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Well it's always something. So I installed the diff and the driveshaft and Houston we have a problem. The ears on the drive shaft that the U-joint mounts in hits the bottom of the shifter housing on the transmission. It uses a conversion joint like this thread https://www.rx7club.com/2nd-generati...shaft-1081644/ said and also which is what Mazdatrix uses in their 3" aluminum driveshaft. At this point I'm just deflated. I was so close. Anyway I'm not sure why the guy in that thread or Mazdatrix doesn't have problems. Only thing I can figure is their shafts look like a slightly different design for those ears with a more aggressive/ more angle on the chamfer. That or the yoke sticks out of the trans more getting it out from under the tail housing. I don't think so though cause using the stock L2 measurement like that thread would put it right under the tail housing. I think I am going to break out the grinder as that seems to be my only option. Shortening the shaft enough to get it out from under the tail housing would have it sticking out from tranny by over 1". Here is a picture of the joint on the diff side.
Last edited by Dak; 07-31-20 at 10:48 PM.
Reason: added link
Well after bolting everything up and looking at it more I've come to the conclusion I'll have shorten the driveshaft. I can't remove enough metal without getting into the groove for the retaining ring. Also I talked to Mazdatrix and that's how they build theirs. Maybe I'll get to drive it soon. I think this driveshaft is the last piece of the puzzle. Of course I haven't put my axles in yet.
I have already put some miles (and smiles) on mine, but not full boost/WOT yet...so far, all good
Took mine on it's maiden voyage today. Seemed to do good. Revs pretty quick. Don't know if it's noticeably quicker than the 4.3 since I haven't drove it in like 8 months but way quicker than the 3.73 in my pickup. I discovered my passenger rear wheel bearing is shot while I was changing axles so still sounds like I have a big mudder tire on that side. I don't think I have the vibration in the chassis I had before though. I noticed in your 13B-REW thread where yours cracked. I discovered that due to having to remove so much metal to clear part of the diff housing that I don't think I'll be able to use the diff as a jacking point anymore(not on this version anyway). I don't think there is enough enough metal there to support the weight of the car. I guess I didn't take that into account. I guess I'll count this one as the prototype. Starting to think on improvements for version 2, but for now once I fix the wheel bearing I'm just gonna drive it for awhile and see how it does. I will post the rest of my pics in the next day or so.
So here's a few more pictures. Up first is the driveshaft solution. Ends up with about 1.5" of pull out. It's really about.100" to .250" more than recommended but it seemed to be the only option I had.
Here is the area of the subframe I had to cut out to clear the flange the driveshaft bolts to. Unfortunately I didn't take a picture before I semi boxed it back in.
And after I ground down the welds for clearance and cleaned up the sub frame some for painting.
Picture of the front diff mount bracket before painting.
Apparently I didn't take any pictures of the painted subframe before I put it in the car.
And fully assembled.
On a side note I see replacing a fuel line in my future.
Last edited by Dak; 09-15-20 at 10:17 AM.
Reason: Added text.
just few cents
- on my setup, i am already pushing 1,3bar of boost on semipports and diff and mount is holding fine after first crack, definately feels better than oem FC diff setup mounting - about 500km on it so far, mostly power runs
- next version of side diff seal spacers/adapters will need to be o-ringed in my case, as oil is slowly seeping between adapter and iron housing....its tight fit, but in my case corrosion in the iron is not helping to seal it properly
nice job! I'm curious on this for the opposite reasons (FC bits in an rx8, long story) how did you do the axle portion? do the rx8 axles spline into the FC rear hub?
what combination of parts did you use for success?
also xometry is our competitor check us out at forecast3d.com instead I'll help you out!
just few cents
- on my setup, i am already pushing 1,3bar of boost on semipports and diff and mount is holding fine after first crack, definately feels better than oem FC diff setup mounting - about 500km on it so far, mostly power runs
- next version of side diff seal spacers/adapters will need to be o-ringed in my case, as oil is slowly seeping between adapter and iron housing....its tight fit, but in my case corrosion in the iron is not helping to seal it properly
Maybe my mistake of making my adapters too lose will end up a good thing. Since I had to epoxy them in with JB Weld maybe that will keep me leak free. I've only got about 70 miles on mine so far. Once I fix my wheel bearing I'll get some more miles on it.
nice job! I'm curious on this for the opposite reasons (FC bits in an rx8, long story) how did you do the axle portion? do the rx8 axles spline into the FC rear hub?
what combination of parts did you use for success?
also xometry is our competitor check us out at forecast3d.com instead I'll help you out!
Thanks. I used TII axles. Since the Diff itself is inter changeable between the TII, FD, and Rx-8 the TII stub shafts snap right in. I just had to make those spacers to relocate the oil seals since the Rx-8 rear is narrower. As to the hub. According to Rockauto the spline count is different. The Rx-8 has 31 and the Rx-7 has 28. You could probably make a custom axle like Ronin speedworks does on their kits and put an Rx-7 end on an Rx-8 axle.
I'll check you guys out. It's gonna be awhile but once I learn to weld aluminum eventually I want to put this FD UIM I have on my N/A LIM and I'm gonna need some flanges made to use in my adapter. Oh I probably need a standalone first too to get the full benefits I hope to gain of a less restrictive intake while still keeping the "supercharging effect" of the VDI intake. Oh I've been kicking around if there is a way to make a bracket/ adapter to adapt Rx-8 rear calipers to the FC as well so that may be my next project.
Thanks. I used TII axles. Since the Diff itself is inter changeable between the TII, FD, and Rx-8 the TII stub shafts snap right in. I just had to make those spacers to relocate the oil seals since the Rx-8 rear is narrower. As to the hub. According to Rockauto the spline count is different. The Rx-8 has 31 and the Rx-7 has 28. You could probably make a custom axle like Ronin speedworks does on their kits and put an Rx-7 end on an Rx-8 axle.
I'll check you guys out. It's gonna be awhile but once I learn to weld aluminum eventually I want to put this FD UIM I have on my N/A LIM and I'm gonna need some flanges made to use in my adapter. Oh I probably need a standalone first too to get the full benefits I hope to gain of a less restrictive intake while still keeping the "supercharging effect" of the VDI intake. Oh I've been kicking around if there is a way to make a bracket/ adapter to adapt Rx-8 rear calipers to the FC as well so that may be my next project.
thanks for the details, I was beginning to wonder some frankstein combination of parts to support the next rally car platform (which will likely be dead engine'd s2) I may not need the seal spacers like you as I plan to keep the rx8 diff in the rx8 and use the FC rear suspension so potentially if the lengths are correct I would just need to swap the spline side from an rx8 to an rx7 style and this SHOULD work but general fabrication. but I'm still pretty early on that project because the rally FC still works great
we do some machining but mostly do a lot of 3d Printing (metals and plastics) so if you get a wild design we can always print it out of metal in a way that can't be machined.
I've been working on Z32 rear calipers on the FC for a brake upgrade but running into some clearance issues, I want to avoid any sliding caliper system.
thanks for the details, I was beginning to wonder some frankstein combination of parts to support the next rally car platform (which will likely be dead engine'd s2) I may not need the seal spacers like you as I plan to keep the rx8 diff in the rx8 and use the FC rear suspension so potentially if the lengths are correct I would just need to swap the spline side from an rx8 to an rx7 style and this SHOULD work but general fabrication. but I'm still pretty early on that project because the rally FC still works great
we do some machining but mostly do a lot of 3d Printing (metals and plastics) so if you get a wild design we can always print it out of metal in a way that can't be machined.
I've been working on Z32 rear calipers on the FC for a brake upgrade but running into some clearance issues, I want to avoid any sliding caliper system.
No problem. I was kicking around the RX-8 caliper mainly because it seems the FC ones are NLA and it looked like they used the same style of parking brake setup along with (according to Rockauto) the rotor width being close to the same.
No problem. I was kicking around the RX-8 caliper mainly because it seems the FC ones are NLA and it looked like they used the same style of parking brake setup along with (according to Rockauto) the rotor width being close to the same.
I have used rx8 rear calipers on FD (together with rx8 brake cables) and it works fine. No so much for FC.
For my old drift FC i had adapters for 2 sets of 4 piston FC calipers
one last question, overall length wise how different is the t2 axle to the rx8?
Unfortunately that I don't know. I never had any Rx-8 axles and I didn't take a measurement of the overall length of the TII axle and stub shaft. I relocated the oil seals by0.640" per side after I modified my spacers. I got my original dimension by taking measurements of the rear end widths. Google says the Rx-8 is wider so I'm guessing it's more than my 0.640". Sorry. Maybe hIGGI knows.
So now that I've put about 550 miles on it I thought I'd post an update. Probably be the last one until either something breaks or I make version 2 of the mount. I'm not in any hurry so it'll be awhile. I replaced the wheel bearing and installed my DTSS eliminators. Then of course the the brake fluid leak I forgot about came back with a vengeance. Was leaking where the rod for the parking brake went into the caliper. Luckily Rockauto got some passenger rear calipers in so I snagged one and fixed that. Everything seems to be good now except for I have some vibration when not under load at speed. Like if I put the clutch in at 60mph or so for example or if I'm coasting with the clutch out but no real accel or deccel load. It is smooth under acceleration and for the most part during decceleration. Not sure if it's from the amount of pullout on the driveshaft as the company who made it warned it could cause some vibration or if it's normal from using the competition diff mounts. I did have a small leak on one of the axle seals but it seems to have went away. I've had some full throttle pulls from a roll through first and second but no hard launches and all's held up well. I'm pretty sure it will for now as I'm probably not making much above stock power levels.
As for the gearing after more driving I think I can tell a difference. I like it but I think I may eventually go back to the 4.30 gearing. I think I am going to pick up another Rx8 rear from an auto while they're still cheap so I'll have a set of 4.30 gears around, and I want to pick up a torsen diff from a third gen while they're around and not too expensive since it sounds like this super LSD will eventually break those ears off the cones. Back on topic. It's hard to explain the gearing. From a pure acceleration standpoint I like it. From a daily driven stand I find my revs are a little higher than I was used to in a given gear. When in town it's taking some getting used to. On the high way it seems happy turning those higher revs so I find myself driving faster. Sometimes it feels like it's being held back and just wants to be unleashed. It only threw my speedometer off by 5mph, reads faster than I am going, but it already was 2 or 3mph off. Too soon to tell about fuel mileage. First check was 19mpg which is normal for this time of year. Second was 16mpg but there wasn't much highway on that check. Mostly short trips and city driving. That's all I guess until I have something else to report.
be careful, the auto 4.30 diff is a different open-type design and won’t accept a limited slip, uses different axle stubs, etc.
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Are you saying you can't put a LSD like the torsen from a FD in the Housing of the auto RX8 rear end? Hmm that might slightly change things in that I'd have to move the 4.3 gearset from the auto into my current rear housing. As far as the axle stubs the TII, FD, and Super LSD from the Rx8 are all splined the same and the FD and RX8 use the same oil seal. So if it's just a matter of the splines in the diff itself I'd be throwing it away anyway.
yes, the RX8 diff with LSD is internally interchangeable with the FD (I posted an RX8 LSD up FS on here about 13 years ago), but I’m not entirely sure that the Auto diff can do that. I’m just warning you to be careful and not just assume. The 4.3 R&P can be used in the LSD diff, but whether the bearing carriers, internal clearances, etc. are the same is a question mark. They have two separate parts diagrams for each
yes, the RX8 diff with LSD is internally interchangeable with the FD (I posted an RX8 LSD up FS on here about 13 years ago), but I’m not entirely sure that the Auto diff can do that. I’m just warning you to be careful and not just assume. The 4.3 R&P can be used in the LSD diff, but whether the bearing carriers, internal clearances, etc. are the same is a question mark. They have two separate parts diagrams for each.
I had noticed that there were two diagrams and wondered what the differences were other than the diff itself. I looked on Jim Ellis and they show the part# for both housings and carrier bearings to be the same. I haven't cross referenced the other parts but the last time I looked the complete auto rear ends were still so cheap if I could only use the ring and pinon and had to swap it to my manual rear end I'd still save nearly $400 vs. buying a 4.3 gear set from Mazdatrix.
07-31-20, 10:47 PM
