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MG MG Y Type - Pre-selected Pinion Bearing Set of Y Diff

When trying to fit new bearings to the differential carrier, I realised that the crown wheel's teeth (marked blue) touch the rear surface of the cone of the big rear bearing H (marked red).
The workshop manual quotes that the red pinion bearing set consisting of bearings H & J as well as distance piece G was pre-selected and was only available in sets.
On page 5 of the manual (see attachment), unfortunately there is no measurement given of the complete length of the red bearings and spacer assembly.

Does anyone, by chance have a stripped differential with the original (marked red) pinion/spacer assembly's overall length - or does anyone know a way to overcome this problem?

Thank you (sorry about being so technical)
Anton, YT 4220


Anton Piller

I came across this problem 30 odd years ago on a nissan 4x4.Different brand of bearings. If the bearing is in the housing all the way home then the inner bearing cone is probable deeper [thicker] pushing the pinion into the crown wheel.Also the cup of the bearing could be thicker? This can also through out the preload on the bearings as the spacer is a matched set. Time to get out the calipers to do some measuring
R Wood

It's a common mistake for the main pinion bearing not being pushed right home
Sometimes they get pushed in till flush with the housing ,but that depends on the housing thickness itself and usually the bearing will go in further past being flush
William Revit

Check the easy fix first as William pointed out before pulling your axle to bits.HOPE he is right
R Wood


Gentlemen

Thank you for your advice. I did tripple check wether the bearing components are right home - which they are/were.
Regarding the pinion bearings: I can only conclude that the thickness of the inner bearing cone and maybe the cup of the currently sold Timken bearings are deeper/thicker, than the original supplier's components (from remembrance noot Timken). This would especially affect the hight of the bearing cone on the toothed pinion side and explain the grinding noise made by the touching ring gear.

At the bottom of page G8 of the workshop manual, there is a sentence that I do not understand:
"tighten the different adjusting nuts until the cups are loaded so this distance is increased by .006 in. (.15mm.)".
It does not make sens to me that if I tighten the adjustment nuts, the distance is increased??!!

Please explain
Anton


Anton Piller

Hi Anton,Just read the manual. The pinion depth is a very important setting . If it is not set at the correct depth the crown wheel will not mesh correctly. [Noise and damage to gears] When setting the crown wheel preload the adjusting nuts on the sides push on the bearings. As they put pressure on the force is spreading the bearing caps apart giving the increased distance...GOOD LUCK BOB
R Wood

Thank you Bob for your explanation. I have to get a set of new bearings locally in Switzerland before I tackle the diff for the third time - together with my master mechanic friend.
He said, he does not want to fit the new bearings before it is not clear what caused the damage of the bearings in the first place.

When the car initially hit the road after its 35 year restoration, the diff had been outfitted with new bearings (all done and pre-loaded according to the workshop manual). After driving the first 1200 KM, I realised that the front bearing of the pinion had developed approximately 2 mm play, length-wise. the diff was taken out and pre-loaded again.

After driving another couple of hundred kilometres, noise developed again and after taking the diff out it showed that all four bearings were badly damaged - the lenght of the taper rollers was reduced by about 0.2 mm because they aparently where rubbing against the inner races of the cones.

I've been to four knowledgeable workshops to ask advice, but no one came up with a conclusion. They all where puzzled and "never have seen anything like this before".

keep your fingers cross
Anton

Anton Piller

Anton, could it be a lubrication issue ?. When I had a YT diff centre setup by a specialist about 15 years ago, they advised me to use Limited Slip Diff Oil & not regular Diff oil. They said "these older diffs need sticky oil". They even supplied the bottle of oil with the centre - use this or no warranty !.

Perhaps Bob might have some advice on this.

Good Luck

Tony
A L SLATTERY

Tony has a very good point.. EP Hypoid oil is recommended at NTG and I agree .The wrong oil in a diff is not good on the ears or the pocket.. [apprentices]If this is the third time, the spacer
needs to be measured as it will be under size in length.The bearings must be knock on tight on the pinion and in the housing.Tighten the pinion to the correct torque without the seal and THEN check the preload . A short spacer will make it too tight .Bearing H and J will clamp spacer G , if it is not fully tighten it will work loose every time. A lot of the problem points to the spacer being loose.[shortened .
rollers].Get the calipers out ,, GOOD LUCK BOB
R Wood


Tony & Bob

RE. the oil: I always used Hypoid oil with this diff center (Liqui-Moly LM8968) and after the last "re-tigthening" I had filled up with the same grade but in a LS (Limited Slip) version.

Re. the spacer:I do have a spare spacer that hopefully might solve the (not good on the ears or the pocket" problem.

What still has me and everyone else puzzled, is the fact that the rollers of the two crown wheel bearings where shortened as well. There must have been one hell of a force working there.

I will undertake a fourth overhaul, again exactly according to the workshop manual - but I will take my time, because each new set of bearings costs 399.- Swiss Franks which is about the same in Australian Dollars....

cheers
Anton


Anton Piller

Penrite make a very good EP Hypoid oil - see https://www.mg-cars.org.uk/imgytr/penrite.shtml. Not cheap ... but then neither is rebuilding an MG Y diff after you have trashed it using an inferior oli I guess.

Paul
Paul Barrow

I had a chat with the diff builder at work.That is his job every day at Komatsu. We both think the roller wear is from to much end float.When you start to assemble your pinion measurement depth F on the diagram MUST be within spec.The spacer will be warn , spec is in the manual,if still going OK torque the flange nut and only THEN check preload.If it is getting too tight before it is fully torqued STOP and check why. BOB
R Wood


BOB

We will tackle the diff next week Tuesday.

Keep you posted
Anton
Anton Piller


Gentlemen

Attached please find a picture of the rollers of the rear pinion bearing. There should be concave endentments on top of each roller - instead there are raised (convex) portions visible. All in all there must have been about 0.5 mm of material ground away. The rollers of all four bearings look like this!

Once the differential is back in place again, I will check if the length of the propshaft is correct. The workshop manual quotes only one "face to face" length of 1.187 Meter.

This is why, I will check the propshaft's length when fitted "A" with the rar axle in its uppermost possible position / and "B" with the rear axle in its lowest possible position. My Master-Mechanic friend is questioning the length of the shaft - if it where too long it would put strain on the bearings.....

have a ball
Anton


Anton Piller


Gentlemen

One last question before I tackle the diff. On page G-9 of the workshop Manual it says:
"without creeping over the heel, which would of course, produce very noisy operation."

Even though, I will never be able to check the markings - once the diff will be fitted to the car, I wonder what (where) the heel is:

- is it the inner edge/corner of the teeth?
- is it the outer edge/corner of the teeth?
- or could it be both?

regards
Anton

Anton Piller

Hi Anton The toe is the inner side of the crown wheel and heel is the outer side of the crown wheel gear. The markings can be checked before fitting with a blue or yellow paste from car parts outlets.It is painted on the gears then rotated to get a pattern.Check on U tube as there is some good info on there. ..It is not a crushable spacer type just a solid type .GOOD LOOK and take your time to check a few different videos out.
R Wood


Thanks, BOB

I'd never come across the terms "Heel & Toe" in connection with a diff before - now, I know :o)

cheers and greetings from Switzerland
Anton
Anton Piller

Them bearings look like there's either been too much preload or the oil is crap or contaminated---Make sure the whole housing is washed out and clean, rubbish has a habit of hiding up in the axle tubes

There's a saying when adjusting diff tooth paterns

Toe and heel move the wheel
face and flank move the crank

if you need to move the marking towards the toe the crown wheel is moved closer to the pinion (reduces backlash
if you need to move the mark out towards the heel then the crownwheel needs moving away from the pinion (increases backlash)

same with face and flank markings
If the mark needs to go deeper into the tooth move the pinion in
If the mark needs lifting up the tooth move the pinion out
William Revit


BOB

I am sure my Master-Mechanic friend and I got the preloading of pinion and crown wheel right, as well as the backlash - see attached photograph. Regarding the axle theeth markings, they adhere to drawing G.8. on page G9 of the workshop manual.
Hopoefully this darned thing will not seize up again!

It was quite a job, taking two four hour sessions to become perfect and as a little side effect, I am getting better by the day....

Thank you for your support

Anton
YT 4220

Anton Piller

Bit hard to tell from that pic----I hate bearing blue
Best to use a nice bright ochre mixed with oil
I usually lightly paint both sides of one crowwheel tooth then hold the pinion for a bit of resistance then wind the c/wheel back and forth through the pinion 5-6 times then wind it up top and have a look at the result
When I'm happy then do the same at a couple of different spots on the c/wheel just to check
I've stayed away from the thread as Rob was giving good advice and we don't need too many cooks in the kitchen
Hope it all goes well

What did your man decide was causing the c/wheel teeth to hit----?

willy
William Revit

I agree 100% with William,Did you find the problem of the pinion depth?? Time and your ears will let you know how well the rebuild went,diffs are not for the first time mechanics. Fingers crossed BOB
R Wood


Dear Willy & Bob

Well the reason for all four bearings being damaged is a puzzle for everyone I show the bearings to. As there where:

- Motor Mechanics trade school teacher. He is the man who gave me a hand and guided me. He has done many differentials in his long trade live and coincidentally is very XPAG savvy (owning a TD for 50 years).
- Army Vehicle Service floor manager (who lent me the pre-loading tool)
- Formula three workshop owner, who even partially stripped the diff
- Many other knowledgeable guys

There was a lot of head scratching and statements like "I've never seen anything like this".

One guy came up with the idea that maybe the prop shaft is wrong (too long/short), which is something, I can only check with the diff in place.

It will take some time before, I will be able to take the car for a spin. At present, I am waiting for a magnetised drain plug for the rear axle from NTG.
Once the car is ready to move, I will have to wait for a spell of sunny, dry weather, because I will not drive the car when the roads are salted because of icy and snowy Swiss conditions....

cheers
Anton


Anton Piller

This thread was discussed between 28/11/2019 and 12/12/2019

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