3.7 Diff gears

290GTP · 07-01-2011, 02:34 PM

Has anyone put 3.7 diff gears in their AU XR8? Results, good or bad? What about re-calibrating the speedo?

I never really considered it before but i found a fully rebuilt LSD housing with 3.7's in it for sale & it got me thinking it that it might wake the old girl up a tad.

Thanks guys

T3man · 07-01-2011, 03:05 PM

You already have 3.45 so you won't even feel the difference going to 3.7. If you got it for free OK otherwise not worth the money.

290GTP · 07-01-2011, 03:41 PM

Thanks for that. My LSD's feeling a little tired (single spinning a bit), was thinking it might be a reasonable upgrade for the money.

T3man · 07-01-2011, 04:42 PM

Well if you have to repair your LSD and the one on offer is guaranteed rebuilt for the same price then it's probably good buying - just don't expect anything extra from the 3.7 - speedo is able to be corrected with a black box - available from shiftkits.

290GTP · 10-01-2011, 08:18 PM

Cool, thanks again.

GK · 11-01-2011, 01:14 PM

You should be able to go to Ford and get a different ratio cog for the speedo drive. As you're only going from 3.45 to 3.7, they should have one that will get the speedo close to right.

When I did my manual conversion in the SR, I went from the 3.08 ratio to 3.7. Speedo was out a loooooong way. I got the best cog for the speedo drive that Ford could give me (i.e. the largest ratio change they allow for), and it's still out by 8%. As most speedos are out by 2-3 kays at 100kmph, I'd say that was as close as I was going to get without the box mentioned by T3man. My jump was three intervals, starting at 3.08 to (1)3.23, (2)3.45 and (3)3.7. yours is one jump, so Ford should have you covered.

GK

SIKSIX · 11-01-2011, 02:18 PM

Hi BigRed220, I had 3.23 as a standard ratio then went to 3.73 with LSD and it was a noticible difference. Then went back to 3.45 because i managed to fracture the pinion gear on the 3.73 gearset, from what my diff guy said he rekons 3.73 are hit and miss because of the way they need to be setup. he rekons that they need alot of shimming which under big loads they can move and load up the gearset incorrectly resulting in fractured gears if your lucky. or worse, blown casing.

But then again my mate has a S2 XR8 ute and has had 3.73 for ages now and has had no dramas. i got my frist diff setup at a el cheapo workshop thinking i'll save money. he went to where i go now and both of us have had no dramas.

I think its worth the gear change from a performance point of veiw, and the speedo can be easily and accurately calibrated to the exact km/h with a Jaycar speedo corrector
http://www.jaycar.com.au/productResu...x=0&SUBMIT.y=0

Hope that helps.

T3man · 11-01-2011, 03:15 PM

Ford can't supply a gear to suit any diff ratio lower than 3.45 (black 22 teeth) because that is the lowest factory option. So you need the signal bender if you want to get it accurate. If you buy the Jaycar one you have to solder it together yourself - if you buy the Shiftkits one it is the same thing but they have assembled it for you already.

Once again though I can assure you that you will gain absolutely nothing in performance from a 7% change in diff ratio. The only benefit would be if you did a lot of towing in which case you will use less fuel because the engine will be under less load. This is why I have 3.7s in my wagon.