I need a new crown wheel and pinion for my MKIV as the original is beyond being serviceable. I have found a New Old Stock original Jaguar set but can’t identify what car it ought to fit? It has 39 teeth on the crown wheel whereas mine has 49. The Part Number on the box is 3922 with 522 stamped on the Crown Wheel.
The part is with the seller but going on the photo I have it looks like it could be 8 teeth on the pinion? The would be a 4.88:1 diff fitted to a 1 1/2 Litre car. Is there any reason why you couldn’t fit it to a 3 1/2 Litre car? I’m sorry to say that I have never really understood diff’s and ratio’s.
The 4.88 , or similar ratio will be hopeless in a 3 1/2 litre and thet are a different HA between the 2 cars AS Peter said they are very strong , unless left with water n them. I’ll ask locally for you.
The diff is with Ivan S at his farm. I have seen the crown wheel and pinion and during a previous rebuild the two parts were not aligned correctly resulting in them now being unserviceable, sadly. KB and Ivan are also asking around for a serviceable set. I’m sure that someone with a 1 1/2 Litre would like to have a new gear set!
Thank you for the information. As you can see from my response to Ed, the diff was set up incorrectly leading to the dramatic wearing, mostly on the pinion. Would you mind asking your sources in the UK for me please?
I will need to read an article explaining gear ratio’s, especially diff’s in order to understand them.
By the way, with the help of a kindly Jag Club member out here, I was able to view Lavender Grey on an un-restored bonnet which coincidentally perfectly matched the original colour found underneath paint on the boot hinges. That means that I will have the car in the correct, original colour. Very exciting!
The axle ratio is very simple. Just divide the number of crown wheel teeth by the number of pinion teeth. So if your pinion had 9 teeth and your crown wheel 36 teeth then the ratio is 4 :1.
This means that with your engine running at 2000 rpm your wheels will be rotating at 500 rpm. If the ratio had been 5 : 1 then for the same engine revs your wheels would only rotate at 400 rpm. So the larger the axle ratio the slower the car.
I have experience of two cars with horribly noisey axles. My SS was a real grinder but with the meshing set correctly it is a nice quiet axle. A friend’s MG was similarly transformed by just replacing the bearings. Set your axle up correctly and try it before swapping the gears.
Not quite right, according to the parts books. The 3.5 Litre Mark IV and V used the 47 tooth crown with 11 tooth pinion for a 4.27 ratio. The 2.5 Litre Mark IV and V used a 50 tooth crown with 11 tooth pinion to give a 4.54 ratio.
Is it possible your car has been running around with a mismatched gear set? That would explain how they got chewed up.
Or could there be an error in the parts books?
The part number of the 11x50 set is given as 2HA-100/1 in the Mark IV book, but as 2HA-100/2 in the Mark V book.
The part number of the 11x47 set is given as 2HA-100/2 in the Mark IV book, but as 2HA-100/4 in the Mark V book.
I’ve read un the MKIV & MKV Service Manuals that the Crown Wheel ought to be 47 teeth with the Pinion 11 for a 3.5 L. No doubt that is the the case. I’ll recount the Crown Wheel teeth next time I get to it.