Thread: Series 3 LWB diff ratio

The diff ratio of all Series Landrovers except for some very early ones and the Stage 1 V8 and Isuzu is 4.7:1. Series 3 Stage 1 is 3.54:1. So your six should be 4.7.

To check what ratio you have, chock the front wheels and one back one, handbrake off and out of gear and not in four wheel drive. Jack up the other back wheel and rotate it one turn, counting the number of turns the prop shaft makes. This will give you half the actual ratio, seeing that the differential with one wheel not moving acts as a two to one ratio. So if you have a 4.7 diff, you should see the prop shaft turn a little less than two and a half turns.

If you have both wheels off the ground, and the handbrake is on or it is in gear, and turn one wheel, the other will turn the same amount in the opposite direction, as a result of the differential action.

Hope this helps.

John

Yes, got just over 2 turns but that was with both wheels up. So if I have a 4.7 then that is why people go to 3.54 to get better performance obviously.

I only had both wheels up to investigate a "lumpy" feeling in my rear, seems one rear tyre has a low point in it, as I rotate it there is a flat spot on one tyre. Strangely when looking from the inside of the wheel as it rotates, the drum seems to rotate a little strangely, almost like the drum is slightly eliptical (ie rather than a consistent space between the backing plate if you watch one part the drum moves closer and then further away as it rotates) but the centre of the hub rotates evenly. Not sure how a drum gets this wonky but probably need a new one?

Originally Posted by pfillery

Yes, got just over 2 turns but that was with both wheels up. So if I have a 4.7 then that is why people go to 3.54 to get better performance obviously.

I only had both wheels up to investigate a "lumpy" feeling in my rear, seems one rear tyre has a low point in it, as I rotate it there is a flat spot on one tyre. Strangely when looking from the inside of the wheel as it rotates, the drum seems to rotate a little strangely, almost like the drum is slightly eliptical (ie rather than a consistent space between the backing plate if you watch one part the drum moves closer and then further away as it rotates) but the centre of the hub rotates evenly. Not sure how a drum gets this wonky but probably need a new one?

If the brake drum is out of round, this will result in a flat spot on the tyre. Very unusual, however, to be enough out of round for it to be easily seen - although the outside of the drum is not the bit that matters. A likely cause of the apparent out of round, however, is if the drum has been put on the hub with some foreign material between it and the surface it clamps against, so it is cocked at an angle. I would be removing the drum to check this. If it has been used significantly like this, by now the drum will be out of round.

As to how drums get out of round - either by the route I suggested, or as a result of severe overheating.

John

All the drums came off when the car was roadworthied, as I like to be thorough and cleaned the insides of the drums (the car had sat for a while unused so there was some surface rust on the inside of the drum which I wanted to clean out) so I'm certain there was no foreign matter in between. Besides, if there was something in between the drum and the hub, the direction of the "out" would be different to this. It is almost like someone has squashed the drum from the top to the bottom, making it slightly oval in shape as opposed to wobbling of the flat surface at the front where the wheel fits. What is unusual is that the way the drum fits over the hub with only minimal clearance, and the hub is central as far as I can see and spins evenly, is how it could have got like that. Not terribly easy to find spare lwb 6cyl drums around though. Unless its the backing plate that is uneven of course, but this is unlikely to cause a flat spot on the tyre. Could be a coincidence too.

Any easy way to tell if the drum is true and square (circular) at home without fancy jigs or tools?

Probably the simplest way, albeit a bit of work, is to remove the wheel cylinder, and make an adjustable pointer, clamped or bolted to the backing plate, that points to the inside of the drum through the wheel cylinder hole. Adjust it till it touches the drum, then back it off slightly - spin the drum, should not touch anywhere. Adjust until it just touches, should touch evenly all the way round. Ideally the pointer should be a dial gauge, but the above should work.

You can get a reasonable idea by backing off one shoe, then adjust up the other until is barely touches. Spin the hub so the drum moves "anti-servo", that is, so that the surface of the drum moves towards the wheel cylinder along the shoe, and it should drag evenly through a full turn. Problem with this method is adjusting the shoe so it touches enough to hear or feel, but you can still turn the hub. May be worth putting the wheel back on for this exercise.

For this test, the wheel bearings need to be correctly adjusted.

John

John's idea is a good one. Without having one in front of me to look at; is it possible to take the drum off and fit it back onto the hub inside-out, so that the friction surface is visible? If so; clamp it with the wheel nuts and spin the hub, whilst doing John's test. A magnetic-base and a dial indicator would be the best way as the actual ovality could be measured.

Alternatively; remove the drums and get them checked and measured by a brake shop,

Cheers Charlie

I'll try those couple of suggestions thanks guys.

With a flat spot on a tyre which JDNSW suggested could be caused by the brake drum being wonky, is this something that will go away when the drum issue is resolved? Or is it a permanent defect in the tyre requiring replacement? The tyres are only 3 years old with heaps of tread and being a full matching set of 7.50x16 the last thing I want is to have one odd tyre. What are your thoughts?

Originally Posted by pfillery

I'll try those couple of suggestions thanks guys.

With a flat spot on a tyre which JDNSW suggested could be caused by the brake drum being wonky, is this something that will go away when the drum issue is resolved? Or is it a permanent defect in the tyre requiring replacement? The tyres are only 3 years old with heaps of tread and being a full matching set of 7.50x16 the last thing I want is to have one odd tyre. What are your thoughts?

Depends how bad it is! If there is plenty of tread and it not too bad, it may wear out, but could be annoyingly noisy until it does. Provided there is still plenty of tread I would not think it is a safety issue.

John