MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - differential exploration

This weekends project is to explore the differential. To that end I have some questions I need some help with.
1) where the heck do you find hypoid oil? I've been to all the typical retailers and they have no idea what I'm talking about
2) what size fitting is used to remove the plugs?
3) I think there is a leak at the nose of the diff. where it connects with the dive shaft: there's alway a good sheen of lite oil on the diff. nose body and on the underside of the trunk above the nose of the diff. what's involved with diagnosing and repairing this.

thanks as always for you attention and help
Tysen

Hi Tysen. Any good auto parts store, or lubricant specialist should be able to obtain the gear oil you need for your rear axle. I think 90 weight is required. If memory serves, a 3/8 inch drive ratchet end fits the square recess in the plugs, and works fine to remove them. It sounds like your pinion seal is leaking and needs to be replaced. It is a fairly easy job, and can be done with the axle in the car. The driveshaft needs to be removed first. The drive flange needs to be removed next, and then the seal cover. Then the old seal can be removed, and the new seal installed. Be sure to lubricate the new seal with gear oil before installing it. You might want to replace the 2 axle seals also, as a preventative measure. Usually if one seal is tired, the rest usually arent far behind! Cheers! GLenn
Glenn

As Glenn said, remove the pinion flange and you will have access to the seal. Easier said than done unfortunately. You will need some type of bar which will hold the pinion flange while you loosen the pinion nut. I made up a tool using a piece of steel with holes drilled to match the bolt pattern and a large hole in the center big enough to allow clearance for the socket needed for the pinon nut. I welded this to a length of 3/4" pipe to get the necessary leverage. If you don't have access to the welding equipment necessary you might be able to wedge a bar between two bolts in one side of the flange, but these are easy to slip and bust knuckles. Get a good service manual for reference as far as torque settings when replacing the pinion nut.
Bill Young

You might want to try Redline synthetic gear oil for your diff. I have their oil in both the transmission and diff now and it may be my imagination but I think the gears are quieter than before and shifting is smoother.
Tom Heath

In practice Glen is correct. In our MGAs the preload on the pinion bearing is set by shims and need not be checked when changing the pinion seal. The only real precaution to take is to set the torque on the pinion nut to 140 ft lbs (19.4 kg m.) On most modern cars there is a crush sleeve in place of the pinion bearing spacer and just taking it apart and puting it back together can cause the diff to whine.
The hole in the diff plug is closer to 7/16 than 3/8 if it is not too tight a 3/8 rachet will work but if too tight don't strip it out. Get a 7/16 square shank punch to stick in the hole and a big cresent wrench to turn the punch.
The MG factory sevice manual calls for 90 wt above 10 degrees F and 80 below 10 F. That was before multiweight oils, use a good gl-5 75-90 gear oil, I prefer synthetic.
The word hypoid is an archaic word in reference to gear oil it comes from the fact that the gears are hypoid, or bevel cut, or angle not straight cut.
See link
http://yarchive.net/car/hypoid_gear_oil.html
Safety Fast, Randy
R J Brown

Tysen,
As Randy said, the term Hypoid refers to gears with angled teeth as opposed to straight cut teeth. These angled, hypoid, gears run more smoothly and more quietly than straight gears. However, their design causes more friction than straight gears and therefore requires different lubrication. Current gear oils use an EP (extreme pressure) rating to describe oils formerly referred to as Hypoid oil. Almost all name brand gear oil is EP rated and appropriate for MG differentials.
Bill
Bill Boorse

Although what has been said is basically correct, the definitions are slightly inaccurate.
You have straight cut teeth and helical teeth. The curved teeth are called helical teeth.
Hypoid means that the axis of the pinion gear does not intersect the axis crown wheel gear (the pinion is below the center of the crown wheel).


Mick
Mick Anderson

Typing corrected!!

Although what has been said is basically correct, the definitions are slightly inaccurate.
You have straight cut teeth and helical teeth. The curved teeth are called helical teeth.
Hypoid means that the axis of the pinion gear does not intersect the axis of the crown wheel gear (the pinion is below the center of the crown wheel).


Mick
Mick Anderson

Hi Mick.

I thought that gears with curved teeth on parallel shafts (eg in a gear box) were helical.

Curved teeth on shafts at an angle to each other, but with the centerlines intersecting, (or at right angles to each other, eg a Ducati cam shaft drive) were spiral bevel?

Cheers
ian F



Ian Fraser

Hi Tyson

You need to find an oil that has the designation EP80, or EP90. It may also have the words Extreme pressure, and/or hypoid

Cheers
Ian F
Ian Fraser

Hi Ian,

You are correct (as usual). I did a poor job of explaining.
The best way is to have a look at all the different types at:

http://www.arrowgear.com/products/spiral_bevel_gears.htm

Click on the links at the top of the page for photos and explanations of the various types.

Mick
Mick Anderson

Hi Mick

What a neat site, thanks.

I came across spiral bevel gears when I rebuilt a pair of heads on my early Ducati 750 Sport (non desmo). About a day each shim in/shim out to get proper mesh, plus shim in/shim out for the valve clearances.

There is one last orientation, where shafts are non parallel, and their axies don't meet at all. (a bit like a 'bent hypoid')are they 'skew gears'?

Cheers
Ian F



Ian Fraser

Hi Ian,

The correct term is "crossed helical" and the shafts are "skew" shafts. See at:

http://www.engineersedge.com/gear_design.htm

This is the design in the oil pump drive, the tacho drive, and the rack and pinion steering.

Mick
Mick Anderson

Damm, another mistake.
The rack and pinion is not a crossed helical gear, but a normal helical gear.
The "shafts" are parallel. Imagine the rack bent into a large circle. The rack turns around an parallel axis.

Mick
Mick Anderson

Hi Mick
I think that you were right the first time.

Keeping to MG's - the pinion shaft on (at least) a MGA and MGB steering box enters at a angle to the rack.

If the rack is regarded as a wheel of infinite radius, the axis of this 'big' wheel is at a skew with the axis of the pinion shaft.

(Hi Tyson, apologies for hyjacking your thread, but it looks like you have your answers. Dont hesitate to tell us to b*gg*r off if you like, neither my cuzzie across the ditch or myself will be offended. :))

Cheers
Ian F
Ian Fraser

Ian as I look at what I bought today from Penzoil (a 5 gallon pail of GL-5 SAE 75-90 synthetic gear oil)I believe that current oil standards call gear oil GL-4, GL-5, GL-6. the oils also are given an SAE weight. Such as API GL-5 SAE 75-90.
I don't believe EP for extreme pressure is used on the packaging any more.
Also checking the fluid requirement listed by current auto makers I see the GL #s and no reference to EP.
http://www.pzlqs.com/Tech/Pdsheet/DomesticMarketing/Gear&Transmission/pdf/SyntheticSAE75W90GL-5.PDF
this is the product I bought

I believe Tyson's question was what to look for in a store, and I believe that GL-5 with an apropriate SAE weight is what you will find on the product today.
I'm not an engineer I just fix cars.

Randy
R J Brown

Hi Randy

You are most probably correct with the labelling on modern oil containers - the old EP designation is now redundant, and that new containers are labeled as API GL-5 etc


As I look at my Duckhams 4litre container(admittedly bought some time ago), I see -

Duckhams Hypoid 80W-90 gear oil. An extreme pressure gear oil for hypoid final drives and transmissions requiring E.P. type oils.

I also see API Classification GL-5.


Tyson

I beleive that you now have the 'good oil' on what to get.

Cheers
Ian Fraser

Ian Fraser

This thread was discussed between 16/09/2005 and 17/09/2005

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.