Troopy Gearbox/Transfer Reverse Gear Noise?

Submitted: Monday, Jan 14, 2019 at 12:51
ThreadID: 137676 Views:2335 Replies:4 FollowUps:4
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Hello Everyone,

I posted this on LCOOL but there seems to be a lot of knowledge here too.

My 2002 troopcarrier is making a fairly loud clunking noise in reverse gear. I'd like to figure out what it is before I head out bush again. It's been doing this for a couple of months (I drove 10 000km across Australia in the meantime and the noise has not changed)

I've ruled out hubs, CV's, unijoints, engine mounts, front and rear diffs, and the tailshaft. It really sounds like it's coming from the gearbox/transfer case if you listen from outside the vehicle.

My first thought after looking at the drivetrain is that it's a chipped tooth on the reverse gear cog, but for the following reasons I'm wondering whether it might actually be related to something in the transfer case.

-The noise only occurs when reverse gear is selected and the clutch is engaged. You can roll backwards in neutral or with the clutch in while reverse is selected and the noise is not there.

-The noise increases in frequency when low-range is selected (how is this possible is it's a problem in the gearbox?)

-The oil that came out of the transfer was burnt.

-There are some fine metal particles attached to the drain plug magnet on the transfer case but no particles larger than a tiny flake.

-I opened the inspection port on the transfer case and had a look inside. The cogs look OK. There is considerable (~5mm) radial play when I rotate the cog I can feel with my hand through this port (the vehicle was in neutral at the time).

Any thoughts? A reco transfer case is much cheaper than a whole gearbox/transfer swap!

Many thanks,

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Reply By: Ron N - Monday, Jan 14, 2019 at 13:20

Monday, Jan 14, 2019 at 13:20
Dave, I'd have to say you have either a cracked tooth on the reverse gear in the main gearbox, or the bearing on the reverse gear idler shaft is failing.

Be wary of Koyo bearings in the repair, if the bearing in needed.
My workshop (truck mechanic) neighbour, Joe, rebuilt two Landcruiser gearboxes a few years ago - and both failed again within 10,000 kms - meaning Joe had to rebuild them both again.

When he stripped them down, he found the Koyo bearings he'd installed on the reverse gear idler shaft, on both gearboxes, had rapidly failed.
I won't repeat his words as regards what he thinks of Koyo bearings, but they can't be written here.

Always check the country of manufacture when buying bearings - Koyo are notorious for now sourcing bearings globally, and not listing where they are manufactured.
As you are probably aware, a lot of Chinese bearings can't cut the mustard.

Cheers, Ron.
AnswerID: 623210

Follow Up By: TroopyTrouble - Monday, Jan 14, 2019 at 13:26

Monday, Jan 14, 2019 at 13:26
Thanks Ron!

Can you explain how the noise could increase in frequency when low range is selected? If it's a cracked tooth or bearing on reverse gear in the box, wouldn't the gear be spinning at the same rate regardless of the hi/lo range selection?

FollowupID: 896340

Follow Up By: Ron N - Monday, Jan 14, 2019 at 20:27

Monday, Jan 14, 2019 at 20:27
TT - That increase in frequency is difficult to explain. However, it may be that the heavier load being exerted on the reverse gear when in low range, is making a bigger worn area of the bearing or rollers (or teeth) produce noise, that it doesn't do under the more moderate load, when using high range.

The gears are spinning at the same rate if the engine RPM is the same in both high and low range - but to produce the same ground speed, the engine and gearbox is turning at a high RPM when in low range.

Cheers, Ron.
FollowupID: 896359

Follow Up By: RMD - Monday, Jan 14, 2019 at 20:45

Monday, Jan 14, 2019 at 20:45
Stress on the reverse gear is lessened when using low ratio not an increase because of the mechanical advantage now in play over the rear wheels. No increase in load at all under same terrain, less in fact.
FollowupID: 896360

Reply By: RMD - Monday, Jan 14, 2019 at 14:50

Monday, Jan 14, 2019 at 14:50
Troops trouble,
The gearoil shouldn’t be burnt, aged perhaps and maybe quite brown when new. Do you know the initial colour. Colour can be misleading if origins aren’t known.
There will be noticeable movement (rotary)of transfer gears, but the movement you mentioned shouldn’t be the slack between mating gears. All rotating parts which mesh, gears and dogs all have a clearance so I hope that fact isn’t confusing you.
The engine and gearbox speed WILL increase when low is selected to compensate for the low range being selected. That WILL make the reverse sound more frequent, sound faster.
Obviously if a gear is under load and has a damaged tooth it will make noise, loud click, and if it can easily transfer rotary motion when not loaded then no noise will be heard.
Remove the tailshaft and have someone press the clutch in.
Then release clutch until a slight resistance is felt while turning the rear TC flange. If a reverse tooth is broken off or partially broken in it’s height you will feel the jump as it passes other teeth. Then you will know for sure. Most likely a tooth or bits of it are attached to the gearbox drain magnet.
AnswerID: 623213

Follow Up By: RMD - Monday, Jan 14, 2019 at 20:48

Monday, Jan 14, 2019 at 20:48
The fault does not appear to be transfer case related to me. Nothing you have said indicates transfer case. It is just that is where your focus is, likey not to be that if it is heard when reverse is selected as nothing changes in the transfer case with reverse being selected.
FollowupID: 896361

Reply By: Member - nickb "boab" - Tuesday, Jan 15, 2019 at 06:09

Tuesday, Jan 15, 2019 at 06:09
How are you determining/ diagnosing where the noise is coming from ? On a hoist etc
Cheers Nick b

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AnswerID: 623223

Reply By: Athol W1 - Tuesday, Jan 15, 2019 at 09:32

Tuesday, Jan 15, 2019 at 09:32
As the noise only appears when in reverse gear then it can not be any where else than in the gearbox.

As the frequency of the noise increases when low range is selected (should be by about 2.5 times) then the source of that noise can only be from the gearbox.

As the noise is only there when reverse gear is selected then it must be something in the gear set that is only engaged when reverse gear is in use.

Unfortunately there is no option but to have a complete strip down of the gear box and inspection to determine exactly the source of the noise, be that chipped/broken gear or bearings.

Athol (motor mechanic now retired)
AnswerID: 623224

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