Spec E46 Build Part VIII: Differential Cooling

Posted on 2015/07/04 by Chad

I’ve previously covered the addition of the DiffsOnline LSD differential in Part IV, here I’ll discuss a custom cooling solution for the differential.

A track driven clutch type differential can easily reach temps in excess of 250 F without much effort. Running a differential hot reduces the life of the clutch packs, which can reduce lock up and lead to poor performance. The simple solution is running a finned aluminum differential cover, which BMW produced. But relying on air flow under the car to cool down a race rear end will only do so much and you can still expect hot temps. You also lose ground clearance, something I’d like to avoid when you may take the occasional off-track excursion.

The other solution is an external cooler. BimmerWorld produces a kit for this, which is fairly universal. The GTS E36 build I picked up a while back came with boxes of parts, one being a mostly complete differential cooler. It’s a pretty simple setup; a self priming pump to draw fluid from the differential, a heat exchanger, a fan, and various fittings and hose.

I placed the cooler at the rear of the spare tire well, mounted on some fabricated aluminum mounts I made from angle stock. I also used rubber idolater mounts from McMaster Carr to contend with vibrations.

The lines run through the sheetmetal using AN bulkhead fittings. The setup was pretty compact because I was also mounting my cooling shirt cooler in the spare tire well. Because of these constraints I had to try a few different AN hose ends to get the angles just right.

Eventually I came up with the right combination and was able to have everything fit nicely. Under the car, the braided stainless lines run to the differential cover. The drain and fill plug were replaced with AN adapters from Setrab.

The completed setup:

Spec E46 Build Part IV: Drivetrain

Posted on 2015/06/12 by Chad

The Spec E46 rules specify the following in regards to the drivetrain:

1. Either the 5 or 6-speed E46 330 manual transmission may be used.
2. Flywheel and clutch assembly may be replaced provided they use the stock hydraulic actuating mechanism. Clutch must be a single disc type.
3. Shifter mechanism may be replaced or modified.
4. Motor and transmission mounts may be replaced.
5. Upgraded differential is permitted using a 3.46 gear ratio, factory housing, flanges, and mounting points. The internal parts of the differential are otherwise unrestricted, including the use of limited slip units.
6. Finned and/or larger capacity differential cover may be used.
7. Differential bushings may be replaced.

I already had a couple ZF320 5-speed boxes laying around, to include the one from the M Coupe that was removed during the upgrade to the 6-speed. Since it only had ~30k miles, I decided to donate it to the cause. Before installing it I decided to upgrade/replace the detents, which are known to begin sticking and causing shift issues like the 5th gear lean. The newer shift pin detent design has a coating to reduce friction and chances of binding. I won’t cover the how to, since I already have on on the site.

ZF 5 Speed Shift Pin Replacement Guide

I also replaced the weak plastic clutch pivot pin with a stainless steel one from Rogue Engineering.

Clutch options are pretty wide open, as long as it is a single disc design. Rather than guess at what would be the best option, I went with what the majority of SE46ers are using, the Tilton flywheel/clutch combo.

This package is super light at only 13.6 pounds, shaving 23 pounds over the stock dual mass unit. There’s not springs in the disc, so I would imagine this setup is best reserved for a true track car. The assembly has a very high quality feel to it, no stamped metal.

The differential rules are open, as long as it is a 3.46 ratio. I went with a Diffsonline custom ramp and lock up setup. Certainly not cheap, but a quality piece. I also welded on a 1/8th NPT aluminum bung to the rear cover to add a temp sensor for the AiM MXL. The other fittings in the photo are for a differential cooler, which I’ll cover in another post. The rear subframe OE rubber bushings were removed and solid aluminum ones from Bimmerworld were installed to eliminate any driveline flex and movement in the suspension mounting points. They were very tight going in, freezing the bushings and heating the subframe certainly helped.

While everything was pulled apart, I went ahead and also replaced the rear wheel bearings. Certainly not a fun job, though I found a generic FWD wheel bearing kit from Harbor Freight actually works quite well on E36/46 rear wheel bearings. The front bearings looked brand new, so I left them alone for the time being.

I also replaced the original driveshaft, which had a lot of bearing play at the u-joints. Rather than another OE junk yard shaft, I purchased a rebuildable unit from BimmerWorld. These driveshafts have snap rings retaining the u-joint caps rather than staked into place. It also comes with a new carrier bearing, which tend to wear out, especially on a 120k mile car.

As for engine and transmission mounts, I decided to go with Rogue Engineering transmission mounts and BimmerWorld N Group replica mounts. Many SE46 builders are going solid aluminum on both mounts, but I have a few reservations about using a solid mount. Sure they eliminate any slop or misalignment that can occur with shifting, but that’s a lot of stress being carried directly to chassis. I was concerned with accelerated fatigue and possible issues with things like knock sensors. I’ve found the mount combination (N Group and RE) to be plenty stiff while still allowing the harsh vibrations to not create third order effects down the line.

Giubo (aka Guibo, aka Flex Disc) Change

Posted on 2014/09/11 by Chad

During my M3 Sedan refresh I skipped one critical step: replacing the giubo (often misspelled as guibo.) For some reason I had in my mind that it had been recently been replaced by the previous owner. Here’s a tip: if you already have the exhaust and driveshaft out, go ahead and replace the giubo!

Fast forward to last week, where I’m giving the car a good inspection prior to a track weekend at Road Atlanta. I had the car up on jack-stands to check on several things. One known issue was that the transmission tunnel sound insulation material was sagging badly and rubbing on the giubo.

I had previously attempted to solve this issue by hot-gluing the mat to the sheet metal of the tunnel. This was after trying some HVAC aluminum tape, which simply didn’t stick to the fabric material of the insulation. One problem: I seriously underestimated the amount of heat in the area, resulting in the hot glue simply melting again and dripping off.

Unfortunately there is no way to easily replace this insulation without removing the transmission, as it goes forward up into the engine bay. I’ll save that work for when I eventually have to do a clutch replacement. For the time being I knew I had to do something to stop the interference, so I simply cut out the offending material.

While I was in the area removing this insulation, I took a good look at the giubo. It had been rubbing on the insulation for some time, wearing a hole in the material and polishing the edge of the rubber giubo. The giubo was still obviously in one piece but was looking a little worn. I went back to the detailed Excel spreadsheet maintenance record the previous owner had provided me, which covered all work back to its first oil change at the dealership. I couldn’t find anywhere that showed the giubo had ever been replaced…. hmmm. So I ordered up a new one, along with six new lock nuts.

Removing the giubo is pretty straight forward and there are plenty of DIY’s out there (as well as the Bentley manual) that cover all the steps. So I’ll just show you the results.

Yep, that’s no good. Now you can easily get away with some superficial cracks, but these were all the way through. When flexing the disc with both hands, I could really see how bad it was. Then I checked the molded in manufactured date and was amazed to find it was original, from 1997!

Now that’s pretty impressive to see a 17 year old rubber part last this long, especially given how prone these giubos are to giving up the ghost. I got lucky here, and good thing I replaced it before an upcoming track day. I certainly wouldn’t want to try to replace it in a hot and humid paddock.

Poor Man’s E36 Differential Fill Plug Tool

Posted on 2014/05/15 by Chad

The differential on the E36 chassis backs right up against the spare tire well, limiting access to the drain and fill plugs, particularly the latter. Both plugs require a 14mm Allen bit, which you can find for cheap at your local autoparts store. The problem is that these bits are most often a 1/2″ drive, and there simply isn’t enough room between the spare tire well’s sheet-metal and the diff cover to get a ratchet and bit in there.

Now there are some specialized tools available, but a cutoff wheel or hack saw can make one out of your cheap store-brand Allen bit. Then all you need is a 14mm ratcheting wrench to loosen and tighten the plug.

Note: Remember to just hand tighten (no gorilla strength) the plugs. Do not use the OEM torque specs, as those are dry thread torques. You will crack the relatively weak cast aluminum cover if you over-tighten, which is very easy to do when using a 1/2″ ratchet.

Post-Track Inspections and Repairs

Posted on 2014/04/28 by Chad

Following my first track day with the M3 Sedan, I placed it back on jack stands for my standard post-track inspection. If anything is going to loosen or break, your best chance of finding it is immediately after a flogging on the track.

I should note that during a few slow speed drives around the paddock at TWS, I kept hearing a squeaking sound. It was rev-matched to the rotation of the wheels, so it was either at the wheels/hubs or the rear axles. A quick visual didn’t reveal anything, and eventually the sound subsided. I should be thanking my lucky stars, because the sound was coming from the Torx bolts that fasten the inboard CVs to the differential stubs. Several of them had loosened and backed out enough to rub the CV rubber boot. My first clue was a bit of grease flung on the brand new blue anodized Turner lower control arms.

Obviously this could have been disastrous had the CV become unfastened completely from the differential, especially at the 130+ mph attained at TWS. I neglected to grab any photos of the issue, so you’ll have to imagine what I’m describing. To make sure they wouldn’t back off again, I used the impact wrench with a very long extension to tighten all the bolts accessed through the wheel well, with the wheel removed obviously.

While I was at the rear, I also noticed that the left lower shock mount bolt had loosened. I went to tighten it up with an 18mm ratcheting wrench, only to find it stripped. I had previously discovered some thread damage on the trailing arm, which I thought I had solved by running a tap into the threads. Unfortunately the threads were damaged beyond simple repair, with about 10mm of thread being completely wiped out.

A slightly longer bolt might have been the cheap and easy fix, but at the cost of reduced thread engagement. To properly repair this would require an insert or HeliCoil. I’ve had to make HeliCoil repairs on parts before, such as my Moroso oil pan and the pan mounting holes of my S50. The principle is simple: drill out the old damaged threads, re-tap the hole with an up-sized tap, then thread in the HeliCoil insert which reproduces the original size threads. The inserts are literally coils made of stainless steel. The kits can be found at most auto parts stores or Fastenal, except in the thread pitch which I needed. Fortunately they are available on Amazon or elsewhere online. The complete kit comes with the required tap, inserts, and a tool for threading in the insert. You must provide the appropriately sized drill bit and tap handle.

The photos below show the damaged threads and taping the new ones (after drilling out, not shown.) Make sure you cut in a few millimeters at a time, then backing out the tap and cleaning out the hole with some compressed air. Since this is a blind hole, all the metal shavings will just begin to pile up inside otherwise.

With the new threads cut, I could now insert the HeliCoil thread restorer. The insert is wound up on the inserting tool, then held against the surface of the hole. Then it is screwed into the hole using a tap handle. This part can be a bit tricky, as you try to engage the insert in the newly cut threads. Fortunately I got lucky and it went in the first time, unlike my multiple trials with the Moroso pan. There is a little tang at the end of the coil that the inserting tool grabs on to rotate it. This tang is notched at the point it bends off from the coils, so that it can be easily snapped off once the coil is fully inserted. I used a simple flat punch and hammer to knock it loose, then some compressed air to blow it out of the hole.

The photos below show the HeliCoil inserted with the tang still in place and with the tang punched out and in my hand. And finally some photos of the completed work. The results are restored threads that are just as, if not stronger than the original.

Eat, Sleep, Tinker.

No, it's not done yet…

Category Archives: Drivetrain