Anyone actually done the early rwd 626 3.63 gear swap into their Miata? Need you to chime in!!!

My 94 is in the shop to get the 626 ring and pinion swapped in. Problem is the pinion gear, while the same length, has fatter gears that hit the Miata housing. The 626 pinion flattened area for the bearing, the one next to the gears, is shorter plus the bearings are shorter.

Do I need to use the 626 housing? Is it OK to use the taller Miata bearings on the shorter flat area on the 626 pinion? Just shim the biotch out? Use the 626 bearing and race from the 626 housing? etc.....

Just don't see how to make this work! The car's in the shop with the rear end torn apart. Quick help will be hugely appreciated!!!!

In the pic the 626 bearing and pinion on the left, the 4.1 pinion and bearing from my 94 Miata are on the right. You can see the much fatter gears on the 626 unit as well as how much shorter the 626 bearings and bearing race on the shaft is.

HELP PLEASE!

 

Bob Bundy did the 626 3.63 swap a while ago. He put an OSGiken in recently so I don't know if he did anything with the gears at that point. Shoot him a note and he'll have the answer.
-h

 

The only way I can see that working is to put the Miata bearing on the 626 pinion. But yes, there's a conflict on the bearing size vs. the pinion bearing surface. Try PMing Joe Perez, he posted about having one in his car.

 

I agree, it looks like it will work if the larger miata bearing will fit on the 626 pinion gear. It looks like the amount of shaft that is available for the larger bearing is limited. Any walk of the bearing could be bad news. (They may not be an issue though once everywhere is together)

 

Actually I wouldn't do the "only way I see that working" because it wouldn't work. It will bias load on the bearing with the lack of pinion surface. I assumed the bearing angles were different just by looking at the photo. I guess if it were me, I'd be looking for a short bearing with the same angle as the Miata bearing. That might keep the pinion from seating so deep into the housing and avoid the interference... of course I'm just speculating. Here's hoping to a Friday solution.

 

Guess I'll be pm'ing bbundy and JP to see if they have any suggestions or answers! Keeping my fingers crossed that this may still work. Thanks guys.

 

Well, JP hasn't done anything with his 626 gears yet. Haven't heard back from Bbundy yet. Hopefully he has some insight into this.

 

What happens when you slide the miata bearing on the 626 shaft, is this actually a viable solution?

I would trust it on my car, it's not a daily though. Certainly risking a lot (pumpkin, gears, diff) if it does explode.

 

I forwarded the pic to a friend that actually has a 626 3.63 R&P and here's what he said:

Quote:

No, I haven't seen that. the set I have is mostly identical to the Miata 7" rear (at least interchangeable). I know several people who have used the gear set. Maybe there was a running change?

I hate that "running change" part- it's happened to me.

 

I used the exact spacers and bearings that were in the miata housing that I took apart. dont remember the bearings being different sized. I made a special tool to work in my press to get the pressed on bearing off the pinion without damaging it. Although I think you could just replace the bearings as well. There is a spacer under the pressed on pinion bearing as well that needs to be kept with the same housing it came out of.

Mazda uses swapping in different spacer thicknesses to adjust the mesh of the ring and pinion. From what I have experienced ring and pinions and bearings are made to ultra tight machining tolerances, The housing not quite as much. This makes the adjustment spacers and the housing a matched set. As long as you keep the spacers and housing together different ring and pinions can be put in without having to set the adjustment of anything but the backlash which has threaded collars to set.

Bob

 

Any update Casey? What'd you end up doing?

 

Shop got it together last night and the car buttoned up this morning. I forwarded Bbundy's info to Eddie at AR Auto where I had the car. All that needed doing was grinding away some of the interior of the housing. Bob's housing was close, mine made significant contact. Eddie doesn't like things not going perfectly together so this seemed like a bigger problem than it should have.

Like Bob, we used the Miata bearing and race. The bearing has less than 1/4" that isn't supported due to the shorter shaft section on the 626 unit. Hopefully that doesn't bite me in in the *** down the road.

First driving impressions are great. Much nicer to drive around town and on the freeway. Well worth the effort on a daily driver NA with the 6 speed tranny.

Big thanks to Bob for coming to the rescue!!! Hope to be back on the track soon.

 

Great to hear, Casey. I'll have to swing by and check out the new&improved ride.

 

sorry to necro this, but is there some sort of electronics needed to keep the speedo accurate with these gears? Just asking because its listed in the 3.63 gears some vendors carry. But 3.9 would most likely need to be sourced through lots of searching.

 

There's a widely available NB style electronic sensor, there's a Mr. Potato head job for mechanical speedos.

 

would you happen to know the part number for the NB style electronic sensor?

 

Google.

 

problem is, there's a few with different part #s, and none say which gearing they're made for.

 

I'm typing on my phone but the OEM speedo sensor for any of the 6 speed NBs through '03 should be for 3.9 gears.

 

good to know. But I find them listed for 01-03 and 99-05