I have a 76 cosmo with the stock 5 link solid rear axle and disc brakes, and I plan to put a streetported NA 6 port from an 87 rx7 in. I want the Cosmo to look stock on the outside when the restoration is complete, but under the hood and the drive train can be anything.

I was wondering how strong are these axles?
How much torque can they handle?
Will I need to change my axle?
Is this the same axle used in the other rotary cars of that time?
Brake upgrades, what is necessary and what options are available?

 

As long as you aren't going crazy with the power adders then the 76 rear end should be fine. You need to know that i have no idea where to source a LSD unit for it and there are no options for rear gear ratios. If you think you are going to need an axle you better have one made. When we go our first Cosmo and I have a few of them.... it needed an axle we ended up buying 2 more cars when all i needed was one axle. There are no rear brake upgrades available as it is a unique drum/disc setup and lastly the axles are specfic to the Cosmo

 

My Cosmo also has an automatic transmission and I would like to install a 5 speed manual.
If I were to change the axle what would a good replacement, any make?
In the end I just what the front hubs to match the rear, so I will only need 1 rim size.

 

If you want to install a 5-speed the fastest and easiest swap is a 79-80 Rx7 tranny or else look for an old school ribcase 5-speed either way you should not need to change anything else, you will need to put a jumper wire in the shifter lockout wiring or it won't start.

If you are want to change up suspension and stuff there is no other car I know of that uses the 4X120 bolt pattern so you are kind of screwed, if you change the rear axle then the fronts won't match, if you use Rx4 ft suspension and hubs the rear axle won't match. So it really is a matter of finding what you want suspension wise and possibily have the hubs drilled to match each other

 

My 76 RX4 most likly had the same diff and axles, a four pinion carrer and a realt thick axle as compaired to most other cars in it's class, even better built then the B2200 pick up. So be strong I think you go to go with even a 350 cu . I did a swop on a 75 RX4 for a frend, a 1st gen LSD, it seemed a little litter but the it had LSD and disk brakes. Sit went from a 3.65 to a 4.10. I personel liked the 3.65 keeps 1st gear from windding to fast. I found this out when I did a swop on my 76 RX4 with a 2nd gen rear end, would like to have it back (3.65) but there no way around it, But the agin with front and rear with much better brakes now has become fun to drive