What’s my FRONT diff?

Hello

This is more of a two-part curiosity question but one I’ve wondered about since learning the little I think I know and we all know how dangerous a little knowledge can be.

The rear diff for my LH119 is a ‘G145’ and there are plenty or resources that describe this is a:
G = 8.00 inches
14 = 4.875 ratio
5 = 4 pinion limited slip
This all seems about right based on revs and the way it performs. BTW with a LSD, with both wheels off the ground (and gearbox engaged) when you hand turn one wheel the other spins in the same direction. With an open diff the other wheel turns backwards but a broken open diff spins the other wheel the same as the spun one. As I’ve found to my cost.

I’ve read that the front diff is a 7.5 inch open variety but not managed to find any other info, so:

1 – does anyone know the model, code, pinions etc for the front diffs? I can’t find anything.

2 – if the front diff is a 7.5 inch how is the different crown wheel (ring gear) size matched to the rear? Is there a gearing in the transfer box to spin the prop shaft going to the front diff at a different speed (to the rear) or do both prop shafts turn at the same revs (my guess) but then is the gearing in the diff different to accommodate the different crown wheel size? Therefore the gear ratio is effectively higher in the front diff?  If so what is this?

Cheers!

Hey Buddy

The ring gear size doesn’t affect the gear ratio.  You can have different ring gear sizes on the front and back, what matters is the effective gear ratio ie 3:73.1 for both if that makes sense. The output is determined by the ratio between the teeth on the ring gear vs the teeth on the pinion. Like a clock the teeth size doesn’t matter. The number does.

The benefits of a larger stronger ring gear are self evident.

The front diff is an IFS 7.5 differential. Same basic design as a 4Runner/pickup/hilux with the same advantages and limitations.

Our Hiace has I believe a 4.10 rear LSD which would mean the front clamshell would also be 4.10.

Diff code would be F292 or F294 depending on which center section is in our van. Yours would be an F142 or F144.

Does that clear things up Sir?  Have an awesome day,

-Bryan

Gotcha!


Yes that does make sense and thanks for the detailed reply.

Based on your ‘handle’ you have a G295 as a rear diff, which is as you say a
G = 8.00 inches
29 = 4.100 and
5 = 4 pinion limited slip.

So the only difference is the ratio(s). I expect your engine and auto box is optimised for lower prop shaft speeds compared to my 3L and G52 5-speed manual.

4.875 to 4.100 doesn’t sound a lot but it’s ~15%. As I’ve put elsewhere my 195/80/R15 tyres will lengthen my gearing (over OEM tyres) but performance is still at the expense of power output and the 3L is less powerful then the 1KZ-TE.

It makes complete sense for both prop shafts to be spinning at the same rate. I had wondered if (any) gearing in the transfer made any difference but completely get that this is overly complicated.

I can see that as the crown wheel gets smaller and the driven ratio reduces, the diff gets more fragile.

On this basis I agree that mine will be a F142 or F144. As I’ve no oil in the diff (nominally drained but with fill and drain caps in place) I might be able to poke an endoscope in to see if it’s a 2- or 4-pinion setup.

I’d like to see if the front diff is labelled or a code is stamped but I’ve not been able to find one and my curiosity is just that.

Thanks for your thoughts on this, which I completely get.

With limited operational use due to selectable front hubs and part-time 4WD my front diff is good. I am changing all four front driveshaft CV boots with OEM Toyota ones. They were pricey but are superb quality in all respects. I went with OEM because there seemed to be a lot of options and my local dealership were very confident they got this right. The drive shafts are good and the original boots had held up well (mostly) but it’s time to renew.

As part of my rear axle refresh I might get the rear diff serviced professionally. It’s still within operational tolerance (just) and I think I could do this but don’t have the expertise to know if the result would be correct and proper for the future. I might also go for metal over OEM LSD clutches. I need to research more.

There are some great ‘Timmy the Toolman’ YT vids on both front drive shaft rebooting, which I’ve been referring to for my fronts and a recent sort of collab with East Coast Gear Supply where the CEO was very generous with his time in a diff rebuild.


Thanks!