DMAX shake/wobble/surge under low RPM

[mydmax]

Mike C
I think that was referring to the wobble which may have been evident at the front yoke sleeve bearing. Simply greasing it or inspecting it doesn't require tailshaft removal. As far as I know he has only raised it and had problems afterwards. As mentioned, he is the only one which i know of having to lower the pinion flange attitude, which is why I asked if he had the correction wedges the right way around, because in wrongly they would definitely lower the pinion which is odd.

[ENC]

Did you really have to lower the pinion flange? You said it was the thick end was fitted to the front. BUT as mentioned, nearly everything,yes, everything I have seen would have the thick bit at the rear.

Like I said , Thats what my original measurements indicated but after I bought a small digital level and did alot of rechecking, I didnt need the shims at all. Turns out, it was within half a deg loaded and unloaded without the shims. I have found someone with a set of genuine Isuzu and will be doing a swap for a couple of hours on the weekend and that will remove the non genuine (yes it has wheel rings fitted) wheels out of the equation. I am running out of ideas.

[mydmax]

ENC
You have to have taken the wedge shims out to do the final check to now say to is ok. IF now ok, then the angles must have been way out and different to each other with the wedges installed. When you say "IT", does that mean one only universal, or is the other uni included in the "within half a degree" statement, ie difference between the two? Pretty unclear.
What are "wheel rings and why do you mention those? If you mean wheel spacers between axle flange and rim, you are foolish to use that style of modification. No insurance even if it isn't the cause of an accident!

It is the relationship of both uni angles and their closeness to each other in drive angle which you are wanting to be small angles.
Something in all this doesn't add up!

[ENC]

ENC
You have to have taken the wedge shims out to do the final check to now say to is ok. IF now ok, then the angles must have been way out and different to each other with the wedges installed. When you say "IT", does that mean one only universal, or is the other uni included in the "within half a degree" statement, ie difference between the two? Pretty unclear.
What are "wheel rings and why do you mention those? If you mean wheel spacers between axle flange and rim, you are foolish to use that style of modification. No insurance even if it isn't the cause of an accident!

It is the relationship of both uni angles and their closeness to each other in drive angle which you are wanting to be small angles.
Something in all this doesn't add up!

''IT'' was referring to the angle difference between the both universal, and yes like I said the initial measurements were incorrect, and we didnt need the wedges and with or without the wedges the vibration didnt get any worse or better. Hope that make sense.

Cheers Ian

[mydmax]

All sounds lovely, but what is the angle the unis are actually driving through. That is the decider. Their evenness just should be!

Also. Have you checked your engine mounts. Ie, jacked up the LHS of the engine to see if the engine mount is stuffed. That will give you vibes and shudders under load.

With the wedges in spring seats, Did you have the thick end to the rear? You say no difference in or out but raising the pinion, not dropping it might bring the unis into close alignment AND also mostly eliminate excessive drive angle. As said, I have never seen anyone needing to lower the pinion attitude with replacement springs!

[ENC]

All sounds lovely, but what is the angle the unis are actually driving through. That is the decider. Their evenness just should be!

Also. Have you checked your engine mounts. Ie, jacked up the LHS of the engine to see if the engine mount is stuffed. That will give you vibes and shudders under load.

With the wedges in spring seats, Did you have the thick end to the rear? You say no difference in or out but raising the pinion, not dropping it might bring the unis into close alignment AND also mostly eliminate excessive drive angle. As said, I have never seen anyone needing to lower the pinion attitude with replacement springs!

Thanks for that, I will check my engine mounts . Below is what I have ATM, is that what you are asking??
Cheers Ian

[mydmax]

G'day ian
Yes that is what I am asking. Those angle are sort of ok but how much do they alter when loaded? If the spring distortion under load increases the rear angle and also the front angle to some extent, then they are going away from each other and beginning to introduce vibes.
Does the load make the pinion point down more or up or stay much the same.
I haven't measured an Isuzu but a ranger is around 1 degree on both ends when new/empty.

The springs may be flexing under load, one end of the spring flexing/altering more than the other and therefore alters the pinion angle and uni drive angle. Only testing will reveal if happening.

[ENC]

G'day ian
Yes that is what I am asking. Those angle are sort of ok but how much do they alter when loaded? If the spring distortion under load increases the rear angle and also the front angle to some extent, then they are going away from each other and beginning to introduce vibes.
Does the load make the pinion point down more or up or stay much the same.
I haven't measured an Isuzu but a ranger is around 1 degree on both ends when new/empty.

The springs may be flexing under load, one end of the spring flexing/altering more than the other and therefore alters the pinion angle and uni drive angle. Only testing will reveal if happening.

I just realised that the 8 Degs should be 8.2 and redrew it. I have also attached the loaded angles

[mydmax]

I don't know the angle the of your correction wedges but I would be fitting them with the thick end to the rear of the spring seat, That will bring the pinion flange up a little and therefore reducing both the rear uni more than the front uni and largely go towards having just a little of angle on both but both will be near perfect and low drive angle in both situations.

A universal joint, if driven with high torque and more angle than it likes, WILL try and "open up" as it revolves and tries to flick sideways as the uni yokes move past each 1/4 turn. If allowed to or too much angle that will drive the rear gearbox mount into a cyclic vibration and it will shake the extension housing in a rotary pattern which is only controlled by the rear rubber mount on the Transfer case. It could be, that the angles are getting it into a harmonic which is then felt through the vehicle chassis.

[ENC]

I don't know the angle the of your correction wedges but I would be fitting them with the thick end to the rear of the spring seat, That will bring the pinion flange up a little and therefore reducing both the rear uni more than the front uni and largely go towards having just a little of angle on both but both will be near perfect and low drive angle in both situations.

A universal joint, if driven with high torque and more angle than it likes, WILL try and "open up" as it revolves and tries to flick sideways as the uni yokes move past each 1/4 turn. If allowed to or too much angle that will drive the rear gearbox mount into a cyclic vibration and it will shake the extension housing in a rotary pattern which is only controlled by the rear rubber mount on the Transfer case. It could be, that the angles are getting it into a harmonic which is then felt through the vehicle chassis.

I did some quick calculations, See below