Purchase and Preparation

• Mahle-Letrika part number 11203205, 100 amp alternator replaces Land Rover AMR5425. This part number corresponds to the Discovery 300 tdi alternator commonly used to upgrade Defenders to 100 amp output.
• The pulley supplied with the Mahle-Letrika unit is the 61 mm size normally found on the early 300tdi engines. Later engines were supplied with a 49 mm pulley to spin the alternator faster and produce more output at idle. You can swap the pulleys, or install as suppied. Be advised that there are two belt lengths for the different pulley diameters - ERR3287 is 1595 mm in length and suits the 61 mm pulley and ERR5911 is 1575 mm in length and suits the smaller 49 mm pulley. The belt tensioner is the same part for both belt lengths.
• Your failed alternator may have an external cooling fan mounted on the output shaft; it will not fit the Mahle-Letrika part. The units cooling fan is mounted internally. Affix the pulley without it - it is not required for proper serpentine belt alignment.
• Mahle-Letrika part number 11203205 includes a plastic heat shield. Prior to install, remove it, locate your D and B posts and remove the fasteners. This will ease identifying the required posts with the alternator in situ.
• For ease of future removal, use anti-seize paste on the full length of the M8 x 125 mm top mounting bolt.
• For ease of future removal, use loctite thread locker blue on the bottom M8 x 30mm mounting bolt to both secure the fastener and prevent it from seizing in the housing.

Installation

• Threading the bottom bracket bolt is difficult with the radiator/intercooler in situ; there will be no visibility to ensure the holes align. In my experience, they won’t with the top bolt in place. Hang the alternator by a thin diameter screwdriver through the bulkhead side of the top mounting bracket. By thus supporting the alternator’s weight, the front of the unit will move freely in any direction using one hand. Thread the bottom bolt in a few finger turns. Next, manipulate the alternator to line-up the top mounting holes - my top bolt required a few tippy-taps with a hammer.
• The alternator cables are too short to reach the provided notch in the heat shield - it is at the 6 o’clock position. Using a hacksaw, I cut a new notch for the cables in the 2 o’clock position, and a 1 inch gash in my index finger. It was after midnight with a looming two hour drive to my daughter’s camp the next morning. I used my hand rather than the vice a few steps away. Sorry Michelle - I am normally very safe.
• There is some debate as to whether the brown factory cable from the alternator to the starter is of sufficient gauge to handle the increased alternator output. I drove over 200 km’s at highway speed, and I did not find excessive cable temperatures. I admit this test is not scientific. In the future, I plan to add an additional cable from the alternator to the starter post to assist with the increased amp load.

Update - February 2021

Approaching 4 years since the July 20th, 2017 install date. This alternator has been reliable through cold Canadian winters and climbing long grades in high temperature, high humidity Guatemala.