A few diff questions...

[MWP]

Hi all,

Im a bit of a n00b to diff stuff...

Ive found an RN25 (G series) diff to go in my 1UZ RA28 at a local wrecker.
The wrecker will also sell me a 4-pinion (i assume a Torsen) center for it with a 4.3 ratio gearset.

Are there ways to check the condition of the center before buying (the center will be out of the housing)?
Should i just look for signs of wear/chipping on the gear teeth?
Anything else i should look for?

After having the diff mounts changed, is it a simple operation to install the LSD center, or should i get a diff shop to do this?

Thanks.

[Draven]

when swapping centres, changing carrier bearings etc is generally a good idea. I wasn't too keen on doing the job myself, so I paid for it to be done.

I know Wayne (the guy with eleventy billion MA61s) did the swap himself (for a tru-trac centre), so it's not impossible for a DIY

[MWP]

Ok, thanks.
I did think it would be a workshop job, but wanted to make sure.

Any ideas on what i should look for when checking the LSD/gears for wear?

[SillyCarS]

i posted up a bit about this when i built mine, a crazy brittish guy that has done a few drift cars diffs over here showed me how to do it, his buisiness is called 4x4 power transmissions or something like that up main north rd, i rocked up expecting him to be just like any other 4x4 guy and just have my hilux centre put together, but in the end i stumbled on a rare find

to see if the centre is any good you'll need to lock it in a vice and "crack it" ie roll the inside of the centre around using an axle, but to do this you need to weld a bar on the end, as the eccentric old geezer told me 3 feet long exactly

but if you going to go to all the trouble you may as well pull the whole centre apart and beef it up a bit with some washers cos essentially yes you have an lsd but its nothing you'll drift in (depending on your application too ofcourse), i wouldn't think its a torsion either its a 4 point pinnion lsd (stock hilux) as torsion i think were more of supra/cressida thing though i could be wrong

does it look like this:



then when you put it all back togeher use that spraycrete powder and regular engine oil, paint it on the gears and roll it around in the vice (while making adjustments) to get a nice mesh

aw yeah when you DO replace all the bearings don't press them on cos you cant feel when theyre just right, instead what you do is weld the old bearing cup on the end of a pipe and whack them on with a hammer. this way the inners of the bearings are touching each other and you wont ruin your nice new bearing, NEVER put bearings on with a hammer and a block of wood like some fool on here told me to

i think thats it

[Norbie]

Setting up a diff is a bit of a black art, I'd recommend paying a diff shop to do it. It's not very expensive and you know it will be done right the first time!

[MWP]

Wow, thanks for the info SillyCarS.
Im down south, but i think i might give them a call anyway since you give such a strong recommendation for them.

The center the wrecker wants to sell me will be from a different car/4wd/truck... im not sure which.
They checked the diff code which said 4-pinion LSD. As i understand it, 2-pinion LSDs are the clutch pack type (as in your photo above).

Ill go have a look at it tomorrow.
Ill make sure that its got a warranty, and that they will take it back if the diff shop says its well worn.

[edit]
Oh BTW, SillyCarS...
Who did the diff mounts change for you?

[ae95]

i'd definately take the diff to a diff shop to get the crownwheel and pinion swapped over

they know how to set just the right amount of backlash, which makes for a less noisy and stronger diff.

[Norbie]

They checked the diff code which said 4-pinion LSD. As i understand it, 2-pinion LSDs are the clutch pack type (as in your photo above).

Clutch LSD's may be either 2-pinion or 4-pinion. Torsen LSD's do not have pinions at all.

[SillyCarS]

yeah thats a four pinnion pictured aboved, the amount of "backlash" you want is 10 thou

also MWP 4.3's in the diff is pretty high, i'd be looking for a 3.9 or something out of a supra/cressida but then you will need to used a spacer on the ring gear, having said that i was lucky to find some 4.1 gears from a hilux

to figure out how much space you need you measure from the centre of one of the inner pinnions to the face the ring gear sits on and that is your diff's offset

having said that though its a 3mm spacer that is required

[The Witzl]

a 4.3:1 ratio diff with a 1UZ sure would make it get up and boogie.

... or do huge skids and not go anywhere.

[SillyCarS]

MWP sorry for highjacking i'll edit my post if you like:

4.3s might kill your top speed, with a big torquey motor, especially turbo'd (cos turbs love load) lower diff ratios a better suited (to drag/acceleration)

but then having said this what is the application? for example a 13bt that revs to 9000rpm will own on the qt mile with 4.3's in the diff but top speed will be sacraficed

i've gone for 4.1s in my '23 as i have the w58 (close first four gears and a much higher 5th gear) but im only packing 1g pwr in a car thats on par with a tonne

any higher than 4.3's ie 4.56 and above and you'd be driving 45 degrees up into the japanese alps at about 5km/hr

there's no sure fire answer though as it depends on a lot of things: application, power, weight, boosted non boosted, gearbox etc

any comments on setups that work well would be appreciated, as you could look at it from the point of view of:

its v8 therefore more torque, therefore can turn 4.3s at higher speed

or

it a v8 therefore low revs with lots of torque, therfore low revs plus 3.9s for high speed

is that stupid or is it just me?

[Sciflyer]

1UZ is not a particularily torquey engine though, relatively speaking, it likes some revs

plus with non-factory ECU you can rev to 7k pretty safely (although youre past peak power at that point

So a 4.3 ratio *may* not be as unsuitable as you think

[clubagreenie]

Backlash is set by two things. Pinion height (pinion gear, not the centre pinions) which needs to be reset if you are replacing centre, carrier bearings etc. Change the pinion bearings and have it reshimmed for height and preload, but the gear lap is also considered in this.

Sillicar, so the method I've used for 25+ years, press with the correct size bush to fit the bearing inner doesn't work without damage? Wacking the bearing cup over the new bearing will damage it, you need to press/push the inside of the bearing onto the sleeve. Force on the bearing rollers will at least distort the cage.

[SillyCarS]

this way the inners of the bearings are touching each other and you wont ruin your nice new bearing, NEVER put bearings on with a hammer and a block of wood like some fool on here told me to

whats your point

[MWP]

Clutch LSD's may be either 2-pinion or 4-pinion. Torsen LSD's do not have pinions at all.

Hm ok, i need to do more reading.
I know there is nothing wrong with clutch-pack LSDs, but as im buying 2nd hand and as Torsen's have a longer life span, a Torsen seems like a better choice.
Any opinions on this?

also MWP 4.3's in the diff is pretty high, i'd be looking for a 3.9 or something out of a supra/cressida but then you will need to used a spacer on the ring gear, having said that i was lucky to find some 4.1 gears from a hilux

Ive done the calcs, and 100kph in 5th (W58) will put me at ~3000RPM.
With a 4.1, thats only dropped by another 200RPM. So not much of a difference.
This is not going to be a 1/4 mile car. Its going to be a track/hillclimb/motorkhana/hills car. So besides the high cruising RPM, i think a 4.3 or 4.1 will do quite nicely.
Itll always be NA'ed... turbo 1UZ can never be legal in a RA28. Ill do head work, etc in the future, move the powerband up a little.