Technical Tips

Upgrading Alternators

Even when new the alternators on 70s vintage cars seemed unable to run headlights, wipers, defroster and radio, all of which (excpet the radio) are required to drive the car in a rainy night.

First, the Vintage Triumph Register has a nice set of articles on this subject. See

Converting a Vixen S3 to Lucas 23 ACR

I replaced the Lucas Dynamo on my Vixen S3 with a Lucas 23 or 25 ACR unit which has worked fine to operate 400W of lighting when I was road rallying the car. What made my conversion more tricky was to convert to a Poly-Vee belt for both the alternator and water pump.
I made a alternator bracket out of solid billet and have a one piece rod acting as the pivot with an R pin locking the nuts on. I also change to a Cosworth nylon tensioning bracket. The wiring is the easy bit. The Poly-Vee conversion was because the ordinary belt gets burnt out driving a 23 or 25 ACR unit.

John E. Uphan

2500M to 105 Ampere GM Unit

I'm in the process of upgrading the alternator in my '74 2500M. Here's what I'm using:
- Powermasters #278611 105-Amp alternator. This is a GM-style, one-wire alternator with built-in regulator, available chrome or polished, with a few different mounting ear positions available. They also offer it with a three-wire configuration.

- March Performance RA-2.500 tensioner assembly - a really nice turnbuckle-style stainless tensioner.

The alternator has a 10mm mounting hole, but the TR-6 has a 3/8" hole. Powermasters offers a sleeve to compensate, I had a SS bolt machined with the step.

I like the alternator positioned a little farther from the engine than the Lucas was, I think it looks better and clears the coolant tank hose better. The tensioner I'm using has enough adjustment range to get it out there, but I had to replace the belt with a longer one. A Dayco #17460 is the right size.

For the belt to line up correctly with the pulleys either the mounting block on the alternator or the mounting block on the engine need to be milled down about 1/4". I haven't done this and may try running it with the belt out of alignment and see what happens (fingers crossed).

You can see a photo at

Joe Truchsess

3000M to Bosch Alternator

For a 3000M series car at least it is possible to use standard Bosch alternators used in many European cars without any modifications, they even have the same harness connectors as the Lucas ones.

I changed from an original Lucas to a Bosch in my car when the Lucas broke down, (one bearing sheared, not any electric fault), I used a secondhand Bosch alternator from an European Ford car but most Bosch alternators have the same mounting holes and same connectors, the one I used give 55A, no modification at all was necessary. The Bosch generators come in many different Ampere ratings from 35A and up, I think some of the latest ones give more than 100A. I payed 150 SEK, (about 10GBP) for a secondhand tested one from a car scrap yard, it works perfectly.

The intention was to use the Bosch alternator as a temporary replacement while I was repairing the Lucas alternator but as with many of these things I never seem to find the time.


BR Hans


Last updated on 11 November 2002.