracy, support Ukraine.

[stormforge]

I haven't had the shaft balanced and the nearest place with a machine is 2-3 hours away. I've been hoping that nothing I've done to it would change the balance significantly -- but who can say?

That said, it was smooth as silk for about 10,000 miles between rebuilding the shaft and changing the engine mounts. I suppose there are enough variables in this equation that maybe the shaft is screwy, but it just happened to work well in the previous configuration...

-Bill
'89 Syncro

[stormforge]

So, folks who have rebuilt your driveshafts with new u-joints and guibo -- did you get the shaft balanced? Was it out of balance after the rebuild?

Thanks!
-Bill
'89 Syncro

[davevickery]

[stormforge]

I started this saga by replacing the 4 rubber mounts on the mustache bar with OEM-style ones.

My rubber sandwich transmission mounts are older (maybe original?) but really look pretty good. I do notice that the two mounts at the back end of the front transaxle aren't really compressed at rest -- meaning that it takes very little force to wiggle the rear nose of the front transaxle around...

I have tried the "van-cafe" method with loose bolts on the front transaxle to no avail. I'm thinking I might add a washer to the front mounts to compress the rubber a little bit so things aren't so jiggly.

Thanks!
-Bill
'89 Syncro

[davevickery]

I resisted replacing my transaxle mounts for a long time. They are very expensive considering you need 10 and mine seemed to be in good condition for rubber. But it made a big difference and I just did the fronts.

Here is a pic of what mine looked like. You might think yours are fine but if they are out of shape it make cause extra vibration to get through. I even tried shortening one of the inner metal bushings first thinking that would isolate the differential from metal to metal contact. That didn't help. I've heard mixed results with the aftermarket ones. And the good thing about replacing bushings is even if it doesn't solve the problem, it isn't crazy to replace them every 200K miles.

The second photo is the old one. You can see that the top has been pushed down compared to the new one.

[stormforge]

Thanks Dave! Very interesting pictures! My rubber bushings look surprisingly nice for 30 years -- but now I wonder if they are all misshapen?

Did the new front bushings solve your driveshaft problem?

They are *really* expensive. $3-400 for a full set? Maybe I'll buy one and do a comparison.

Thanks!
-Bill
'89 Syncro

[davevickery]

I don't remember the order I did things. I think I replaced the driveshaft then did the diff bushings. I gave away that drive shaft and the person that tried it also did not like it and tossed it. It was basically new and was smooth at first, so I didn't think to question it. Mine van isn't as smooth as new landcruiser, but for a syncro it's good. I may still replace the rear trans mounts that I never bothered with. It is surprising how much they cost if you decide to just do them all. But now I only have 4 to go.

[Black'n'White]

[stormforge]

I'd certainly be concerned about the fluid and the play from your front transaxle input shaft -- neither of those things sound right. Maybe a bad seal and/or bearing on that input shaft?

-Bill
'89 Syncro

[stormforge]

FYI -- here are links to the scaled SVG image of my alignment target and the spreadsheet that I used to produce the target. The target takes into account the length of my laser. If your laser is a different length then your result will be (only very slightly) wrong... Please feel free to check my math!

Target: https://drive.google.com/open?id=1Cv_R3ra_UveSBWY4BTaLgtQU8tm0dOIc
Calcs: https://drive.google.com/open?id=1JSycz6mu29oSspzJ2EKY_mwC1qOMNwdRF-VOy-cqADA

-Bill
'89 Syncro

[MarkWard]

.010” runout seems like a lot but don’t know a spec for you. While the flanges are centered, you would have the a slightly oblong rotating shaft.
There was an old driveshaft balancing method using hose clamps and some test drives. I’ll bet the google has the method illustrated somewhere. Maybe you could try and affect the vibration with clamps.
_________________
☮️

[Black'n'White]

[Black'n'White]

[stormforge]

I actually went back and checked runout on the driveshaft tube rather than the u-joint flange and I saw surprisingly little -- something like 4-6 thou at both ends. Much better than I would have guessed. I haven't checked, but I would guess that my transaxle input/output flanges are probably better than that.

Right now for my problem I'm leaning towards bad front transaxle mounts. There's a lot of play in the rear of the transaxle which comes from those rubber mounts -- I can wiggle it all around with very little force... I haven't had time to swap them out and test yet.

-Bill

[Black'n'White]

In the FWIW department, I wasn't happy with the laser pointer I was using. It had a momentary push button switch on it, and wasn't making consistent contact when held down with a tape wrap, even with a piece of popsicle stick over it for more leverage.

Today I received a pair of these (see link below) in the mail, and they seem to be very suited to the job. They have a slider switch that stays on by itself, and the housing is one diameter the full length, which lends itself to mounting in the bore of the flange adaptor. And they take a AA battery, so they'll run almost forever; no worries about just leaving them on during use.

https://smile.amazon.com/gp/product/B076P8YRR1/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
_________________
'87 Syncro/Westy Homebrew
Whatever it takes...

[MsTaboo]