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Retroanaconda

Noisy LT77 Gearbox

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Retroanaconda    127

Folks,

The car developed a new noise this week, a 'rumbling bearing' kind of noise present in third and fifth gears either when power is applied or on the overrrun. It is most noticeable on overrun in third gear, when slowing for a roundabout for example. No noise in first, second or fourth from what I can hear. The frequency of the noise increases and decreases commensurate with road speed. I can't replicate it by running through the box with the transfer box in neutral, suggesting it relies on load being applied to the box. The fact that it is only present in certain gears leads me to suspect only the gearbox, rather than other drivetrain components.

The gearbox is pretty old however I'm not sure what actual age it is or how many miles it has done. The car has done 290k and the gearbox was in place when I bought it at 140k and didn't look new then, so there is at least 150k on it. In theory it could be original to the car however the mileage and the fact that the output splines were revealed to be in remarkably good order during a transfer box swap a number of years ago lead me to suspect it has been changed at some point. Not sure what the life expectancy of an LT77 is to be honest?

I have read about LT77 gearboxes doing many tens of thousands of miles with rumbly bearings without it getting worse or failing catastrophically, however l need to be able to rely on the car so my plan to start with is to change the oil, having a close look at what comes out, and then monitor the noise with a view to replacing the gearbox later in the year.

I wonder though if anybody has any relevant experience that they could share?

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Sounds like a layshaft bearing starting to throw the towel in. 

 

The layshaft gets faster with road speed, the reason you won't hear it in 4th is that 4th is straight through the gearbox, so although the layshaft rotates, it won't be under load.

 

I've had one go on me in spectacular fashion a few years ago. Used 4 high and low to get me home.

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Retroanaconda    127

That makes sense, except that there's no noise in first or second, unless there's a bearing on the layshaft that is only loaded when third/fifth is engaged and not when first/second is.

Changed the oil this morning, it was long long overdue however apart from being slightly discoloured showed no signs of major problems internally. Drain plug had usual small amount of filings on it, and the filter in the extension housing was fairly clean.

New oil is in and has maybe made it slightly less audible but noise is still there, I will monitor going forward I think. The car spends a lot of time in fifth gear, so I'll be able to see if it gets worse.

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Snagger    197

The lay shaft is loaded in first and second too, but the tangental loads are less and the shaft rpm less for a given engine rpm than in third or fifth.  Vulcan's suggestion of lay shaft bearings makes sense to me.

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Retroanaconda    127

Thanks guys. Noise now audible in first and second too, so all gears except fourth which very much suggests layshaft bearings as above.

For all I know it may well rattle away quite happily for some time, however I think I will bring forward the repair schedule, doing 750 odd miles a week I really don't want it going bang on me.

I foresee a 'fun weekend' in my near future.

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reb78    140

How does it compare to mine James?

 

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Retroanaconda    127

That sounds quite like it, mine's not quite as loud as that but it's a similar noise certainly. A shared characteristic in that it's most noticeable on overrun. How has yours developed, if at all?

I've got another box coming (punt off eBay - wish me luck!) and will try and get it swapped as soon as possible.

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reb78    140

I took mine back to the reconditioner. 70k wasn't acceptable IMO. They hadn't used Timken bearings and one had failed. Visible score marks on the rollers. The syncro rings that were in it were also very poor, so they were replaced at the same time (not the cause of the noise, but caused a really dreadful 3-2 and 4-3 shift). A leak or two later and I may have an acceptable box for now... 

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MuddyWinny    5

I had a whirring noise proportional to road speed and put it down to gearbox bearings.

A number of months later (I don't do that many miles in a year) I heard a 'ping' when pulling away although all seemed ok.

It tuned out to be the cross pin in the front diff which had worn to the point of snapping.

With a decent second hand diff fitted things were a bit quieter.

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Retroanaconda    127
On 25/04/2017 at 10:04 PM, reb78 said:

I took mine back to the reconditioner. 70k wasn't acceptable IMO. They hadn't used Timken bearings and one had failed. Visible score marks on the rollers. The syncro rings that were in it were also very poor, so they were replaced at the same time (not the cause of the noise, but caused a really dreadful 3-2 and 4-3 shift). A leak or two later and I may have an acceptable box for now... 

Would you be willing to share the name of said reconditioner? By PM if you'd rather.

 

On 26/04/2017 at 1:31 PM, MuddyWinny said:

I had a whirring noise proportional to road speed and put it down to gearbox bearings.

A number of months later (I don't do that many miles in a year) I heard a 'ping' when pulling away although all seemed ok.

It tuned out to be the cross pin in the front diff which had worn to the point of snapping.

With a decent second hand diff fitted things were a bit quieter.

Pretty sure mine is gearbox, in fact I'm sure of it. I can hear a faint rumble at idle which goes away when I put my foot on the clutch (i.e. when layshaft slows down and stops) and its present in all gears except fourth.

Done a video of the noise for reference, in this case on overrun in third gear. The best capture of it is toward the end.

 

 

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MuddyWinny    5

That's a fair point about the noise going when the clutch is disengaged.

The noise I had sounded different and was louder on acceleration (i.e. when torque applied from the engine).

Apologies if I've added confusion to the mix.

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Retroanaconda    127

Just to close this one out - I swapped the gearbox at the weekend (ably assisted by a very helpful forum member) and all has returned to normal. Old box sounded quite rough when turned by hand once removed from the vehicle, it may have lasted for another 100,000 miles or might have failed tomorrow, who knows.

Interestingly more filings had accumulated on the drain plug magnet since I changed the oil a couple of weeks ago than had done so in the previous few years, so it seems something was breaking up inside.

Thanks to all for the help.

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reb78    140

That 'helpful forum member' is a good chap James. He took a Sunday afternoon and a Monday evening out of his time to help me out this last week. Thanks Neil!

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V8 Freak    73

Always happy to help out guys....

Good to see you both again too :)

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