Changing Ring and Pinion

madjak · Postby **madjak** » Tue Jul 07, 2015 1:03 pm

I've pulled apart my 1.8 torsen 4.1 diff to install a 4.778 ring and pinion from a Kia. Just for documentation purposes, the bearing on the pinion from the Kia is smaller than the Mazda pinion bearing. I managed to get this off with a hammer and punch working my way around, knocking it off. I've purchased a replacement bearing ($40) which I'll drop on tonight.

My question is around the crush sleeve. Given that the crush sleeve is set to the housing, can this be reused with a different pinion if it's torqued to the same spec? You can also purchase solid pinion spacers with a shim kit from Weir Performance which is supposedly a lot stronger than the crush sleeve. I've read some posts on the RX7 forum that state that this is the weakest part of a diff, and than with hard launches, the crush sleeve crushes a bit and puts slop in the pinion bearing.

Has anyone done this before? I was actually thinking I could machine up my own solid pinion spacer and just purchase a shim kit locally.

Last question... this diff is for a track car, and I've heard that you can set the pinion bearing a tad looser for less friction. It shortens the life but then I'm probably only doing 1000km a year on it. Once again, anyone have any knowledge on this?

manga_blue · Postby **manga_blue** » Tue Jul 07, 2015 1:19 pm

Good question, I need these answers too.

Just personal opinion but I really hate any free play in the diff. It makes it just that much harder to get smooth transitions when you're trying to feather through a sweeper in third or want to go hard on/off/on/off/on in second through something like the cleavage at Winton.

madjak · Postby **madjak** » Tue Jul 07, 2015 1:35 pm

manga_blue wrote:Good question, I need these answers too.

Just personal opinion but I really hate any free play in the diff. It makes it just that much harder to get smooth transitions when you're trying to feather through a sweeper in third or want to go hard on/off/on/off/on in second through something like the cleavage at Winton.

yes true... I think the idea of freeing the diff slightly only applies to the pinion and not the carrier bearings. You don't want the ring gear moving across under load and reducing the backlash as this will quickly wear the ring gear and create the slop you're talking about.

I'll do some more research! For now I'll probably try setting it back up again with the crush sleeve I have. If I get issues I can always drop it back out and re-do it.

I'm looking forward to some crazy gearing! 6-speed + 4.778

Ned Loh · Postby **Ned Loh** » Wed Jul 08, 2015 10:35 am

madjak wrote:
manga_blue wrote:I'm looking forward to some crazy gearing! 6-speed + 4.778

Because I am too lazy to work it out, but you must have...what is your calculated top speed?

93_Clubman · Postby **93_Clubman** » Wed Jul 08, 2015 12:44 pm

flycasta (Duane) on here is the diff man:
memberlist.php?mode=viewprofile&u=2315

madjak · Postby **madjak** » Wed Jul 08, 2015 1:24 pm

I think I have it sussed... Picked up the bearing and it measures the exact same specs as the one that was in there originally. Also the pinion gear height is dead on identical so I think I can use the same shim as before and it should place the pinion at the correct height. I think it was just luck that the pinions are the same as they usually vary +/- 0.2mm.

I'm going to set the diff up with the existing crush sleeve, check the backlash etc and make sure that it's all good and then either go for a machined solid spacer or buy a new crush sleeve.

Top speed should be around 223 km/h @ 8300 rpm in 6th... with the 4.1 it was 260km/h. On the tracks I'm running, I'm not even close.
At 110 km/h I'll be doing nearly 4100 rpm.

The main reason for changing diff that on the two main tracks here I'm in an awkward gear (high in revs in 2nd or to low in 3rd) and have to switch from 2nd to 3rd on a hard right bend. I often hit 5th instead of 3rd. This diff should let me sit in a better rev range in 3rd and let me run to 6th on the main straight. This also means I'm shifting 3-6 which is a 'H' pattern rather than 2-5 which crossed. It may cause me problems in other corners though so we'll just have to see how it goes as maybe a 4.3 is better. This is why I want to be able to switch diff internals myself rather than pay for it to be done.