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Transmission query...


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I've begun to investigate further the transmission issues that I picked up (or lost) at Seven Sisters over the weekend...

The car is a 1992, 3.9 Efi Auto with Borg Warner T/box.

I've pulled both half shafts out of the rear axle and they are fine - the wrong ones - but good condition!! The symptoms I have at the moment are:

1. Drive to both front and rear from the T/box with no load on the vehicle (all jacked up and in drive or reverse)

2. No motion what-so-ever of any of the road wheels

3. When I put it from drive to Park there is a nasty noise that I can only describe as something like the frayed ends of a bit of wire rope being hit by something rotating very quickly - does that make sense??

When I drained the oil out of the rear diff, there was no sign of any lumps of metal in it....the oil - not the diff!! :lol: There appears to be teeth still on the rings in the diff when I shine a torch in there...

Now, I am unsure of which end of the drive shaft to start looking further.... Do I take the diff out and check that it's OK, or do I start looking at the T/box end?? :unsure: Common sense tells me to take the diff out anyway, but if it sounds like something that someone else has experienced, I would welcome some pointers...I'm a little perplexed by the whole thing!! :huh:

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stick the vehicle in drive and see if the props are rotating with any force. If they are rotating as you would expect (and slow down and speed up with engine acceleration) then you have pretty much ruled out t/box issues- UNLESS the chains in the T-box are slipping which is quite possible.

Realistically you are much morelikely to break a half shaft than an actual diff, so i would look at the T-box as the likely culprit.

BW t-boxes work off chains in the box which have to take all the drive of the engine- they are great off road because they allow part slippage if necessary and are totally fit and forget. However if you start to get wear in the T-box then you van have problems- i had issues with mine because it wouldn't unlock which made going round tight corners fun- i found going round corners quickly to be the most effective "work around" because it took the weight off the inside wheel which could then spin the transmission wind up away!

Does it have the same symptons in all 10 gears?

IIRC you can drain the fluid from the BW box and have a look at it- it's been quite a while since i did this, but i think the fluid should be bright red like Auto box fluid, if it's brown then you have problems (this paragraph might be complete rubbish but i seem to remember it being right!)

not a huge amount of help i'm afraid.

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What Pugwash says about chains in boxes is probably all true but there's no such devil-worshipping jiggery-pokery in a diff, prop movement = wheel movement. If you have one and not the other, then there's something wrong with that axle. You could turn a prop and look in through the oil filler hole to see if the crownwheel's spinning, but if you pulled two intact (rear) halfshafts you're going to need to drop the diff out anyway. The front is similar but a little more complicated because of the CVs.

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Cheers chaps!! I was gradually convincing myself that the diff is going to have to come out, but you've confirmed it for me!!

The one thing that still worries me is the noise, could this be what Jim is describing in the T/box??

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it's possible

do you definitely have drive to both propshafts? the thing to watch out for is that the props are moving with force- they might just be rotating due to residual drive in the t-box. Very carefully try and see if you can prevent one of the props from rotating when in drive. if you stop one, then you have a t-box issue, if they rotate as you would expect then you have an issue somewhere else!

just seems so unlikely that you have buggered both axles!

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Turns out that the front one was bu##ered before I bought it, but I didn't check it when looking at the car!! Found out on the first gravelly hill at Seven Sisters on Saturday morning!!

It's only the rear one that I've broken.....and there was definitely a metallic cracking/rattling sound when it went!!

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IIRC you can drain the fluid from the BW box and have a look at it- it's been quite a while since i did this, but i think the fluid should be bright red like Auto box fluid, if it's brown then you have problems (this paragraph might be complete rubbish but i seem to remember it being right!)

BW is filled with ATF, so you're right on the money.

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Pugwash - it's worth pointing out that if there is any rotation of the prop shafts, no matter how it is derived or how much torque there is being transmitted by the BW box, the wheels will turn unless the axle components are damaged.

There may also be a problem with the BW box, but since the props are rotating and the wheels are not, the problem MUST lie in the axles.

Si

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3. When I put it from drive to Park there is a nasty noise that I can only describe as something like the frayed ends of a bit of wire rope being hit by something rotating very quickly - does that make sense??
The one thing that still worries me is the noise, could this be what Jim is describing in the T/box??

The "noise" is almost certainly the park ratchet struggling to engage, because the gearbox/transfer box and props are still rotating when you are selecting park after it has been in drive.

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true true, but i wasn't sure that the T-box had been ruled out.

I had a BW go wrong a while ago and convinced myself it was the axles, even going so far to buy second hand known good ones and swapping them out- felt a bit silly when i realised that the BW had broke- i hadn't thought of checking to make sure the props were turning under drive. Felt a bit silly then!

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Rear diff US.
DUR.

I'm going to be stoopid here, but what do the US and DUR mean?? Are they some kind of "geek speak"??? :lol:

As far as I can work out, the BW is turning the prop shafts with quite a force. As pugwash says, this doesn't mean that there isn't a fault with the T/box, but I am more inclined to look at the axle (as Simon suggests) before going further up the drive train.

Something else I noticed was that the BW was spinning both front and rear props, even under no-load conditions. Is this because it is sensing that the back isn't turning the wheels and therefore engages to transfer some of the drive to the front, or is it supposed to do that??

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Adrian,

You need to look at the BW as a locked differential that unlocks to allow cornering. Whilst it doesn't strictly behave that way if you want to get technical, to all intents and purposes it permanently drives both props.

As said above, if the props are turning and the wheels are not then there is a discontinuity (i.e something is bust :lol: ) between the axle end of the prop and the wheel. As you have eliminated half shafts then it is the diff or pinion gear. There are no other options.

Once you have investigated that and remedied it, then you can look at the BW if you still have problems.

US means useless.

DUR means Chris double posted ( at a guess :lol: ), a bit like a Homer-esque D'oh!!

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Ah, the techno babble becomes clear!! Ta Bish and Mark!!!

As for the BW - thanks for the plain english explanation. I was getting a little confused (not hard for me really) about the way it works. That helps a great deal! Even the basic info I've found on the net makes me scratch my head!!

I knew I should have taken the diffs off the bloke I picked up the new shafts from!!! That'll learn me for getting the parts before I've taken it apart!

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