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  #1  
Old 01-06-2007, 06:19 PM
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Stuck in the Mud

I am posting here among friends because we share the same type of transmission with a centre LSD and you, unlike me, have experience in snow.

Last night my wife and I attended a country dance, which was great. I parked off the road on grass and my back wheels were on some soft stuff. (Do I need to confirm, driving the SVX? ) On return and trying to get under way there was wheel spin and applying the normal technique of not too many revs, which could dig wheels in, I got nowhere. I engaged the "manual" option, which starts the car in second and is stated as being provided for these conditions, but still to no avail.

I had been limiting RPM to say 2500 but after some thought I increased things to say 4,000 and this resulted in traction. I have not investigated fully as to why all wheels did not at first engage, and at this stage I am left with :-

Transmission line pressure called for more revs, but not likely.

TCU Expected more revs or an increased throttle opening.

Buzzing the wheels a bit resulted in digging down to something firmer.

To be honest I was disappointed with the cars performance and would like comments from you up there who have snow experience.

N.B. The down under king of the transmission world is not welcome within this thread, as I have absolutely no respect for his opinion, much less any aledged facts put forward.
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Old 01-07-2007, 02:02 AM
ItsPeteReally ItsPeteReally is offline
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Quote:
Originally Posted by Trevor
I
Last night my wife and I attended a country dance, which was great. I parked off the road on grass and my back wheels were on some soft stuff. (Do I need to confirm, driving the SVX? ) On return and trying to get under way there was wheel spin and applying the normal technique of not too many revs, which could dig wheels in, I got nowhere. I engaged the "manual" option, which starts the car in second and is stated as being provided for these conditions, but still to no avail.

I had been limiting RPM to say 2500 but after some thought I increased things to say 4,000 and this resulted in traction. I have not investigated fully as to why all wheels did not at first engage, and at this stage I am left with :-
Mud is funny stuff, and momentum is all important. When you are stationary, you don't have any!

I'll accept that we will have to rely on your impression that the transmission took a considerable time to lock up and asking the good lady wife to wade through the mud to verify which wheels were spinning was probably inadvisable

In my experience it does take a little time for the transmission to lock up, maybe half a second or so after the wheels start to spin. This is not unreasonable, considering that a solenoid has to operate, fluid has to flow and build up pressure, and other arcane mechanical gubbins has to leap into action - perhaps for the first time in many months (or in your case possibly years).

My guess, and it is only a guess, that nothing's broke and that whatever was previously sticky, gummed up, or stiff, has now magically got better after that little bit of gentle exercise.

There's only one way to be sure though! Which way to the nearest muddy field?
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  #3  
Old 01-07-2007, 09:18 AM
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You know more about this than I do Trevor.

Perhaps you have a solenoid problem and your front wheels are not being driven. Have you tried inserting the diff lock fuse and seeing if it makes any difference?

As I understand it, the rear diff has a viscous coupling which requires a substantial speed difference between the two rear wheels before it binds them together. Possibly one rear wheel was spinning and the other was stationary. When you increased the RPM, the extra spin locked up the rear diff and got you moving?

Phil.
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  #4  
Old 01-07-2007, 03:41 PM
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Quote:
Originally Posted by b3lha
You know more about this than I do Trevor.

Perhaps you have a solenoid problem and your front wheels are not being driven. Have you tried inserting the diff lock fuse and seeing if it makes any difference?

As I understand it, the rear diff has a viscous coupling which requires a substantial speed difference between the two rear wheels before it binds them together. Possibly one rear wheel was spinning and the other was stationary. When you increased the RPM, the extra spin locked up the rear diff and got you moving?

Phil.
Thanks Phil,

I don't think I have a fault as a problem and am confident I have normal AWD. It would appear that revs are required on several counts before all comes into play.

I had not thought of one back wheel spinning due to the LSD not locking up, in view of our featured AWD. It was the rears which were on soft stuff and I am sure you have the answer.

P.S. Please do not mention solenoids.
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Old 01-09-2007, 10:15 AM
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Talking Solenoids? Who said that?!! 4-letter word. The duty one, anyway

Quote:
Originally Posted by Trevor
Thanks Phil,

I don't think I have a fault as a problem and am confident I have normal AWD. It would appear that revs are required on several counts before all comes into play.

I had not thought of one back wheel spinning due to the LSD not locking up, in view of our featured AWD. It was the rears which were on soft stuff and I am sure you have the answer.

P.S. Please do not mention solenoids.

I think Pete's point about moving from standstill says a lot. Shifting all the car's weight take a lot of torque. As our road tyres have zero grip in slippy conditions, they can spin freely in low grip situations. Perhaps the percentage weight of the LSD is set low, so as not to jerk around the luxury ride.

I figure if you were wearing traction lug tyres like a jeep, she would just pull out of the muck without a chirp.

The other point is like what Phill said; if I was in a situation like you describe, as soon as I realised one wheel was spinning, I would pull the diff fuse to give it a better chance of rocking it's way out of bother.

Joe
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  #6  
Old 01-09-2007, 02:15 PM
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Quote:
Originally Posted by svxistentialist
I think Pete's point about moving from standstill says a lot. Shifting all the car's weight take a lot of torque. As our road tyres have zero grip in slippy conditions, they can spin freely in low grip situations. Perhaps the percentage weight of the LSD is set low, so as not to jerk around the luxury ride.

I figure if you were wearing traction lug tyres like a jeep, she would just pull out of the muck without a chirp.

The other point is like what Phill said; if I was in a situation like you describe, as soon as I realised one wheel was spinning, I would pull the diff fuse to give it a better chance of rocking it's way out of bother.

Joe
Hi Joe,

I had no trouble getting traction as soon as I used RPM, my point was one of interest as to the exact reasons why. I won my car club's mud trial many years ago, in/on an AC sports car with a Ford V8 engine transplant, I had at the time.

What are you suggesting with - "I would pull the diff fuse to give it a better chance of rocking it's way out of bother."

Inserting a fuse would lock up the centre controlled LSD on my JDM car, but would have no affect on the rear LSD?

Cheers, Trevor.
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  #7  
Old 01-09-2007, 09:48 PM
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Trevor,
Having driven some in the snow here in western Virginia, I have never experienced the situation you described. Like you initially did, I have always started off with low RPM's or gone directly to the "manual" button to start off in 2nd gear. However, Pete's comments do make sense to me. Perhaps is is somewhat like the anti-lock brakes - one should exercise the capability from time to time to keep things freed up?

Harry

PS: I like the idea of a "country dance". Sounds like fun!!
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  #8  
Old 01-09-2007, 11:32 PM
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Quote:
Originally Posted by newsvx
Trevor,
Having driven some in the snow here in western Virginia, I have never experienced the situation you described. Like you initially did, I have always started off with low RPM's or gone directly to the "manual" button to start off in 2nd gear. However, Pete's comments do make sense to me. Perhaps is is somewhat like the anti-lock brakes - one should exercise the capability from time to time to keep things freed up?

Harry

PS: I like the idea of a "country dance". Sounds like fun!!
Hi Harry, nice to meet you here.

It does appear that a few revs are required to lock things up, from what has been diagnosed.

The dance is something else and is run entirely on an amateur basis by a citizens group, at a very nice small community hall. The venue is about a 40 minute drive for us, to a spot on the second harbor we have to the west i.e. the Manukau.

The small band comprises, drums base guitar and two other guitars. The leading guitarist is a solo act on his own. The drummer, who sometimes swaps with one guitar, likewise, and all do vocals well. I am very fussy when it comes to music and it is not often that I can simply listen.

These guys are great and have really have their heart in it. How wonderful to not get pounded by a drum machine and electronic backing,

My wife and I went by chance a couple of years ago and now attend as often as the dance is held. Currently a winter and summer dance. Come and join us, it would be your kind of music.

We have a tradition here of, "ladies please bring a plate". This has confused some folk from overseas, who do not understand what is meant. The result is the most wonderful home grown/made supper you can imagine.

Cheers, Trevor.
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Last edited by Trevor; 01-09-2007 at 11:34 PM.
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Old 01-10-2007, 03:44 AM
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Trevor,
I have been looking at the Wikipedia entry on limited slip differentials and the following extract may have a bearing on what you experienced.
Quote:
Typically a visco-differential that has covered 60,000 miles or more will be functioning largely as an open differential; this is a known weakness of the original Eunos Roadster sports car. The silicone oil is factory sealed in a separate chamber from the gear oil surrounding the rest of the diff. This is not serviceable and when the diff's behaviour deteriorates, the VLSD centre is replaced.
So you may well have been in the position where only one rear wheel was spinning and the 60:40 torque split allowed only two thirds of the spinning rear wheel's torque to be delivered to the front wheels. If, as seems to be the case, this was insufficient to pull the car out of the mire, then the car could only break free after the gearbox had locked up. Which your's presumably eventually did.
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Old 01-10-2007, 08:13 AM
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Quote:
Originally Posted by Trevor
Hi Harry, nice to meet you here.



These guys are great and have really have their heart in it. How wonderful to not get pounded by a drum machine and electronic backing,

My wife and I went by chance a couple of years ago and now attend as often as the dance is held. Currently a winter and summer dance. Come and join us, it would be your kind of music.

We have a tradition here of, "ladies please bring a plate". This has confused some folk from overseas, who do not understand what is meant. The result is the most wonderful home grown/made supper you can imagine.

Cheers, Trevor.
Sounds like fun, Trevor. I wish I could get "down under"!! The "ladies please bring a plate" is what we, in the country here, call a "pot luck" supper - you never know what someone will be bringing. These surprises are always good!!The ladies (and sometimes guys) like to show off their cooking skills...

Sorry to digress from the original topic .....

Harry
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Old 01-10-2007, 09:46 PM
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Mmmm...Cooking..

Well, it's ALMOST morning time (quarter to tomorrow by my clock) and your country cooking discussion sure has me wanting some breakfast....
On a lighter note, relating to the quote
Quote:
Typically a visco-differential that has covered 60,000 miles or more will be functioning largely as an open differential; this is a known weakness of the original Eunos Roadster sports car. The silicone oil is factory sealed in a separate chamber from the gear oil surrounding the rest of the diff. This is not serviceable and when the diff's behaviour deteriorates, the VLSD centre is replaced.
Heres a diagram...Now, according to the list below, part number 2 of this diagram is the "Visco diff assembly rr"....Would that be the part to replace in this instance?
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Old 01-10-2007, 11:41 PM
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Quote:
Originally Posted by It's Just Eric
Heres a diagram...Now, according to the list below, part number 2 of this diagram is the "Visco diff assembly rr"....Would that be the part to replace in this instance?
Well........ that has to be the part, the eagle eyed will already have spotted that there are no conventional differential gears in the rear axle assembly.

It would appear from looking at the diagram that one wheel is directly geared to the input propellor shaft and the other wheel is driven solely by the output of the 'Visco Diff Assembly'.

This implies that there is a maximum 'stalling torque' that can be delivered through this assembly which, if the Wikipedia article is to be believed, decreases over time, and presumably, at the limit, can effectively leave you with drive through only one rear wheel
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Old 01-12-2007, 08:43 AM
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Am I an idiot?

The answer is almost certainly yes

It appears that there are conventional differential gears in the differential, but they are contained within the visco-diff assembly, and therefore do not appear in the diagram shown above.

The components of the visco-diff assembly are not available as piece parts however, and consequently it has to be changed out as a unit.

I do not know whether the assertions that the Wikipedia article on such differentials makes (e.g. the performance of the limited slip function of these units deteriorates with time) is true or not.
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Old 01-12-2007, 03:52 PM
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For a start, I was all again in mud - dle, thinking that it had been taken that I was driving my Mazda MX5. I was about to refer all to my initial post --- " I parked off the road on grass and my back wheels were on some soft stuff. (Do I need to confirm, driving the SVX? )". However a back track, (On which I did not get stuck!) has sorted things out.

I am sure I know what was going on and am not concerned that my rear LSD could be faulty. The subject is certainly interesting which was my reason for posting. The response is appreciated.

Cheers, Trevor. (Sipping a home brew )
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Old 01-13-2007, 09:40 AM
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Quote:
Originally Posted by Trevor
Hi Joe,

I had no trouble getting traction as soon as I used RPM, my point was one of interest as to the exact reasons why. I won my car club's mud trial many years ago, in/on an AC sports car with a Ford V8 engine transplant, I had at the time.

What are you suggesting with - "I would pull the diff fuse to give it a better chance of rocking it's way out of bother."

Inserting a fuse would lock up the centre controlled LSD on my JDM car, but would have no affect on the rear LSD?

Cheers, Trevor.
Hi Trevor

I have no doubt you are skilled, and not a stick-in-the-mud type of driver

My point, probably foolish, about the diff lock was with available traction. With the 50-50 lock on, and three wheels gripping, I was pre-supposing you might get enough grip from 3 wheels to haul it out of the hole the fourth wheel was digging.

Revving it up may well have given enough torque to the three gripping wheels to haul it out regardless of what the fourth wheel was doing, but maybe I'm wrong about that. Maybe the rear diff did "lock up", and haul the ass.

Joe
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