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1995-2002 Range Rover P38A
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Discussion Starter #1
Transfer Box/Viscous Coupling - Grinding Noise & No Drive

Greetings all

Search has been done but I haven't found anything with similar symptoms other than transfer chain failure, H-L shift movement failure, or viscous coupling failure in which the coupling locks up - none of which seem to be the case for me.

Cause:
  • Driving normally, no unusual noises or vibrations, normal power levels, car has been driven regularly in the preceding weeks.
  • I had slowed down to ~30km/hr due to bad road conditions and when I applied power (maybe with a little vigour...) to resume cruising speed I lost all drive: engine running fine, just no forward movement and a rather nasty grinding/buzzing noise.
  • Managed to coast to a safe location, investigate and fail to resolve, recover home and investigate further.
Effect:
  1. No movement regardless of gear selection
  2. All driveshafts intact
  3. Transfer box motor makes noise and instrument panel shows successful movement from H to L and back again
  4. A significant grinding noise in gear (D, R, 1, 2 3) that varies in speed depending on whether the transfer box is in H (high speed buzz/grind) or L (low speed buzz/grind)
  5. Grinding noise persists slightly when returning to neutral before quietening down
  6. Vehicle rolls freely when in gear (manual push 1-2m back and forth)
The fact that the noise changes frequency depending on selection of H or L leads me to believe that the transfer mechanism still works, and that the problem lies on the output side of the transfer box.

Has anybody experienced similar with a viscous coupling failure? The more common failure modes seem to be total lockup with resulting tyre squeal when cornering, or movement but in 2-wheel drive only.

Thanks in anticipation.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

their is no 2 wheel drive with these vehicles , permanent 4wd only. put a fuse in the fuse slot to go into tow mode ( under seat not shore what number, in hand book )and run the box to see if the grinding is still there if so its not the transfer, just a process of elimination.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Fuse 11 puts the transfer case into neutral, a position between high and low. The range change gears are before the chain and viscous coupling so if the noise goes away with it in neutral you've confirmed it down to the output side of the transfer case. Never heard of a chain breaking but I suppose it's possible and a viscous would usually lock up so you'd still have drive (and no noise). Looks like you'll be dropping the transfer case off. It's not actually difficult, although Rave says to remove the exhaust you don't need to, it'll come out with it still there and you can get to the top bolts with a couple of socket extensions and a knuckle joint. You'll need two people though as it's bloody heavy!
 

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Discussion Starter #4
Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Thanks mad as, looks like I will be buying a new battery for that part of the diagnostic since the beast has been standing a while now.

I know they are permanent 4x4, the 2-wheel drive reference is to cases where people have removed a prop-shaft under duress.
 

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Discussion Starter #5
Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Thank you Richard G, as for my reply to mad as, I will organise a battery and do some diagnostics.

I guess it is coming out regardless!

Hopefully a trolley jack will be useful since I am short of helpers.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

The transfer box weighs 75Kg, if that helps.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Regarding removal of transfer case, I would not recommend use of a trolley jack. You should seriously consider investing in a scissor lift, so you can secure the transfer case and lower in a controlled manner.

Also, when you say quiet down in neutral, does the grinding sound completely go away? If not, bad torque converter would give similar symptom.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Can you move the vehicle when it's in park? Hand brake off.
 

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Discussion Starter #10
Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Thanks all, and notes made on appropriate tools.

My day job limits access to the vehicle, so apologies for huge length of time since last post.

- in P with handbrake off the vehicle can be moved
- in transfer neutral with fuse in and handbrake off:
- there is no grinding in any transmission position with engine running
- diagonal opposite wheels jacked the wheels turn freely by hand
- front left wheel only raised will not rotate (within the limits of the force I felt comfortable applying: leaning hard on a ~1m extension, I realise I don't think I tried turning a rear wheel on its own)
- there is a ticking noise with engine running as P is engaged that that stops on full engagement
- with transfer box "in gear"
- diagonal opposite wheels jacked causes grinding noise when turning by hand
- engine running the grinding persists in transmission N, but with reduced intensity, only stops in P
- transmission in D/R the grinding is louder
- transmission in D the frequency of the grinding varies depending on transfer H/L - higher frequency in H

This is leading me to the conclusion that the transfer chain has snapped:
- the transfer H/L/N selection works/has an effect
- there is drive through the main transmission
- front and rear axles are still connected through the VC
- there is no connection between VC and H/L/N side

Any other suggestions/thoughts?

Now, for the replacement if consensus is a broken chain: I can get a second-hand transfer box for $750 confirmed to have been working when removed from donor. Is it worth spending another $300 for it to receive new bearings and seal kit?
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

Personally, I can't imagine the Transfer case chain snapping. It's a pretty beefy chain in there, so it may loosen and give out machine gun noise, but the odds of it snapping seems very remote to me.

To me, the symptom sounds more like a dead torque converter.
 

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Re: Transfer Box/Viscous Coupling - Grinding Noise & No Driv

While it is indeed unlikely the transfer chain has snapped, all your tests point to the problem being at the output side of the transfer box. Making the chain the prime suspect. You'll have to take the transfer case off and open it up to see what broke. If it was the torque converer, P would still work.
As for the test, with one wheel jacked up and transfer and/or autobox in neutral, you should be able to rotate that wheel, but with significant force and only slowly. You'll have to overcome the resistance of the viscous coupling, but it should be possible. If not, it point to the viscous being locked up, so that will need changing as well. Not hard when you have the transfer box off anyway, so well worth checking.

Filip
 

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Discussion Starter #13
Well, coronavirus travel restrictions caught me at home and I have managed to drop and open the transfer box.

Splines stripped on the VCU outer portion. I will most likely organise a replacement reconditioned box, but am curious as to what might have caused the failure.

From the checks I did before, and that before disassembly the front and rear flanges rotated in unison, it maybe that the VCU has failed-locked. Could the stresses from that have taken out the splines rather than another part of the drive train? There were no obvious signs of tyre scrub or "wind-up" prior to the failure. The failure, as described earlier, was sudden when applying power to accelerate after a section of pot-holed road.

Presumably with the splines gone, and possibly failed-locked, the VCU is now useless, and as VCUs seem to be in short supply it's probably not going to be economical to recondition this transfer box as a spare?

The other thing I have observed is that the male outer splines have about 10mm of fore-aft movement on the inner-spline shaft, is that from movement of the sun-gear within the planetary gear body? Reference RAVE showing a continuous piece between sun-gear and the splines.


286736


286737
 

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Good of you to post some feedback!
The viscous coupling takes quite a bit of force, did you do the test described above with one wheel of the ground and a breaker bar on a wheel nut? Even if it did lock up, the strain would be downstream from the transfer case: props (UJs), diffs, CVs, not the input side.
Some fore-aft movement on the splines is normal, as long as there's no rotational play.

Filip
 

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VCUs are available (see Ashcroft Transmissions) but not cheap and that is on an exchange basis with a further £75 surcharge if, as I would expect, your unit can't be rebuilt.
 

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Discussion Starter #16
Good of you to post some feedback!
The viscous coupling takes quite a bit of force, did you do the test described above with one wheel of the ground and a breaker bar on a wheel nut?
Hi Filip, one wheel up and as much force as I felt comfortable with (say, 75kg close to the end of a ~1m extension) and it wasn't moving.

Replacement box on order now...
 

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That does sound like it's done for. Ashcroft Transmission is a good tip, they do quality rebuilds for a fair price. And with a rebuilt tranfer box, you'll also get a new chain and output shaft, so you'll be good for many more miles. ;-)

Filip
 

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Mine did exactly the same. I removed the transfer box using a trolley jack and 2 assistants. Stripped it and it was exactly like yours.

Also I seem to remember you can remove this part easily with the transfer box on the car, front prop off and remove 6? Bolts and withdraw front output shaft and then viscous coupling comes out.
 

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Yes, you can remove the viscous with the transfer box still on the car. It does help to lower the crossmember a bit to get more room, especially to put the new viscous in.
 
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