Mazda Gearbox ID

[MrBridge]

Anyone Know if this is a Stock Standard R100 4 speed box and Crossmember??
http://www.neodude.com/post/GearboxID.jpg

[Spac]

Nope. That looks a lot like a 808/1300 gearbox. Totally different to an R100 box - the old 10A gearboxes are "clam-shell" - they have two vertcal halves that bolt together. This is unique amongst Mazda gearboxes (only the old 1500 has a similar box, but most of them were column shift).

Only Mazda gearboxes of iinterest that have removable bell-housings (and can therefore be swapped between piston and Mazda motors) are the RX-4, RX-5, Series 4/5 RX-7, and RWD 121 (ie piston RX-5).

[buzz]

and although it appears to be using the stock mounting points, it isnt a 1300 crossmember - these are flat, not made out of 3mm rhs... ;)
I am in fact using a stock 1300 gbox xmember to mount my rx5 box.... so far! The exhaust clears it much more nicely than the one pictured .

[MrBridge]

Great Thanks:) I will be Installing a 12A in my R100.It currently has a 1300 pisston motor.So I'm trying to find out what I need to start?So an Rx5 5spd box will bolt straight on to my crossmember?

Are Rx5 boxes the strongest out of all Early rx's?

[Spac]

Yep. The RX-4 box is esentially the same thing, but with only 4-speeds, and with BETTER ratios. The "ultimate" early box is a 121 5-speed with a RX-5 extension housing - best factory ratios and will fit...
A RX-4 box is the same, just with out the 5th gear.

[THRSTY]

how strong are rx4 boxes?

are they worth rebuilding, or just go and buy something else? how much to rebuild (approximate price)?

[buzz]

THe rx4 is the original heavy duty drag box - they used to cope with 4-500hp ( with a little work and a lotta luck). The rx4 box is shorter than the rx5. The rx5 and s4/5 turbo boxes have very similar external dimension and Spac tells me that with minor mods the s4/5 will bolt up to the rx5 bellhousing (saving needing new flywheel and clutch assembly).
THe rx4/5 boxes are getting a bit old and may be a little hard to come by a good one - hence making the s4/5T version appealing. The rx4 box is handy by being shorter, if that saves you money on a tailshaft fabrication!
The "problem" with the rx4/5 boxes is that they sit at about a 12 degree angle off vertical (to fit the starter), so in a narrow tunnel they can be close to hitting the sides - whereas the s4/5 box is vertical. ....but I believe the base is on an angle (you can't have everything!!!)

Mr Bridge, the rx5 box has the flat base that the gbox mount bolt onto, depending on where the engine is mounted, hence where the box ends up, slotting the gbox mount holes can move the mount forward or back a bit to utilise a stock xmember. Looking closer at the pic, yours might not be mounted to the proper gbox mounts but rather two bolts through the floor - the proper mounts are a bit further back and out by the rails. I don't like the look of your xmember, though, and would recomend getting a stock one for the stock location and if neccesary, welding about a 1/4" to 3/8th" plate to it to go under the gbox mount.
Pity I don't have a digital camera to show what I mean... I had exactly this kind of set up in car I grabbed for parts - my current 1300 w/ 13b & rx5 box mounts to the stock box xmember with just the slotting.

As for rebuild prices, you could honestly spend $600-1000 (incl fitting, etc) on a rebuild of a box that already cost good money, depending on what is wrong.

[THRSTY]

thanks for that buzz. some handy info there.

so does that mean that using an rx4/5 bellhousing to fit another box onto the motor will get the other box sitting at an angle aswell?

[buzz]

I believe it does crank it over the 12 deg as well. That is why for the conversion of a car with a narrow tunnel that perhaps the s4/5 box and bellhousing is better.
Somethingto keep in mind, if you ever plan on competing in motorsports (primarily drags - eg for cars running 10.99 or faster) or running big RPM (like in dyno comps or improved production racing), then some form of containment protection is either mandatory or desireable to go around the clutch and flywheel in case they let go.
The options are currently to either use a steel bellhousing (stock is alloy) or a scattershield - a 1/4" steel plate that totally surrounds the bellhousing and the very back of the engine. They are a great piece of mind protection, but not cheap or easy to fit. If doing a conversion and you plan to either run a really big rpm engine or try for 10's or better then I'd strongly recommend looking into making one of these fit.
There is a group pushing to have textile based bags approved by ANDRA, and this might be done this year, but to date they do not have approval. THese would be the ideal option as they are easy to fit and go over an existing bellhousing... possibly without even needing to remove it.