Gearbox noise during deceleration

[Godber]

I understand this is not an uncommon problem, but maybe someone can explain it so even I understand:)

As soon as I decelerate in 5th gear, the transmission (LT77) is screeching and grinding at a rather uncomfortable level,

which immediately disappears, the moment I accelerate. Total failure, or can that be repaired without too much campaign?  

 

[miketomcat]

Are you sure it's gearbox, I had a uj fail and make a screeching noise on deceleration. 

If it is the gearbox it's likely to be quicker and easier to swap it out, as gearbox rebuilds tend to be time consuming and often require special tools.

Mike

[Snagger]

UJs and mounting rubbers are always the first things to check for transmission noise.  You’d be amazed at how much noise or vibration a bad UJ can make, and the torque direction and magnitude applied to the UJ can produce very specific results.  UJs must account for 95%+ of transmission noise worries.

[Godber]

Thank You, I will investigate in that direction, but I'm wondering, how a failing UJ can produce such a sound, vibration and shuddering yes,

but a grinding sound, it really sounds more like a failing bearing to me.

But hey, there are always new tricks to pick up, and I will not ignore advice, that's for sure:)

 

 

[Mo Murphy]

My experience of this type of fault with grinding on overrun at speed was that the fault lay in the transfer box.

Mo

[reb78]

I know everyone always points to UJs (and they are easy to check first) but every time I have had a noise from down there its been a gearbox issue. 

Edited October 19, 2021 by reb78

[Snagger]

3 hours ago, Godber said:

Thank You, I will investigate in that direction, but I'm wondering, how a failing UJ can produce such a sound, vibration and shuddering yes,

but a grinding sound, it really sounds more like a failing bearing to me.

But hey, there are always new tricks to pick up, and I will not ignore advice, that's for sure:)

 

 

It could well be a transfer box or gear box fault, but it is easier, quicker and cheaper to check the UJs first.  A bad UJ can create all sorts of noises, depending on whether it is loose, seized, off centre, has ridges worn on the bearing surfaces, is dry, has a foreign object stuck in it, the UJ is loose in the yolks and so on.

You do have to remove the prop shafts to test them - it can’t be done on the vehicle, and all the times that you see folk give a twist or wiggle to check a prop in place, they are wasting their time and deluding themselves.  You have to move each UJ fully in each range of motion with torque applied in one direction and then the other on the shaft to feel for binding or tightness as well as any play.

Fingers crossed, you’ll find a UJ issue and have a cheap repair.  If not, you’ll have to start working through the boxes.