Thread: LT95 gearbox noise

Originally Posted by Bush65

That is the idling spring adjustment, not the idle speed adjustment. the idle speed adjustment is on top of the governor.

The idling spring adjustment is for the governor to maintain the idle speed when the load changes, eg air con compressor clutch engages/disengage, or the road grade changes up/down.

The stock idle speed is on the low side and the torsional vibration will be improved if the idle speed is increased, via the idle speed setting screw on top of the governor.

Can you please explain more on what this can do. By adjusting this will my engine better maintain a set idle when the air con kicks in?

Originally Posted by isuzutoo-eh

Hi Adrian,
That sound is normal. They rattle. Someone posted the reason recently, but it is not at all detrimental to the vehicle's operation or longevity.
Enjoy your trip and post lots of photos!

Thanks very much, was concerned that I may need to refurbish box and out lay big bucks. I had a 300Tdi and was comparing against that.

Originally Posted by isuzutoo-eh

Hi Adrian,
That sound is normal. They rattle. Someone posted the reason recently, but it is not at all detrimental to the vehicle's operation or longevity.
Enjoy your trip and post lots of photos!

Cheers, may have saved me a trip to the funny farm.......!

fcnutter,

This post from John is spot on.

Originally Posted by JDNSW

I gather by clutch 'out' you mean with your foot off the pedal, and by 'engaged' you mean with your foot on the pedal (in other words, the opposite to the normal use of the words).

If I am correct in my interpretation of your meaning, this is perfectly normal. The engine accelerates and and decelerates twice per revolution due to the large cylinder size, high compression and relatively light flywheel with only four cylinders. As this happens the free play on the constant mesh gears flops back and forth twice per revolution, creating the noise you hear.

The effect can be minimised by increasing the idling speed slightly, better by fitting a hand throttle so that it can be increased as necessary for different temperatures and degrees of warming up.

John

The advice in some of the other posts that it is normal and not detrimental are misguided.

The 'normal' remark while largely correct, you should understand it is only normal because of some issues that are well documented. I strongly encourage you to not continue to live with this 'normal' condition.

The 'not detrimental' remark, I most certainly don't accept. The LT95 is a strong gearbox and has greater success than lesser gearboxes from the torsional vibration.

Increasing the idle speed is a simple adjustment that will improve the vibration and its affects.

This diagram is a cutaway assembly of the RLD governor, the type used on the Isuzu 4BD1 and 4BD1T.



The 'Control lever' is drawn a little different to what is actually used on most 4BD1 but otherwise it is good enough.

The 'Idling set bolt' shown in the top right corner of the diagram is used to adjust the idle speed. Turn it in toward the control lever to increase the idle speed.

Some governors that have not been serviced since leaving the factory, may have a tamperproof shroud over the 'Full speed set bolt', hiding the end of the screw and its locknut. There is no shroud over the idling adjustment.

Both of these screws simply limit how far the control lever can travel, either to minimum or maximum speed position.

The 'Idling spring' adjustment is shown at the bottom right of the diagram. This spring pressure setting affects the governor action during idling, to return the engine speed if it rises because load has reduces or if it slows because load has increased.

Some of the RLD governors do not have the hexagon caps over the idling spring and governor spring adjustments, as shown in this diagram. They have welch plugs.

Originally Posted by Bush65

This diagram is a cutaway assembly of the RLD governor, the type used on the Isuzu 4BD1 and 4BD1T.



The 'Control lever' is drawn a little different to what is actually used on most 4BD1 but otherwise it is good enough.

The 'Idling set bolt' shown in the top right corner of the diagram is used to adjust the idle speed. Turn it in toward the control lever to increase the idle speed.

Some governors that have not been serviced since leaving the factory, may have a tamperproof shroud over the 'Full speed set bolt', hiding the end of the screw and its locknut. There is no shroud over the idling adjustment.

Both of these screws simply limit how far the control lever can travel, either to minimum or maximum speed position.

The 'Idling spring' adjustment is shown at the bottom right of the diagram. This spring pressure setting affects the governor action during idling, to return the engine speed if it rises because load has reduces or if it slows because load has increased.

Some of the RLD governors do not have the hexagon caps over the idling spring and governor spring adjustments, as shown in this diagram. They have welch plugs.

So turning the idle spring out weakens the spring tension making it harder for it to return to idle speed?? if that’s what I have done DUH

Thanks for that diagram Bush65. Very useful.

As luck would have it, I did adjust the correct screw to raise my idle

My Full Speed Set screw was wired in a fixed position, so no accidentally changing that one.

Originally Posted by County3.9

Can you please explain more on what this can do. By adjusting this will my engine better maintain a set idle when the air con kicks in?

This is from the injection pump manual.


This is the data for the 1986 on 4BD1 from the Isuzu 4BD1 4BD1T engine manual. The diagram superimposes the full load and idling performance curves.


These two both from the injection pump manual for the adjustment of points on a typical idling performance curve.