Laminar's M3 5.0 swap: Fünf-Null

[Laminar]

Saturday night I ended up doing just that - the left front tire was rubbing enough to catch the inner lip of the front fender.



I pounded the lip back in and raised both sides by 1 1/4 turns. I also adjusted the front sway bar (UUC) from full soft to medium. I did note that the front control arms still angle upward from the subframe up to the knuckles, which isn't ideal. The front tires had some pretty good wear on them for the 13 runs the car did.



Also Saturday my friend that drove it on the fun runs asked if he could co-drive Sunday. The allure of RWD was too great for him.

So I showed up Sunday and checked out the course.



The first stretch was a straight-up drag strip from the starting line to the first corner, about 230 feet, slightly uphill. Historically I've had trouble with wheel hop when launching, but Sunday I did not - grip was there and the car was able to bite really well. The car still ultimately pushed, but definitely not as bad as the day before. I started my tire pressures lower per my experiences the day before - down at 35 front and 36 rear from 37 f/r the day before. Grip was good, it wasn't as mushy for the (once again) very tight finish, but the car didn't really want to steer with the throttle, it would mostly push.



My first run was a clean 50.7 on unchecked tire pressures (didn't have time to grab the pump since co-driven cars ran first), my codriver did a clean 49.7 with the tires set properly. My next run was a 49.6 and I mentioned to my codriver that I heard the trans crunch second as I did a hard 1-2 shift during the drag strip portion, laughing about the abuse I subject the poor Mustang T5 to. We were learning the course, and the car definitely liked being heated up, which co-driving facilitated very well. The tires were strong from the get-go and the brakes were significantly stronger than they usually are. On my codriver's next run he launched decently hard and went for a pretty violent 1-2 shift. I heard a bang and winced, but we kept going. After that, I could feel a vibration during every acceleration zone, but he finished the run with a 49.0.

As soon as we got back to the grid, I jumped out and ran to the pits for my jack and jackstand. I knew something had broken and suspected the front diff mount bolt (been there...twice), the driveshaft, or something on the trans. This is what we found:





I did not expect the weak link in the drivetrain to be the diff ears, but there it is. One thing I do see is that the driver's side mount looks loose, like that bolt may have backed out. I wonder if that allowed some play which shock loaded the other side, snapping it. So we pushed the car back to the pits.



We drove his Cobalt SS for the rest of the day but neither of us managed to land a quicker clean run, putting us at 17th and 24th raw for the day.

So now I need a new diff cover. The local wrecking yard has a couple E46s and a couple 7 series...es, but no E36s. And since I'm opening up the diff, I'm also playing with the idea of swapping rear end gears. My realistic rev limit is about 6250, but I'd have no problem doing 6500 at the end of a straight. The current 3.23 puts me at 74mph at 6500rpm in 2nd and 2100rpm at 70mph in 5th. We lost our only airport venue this year, so both of our remaining venues are relatively low speed, barely ever anything above 60mph. If I went to, say, a 3.64 I'd see 66mph at 6500rpm in 2nd and 2350 at 70mph in 5th. The torque curve for this engine is very strong from 3000-5500. With the 3.23, that's 34-63mph, and with the 3.64 that's 30-56mph. I think it would really pep the car up in the slower stuff without losing range on the top end.

Secondly is addressing the car's balance and pushing. I played with the front shocks a bit, increasing front rebound. It made a small difference, but not significant. I ran the last event with the rear sway bar on its stiff setting (and old tires, and different shock settings). The car felt frantic and too willing to step out, which could have been a result of the shocks and tires. It was a good setup for drifting, but not for grip.

I'm feeling good about my alignment, though I wonder how the rear would move with 1/8" toe in vs. 1/4". I need some more time to adjust the shocks. I may tighten the front sway bar to its stiff setting and see how that does. I know most people end up softening (or eliminating) the rear sway bar in order to get power down so I'd feel weird about tightening that back up, but I may try it.

The next autocross event isn't until August so the upside is that I have some time to fix it. The downside is that I don't get to test out any changes or fixes until then. There are local drifting events in July and August, and I'd like to try at least one of them since I like giving my car a chance to break. We'll see how it goes.

[Kevin325i]

Those tire pressures still sound high. My e36 with similar alignment seemed to work best on re71r tires with them 32f 31r HOT. Which was 28ish cold.

[Laminar]

That's good info, thanks. The chalk seemed to clear at the edge of the tread. Maybe I'll drop a few pounds until I see it rolling over for sure.

[tptrsn]

Increasing front rebound is tricky, because it will tend to want to lift your inside front tire a little bit on initial turn-in, which is kind of similar to having a stiffer front bar. It will tend to shift the balance of grip rearward on that transition, since it is effectively keeping the chassis more level by lifting the inside front tire, and thereby allowing the inside rear tire to stay down better and do more gripping. At least that is how I see it lol.

I agree that those tire pressures sound quite a bit higher than I've ever needed for optimal grip with sticky tires like that.

Regarding the diff, I have only used that ECS style bushing on the front bolt, and it has been a bit weird at times... I'm not really sure I like their design all that well. Seems like it doesn't compress the urethane at all, and allows stuff to move around more than I want. IIRC, I ended up shortening the aluminum sleeve a tiny bit, and liked that better. I also went to a 14mm bolt on the front, which seems better so far.

[Laminar]

Increasing front rebound is tricky, because it will tend to want to lift your inside front tire a little bit on initial turn-in, which is kind of similar to having a stiffer front bar. It will tend to shift the balance of grip rearward on that transition, since it is effectively keeping the chassis more level by lifting the inside front tire, and thereby allowing the inside rear tire to stay down better and do more gripping. At least that is how I see it lol.

I'm going by this guide on adjusting the suspension for understeer. My bump was already full soft.

I ended up shortening the aluminum sleeve a tiny bit, and liked that better. I also went to a 14mm bolt on the front, which seems better so far.

I might try that. I do remember having trouble getting them seated all of the way, but I installed those before I had a press. Now I have one.

No issues with the 14mm front bolt here either. I still carry a spare in my toolbag just in case, but I think this demonstrates that the 14mm is doing its job.

[tptrsn]

Good info on the 14mm bolt holding up!! I'm glad to hear it because I want to rip on my car as much as possible this year, and spend less time working on it or building it for a while. Lol

On the topic of that guide, I must have missed the pertinent part when I was skimming through it at high speed. Generally speaking though, if I was going to increase rebound to correct a condition that happens at turn in, I would be increasing it at the end that has comparatively too much grip. Reason being that it tends to lift up the inside tire at that end, and thereby holds the inside tire on the other end of the car on the ground better, giving more grip to that end.

[Kevin325i]

What are your ride heights wheel center to fender lip?


The 14mm bolt held up good for me. I've got a 210 now. Tptrsn let me know and I can rummage around for the drill and tap, probably still have a bolt or two.

[tptrsn]

The 14mm bolt held up good for me. I've got a 210 now. Tptrsn let me know and I can rummage around for the drill and tap, probably still have a bolt or two.

Thank you, I really appreciate the thought!!

I wasn't really clear with what I was trying to say I guess, I have already installed a 14mm bolt, and I was glad to hear that it is holding up. But again, thanks!

[Laminar]

My local wrench-n-go has an E32 ('94) 740iL, which should have a 2.93 210mm diff. For $58.

Of course getting it installed, making it an LSD, getting a decent ratio in there, and shortening the driveshaft would still probably run me over $1000.

[tptrsn]

You can weld, so if it's an open diff, you have the LSD part covered for close to zero dollars. Lol

[Kevin325i]

Where's it at? I'm interested in a 2.93 ratio ring and pinion..

[Laminar]

Wrench-N-Go in Des Moines. They list a '94 740iL, no idea on the condition or what parts are still there. Shogun's post says the 740iL was a 2.93.

[Laminar]

What are your ride heights wheel center to fender lip?

12.5" front, 12.125" rear.

[Laminar]

So here's a conundrum. My local wrecker doesn't have any E36s I can swipe a diff cover off of. The cheapest ones on eBay are $100-125.

But it turns out Dorman (shudder) makes a "strengthened" replacement. They claim more thickness and extra ribbing:

The original equipment differential Cover may break at its mounting position, causing the rear axle to shift in place. Our OE FIX differential Cover features additional Bracing and thicker ribs for a 30% increase in strength over the OE part

The OE cover breaking at its mounting position?? You don't say!

It's $125 on Rock Auto.

[tptrsn]

Looks like the answer to me. Good to know those are out there, btw, thanks!!

[Kevin325i]

12.5" front, 12.125" rear.

Kinda thought your would say that. Either raise the front or lower the rear. With your spring rates and alignment shooting for closer to 1" difference has always felt much better on the car. My car has a couple hundred less pounds on the front though.

I would say try 12.5f 11.5r, give a little extra height to the front left like 0.25"

[Tim Mc]

I'm typically not a fan of Dorman, but that looks like a quality product. I threw an extra away when locating a replacement 3.90 gear...the bummers of moving house.

[Laminar]

Kinda thought your would say that. Either raise the front or lower the rear. With your spring rates and alignment shooting for closer to 1" difference has always felt much better on the car. My car has a couple hundred less pounds on the front though.

I would say try 12.5f 11.5r, give a little extra height to the front left like 0.25"

I'll give that a shot! Do you have a coupe? My curb weight is inline with a stock 6cyl sedan, which always seem to run a couple hundred pounds more than coupes. Tim Mc's stock '97 M3 Sedan was 3237 with no people or fuel, I'm 3184 no people and 1/2 tank.

With driver and 1/2 tank of gas:
Front: 911 868 1779 52.52%
Rear: 807 801 1608 47.48%
1718 1669 3387

[AdamBath]

Did you order the diff cover already? I have an E36 M3 diff in the garage. I don't think I can use the cover on my E30, but maybe I'm mistaken?

Was thinking the Z3M finned cover for my build anyways, so if you're still looking shoot me a PM.

[Laminar]

I did order it already!

[Kevin325i]

I've got a sedan as well. I'm just under 3000 lbs mostly from no ac in the car, and trying to not gain weight from the turbo bits.

[Laminar]

The M3 has been mostly sitting since it broke. I wanted to get my motorcycle fixed up and sold, which I did last Saturday. Then on Sunday, I was at Costco buying fruit, tequila, and baby wipes (only the bare essentials!)



...and saw something. Went home and thought about it a bit, did some research, and went back Monday after work to grab it.



Still had to pick up kids after that.



Went home and had it set up in about an hour.





It's the 5000lb model, so it will do every vehicle I own. Way faster and safer than messing with a jack and jackstands - lifts the car in about 25 seconds. My DD has stupid sideskirts that totally block the pinchweld so jacking it up with anything other than the stock scissor jack is a nightmare - either bend the pinchweld or crush the sideskirts. This should slip in there nicely and have enough flexibility to let me lift from the gaps in the skirts. Wife's car needs a new axle, which will be a piece of cake with this, and the Cougar needs a driveshaft, once again necessitating getting it up in the air.

https://i.imgur.com/fikASZb.gifv

In the meantime, the M3 is ready for surgery.

[Laminar]

Old and busted diff cover: removed.



Gears look to be in great shape, which is nice considering all of the abuse I've dealt out over the past 5 years, and presumably the previous 17 years of its life.



Here's the Dorman "extra bracing" diff cover:



Yeah it's got more ribs, but it's also die cast vs. traditionally cast. I can't find much out there about the strength of a die cast part vs. traditionally cast, so I suppose time will tell if this is actually an upgrade.

Speaking of time, I had a rough time trying to get the new cover installed. I pressed the bushings out of the old cover and into the new cover, got the mating faces all cleaned up, and installed the cover. The problem I ran into is that the bolt holes on the ears don't quite line up:



It's possible that the new part isn't the correct dimension.

It's possible that with the stock squishy rubber bushings, the bolt could be made to fit, but the poly doesn't let them move enough to start.

It's possible that when the ear broke, the other diff mount was carrying the full force of the diff and slightly bent.

In any case, both diff mounts on the subframe look solid, nothing appears to be bent or starting to tear off. A 5lb sledge did nothing to move the ears closer together. I installed one bolt, hooked a ratchet strap to the diff, and tried to pull it across the car to get the second bolt started, but no dice.

Short of cutting the diff mount off the subframe and re-welding it where the diff wants it to be, I'm not sure what to do. Maybe I could get some (M10?) threaded rod, thread it into the diff mounts, and try to pry them together a bit? I'm afraid I'd bend the rod before the mounts moved, though.

[Tim Mc]

Not fun - aftermarket parts that don't fit. Absolutely annoying if it is true. I have no suggestions other than test fit another OEM part - sorry.

[Laminar]

It should have been so easy. Swaybar off, old cover off, new cover on, swaybar on.

But that bolt didn't line up. So I ended up dropping the exhaust, and disconnecting the axles and driveshaft so I could drop the diff, then chop and reweld the diff mount to get the bolts to line up. But it's in there.



New lift is fantastic. The only downside is that I can't roll in from the side, which is handy when pulling the exhaust. Not a big deal, takes four extra seconds to roll in from the back. But now that the exhaust is out, I'm basically obligated to fix it (for like the third time) for more ground clearance so I don't scrape over the tiniest of bumps.



Also since the exhaust was out, I started the car up because...open headers. I let it idle for 15 seconds and goosed the throttle up to like...2000rpm. Wife was upstairs.



I have run it before with open exhaust manifolds, but never open full-length headers. You could definitely feel it in your chest. I almost want to take it around the block like that just to experience the glory and the majesty but I can't imagine how quickly the suburban police would be all over me.