RX2 Diffs

[NASHIE]

Just wondering what the RX2s out there are running (not breaking) in the rear drive department. In the past i have not had many problems with a 4.4 cig centre and stock axles behind a mildport. But with the new bridgeport and 15 inch tyre combo it lasted about 2km(one snapped axel the other badly swisted). I have sent a PM to flycasta regards a 4.77 lsd centre (not sure if he still sells these ?) which I believe should fit or be close into stock Housing with 26 spline E2000 Van axles.

Any feedback greatly appreciated

Cheers Ben

[GT4RALLY]

I had a standard mazda LSD with 4.6:1 ratio and 13" wheels & broke one axle & badly damaged the other in the first event I ran in the rx-2. I have a 12A -BP that makes about 130BHP and now run 15" wheels.

After some research I found that the bearings are too small & the splines too weak for the number of rallies that I do each year. Having said that there are quite a few peple run the standard housing with stifeners that stop the housing bending (and hence reduce the stress & fatigue of the driveshafts). The maintenance on the rx-2 diff is high with the requirement to routinely change bearings & crack-test the driveshafts.


In the end I built a hilux diff for a number of key reasons:

1. it won't break
2. much bigger bearings - so less maintenance
3. the driveshafts are twice the diameter & # of splines
4. they come as an LSD standard which is adjustable for preload
5. the housing requires no strengthening
6. There are as many ratios as you would like (I run a 5.3:1)
7. Parts are cheap & readily available

Bought a 1990ish LSH hilux rear diff & cut the housing and machined the driveshafts back by 70mm each side to match the mazda housing dimensions.

I remember reading a lot of stories on this & other forums about a friend of a friend's budgie that had a hilux diff in thier RX-2 and took it out for some reason or annother (cound't find an actual reason).

After at least 25 rallies including some really rough stuff, some big hits & a high speed multiple roll over the hilux diff is still as good as the day I put it in & all I am going to do over Xmas is give it a coat of paint ready for next season.

I would't bother with the Mazda diff, put something in that's going to last.

RT

[Spac]

/\ All good info. Earlier Hilux diffs are the correct width, and do not require shortening.


There are things that can be done to the standard RX-2 diffs. They have the advantage of being light and having good LSDs.
Double row wheel bearings help a lot, but still leave the standard 24-spline axles as the weak link. Previous experience with Mazda 24-spline axles says that if an axle is straight at the start of a rally, it won't break before the next event (ie: Check them before every rally). This held true for my RX-5 which had more torque, more traction and more weight than an RX-2.

Converting to 28-spline RX-4 axles is another option. The 28-spline axles are essentially indestructable - there's even been a few 9-second drag cars using these axles. Basically requires big billet steel (or alloy?) bearing converters, and widens the track (which is usually a good thing in an RX-2). You also get the much larger RX-4 bearings, which solves that drama.
The tricky bit is getting 28-spline axle gears for the LSD - they're not that hard to find, but you pay lots for them.

The van axles don't work. AFAIK, every van that came with 26-spline axles also had dual rear wheels and floating hubs (don't get excited about the floating hubs! They're super heavy, super ugly, and really only work with the tiny drum brakes from the van).
Having some RX-4 28-spline axles cut down to Capella width and 26-splines could be an option, but you've still got the piddly little wheel bearings and have lost the absolute certainty that you won't break the axles.

Early B1600 diff swap is another option. The centres are basically the same as those in Turbo RX-7s, you can get a big range of ratios (3.6 ~ 5.1, although 4.77s are the most common and shorter ratios are hard to find), they've got 30-spline axles and are the right width for an RX-2/3. They are supposedly also easy to convert to 4x110 stud pattern (for reasons I don't recall right now).

[NASHIE]

Thanks for info guys, helps me out a lot. Agree with the 24 spline axles spac as previously i have only had two let go over a 4/5 year period. The two i just wrecked were mint out of a low km auto, so was a bit at only getting 2km out of them. I would really like to keep the standard housing but its all sounding a bit to mix n match which is a hassle when chasing replacement gear that is already as rare as rocking horse poo. I know the early model hilux diffs are getting hard to source here in the west, so will chase up the 1990 hilux/ B1600 leads.

Cheers Ben

[Kaptainballistik]

Ok, ( Flexes back hands....) First things first...

You want a B1600 diff... Its worked since the dawn of time.

Ive done the dubble row Bearing conversion (More troubble than you could ever realise...) And it will walk the retainers after a Motorkhana....

Tottaly and UTTERLY FORGET the Mazda diff, Even if the Diff is "Winged" (Braced...). As soon as find the cars traction sweet spot it will break the axle in under 10 stage KM's.

Ive twisted a nice fresh one in a Khanacross.

Unless you get the 28 spline full floater setup. Then im still dubious..

The hilux in the lower than 4.4 ratio has pinion gear issues ( High wear rates....). The axles crack at the bearing retaining clip with the things we do to the cars.. ( Ive been in a car that did it with freshish axles...)

Circuit car however... Perfectly fine!!!!! If you get the solid pinion preload spacer and get the axles converted to Screw on retainers they are a good thing In the back of a RX2 / 3 or 7. And you can get ratios down to 6.1....

Besides easily available lower ratios there advantage is the Diffnose is smaller than the B1600/b2600/ bt50 . So you wont have to belt up the floor with a oxy and a sledgehammer.

Remember when I used to break rear arms at every event you Mini Car club / WAC kiddies and I suddenly stopped doing it?

Pete finally let out a secret

Ok, The B 1600............

Its about the same width as the Standard Diff, The 5.1 ratio Does exist , But ive yet to find one in 10 years of looking for the vans that supposedly have them. The part was superceeded by Mazda/ Ford 15 years ago.....

You find one , Ill buy it!!!!!

Screw on retainers, Axles as big as the Hilux the flange can be easily remachined to allow a straight bolt on of your old tailshaft. The spigot is the same.

Did I mention you dDont have to swap tailshafts???

Of course this is only for the B2600 style flange but the LSD centre you get is out of a Bongo SS (Or as we call it...a Spectron!!! or a pimped up Mazda van....)
Centre wise the diff LOOKS like a FC -FD turbo diff but its nothing like it. Fortunately the LSD is easily obtainable from SSS or anyone who wrecks Mazda 4X4's. Its Tough (And allegedly stronger than the Hilux) And you will need to get the preload changed from the paltry 40lbs....

And the axle redrilling is so easy its laughable. ( If you want to do a B1600 -E1800 diff PM me and ill tell you how.....)

That goes for anyone too

The other advantage is the B series diff is a Poor mans "fully floating " diff.

Dissadvantage? Belt the back of the diff tunnel up if you run the car low. ( 20 min work) Its also slightly bigger and heavier.

But your brake knockoff will be vastly improved!!!

Also Craft Diffs has the Jig to do the diff.

So the moral of this story.. Go find a B1600 or a E1800

Edit: Oh , And ive sent Bits of an LSD through the Housing in a small diff, The B1600 diff has done 40+ events without even a Bearing preload spacer change.

[Spac]

Originally Posted by Kaptainballistik

Centre wise the diff LOOKS like a FC -FD turbo diff but its nothing like it.

Not true. The flange that the crown-wheel bolts to is moved over to suit the shorter ratios, but otherwise they are very similar.

If you use a ute/late van ratio on an RX-7 LSD hemisphere, you need an 8mm(? - I can't remember the exact measurement) spacer between the hemi and the crownwheel.
The 4.77 ratio 'kits' for the FD RX-7s have these spacers - Google will help if you can't visualise.

Typically, the Mazda commercial LSDs need work for motorsport use (same is true of Hilux LSDs). They have way too little pre-load, and the ramps are often curved - basically making a nice plate LSD behave more like a Detroit locker (ie: Slow to react, and relatively harsh when it does).




Challenge for KB: Show me a pic of a broken Mazda 28-spine axle.

[Kaptainballistik]

Cant show you a Broken 28 spline Axle But I could have shown you a Broken Diff carrier!!! ( actually ive seen a few....)



Try doing THAT to a B1600......

On the FC-FD diff thing, I know gentleman who have attempted the Centreswap . The quote was that It looks close but its actually miles out. But I digress... Because spacers make anything fit ( That and a hammer...)

I must talk to you more of this 4.77 conversion, Sounds mondo fun!!!

The other B1600 qwerk is that its meant for a much larger car so the U shaped Difframps are not an issue...Its lockup can be varied by how hard you stand on the throttle!! Its got alot of plate area in the Diffplates..

Its alot nicer diff to drive the car with than the Mazda comp diff was....Especially in the wet driving up near Springwood where the old diff would try to send you sideways at constant throttle going around the sweeper...At the speedlimit

Each to his own I guess.....

[Spac]

The RX-5 with a locker would stretch and loosen the 8mm bolts that hold the centre into the housing. Never even twisted an axle, despite semi-slicks and brutal abuse (albeit with minimal HP).
A braced housing would have helped, as would some higher tensile bolts (seems so obvious now, but didn't occur to me back then).

We've done the ute hemisphere into an FC carrier. The only difference is the location of the CW flange. Your source is unreliable.

[imortl]

I got a 4.77:1 off flycasta but it did take him some time to find.

Not sure how it runs yet, will know for sure about the ratios when I get to the Oran Park track day!! :-)

[Kaptainballistik]

Originally Posted by Spac

The RX-5 with a locker would stretch and loosen the 8mm bolts that hold the centre into the housing. Never even twisted an axle, despite semi-slicks and brutal abuse (albeit with minimal HP).
A braced housing would have helped, as would some higher tensile bolts (seems so obvious now, but didn't occur to me back then).

We've done the ute hemisphere into an FC carrier. The only difference is the location of the CW flange. Your source is unreliable.

You stretched the Bolts in the housing??? Yes young man, Brace that diff....

I only managed to make the housing pinch the centre so you needed some cold chisels as wedges to get it out.....:hide:

[NASHIE]

Thanks for all your feedback. I should of done a search first, as this topic has been covered a few times . Have decided to go the hilux swap for the main reason of easily obtaining 5.2 ratio centres, which i think will be spot-on for 15s, c/r box and bridge. The short run with 4.4 centre i could barely get out of first gear
Have sourced a mid 80s housing for $300 which is 40mm wider than rx2, which i will make up in rim offset. This means carrying two spares or getting 5x114 front hubs and spacers
Can get 5.2 open centre out of a hiace van for $100, which i will weld up for now till (the minister of war and finance has her back turned) i sus out the lsd options.

[Spac]

Watch out that not all Hilux/HiAce centres are interchangable. The early ones have smaller bearings and require conversion bearings.

5x114.3 stud pattern FTMFW. Saves the pain of chasing down 4x110 15s at not-outrageous prices.

[Kaptainballistik]

What spac said.....

PS Do you REALLY want to drive a RX2 with a Locker? ( Yes Fifield, I know you are ok with one...But you're MAD ) For the $200-$300?

Also, After running the Wide rear track setup myself, Try it first because it does make the car turn in better.

And its alot happier to slide.

Which would offset the Locker not wanting to turn. But thats a Fifeld knows best thing....

[afifield]

Thought my ears were burning.....

My recommendation would be to not run a locker unless you are prepared to go to wider track on the front and rear. This will greatly increase stability and predictability (i.e. gentle lift off oversteer). Be prepared to change spring and shock rates to find something you like too.
It's a different driving style, but if you stick to the basics (brake before the corner and drive through it), you should be OK.

I have the 28 spline/RX4 conversion that Spac mentioned, and have never broken/bent/twisted an axle, nor have I had any issues with the centre. The only problem is axle end float due to the single row bearings. I have been told that double row bearings will solve this, but I'm not sure how successful I'll be with the extension blocks, so haven't tried it yet.
Axles have been converted to 4x114.3 to match the front hubs.

[NASHIE]

Will double check Spac, there both G series so at worst should be able to swap ring and pinion?.
Only know lockers, all this LSD breakaways etc is all a bit high tech for me. Put it this way, i only changed brake pads once in five years , its all in the right foot. Apart from my very rusty driving the only thing that's changing this time around is the 15s, bridgeport and now the diff. Not totally sold on the bridge ie power only coming on from 5000rpm, but until the diff is sorted i will reserve my final decision ( thinking 13B extendport might be the go)