LSD or not?

[Taxi_Driver]

Hi all. New to MX5 ownership and the forum. Owned my MX5 for only 9 days and loving it. Trying to get to know her a little better. Is there any way to find out which diff is fitted to my car. I’m sure it’s the original. It’s a MK2 1998 in classic red. The sticker on the door shut tells me it’s a 1.8 with sports suspension and the colour code, but little else. The Vin No. is JMZNB18P200113953 if that helps.

I’ve read lots of posts about identifying diff’s, but most involve either taking the diff out and apart. Or they’re unreliable tests, like jacking up the back and spinning wheels, or dumping the clutch and looking for rubber marks. Someone, somewhere said they could find out if they had the Vin No. But I can’t find that post again, I’ve read so many this last weekend.

So, if anyone knows a way to tell which diff I have without tearing the car apart or abusing it, I’m really curious to know.

Thanks all.

[mal_jones]

Hello and welcome.    The easy way to tell if you have a LSD or not is to jack up the rear of the car and turn a wheel, if both wheels turn the same way you have LSD.  

[Taxi_Driver]

Hi, thanks for the quick reply.
Is this a reliable method? I’ve read some posts that say not.

[Razor_Blue]

@mal jones

Hello and welcome.    The easy way to tell if you have a LSD or not is to jack up the rear of the car and turn a wheel, if both wheels turn the same way you have LSD.  

Let me add a bit more

If you put the car in gear so that the prop shaft cannot rotate and then turn a wheel the other wheel will turn in the opposite direction. You may well feel the ftiction of the LSD mech but it will go in the opposite direction.

If you put the car in neutral so that the prop shaft can rotate freely and then turn a wheel the other wheel may go in the same direction pulled round by the friction in the LSD mech. Depending on the relative friction of the gearbox and the diff the other wheel may just sit there.

Whether you can judge if you have LSD by this method I really dont’t know. Sorry to be not very helpful.

R-b

 

 

[Gra]

From the information you have given from the door sticker, I would say that you have a 1.8is, in which case it will have a LSD.

 

Gra

[Taxi_Driver]

@Razor Blue

@mal jones

Hello and welcome.    The easy way to tell if you have a LSD or not is to jack up the rear of the car and turn a wheel, if both wheels turn the same way you have LSD.  

Let me add a bit more

If you put the car in gear so that the prop shaft cannot rotate and then turn a wheel the other wheel will turn in the opposite direction. You may well feel the ftiction of the LSD mech but it will go in the opposite direction.

If you put the car in neutral so that the prop shaft can rotate freely and then turn a wheel the other wheel may go in the same direction pulled round by the friction in the LSD mech. Depending on the relative friction of the gearbox and the diff the other wheel may just sit there.

Whether you can judge if you have LSD by this method I really dont’t know. Sorry to be not very helpful.

R-b

 

 

So, I jack the car up, put it in neutral and spin a back wheel. If the other wheel turns the same way, I definately have a LSD. However, if there’s no movement on the other wheel, it’s inconclusive?

PS. Thanks Gra, I think it is the S model. Sticker on door shut says ‘Suspension - SPORTS S’

[Horrgakx]

Why not get on some wet grass and spin the rear wheels up?

(obviously not the local park mind you).

[Taxi_Driver]

@Horrgakx

Why not get on some wet grass and spin the rear wheels up?

(obviously not the local park mind you).

I’m not sure what that would tell me. I’d expect both wheels to spin regardless of an open or LSD. Besides, I have one goodyear and one continental on the rear. I’m sure the tyres grip differently and that may also give a misleading result.

[mal_jones]

I grew up with rally cars and as with my S-Ltd if the back wheels are off the ground and the car out of gear if you have LSD both wheels will spin the same way when turning one of the wheels, if you have a standard dif the wheels will turn in oposite directions. It has been this way with every rear wheeled cars that I have owned some with LSD (Mk1 and Mk2 Escorts, and Talbot Sunbeam) and others with out. It evan worked with Minis with LSD all though you tended to know if they were fitted with LSD when you drove them as they tried to pull your arms out of their sockets. Normally when fitted with a SC gearbox.   So spin those wheels and see what happens.

[Gra]

Take a look at the sticker again. If it has ABS printed just to the right of Sports S then your car is definately an iS model and will have a LSD.

 

Gra

[ast]

A 1993 S-Limited would have had a viscous LSD. The spin test works. Mk2s, if a LSD was fitted, it would have bee a Torsen, and so obviously the spin test won’t work. The Mk2 1.8iS should have have a Torsen T2 fitted. If you remove the filler, with a torch, you may see the gears; worm gears = Torsen, spider gears = Open.

You could measure torque bias ratio (TBR). From Miataforum and Lance Schall:

Originally Posted by Lance Schall

With all the discussion that invariably follows a “Do I have a Torsen?”, I thought this post would attract some attention. I originally put it up in Power Mods where it rapidly sank into obscurity. I did get one encouraging response offline, so here it is again:

In case you are interested, here is a way to test for a Torsen. This will verify the existence of a Torsen and measure the TBR (bottom of page): The driveshaft is constrained by leaving the car in gear. Ropes are tied through the spokes and wrapped over the wheels. A constant torque is applied, given by multiplying the weights by the radius of the tire. It doesn’t matter too much what that torque is since we are only interested in the ratio between the weights. The reason I used medium large weights (bigger than I could easily throw around) is that the operational torque applied to the halfshafts is on the order of 1000 ft-lb and I wanted to get closer to normal operational forces than I would have with, say, 10 pound weights. However, the Torsen should have this same ratio with any weight I used. That is its design feature. I measured TBR of 2.3 in coast and 2.5 in power direction. Experimental error suggests that it might be 2.4 in both directions. This is with a Type 2. This picture is 115 lbs on one side and 50 on the other. 115/50 = 2.3. Weights greater than 120-125 on the heavy side make the larger weight fall to the ground, rolling up the lighter 50 lb weight.

An open differential would not support a weight difference anything like this. Internal friction would allow some mismatch, but nothing like 2.4:1. Theoretically an open differential has a TBR of 1:1. I measured a Miata open differential to have a TBR of 1.2:1.

[Roadster_Robbie]

I’ve checked on the parts catalogue for the VIN you have quoted and it states "with L.S.DIFF.

[Taxi_Driver]

@Roadster Robbie

I’ve checked on the parts catalogue for the VIN you have quoted and it states "with L.S.DIFF.

Thank you.

[Taxi_Driver]

@Gra

Take a look at the sticker again. If it has ABS printed just to the right of Sports S then your car is definately an iS model and will have a LSD.

 

Gra

 

Yes it has ABS printed on the sticker.

Thanks to everyone who posted on this thread.