Window Motor Conversion - Part 1

Converting front E9 window 3 wire motors to later model E28 2 wire type

Overview

This procedure describes the conversion of the left front E-9 electic window motor from a 3 wire 2 piece motor to a later model 1 piece 2 wire motor from a BMW 5 series sedan. The is based on a 72 3.0cs with electric windows. It should work for any E-9 coupe however it is possible there will be slight variations particularly 74 on when electric window motors changed styles.  I've been told that the regulator in a 73 coupe is a slightly different design and doesn't require it to be cut to make the new motor fit.  Let me know if you can confirm this

Tools Required

• • 10 & 13 MM sockets and ratchets 

  • Electric Drill 

  • Drill Bits: 23/64" & 15/64" 

  • Dremel or similar grinding / cutoff tool 

Parts Required 

• • BMW e28 rear window motor 

  • 4 nylon spacers 

  • Electrical wire to ground switch 

  • Wire nut to cap existing motor ground 

  • 2 bullet end crimp electrical connectors 

  • Electrical wire 

  • 3 Female insulated connectors 

  • Spade splitter or wire splice equivalent 

Sourcing the E28 Window Motor

This conversion uses the rear window motor from a E28 5 series (84-88 533i, 528e, 535i, 535is).  These can usually be sourced at a pick and pull salvage yard. 

These used to be be readily available however the E-28 pickings have become slim in the pick & pull yards

For the drivers door use the left rear e28 motor and for the passenger side the right use the right rear E-28 motor

I recommend getting both even if you are only doing one window

This is the left rear e28m motor and it's wiring connection with bullet connectors added to the end. 

Removing the e28 New Motor 

If you get your motor from a pick and pull you'll need to remove the old motor otherwise skip to the next step. 

Removing the rear window motor in the e28 is pretty straight forward.  (Sorry no photos)

It is much simpler for the E9 as it doesn't have the helper / tension spring.  Here is a quick summary with a few hints

• • The rear door handle pull only has one screw attaching it at the rear. Once you remove the screw from rear turn the door pull 90 degrees and locking peg should come free in the front. You many need to turn it back and forth a bit but it will come off

  • Remove the door panel 

  • Disconnect the electrical connector (Black quick connect in above image) 

  • Unbolt the hex bolts holding in the regulator (Should be 10mm) 

  • Slide the regulator arm so that it aligns with the hole in the track and remove it from the door 

  • Remove the motor from the regulator, Some models have a large phillips head screw instead of of a hex nut so bring a large phillps screwdriver and perhaps a hammer to free it. 

Cut off the other half of the wire connector as far back as you can

Below is a comparison of the new style motor on the left and old motor and gearbox on the right 

Closeup of the new an old gearbox. Notice the difference in the mounting bolt holes on the left side.

Removing Existing Motor

Once you have the new motor the next step is to remove the current motor and regulator from the door. 

It's a pretty straighforward process however if you are unfamiliar with this follow these steps:

• • Removing Door panel and regulator

  • Disassemble window regulator

Before you can install the new motor you will need to make some modifications the regulator

Start by manually compressing the regulator arm and lock it into position using a large screwdriver as shown below.

Installing the E-28 Motor

The reminder of the instructions will refer to the mounting holes as numbered in the image above . 

Note that the #3 hole will not be used. When installing the new gearbox you will use the bolts and screws that came with the new motor. 

Mouting #1 is a recessed phillips head screw which goes through the access hole and screws into the upper portion of the gear box.

The old and new motors mounting posts have different centering ridges which requires one of the mounting hole be drilled out and a new one (the 4th) to be added. 

The centering post on hole #2 is show below.

The old recess phillips is too small for the new motor you will need to use the screw that came with the new motor. 

The problem is the head of the new screw is too large to fit through access hole for #1 and the threads are tool large to pass through the existing hole in the regulator base (not the rotating gear)

You can either:

• • Drill out the access hole in the gear

  • Use a grinder / dremel to remove the outer portion of the screw head. 

I choose the latter, the modification to the screw is visible in the above photo

In addition access hole #1 will need to be drilled out in the regulator base using a 15/64" drill bit in order for the screw threads to pass through

The next step it to test fit the gear box and to mark the position of the new mounting hole. 

Note the above picture already has hole #4 already drilled, yours won't have this at this point.

The mounting points #1 and #2 will line up directly from the new motor. 

You may need to adjust the screwdriver slightly to make sure the phillips head screw for #1 will pass through without binding.

You may encounter some misalignment between the rotating regulator gear (the large one) and the smaller gear on the new motor. 

A 9V battery can be used to turn the window motor back and forth by reversing the polarity to get the correct alignment.

Insert and tighten #1 and #2 screw and bolt

While the motor is mounted outline the portion which motor that interferes with the regulator frame. 

It will look something like the shape below. You will cut this out after removing the motor

Unbolt the motor

The next step is to cutout the portion of the regulator that you marked above and mark the new 3rd mounting point (hole #4)

I used a small Dremel cutoff wheel to remove as little as possible. Once this portion of the regulator is removed reattached the motor at points #1 and #2

From the back side of the regulator mark the position of the new hole that will be the new 3rd mounting point, hole #4, for the new motor.

Unbolt the motor

The next step is the most difficult part to get correct. I started by drilling using a small drill bit a new mouting hole #4 working my way up to larger and larger holes using a Dremel to correctly center the mounting hole. I test fit the motor several time correcting my grinding and drilling as I went. If you have a drill press this might be easier to center the hole correctly. The final hole size is 23/64"

The image below shows the final mounting position with all 3 bolts in place. Note the old #3 hole is unused. 

Next, Wiring and installation