Friday, September 11, 2009

Transmission replacement: a plan of attack

I bought a lovely 1973 BMW Bavaria from the pick-n-pull junkyard a few months back.  The car unfortunately had a barely-working Borg Warner automatic transmission but otherwise is in great shape and I love the color.  I bought the Bavaria with the intention of replacing the automatic with a manual gearbox as soon as possible and my friend Jason in WA state happened to have a spare.  He also happened to be hosting a BMW Bavaria meet-up, WestFest 2009 at his house, so it made sense to pack some bags and head up there on a little road trip.

As bad as the transmission was, I thought I'd make it, especially after giving it a quick servicing and fluid change.  The oil pan was filled with metal shavings and the filter looked disgusting.  The oil that drained out didn't look like ATF.  Still, I changed the parts out, cleaned it up, and put it back together with new ATF.  It worked pretty well for a while, though reverse was a bit spotty up slight hills.  We made it to Jason's just fine and even took it on a group drive up the back of Mt. St. Helen.  Finally, on the way back to Jason's, we headed up a very steep hill and, half a mile from his house, the transmission stopped putting power to the driveshaft.  Oops.

On a positive note, the car is now at Jason's house and we have that spare Getrag 5-speed manual transmission, a lift, and lots of tools and fluids ready to go.  I'm headed up there in a week to swap in the manual gearbox and then drive the car home to San Francisco.  Here's an approximate check list of what's needed to convert an automatic Bavaria to a 5-speed:

  • Getrag 265 5-speed manual gearbox and bel housing.  This typically comes out of a 1980 or 1981 528i but there are other options.  However most of the associated parts (shifter, crossmember, etc) will need to be from an E12 528i, even if your transmission is from another model.
  • The transmission crossmember and mount.  This is used to hold the transmission in the car and it has to be out of a 1981 528i 5-speed.  It's not an expensive part new, so if you can't find a used one, order a new one along with a new mount.
  • The shifter.  Namely you need the shift tower (the big black metal piece), two new shift tower bushings (they're little blocks that hold the tower to the gearbox), the shifter, and the shifter linkage rod and associated clips and bushings, and an insulation pad.  You also need the shit tower rear mount, which is called a "Christmas tree" due to its shape.  It needs two metal brackets and you'll drill a hole in the tunnel for one of them to mount.  These diagrams make it clear.  Make sure you really have all this stuff, the shifter doesn't really work without it.
  • A clutch kit (or the entire set of clutch parts from the donor car).  This is typically the clutch disc, pressure plate, throw-out (release) bearing, and a pilot bearing.  Buy the new-style one-piece (sealed) bearing.  You also need the clutch fork and pivot piece.
  • A clutch slave cylinder: the 1981 528i one will work fine.
  • A clutch master cylinder: the 1981 528i one will work fine.  The mounting point for it already exists, it's where the automatic harness runs through the firewall.
  • A manual transmission car's brake fluid reservoir (it's the same as the automatic one except that there's a third line for the clutch, they're available brand new for about $20) along with some hydraulic lines.  I recommend calling Jim or Spence at Mesa Performance for the lines as they can send you the correct length of hard and flexible line to use.
  • A flywheel from a manual-transmission M30 engine.  You want the earlier (pre-E34 5-series) single-mass type.
  • A set of bel housing bolts for the 5-speed as described in the parts book.  The automatic bel housing has different bolts so you need to buy the right ones unless you have the ones from your donor car.
  • A set of pedals from a manual-transmission Bavaria: the brake pedal, clutch pedal, and the bushings and springs inside them.  These may be hard to find!  You also want the "fit bolt" and bushings shown here, they're used to connect the clutch master cylinder to the clutch pedal.  In addition, get the clutch pedal return spring if you can.
  • A flex disc (or 'guibo') of the automatic style rather than the kind found on the manual cars.  You'll then be able to reuse the driveshaft bolts from your car, and this kind of link is more durable.  The part number is 26 11 1 209 168 or 26 11 7 511 454. 
  • You should also buy a rear main seal and change that out while you're in there, unless you're sure yours is fine.
  • I recommend buying a new reverse light switch for the transmission just in case the one already in it is bad, it's a very inexpensive part.  You'll need the reverse light switch harness from a manual car, or you can make your own.
  • The manual transmission style center console shifter part for the Bavaria.
  • A manual transmission Bavaria or E12 (530i or 528i) radiator would be nice, but not required.
That should about cover it, I hope.  I sort of cheated because my friend Crow and I recently did the same conversion on his 1973 Bavaria so I got to experience it first-hand and refresh my memory on some details.  Craig Dinger has a very good auto-to-manual writeup with pictures and notes about the wiring changes required for 1974 and later cars.  I recommend having that handy.  The SSR site also has step-by-step instructions for the conversion to a 4-speed along with wiring instructions for 1973 and earlier cars.

On a side note: the automatic transmission is a bit longer than the Getrag 4-speed that should have come with the car.  The Getrag 5-speed, however, is about the same length as the automatic.  This means that the automatic car's drive shaft and speedometer cable line up with the 5-speed but not the 4-speed (the speedometer cable is too long and the drive shaft is too short).   I recommend replacing your automatic with the 5-speed unless you've found a 4-speed E3 parts car with everything you need.
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