LT77 gearbox whine

[mrtask]

I transplanted an LT77 into my 3500 the other year. Recently I have started to hear a whining noise when driving with the window down. Pretty high pitched, sounds like whirring fluid. I think it goes away when I dip the clutch, which is why I suspect a gearbox issue. I've also been told the differential extension housing bearing can expire, but I would have thought that would make a more metallic noise, not this peculiar sort of jet engine/turbine whine I'm hearing. Anybody have any ideas as to what might be the issue? All sensible speculations welcome.
I'll just add, the new disconcerting noise is not the high pitched sound of the tiny spring in the gear lever, that is a much higher pitched sound which I can quieten by twisting the redundant-but-authentic-looking plastic bit that is no longer necessary to select reverse. I'm so in tune with all the various noises my car makes, I know straight away when it develops a new audible symptom of impending expense!

 

[harveyp6]

I've also been told the differential extension housing bearing can expire,

I never experienced a diff pinion bearing failure. I replaced plenty of pinion seals but even with those leaking it never seemed to affect the bearing.

 

[sdibbers]

To add to Harvey’s comments. The diff wouldn’t whine if the car Is stationary.

I’ve had LT77 boxes in TR7’s in the past. They tend to have rattly idle shafts as standard. But that’s not the sound you’re describing.

My guess is the clutch release bearing is still touching the pressure plate when the clutch pedal is released. The noise goes away because the pressure builds on the bearing. I would try removing the slave cylinder temporarily and starting the car, if the noise has gone adjust the pushrod length to give a little more room.

One other (distant) possibility is that the oil level has dropped internally, or the fibre gears on the gearboxes internal oil pump have stripped. But if that was the case the box wouldn’t last long.

 

[mrtask]

I never experienced a diff pinion bearing failure. I replaced plenty of pinion seals but even with those leaking it never seemed to affect the bearing.

That is some small reassurance at least! The P6er I met at the Enfield Pageant who suggested the diff bearing as a point of failure also opined that the tappety(?) noise my engine makes (I don't think I've posted about that noise yet!) is piston skirt slap. I rather think he was painting two worst case scenarios. He was grinning whilst he offered his diagnoses.

if that was the case the box wouldn’t last long.

That's my worry.

 

[sdibbers]

That's my worry.

the noise is wrong for that (I speak from experience, had the oil pump fail on the M25 at 11pm many years ago. Car got slower and slower). Try feeling for a lack of play in the clutch release bearing arm. It should be s little loose when at rest. If it feels like its stiff with no play I bet that's your issue.

 

[jp928]

"Doctor,doctor, it hurts when I do THIS!". - Dont do THIS.
Years ago (MANY!) I helped a guy pull a P4 box and fit new bearings - except for one that was very difficult. Got it back together, filled with oil, started it up- bearing noise! Pulled it back out, replaced the one we missed, refitted - still noisy. Took advice - they are all noisy UNTIL YOU PUT THE COVER BACK!! On a P4 its a LARGE central piece of the floor - the box comes out upwards.
Have you been able to check the oil pump is working?
Shut the window, until you get a serious symptom.

 

[mrtask]

I had to have the expensively refurbished gearbox rebuilt last year after it came to a noisy crunching halt. Turned out the internal oil pump had never been functional, and I'd been driving for a whole year with it "splash oiling" alone! Which explained why the gearbox tunnel had always got so hot. The company who then put it back together said I'd also managed to chip off a few reverse teeth, but that there were enough to get on with! I just have to remember not to pull right up against any immobile objects before selecting reverse, in case I'm at the spot on the gear where there aren't any teeth!
Prior to developing this new whine it had begun to make quite the metallic noise idling in neutral. It now occurs to me that clattery sound has been replaced by this new whine. I have been blithely carrying on as you suggest @jp928 , but I imagine earlier attention might have been advisable. I'm putting my money (and I do so hope it won't end up being a whole lot of it!) on the throw out bearing, but we shall see...
I won't be wielding the spanners myself, I'll have to entrust it to my friendly local mechanic, who knows his way around a P6, and has already had more than a few workshop visits from mine!

 

[cobraboy]

I have been torturing LT77 boxes for many a year now, with mainly good luck. In the beginning the LT77 was filled with hypoid gear oil, this was however not good for gear selection when cold, and customer complaints led BL to recommend ATF as a solution.
I have been told by an experienced gear box guru that ATF is not a very good lubricant, and the bearings don't benefit from using it much.

The recommendation from said guru, and this has been backed up by other sources is to use a thin fully synthetic oil, and if you are going the whole nine yards add some Moly gearbox treatment.

So in one box I have been using Mobil 1 0W 40 and Moly, with good results.

Other options are Castrol Syntrans, or Redline MTL
These provide the lubricant for the bearings and allow smooth shifting.

If you have ATF in there it is possible that the bearings have suffered, although I cannot imagine the box has had a hard life since the rebuild.

 

[mrtask]

I cannot imagine the box has had a hard life since the rebuild.

I rather think my driving style might be quite hard on not just the gearbox but every other component of the car! I do enjoy leathering it about the place, and every now and then I manage to 'buzz the box' a bit by missing a shift. I think the expression is "money shifting!". I also think I'm gonna find out exactly how much in fairly short order...
I'll ask my mechanic what oil he filled it up with last time. I know he did a gearbox flush after about 500 miles.
My car will celebrate turning 50 in a couple of weeks, I hope it stays driveable until then!

 

[quattro]

Other options are Castrol Syntrans, or Redline MTL

I use redline MTL and mine is quiet and a real slick shifter. When I first got the car, changing gear was like stirring a saucepan full of potatoes, so after some research I found the Redline MTL and it has been perfect since.

 

[mrtask]

Took my car out after a whole week without having been able to drive it. I get such withdrawal symptoms if it doesn't get used regularly. Anyway, from cold, the first run up through the gears it didn't want to let me select third although the clutch was definitely fully depressed. I cringe when I hear that buzzing sound. First and second hadn't been a problem, clunky but firmly engaged. Might that perhaps indicate anything in particular, gearbox gurus? Can a clutch stick only in a specific gear!?!?

 

[cobraboy]

Did you find out what lube was put in it ?

 

[sdibbers]

Took my car out after a whole week without having been able to drive it. I get such withdrawal symptoms if it doesn't get used regularly. Anyway, from cold, the first run up through the gears it didn't want to let me select third although the clutch was definitely fully depressed. I cringe when I hear that buzzing sound. First and second hadn't been a problem, clunky but firmly engaged. Might that perhaps indicate anything in particular, gearbox gurus? Can a clutch stick only in a specific gear!?!?

How’s selecting reverse? If the clutch is dragging it will show up as grinding when trying to select reverse. I’ve had a clutch release lever fail on an LT77 box in the past that started as a noise and a gradual inability to fully release.