So I got the car going again and taking it for a nice drive I noticed that around 110km/h it starts to vibrate as if the rear end is going to fall off.
It's definitely coming from the rear of the car and not the front.
I started to think it may be due to the angle of the engine/gearbox, the tailshaft and the differential.
I have read the link:
http://www.ozdat.com/forum/viewtopic.php?f=8&t=25262
Which states the diff angle should be as close as parallel to the gearbox angle.

So I decided to measure the angles and I got the following:
-0.5deg for the Diff
+2 for the tailshaft
+3.5deg for the Engine/gearbox.

Angles were measured using an 'Empire Angle Meter Level/Protractor' and mounting on the flange of the diff (tailshaft removed), the tube of the tailshaft and the output shaft of the gearbox. Angles were also corrected (as I jacked up the rear end) according to the angle I had jacked up and subtracted accordingly.

So this isn't the case as the recommendation!

NOTE: I am running the Datsport front end, Datsport gearbox cross member, Datsport rear moustache diff bar. I have put the whiteline diff bushes with the thick part on top and the thin on the bottom. Previously I had the thin on top, but this would increase the angle (raise the rear of the diff up pointing the front of the diff lower into the ground, which I would assume would make the whole thing worse.

See attached image which describes it graphically.

So what I am trying to find out is: Who is running a similar setup and has the moustache bar bushes swapped (small at the top, thick at the bottom - opposite to what I have)?
Has anyone else had vibration issues?

As a few quick checks, I am thinking of swapping the moustache bar bushes and also checking the tailshaft is balanced properly.
Does anyone else have any recommendations?

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Hey Nik,
Edited: Assuming all things are adjusted to take into consideration the height of the car, the angles should equal 180deg right? If your motor has an angle down at 3.5deg. And the Diff is angled up at .5deg. shouldn't the tail shaft be at 3deg not 2deg?

I made my own moustache bar for the R200, I had the bushes flipped so that the thin ones were on top. I got the chance to drive it above 80kmh with the R200 before I pulled it again and it was fine, not at 110 though. My R180 had the moustache bar flipped so that the rear was as high as it could go. Noticed no issues with vibration. Certainly not like you're describing.

I've also gone through two versions of my own Gearbox Crossmember and also an Original Datsport item. Again, noticed no vibration that you are describing with any of them, the last one I've made tucks the gearbox up as high as it can go. Worst i've had is in 5th gear, the rear view mirror would vibrate a little bit. No shaking.

The theory is correct in terms of balance, but even slight degree deflection the wrong way should be taken out by the universal joints in the prop shaft. If that hasn't been changed and there was no issue with the last Diff, I would wonder if there is something else not quite right. It would 'whip' like you are describing, but there is only 3deg deflection, its not heaps.

CV's are ok?
What are the rear wheel angles doing since the diff is out? If it was sitting on the bushes of the K frame for some time they may have deformed?
Last case would be diff, You had 13mm bolts, is there a chance that they were not drilled out concentric to the hemisphere and there is some run-out on the crown wheel causing a vibration? (that is a big guess), but I would troubleshoot easiest to more difficult.

_________________
Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Hi Ross,

Thanks for the response. The tailshaft angle is definitely 2degrees. I measured it as it was based on the height of the gearbox and the differential with respect to each other.

With the moustache bar you made, was it similar in height as to an R180 or similar? I can't remember whether my moustache bar on the R180 was flipped or not to push the rear of the diff as high as it could go. I would assume this would make the problem worse? I thought you wanted to have the differential and gearbox angles parallel?

You are right though, there isn't that much angularity on the whole thing. 3.5deg at the engine isn't that much compared to the diff.

I have sent the tailshaft out to be checked for balance. I will get the tyres re-balanced too as they may be flat spotted for sitting so long? I would assume though the fronts would be the same!?

When Les put the diff together, he said the company that did the work on the diff did a great job and the finish was excellent, so I don't think this is causing the issue.
Perhaps I could rip the back of the diff housing off and check for any run-out, but I'm fairly sure Les would have done this and found it to be all OK.

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Quick note:
I have had the tailshaft re-balanced after fitment of the new flange to accept the R200.
Seems it was slightly out. Not sure if this is causing the issue or not.
Next check is the rear bush of the gearbox.

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Hey mate. I was pretty tired when I wrote my reply. It makes more sense to me now regarding the tail shaft angle relative to the height of the rear sub frame and diff attachment.
Biggest concern will be the gearbox to diff angle so that the uni's are balanced. Otherwise you'd get an elliptical type pattern of the prop shaft. Like a skipping rope.

That article you posted about a while back explains it well. So really, it's a 4 degree deflection. I would still think that the joints should offset that deflection so hopefully the balance sorts out the issue for you!

I doubt it'll be the runout of the ring gear, it was just a thought. But as I've learnt. It only takes 1/10th of a mm to effect contact patterns.

There's no lumps or deformities on the tyres?

_________________
Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Hi Ross, yes, agree. I need to make sure the angle from the gearbox to diff is similar.
I kind of wanted to know whether anyone else has measured their setup too just for comparison purposes before I go on a wild goose chase.
I think I may have found the issue (the tailshaft out of balance), but need to make sure it's all good.
I'll be putting it back together, but wanted to know if I should put the thinner bushes at the top (as this will lower the front of the diff even further)

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Have you asked Lachy or Les about this, Nik? (Les did your diff, didn't he?). I reckon they'd have the right answer for you!

_________________
build-threads.com

Update.
Issue is back....

Tailshaft has been balanced
Wheels have been balanced on the rear (no real change)

Facts:
It may be occurring during normal driving, but you can't really feel it.
When travelling at 110+ there is a point where the vibration just starts to feel ridiculous.
I have changed the bushes in the moustache bar around (slim at the top and thick at the bottom) and re-measured the angles:
Now I have:
-1.0 deg for the Diff
+2ish for the tailshaft
+3.5deg for the Engine/gearbox.
So I don't know if it's still the pinion angle causing the issue. I might actually get some spacers made up for the moustache bar to make it thicker at the top?

Could it be tailshaft?
CV's?
Rear gearbox bush (where the yoke slides in)
Tyres/wheels still?
Rear bearings (recently been changed - to some quality japanese Koyo's...

Feeling under the car, the diff was warm, the inner CV's warm, and the outers where cold.

Driving me NUTS!

Is it easy to replace the rear bush in the gearbox without taking the box out?

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Update.
I ran a dial gauge over most things under the rear end, starting with the tyre run out.
I have at least 1.7mm runout on the tyres! Probably from them sitting for so long while I have been working on the damn thing.
All other turning bits seem to be within spec which is good. So perhaps this is the vibration problem? Would something like this be causing the vibration to be felt through the car? I would think so...

Other than buy new tyres (which I was contemplating anyway), what is a good way of getting them round again? Burnouts?

Is there some way of getting the car up off the ground to stop it flat spotting tyres over time when not in use? Short of buying another pair of jack stands...

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Drive shafts? I've heard the angle of the drive shafts on lowered cars can create pulses that then accentuates itself. Perhaps not if you running cv's it's more related to uni's?

Mate, you can feel a flat spotted tyre definitely, but I doubt that it'll be the tyres. 1.7mm isn't much. Ive had my tyres sitting on the ground for a year since i've had them on, my old ones were even longer. No issues with vibration. My mate had a lump on his tyre once that caused a vibration, but it was protruding about 1cm and was the size of an egg. very distinctive. If you aren't running staggered offsets, swap front to back and take it for a spin and see if its different? I'd imagine that the bag in the tyre would change the contact pattern on the ground anyway, you could also try dropping your pressures down to see how it handles it and if it changes the vibration. Lower pressure would let the side wall flex some more and absorb the protrusion if that is the case?

In terms of prevention, really don't have a solution for that short of reducing weight off the tyres.

_________________
Ongoing Project: 1972 Datsun 510 S13 SR20Det. http://ozdat.com/forum/viewtopic.php?f=33&t=17898
New Daily: D22 Navara (The new workhorse)
Retired 12/2016: MY98 Subaru Impreza RX
Previous Car: Restored Green 1972 Datsun 510, Hot L18

Hi Ross,
It certainly feels like flat spotted tyres. If it's 1.7mm over a large area and you can see it bobbing up and down, it would be the equivalent to a 'lump'.
I will have to swap the tyres around I think and see whether it makes any difference. I don't think it's a protrusion, but more a permanent deformation in the tyre. Having a look through fault finding on these kind of things seems to always come back to tyres.
I had the tyres balanced, but not checked for radial runout which would explain the vibration. Nothing else is out of spec and both tyres have these flat spots.

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Sorry to hear you are still having issues with it Nik, were there any signs of vibration in the gearbox before the diff swap?

_________________
1600 Build: http://ozdat.com/forum/viewtopic.php?f=59&t=22694

Hi Trent.
No vibration in the gearbox. The only noises I got was some small resonance noises in 4th gear, but that hasn't changed.
Haven't had a chance to try swapping the tyres (or measuring the fronts for that matter...).

_________________
1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

I'm dealing with the same frustration here. Any resolution? Here is a good calculator that helped me with calculating the operating angles - http://spicerparts.com/calculators/driv ... calculator.