So you want to weld the diff on a FWD Honda. Or you are just here to laugh at how stupid someone could possibly be to want to weld the diff on a FWD car. Either way, follow along brave soul.
Once you've gotten yourself to this point, the diff will come right out of its little home, and you are ready to start prepping it.
Prep work: get yourself an acetylene torch (you could probably make do with a MAPP gas torch or a large weed burning propane torch, but acetylene is better. Befriend your local commercial plumber or HVAC/Refrigeration tech, they have all kinds of cool tools), a noncontact temp gun (I told you HVAC guys have cool tools), a roll of aluminum foil, and several cans of non-clorinated brake clean.
Then, making sure your axles are still in and fully seated and your tinfoil is covering the ring gear and speedo gear (getting the feeling this is important yet?) Drop the plates you made earlier in, one side at a time, and tack and weld them to the spiders.
Chip away all that slag, and go over the whole thing one final time on either side.
Now, leave the axles in for now, and you've got to let this cool VERY slowly. Wait till it drops to 500 degrees, hit it with the torch for a bit. Wait 5 min. Hit it with the torch briefly. Wait 10, hit with torch. You get the idea. Should take you just shy of an hour to get it down to ~200 or a lil less. At this point, if you've got a welding blanket, wrap it in that and leave it till it cools off.
here are a couple closeups of the new carrier, the welding looks like 💩 but it's got good penetration and that's what matters.
I'd like to start with a couple of links to the pages of people with more skill than myself in both car building and writing. First the very first article I came across that showed me a welded FWD diff was not only possible, but awesome
Second, Race & Track Driving's page on the matter (if you scroll to the bottom of this link, he has many, many more links about welded diffs in FWDs) and lastly, just before we get into it, This EXCELLENT thread on Honda-Tech on how to disassemble (and reassemble) a B series transmission.
Now personally in the past, I have stumbled across other Honda-Tech threads on various matters that would have been insanely helpful, but all the images they uploaded have been taken down. With that in mind, I'm reuploading this image as it's the only one you really need to see to successfully disassemble your B series transmission by following that guide.
Now, let's get down to it. Step 1: follow the H-T guide I just linked above to get your transmission apart and your differential out. Don't forget to drain the transmission fluid first. Don't be too intimidated by this, I was, to the point I asked around for someone else to disassemble and reassemble my transmission and just let me do the diff welding; the only guy local to me wanted $300 just to open it and close it back up. That's insane, so I figured I'd try my hand at it myself. Now I'm pretty stupid and even I got this first try by following that guide, so just take it slow, be careful, and you'll do fine.
Here is my transmission apart with just the casing off and with the gear stacks and shift forks out.
Ah, the last picture ever to be seen of this diff looking like a diff. (Notice the wear on the spider gears from repeatedly spinnning only one wheel under full throttle)
Not carb clean, not electrical contact cleaner, not automotive parts/tool cleaner, not clorinated brake clean, *non-clorinated brake cleaner*
Other cleaners leave behind undesirable deposits which make welds weak and if you weld after using clorinated brake clean you will essentially gas yourself, it's a very unpleasant experience, ask me how I know.
Wrap some aluminum foil around the ring gear, as well as the speed sensor gear (you WANT oil on those parts so if you accidentally get spatter on them, it doesn't stick) and go right to town with the brake clean on the spiders and the pin holding them in. Then, pop an axle in one of the holes, rotate it 90 degrees or so, and go to town again on the spiders. This will get most of the oil and garbage off the metal to be welded.
This is an optional but recommended step: take the acetylene torch out and heat up the spiders to 500* F, let them cool slowly, and again clean with brake clean. This will burn off any impurities that may have not been gotten by the brake clean the first time around.
Pop your passenger side axle and the halfshaft into the diff and it's almost time to get welding. Just one last step. Measure the distance between the large gears and the small gears in the diff carrier. For mine it was about 23mm wide and 50mm long, YMMV. You want this measurement between the faces of the big gears, not the axles, so your plates sit above the axles. Cut a couple chunks of 3/8" thick steel plate to those measurements and verify they fit into the diff.
Get your stick welder out (I use an old Sears 230A AC buzz box that I got on Facebook marketplace for $50, it works fantastic, cannot recommend enough. That or an old Lincoln tombstone or old Miller. Any buzz box that looks like it's been sitting in grandpa's shed for 50-70 years is a great bet.) and grab a handful of 6011 rod. 6011 isn't the strongest rod, but a blind man can weld with it, it penetrates deep, and it's got enough tensile strength for what we need. Make sure your axles are in and fully seated, grab that acetylene torch again, heat the spiders back up to 500* F, toss your ground clamp on the ring gear, cover ring gear and speedo gear with 4x folded tinfoil to protect from spatter, crank the welder somewhere between 3/4 and max and tack.
Tack the 4 spiders together, and also the 2 small spiders to the pin that holds them in, kind of like this:
Pull the axles out only once it's cool. I really had to fight to get mine out. Pried and pried until it worked on the axle, and for the halfshaft I had to put the shaft in a vice and beat the diff a bunch with a soft faced deadblow mallet. Eventually both freed and this is what I ended up with.
Now, if you haven't already, grab your chipping hammer, wire brush and brake clean and get as much slag and spatter and garbage off the diff as you can. Use the brake clean as a rinse afterwards to spray any dirt or grime clinging to the carrier or the gears. If you are wealthy and like doing things properly, now would be a great time to replace the diff bearings. But let's face it, if that was the case, you'd have bought an LSD and been done with it, so like me, you are probably just going to throw it back in the case and button everything up.
That link I shared earlier has instructions on how to get everything back together, again, laid out and described much better than I could do. Follow what he says and you will have good luck. Also, learn from me being an idiot and don't do what I did:
When I got to the step where the countershaft gets hung up and you have to spread the circlip to get it down, I thought I had it spread, but it slipped forward (into the access hole more) and the bearing got hung up on the back of it.
I kept torquing the bolts down but eventually conceded defeat and took it back apart. Cue an hour and a half of scraping goo off the two case halves. But more importantly I cracked the top countershaft bearing. I didn't have access to another bearing so I eventually put it back together with the cracked bearing as is, we will see how many KM I get from it before it explodes.
Anyways, the trick, I found was this: get chisel, wide but not too wide to fit in the access hole, and use it like a pry bar to put a little pressure to keep the circlip seated in its little slot in the back. While you maintain pressure on it, jam your needle nose pliers in and spread them apart nice and far. This is actually much easier to do now that they have the backing of the chisel. I found it very easy to hold this position, needlenose spread with pressure applied with the chisel, with one hand while tapping the case with a deadblow hammer with the other. It went together like butter then, a far cry from the struggle I had with no chisel.
So, put everything back together, button it all up and you are the proud owner of a transmission that puts 100% power to both front wheels regardless of how much traction either wheel has.
I'll let you know how it works after race season rolls around. Till then, stay frosty friends.
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