M5R2 (M5OD-R2) Rebuild Deep Dive

[97Sandbox]

Oh, and I wanted to share this tidbit just because I'm really deep diving these transmissions.

You all should hopefully have a clutch inspection plug in your bell housing. If you still have an original slave cylinder, you may even have a dust boot around your slave cylinder quick connect fitting. But did you know these originally came with a dust cover over the bleed port too?

I never saw one till I pulled that parts transmission at the salvage yard. Grabbed that little guy and threw it in my Mounty to keep the road dust out (it sees a lot of gravel roads).

 

[410Fortune]

Wow

Had no idea never seen that sucker before!! Go
Mazda

Do we need to scan and 3d print some of these parts?

Keep it up! This is how Brett got started.. lol

 

[97Sandbox]

I don't have access to 3D scanning or 3D printing anymore, but that'd be a great idea! If we could 3D print a simple two-piece mold, you could easily make those boots at home out of silicone or urethane.

I'm assuming all the transmissions came with that boot, but they must always get lost or tossed when bleeding the slave.

 

[410Fortune]

Exactly

More and more people are getting access to these things

I was thinking more along the lines of creating shift forks or other out of production hard parts

 

[97Sandbox]

Oh yeah, if you could get a shift fork scanned, it'd be very easy to clean up the worn surfaces in a CAD program with synchronous modeling capabilities. I wonder how a DMLS-printed fork would hold up. There's plenty of prototyping shops that could make those, but I suspect the cost would be pretty steep. It's been almost 3 years since I was doing that kind of stuff for work though...maybe the costs have come way down.

I have to imagine the die cast tooling is still on a shelf somewhere, but the demand is so low, it's not worth setting up for a production run. Maybe we can just ask Mazda to sell us their tooling haha.

 

[97Sandbox]

Cleaned the 2wd case, tail housing, an a block separator plate today. I drilled the bell housing holes for 7/16" bolts and added a dowel punch hole.

Just a 1/4" hole behind the right dowel, worked great!

The 4.2 block plate works, but an older 300/302 block plate doesn't line up at the bottom. They have three holes, all in wrong spots.

But the threaded holes in the transmission go all the way through, so just poke a pencil in and mark. Then you can punch and drill two new holes to line up with the tapped holes in the bell housing.

 

[97Sandbox]

Flying through this 2wd! Got all races and bearings pressed and gears and synchros for 1 through 4 installed. This unit was sold to me as a 1998, but it must've been a 1999 model because it has the three-piece second gear synchro assembly. It all looked good again so it's getting reused just like what went into the 4x4.

Too tired for math, I'll pick up with the input bearing clearance check tomorrow.

 

[97Sandbox]

I did all my input bearing measurements and picked an appropriate shim. Put back the old countershaft shim and torqued down the front cover. Quick gut check: does the input shaft feel snug? I could barely turn the input shaft...uh oh!

Did I get my math wrong? Possibly, but I didn't think so. I laid down the case and spun the input shaft looking for what could be binding. If I had gone with too thick a shim for the input bearing, it could be compressing into the output shaft. But the output shaft spun freely. I had to think about this: the input shaft is in a constant mesh with the countershaft. In neutral, the output shaft can spin free, but the input and counter shafts always spin together. What if the counter shaft is the one bound up and I'm just feeling it through the input shaft?

Now mind you I did not change the counter shaft and the counter shaft doesn't have a recessed pocket in the bearing cover, so machining variation with my replacement cover is not a factor. Since I reused the old shim, the only things that changed were the bearings and races themselves. Those are straight roller bearings, so for them to bind from being axially compressed, something must be pretty wrong. I decided to test my suspensions by loosening the bottom four bolts of the center bearing cover. With those bolts backed off just a hair, everything felt good again. Okay, not ideal, but I know what to do.

Re-torqued the center cover. Removed the front cover and cleaned up the semi-cured RTV. This time I actually measured the depth to the countershaft front bearing. Sure enough, with the new bearings, the original shim is much too thick. But I have a spare shim from the junkyard trans (remember, they don't sell countershaft bearing shim kits)! So I measured the other shim I have: it's still a bit thicker than would be ideal to get the specified clearance, but thin enough there will at least be some clearance. I gave it a quick sanding, cleaned it up, and reassembled everything with fresh RTV. It all feels good now.

The lesson here is to always measure! Even if I can't get it perfect, at least I was able to avoid seriously screwing it up. Who would have guessed the bearings/races vary enough to necessitate a 0.050"+ thinner shim...

 

[97Sandbox]

Reassembled all the 5th/reverse stuff. Fifth gear clearance checked okay. Reverse clearance was a little high, I measured 0.0155-0.0165" and the spec is 0.010-0.014". So I made a 0.004" shim to get back to the middle of the spec.

Torqued and staked lock nuts.

This time I had my wife hold the case still using a four-foot prybar and I used my big adjustable wrench with a length of pipe over the handle. Both of my shoulders stayed attached this time.

Before I put the tail housing on, I snagged this pic to show the rear oil passage that's in the 2wd.

That's all sealed up now.

Before installing the top cover/shift tower, I took out the old shifter bushings and installed new bushings and a new dust cover. I made sure to grind a new groove on the right side of the shifter stub while it was out -- this allows you to bolt an earlier Ranger shifter right onto the M5R2.

I already put a new slave cylinder on too, so this 2wd trans is ready to go!

 

[97Sandbox]

Oh, I forgot. I also made a little block-off plate for the speed sensor hole.

Just some 1/8" aluminum plate with RTV around the hole. I did reassemble the toothed wheel on the output shaft, so it wouldn't be a big deal to add a speed sensor back later (if for some reason I needed to).

 

[97Sandbox]

I guess this is pretty much a wrap on the M5R2 deep dive. I certainly learned a lot and I hope others can too.

One thing that's running through my mind is the cost/benefit of rebuilding these transmissions. I now know it's not unreasonable to have to sink $600+ in rebuild kits/replacement parts into a worn M5R2. If you already have a transmission (or can get one cheap), that's not too bad as long as you have the proper tools. A press, bearing separator, and assortment of torque wrenches are definitely required. You'll also need a reliable way to measure down to the thousandths and some 90 deg snap ring pliers.

But when I look at cores from used parts vendors online, it seems the 4x4 transmissions are going for $450-600 pretty consistently. If I consider that cost, the rebuild parts cost, and the cost of the tools, suddenly $1200-1500 for a remanufactured unit doesn't sound so crazy. Don't get me wrong, I love tinkering with these things and I'm not assigning tool cost or labor to my own rebuilds in my head. But, if I were someone who didn't have the tools or time or interest in learning about these transmissions, a remanufactured transmission would be a very reasonable thing to go for.

The important thing is that we keep these transmissions going so we can keep setting up manual V8 Explorers. If you've built/swapped one, you know how awesome they are. If you haven't, I encourage you to go for it!

 

[410Fortune]

Sbf with a clutch for the win!

Good job and thank you

Where can I buy a good reman for around $1200? They usually charge a core? Just curious what you have found out there

 

[97Sandbox]

eBay is the only place I see them pop up for that little. There's a seller who doesn't include a core charge, but will not warranty their reman unless you send a core back. A quick search shows more reputable looking sites are charging $1400-1800 plus $300-400 for a core. Whether any of those remans can be trusted, I can't say. It hasn't even been long enough to say I trust mine yet haha!

For me, that'd be a whole lot of money and I'd rather use my time and learn some new skills, even if it is a lot of labor (not including the absolute pain it is to pull a core or two in a salvage yard). But for those with more money than time, don't let the price tag stop you from building a sweet three-pedaled V8 Explorer! Basically, I'm just trying to say the price of a reman seems about right now that I've done the work a couple times.

 

[410Fortune]

I’m planning to rebuild my own encouraged by your leadership here
I can’t afford $1500 for a trans when I can diy!!
I will instead continue to collect cores/ rebuilders
Money in the bank!

How hard would it be to convert a rwd unit to 4wd changing the tailhousing and output shaft?

 

[97Sandbox]

I'd estimate it takes me a couple hours to pull a 2wd in the salvage yard and probably more like four for a 4wd (getting the tcase out around that crossmember is a pain). Now that I'm faster, I can get a transmission torn down in under an hour, but if you're stopping to inspect everything, it takes a while. I'd budget a couple hours to clean everything and a couple more hours to get everything for 1-4 assembled and the front shims figured out. A couple more for 5 and reverse components, potentially making shims, and getting the tail housing sealed up. Add another hour for other loose ends like shifter bushings, the oil passages, etc. And another hour or two if you need to replace a shift fork. That adds up to easily 12 hours between pulling a core and rebuilding. I'm sure others could go faster, but IMO this is not a job to rush through.

I can get a transmission for $250 ($200 for the trans + $50 core charge) at my local U-Pull. So I'd be looking at $250 + $650 + 12 hours of work to DIY the job. Whether that's worth saving $1000 likely depends on what tools you already have, your level of ambition, and how hard it is to find the time. I have little kids, so it's not like I can sink a whole day into a rebuild, more like an hour or two a few nights out of the week over the course of a couple weeks.

I wouldn't say the rebuild is necessarily difficult as long as you follow along with a service manual, but it does take a good bit of mechanical inclination to get it all back together just right. If you do have some mechanical inclination, it's a really interesting and satisfying job though!

 

[97Sandbox]

I will instead continue to collect cores/ rebuilders

This is going to be the way we keep these transmissions and swaps going into the future.

How hard would it be to convert a rwd unit to 4wd changing the tailhousing and output shaft?

I don't think it'd be hard at all other than the fact you have to pull and disassemble two transmissions. Since you have to strip the main/output shaft down to nothing before you can clean the gears and put in new synchro rings, you'd just put everything back together on your 4x4 shaft instead of the 2wd one. Then put the transmission back together with a 4x4 tail housing on the back. From what I saw, the guts of the trans are all the same (4.2/4.6 and 2wd/4x4) except for the 2nd gear synchro revision in 1998/1999. The main transmission case is the same for 2wd/4x4, but not between 4.2 and 4.6.

 

[97Sandbox]

From what I saw, the guts of the trans are all the same (4.2/4.6 and 2wd/4x4) except for the 2nd gear synchro revision in 1998/1999. The main transmission case is the same for 2wd/4x4, but not between 4.2 and 4.6.

And this is a good reason to rip apart 4.6 transmissions instead of just walking away when you find them. Although we can't bolt them to a SBF, we can build all their guts into a 4.2 case. I wonder if you could even bolt the '97+ guts into an '88-'95 case...those older transmissions are much more plentiful and you wouldn't even have to drill the bell housing since they're already made for 302/300.

 

[97Sandbox]

Well I thought I had showed you guys everything, but look at these rings I just picked up while cleaning off my work bench:

I didn't even notice during the teardowns, but these 1999+ third gear (I think) and reverse synchro rings have a different profile in the ID and some fancy looking (PVD?) coating. None of the replacement rings in my kit nor any that I see online have this though

 

[97Sandbox]

Bonus! I wanted to add this as it's something I did in my first M5R2 swap that I really like. You may not have caught it in the last picture of the 4x4 transmission.

The bulkhead for the transmission sub harness of the 4R70W clips to a bracket that doesn't fit directly onto the M5R2. But by tapping a hole, and with a little slicing and dicing, it can work nicely. Let's make a bracket for my 2wd.

Drill this hole to 17/64. Tap for M8 bolt.

Take your bracket and mark two straight lines. We're making two cuts and discarding the middle.

You can cut off the two tabs on the piece with the holes too.

Trim some more for aesthetics.

Add a bend to make it more rigid.

Mock it up and tack it together.

Just needs paint!

I just zip tie the O2 sensor pigtails to the bracket that is on each M5R2 piggybacking off one of the tail housing bolts (you can kind of see it in the picture of the 4x4).