6MT Centre Differential Rebuild Project

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Re: 6MT Centre Differential Rebuild Project

Postby bigBADbenny » Fri Oct 09, 2015 12:03 am

Love it, looking forward to perusing all the links :good:
Makes me want to drop a Dccd in, something I've researched :)
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Re: 6MT Centre Differential Rebuild Project

Postby WIDELOAD » Fri Oct 09, 2015 7:54 am

On point Peter.
Top work and research mate! :good:
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Fri Oct 09, 2015 9:26 am

Phase 9 - Trial Reassembly

Took the 5MT Centre Differential unit and attempted a trail reassembly.
The used orings and seals were reused to avoid damaging new seals (which are yet to be manufactured).
http://imgur.com/a/WVoqo
The reassembly was first trialled "wet" with water inside the unit while the plates and discs were restacked back in.

The first image is the C-D housing.

The second image is with the side plate and differential side gear installed.

The third image is with all the plates stacked in. You may probably be able to see the water which came up through the plates as they were stacked in.
They were stacked in sequence - Outer plate then spacer ring then inner plate; Outer plate then spacer ring then inner plate; Outer plate then spacer ring then inner plate; etc, unit the last outer plate was placed in.

The fourth image is with the bronze thrust washer placed on top, ready for the end cap.

At this stage a failure was experienced.
While the end cap would go back on, the end cap would bot go on sufficiently to allow the retaining ring to be inserted to secure the end cap. It was about 0.4mm short (using feeler gauges)

The unit was disassembled cleaned, dried and then reassembled dry.
This time the side plate and differential side gear (mentioned above) were reassembled in a different sequence and tapped securely "home" before proceeding to stack in the plates.
This time the end cap went on sufficiently far and the retaining ring was able to be inserted easily. See the fifth image.

So, the internal flooded volume has still not yet been determined.
However, the ability to reassemble the C-D unit has been proven.
My thoughts from here is to seek out someone in Sydney area who has access to a 10kilogram by 1-Gram electronic scale and do a unflooded and flooded weight.
Can anyone help out, please?

Edit Update
Searching on key word strings "viscous + coupling + fill"; "viscous + coupling + hump"; "viscous + coupling + rebuild"; has turned up various fluid fill volume ratios.

Someone quotes the GKN coupling as 70%
Someone quotes 84%
Someone quotes (about) 90%
Someone quotes 7% to 12% air.
(The links to these figures have been stored in my research files)

To further complicate matters, this links claims that the units are flooded, with no airspace?
https://www.youtube.com/watch?v=feD4D1quS0k

What is apparent is that the fill percentage will affect the onset of "hump" mode.
In hump mode the silicone fluid expands and causes the coupling to "lock-up".
Less fill, a delayed "hump mode", more fill, less time to achieve "hump mode".
"Hump mode" is a desirable characteristic in a all-wheel drive centre differential as it will provide the momentary "kick" to get an AWD out of a bogged situation.
"Hump mode" is not desirable for a front wheel drive car as the sudden onset of hump mode and coupling lock-up causes undesirable handling characteristics in a front-wheel drive car.
Excessive time operating in "hump mode" leads to silicone fluid degradation and viscous coupling failure.
Last edited by BillyCorgi on Fri Oct 09, 2015 7:02 pm, edited 1 time in total.
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Fri Oct 09, 2015 6:02 pm

Time for Reflection

If only I knew then what I know now.....?

It seems that with some degree of 20-20 hindsight, the donor differential from Hodman was disassembled too early.
With 20-20 hindsight, what could have been done was to weigh (accurately) the donor centre-differential prior to disassembly and then to weigh again after disassembly and cleaning out of the bad silicone fluid.
Then we would know the weight of fluid required?

So, silly question.....?
does anyone have a second bad 6MT centre differential that they would care to donate to science?
The worst that can happen to it is it will be refurbished?
This would settle a whole heap of questions and uncertainty surrounding the appropriate fluid charge for the differential.
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Re: 6MT Centre Differential Rebuild Project

Postby bigBADbenny » Fri Oct 09, 2015 7:30 pm

I'd stick with 80-90%, since you're seeking a balance between delay hump and burst.
They blow with stock 10% airspace if abused, but the hump delay would be too great below say 20%...
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Re: 6MT Centre Differential Rebuild Project

Postby Brunsy3.0 » Fri Oct 09, 2015 8:04 pm

If you hit a dead end i got a 6mt centre diff out of my 2007 H6 thats still sitting in the cupboard. Issue is location as im in NT freight would be fairly steep.
Let us know how you go
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Fri Oct 09, 2015 8:16 pm

The unit should be just under 5kg?
Can you check?
With some bubble wrap we can get it into a 5kg prepaid satchel bag for $17.10.
I have some short shift adaptor money to fund the R&D?
Could you check the weight at your Post Office?

I just weighed Hodman's unit and stripped and cleaned to whole unit comes in at just under 4.4kg
I think we may have a goer for a 5kg satchel?
Cheers!

By the way, what is the transmision code on your car? It will be on the plackard on the top of the left hand side front strut tower.
Cheers!
Last edited by BillyCorgi on Fri Oct 09, 2015 8:31 pm, edited 2 times in total.
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Re: 6MT Centre Differential Rebuild Project

Postby Brunsy3.0 » Fri Oct 09, 2015 8:21 pm

Ill check the plate tomorrow for the code. I still got the packaging it came in. So i can weigh it as is ill take a pic for ya
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Re: 6MT Centre Differential Rebuild Project

Postby RX25SE » Fri Oct 09, 2015 9:47 pm

To calculate the required amount of fluid, you could weigh all the parts of the disassembled and cleaned unit and compare it to the weight of an unopened unit.

Then just add the fluid by weight.

Maybe?
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Fri Oct 09, 2015 10:12 pm

Absolutely Correct! That is the new plan!
Except we will weigh the same unit. Once prior to disassembly as-is, then again after disassembly and cleaning.
A half-percent natural variation in weight between two differential assemblies may throw a 25g error into the fluid weight determination.
When we may only be talking about 150 to 200 grams of fluid, this error will be too large.
The error will be reduced when the same differential is used.
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Re: 6MT Centre Differential Rebuild Project

Postby Tonic » Sat Oct 10, 2015 12:42 pm

Good info.... Not that i will act on it .... But at least i know what is going on.
MINE IS STUFFED...big clunk clunk on even half lock turns when hot at the moment.
Was hoping to get closer to end of tax year before replacing it.
You are welcome to it then Billyg might look really ugly!
Clutch is pretty crappola too (170Kkm) so going to renew that too.....
Whats a couple of grand on two bits done eh....
Wife says buy new car but geez it is hard to find a car that performs as well on the road.,,,
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Sat Oct 17, 2015 4:48 pm

Update

Time for an update.
Brunsy3.0 is sending me his dead diff. (Thank you Brunsy)
A 5.0kg x 0.1g electronic scale has been purchased.

It will be a week or so before the diff arrives from Katherine, NT.

When the electronic scales arrive they will be "calibrated" or at least checked for accuracy/repeatability to see how reliable their measurements may be taken.
Then, when Brunsy's diff arrives the item will be weighed as received (and cleaned) and then re-weighed after all the yucky silicone fluid has been removed.
Then, we will have our most accurate estimate for the weight of silicon fluid to be added to the viscous coupling diff.

As things stand, the next post will probably be for checking out the digital scales.
5,000 grams by 0.1gram means one in 50,000 resolution? That means 2^16 or 16 bit accuracy?
Let's see what happens when it arrives?
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Tue Oct 20, 2015 11:37 am

Calibration

The electronic weigh scales arrived today. Bought it off ebay.
http://imgur.com/Nx7ski1

After unpacking and sort of reading the instructions I grabbed 5 things out of the panty cupboard and weighed them.
The weights were recorded after detecting that their was a drift of about 0.5g that stabilised to zero once the unit had "warmed up". I suppose that the strain gauges in the load cells need to warm up by passing current within the Wheatstone Bridge circuit within the load cell.

After having the weights the five items were stacked on the scales in different orders and the individual weights recalculated from the differences in the sums during stacking.
http://imgur.com/KSWIFjD

The maximum error between the weights calculated within the stack to the original separate weigh was plus/minus 0.2gram.
As this was twice the limit of reading I am satisfied that the linearity of the scale reading is sufficiently accurate for the purposes for which is going to be used.
That is, (i) to first determine the weight of silicone fluid in a typical centre differential unit; and (ii) to dispense the correct weight of silicone fluid into the unit during reassembly.

The second differential unit (from Brunsy3.0) is presently on its way from Katherine NT to Sydney, which may take a week.
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
Get your Gear Shift Rejuvenation Kit viewtopic.php?f=68&t=31240
Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
Need to hire a Guard Rolling Machine? viewtopic.php?f=6&t=31899
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Re: 6MT Centre Differential Rebuild Project

Postby tom_kauf » Thu Oct 22, 2015 2:16 pm

BRILLIANT Peter!! :D

So much technical detail - much more than I imagined.

I wish I could help more, but as I think I mentioned, I didn't get my old CD back from the mechanic, and the one from overseas that apparently didn't fit my car didn't have a Part# on the box (or paperwork showing the Part#).

But let me know if you need some Certified Scale Calibration Weights (5kg down to 50mg I think). Similar to the picture below (weighs close to 20kg all up though).
Or maybe you just need the little box with tiny weight flakes (ones that are picked up with tweezers). We use them to certify or calibrate scales as per NMI (National Measurement Institute) guidelines. Ie Supermarket scales. They're usually Class 3 (MPE: Maximum Permissible Error of 5g, but that depends on the smallest increments). So yours are a higher class, but these weights will still work really well (although, your Ebay purchase may not be Certified as a Class X, just an accurate hobby scale).

I can send them to you, if you promise not to lose any (I'll be in trouble otherwise). And remember, these are so finely calibrated and certified against weights with even tighter tolerances, that you have to wear gloves (or tweezers for the small ones) when picking them up. The oils/acid on our hands tarnishes the Brass and affects the weight.

Image
Last edited by tom_kauf on Thu Oct 22, 2015 2:34 pm, edited 2 times in total.
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Re: 6MT Centre Differential Rebuild Project

Postby BillyCorgi » Thu Oct 22, 2015 2:33 pm

Thank you. I am a pedantic little sod, and I want this to go right.
I am sorry that I did not foresee the importance of a good set of scales for this project before Hodman's diff was disassembled.
So sad that sometimes we must learn from our mistakes.

Thanks for the offer for calibration kit, however I think that we can go forward without needing that level of accuracy better than 0.1gram.
We have another centre diff coming from Brunsy3.0 out of the NT. Should be here soon.
I am happy that the ebay scales will allow a reliable and accurate measurement of the weight of the differential assembly and then the weight of the diff less the silicone fluid.
This will provide the most accurate estimate of silicone fluid.
The ebay scales have shown to be linear within their 0 to 5.0kg range and provide a weight within plus/minus 0.2g when using the tare function. That is twice the limit of reading and is the best that could be hoped for when adding or subtracting two readings.

As these scales will be used to dispense the silicone fluid back into the rebuilt viscous coupling, as long as the X.x grams of fluid calculated is the same X.x gram of new fluid dispensed back in, then we should be fine.
As the linearity of the scales has checked out okay, and the repeatability of the scales has checked out okay. I think we are systems go on in the scales department.
Just awaiting Brunsy's diff to arrive.
Cheers!
Get your Short Shift Adaptor viewtopic.php?f=68&t=30525
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Get your Centre Differential Rebuild viewtopic.php?f=6&t=31089
Want a custom built Brake Cylinder Stopper? viewtopic.php?f=6&t=31321
Need to hire a Guard Rolling Machine? viewtopic.php?f=6&t=31899
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