4.89 Ratio Grey Diff

[MalFE]

I was having a shed cleanout recently and came across  my old low ratio diff which I thought had gone to the tip many years ago.
I fitted it in my FE during the mid sixties when I belonged to a sporting club that promoted hill climbs standing 1/4s and lap dashes etc. Amaroo Park was a well known race circuit which also had a hill climb and a short motor cycle circuit (dirt).
I entered my car in the lap dash of the motor bike track, after doing my lap I could hear the diff was making a lot of noise, when home I pulled it out and found the crown wheel was badly scuffed. The circuit I had been on was all left handers except one right hander and evidently the oil went up the axle tube and starved the diff.

Mal.

[Dr_Terry]

I do think that the ratio is 3.89, not 4.89.

Dr Terry

[zulu]

I'm a bit like that Mal never chuck any think out, sounds like an interesting bit of kit
Do you know what it was out of to begin with or is it a holden item

[Harv]

G'day Mal,

Got me curious too... love old speed gear.

The standard diff (3.89:1) has 9 pinion teeth and 35 ring gear teeth (35 / 9 = 3.88888888888888). Interesting to see how many teeth on this one.

(... if the shed clearout gets too serious in the old Holden parts department, let me know and I'll bring the trailer and my wallet around  ).

Cheers,
Andrew

[ardiesse]

Mal,

The more things change . . .

In the early '80s I was briefly into club motorsport.  I'd inherited the family EK Holden, which I'd fitted with a hotted-up X2 motor and disc brakes (Dad was not impressed).  I kept the 3.89 diff in the interests of better acceleration, and boy did I have some fun with 253s and even the occasional 308 off the lights, but that's another story for another time.

I did a dirt-circuit at Amaroo one Sunday.  I started with a quiet diff, and by the day's end it was howling.  All the gear oil ran down the right hand axle tube and stayed there long enough for a lubrication failure of the crownwheel and pinion . . .

Rob

[ardiesse]

Harv,

4.89:1 is as close as dammit to 44/9, and I think 9 and 44 are relatively prime.  You'd have 44 teeth in the crownwheel and 9 in the pinion.

39 and 8 give 4.875, and they're relatively prime.

Rob

[zulu]

Mal sent these pictures re his low ratio diff

I will leave it to Mal to tell the story

Click on image to enlarge


 

[MalFE]

The diff on the left of photo is the low ratio one and the other is a 3.89.
The low ratio one has a much thicker crown wheel & smaller pinion.
The second photo shows the only markings visible on the crown wheel
I had a look at the diff today and counted the teeth, crown wheel 34 & pinion 7 teeth.

Mal.

[ardiesse]

Mal (and Harv),

34/7 = 4.857142...

Fewer, chunkier teeth means less inclined to break when you drop the clutch.
Now the $64 question is whether a differential specialist can lap the gears to get rid of the scuffing.

Rob

[MalFE]

The crown wheel & pinion were purchased from a place at Concord (Sydney) near where American Autos used to be. They stocked a lot of new ex army parts and I was told the diff parts were manufactured in England for  government Holden utes but they must have cancelled the order. I had a spare diff at the time & diff repairer fitted the new parts plus bearings etc.

Mal.

[GreyFC]

Last paragraph:

[mcl1959]

Now that makes those gear sets worth being repaired!

Ken

[GreyFC]

Hey Mal, my friend is very very interested in this diff.  If there a way I could get him in contact with you? 

[MalFE]

Hi GreyFC I will contact you by email

Mal

[GreyFC]

Thank, I know you guys have been in contact, Greg is eagerly awaiting !