View Full Version : Wedge GM alternator for TR7

08-21-2004, 11:04 AM
Would you believe I actually thought I had repaired my Lucas alternator myself? Wretched man that I am, I am now ready to replace the alternator. I have seen a freinds TR6 that was running a GM alternator and he laughed aloud when I told him of my attempts to salvage the Lucas unit. So, does anyone have experience with installing a GM unit on a TR7? I am open to anything and prepared for any derision that might be directed my way. The stinker is that my Lucas alternator appears to be working, but the light on the dash is doing that "flashy thing" and has been off and on for a couple months.

08-21-2004, 06:21 PM
Hi Dale,
Describe that "flashy thing". When does the light flash? Low RPM at idle, constant engine RPM above 2500, or all the time? Do you have a radio in your TR7? If so, put it on AM, select a frequency location that has no station playing and listen for a high pitched whine when you change engine speed. Got Whine then you have Bad diodes and are not developing a full charge causing teh ignition light to com on or flash.
If you want to change to a AC/Delco alternator, you need of course the proper mounting and brackets for positioning of the pulley, then modify the old connector that plugged into the back of the Lucas unit to go onto the threaded stud, and a connection to the ignition light and ampmeter. Take a close look at your friends TR6, the wiring should be similar at the alternator.

08-21-2004, 06:24 PM
Wiring should be easy, but when it comes to mounting one, you are SOL here. I'm going to assume(man that word has gotton me in a lot of trouble) that you are going with the less expensive earlier style alternator with the internal regulator. You have 3 wires going to the alternator. The 1st one runs from the back of the alternator to the battery. There are 2 more on the side. Looking at it from the pully back, the left side plug can run to the back of the alternator(or to the battery) and the 2nd one goes to the dash light. I'm not very good at explaining this so let me know if this just confused you even more. I would think(that phrase is just as bad) that mounting one wouldn't be too hard.

Mark Beiser
08-21-2004, 08:39 PM
I have seen several sites on the net that have instructions for doing it, but the mounting is a pain.

Question though, have you had the alternator checked? The Auto Zone near me actually had the correct adaptor for thier machine to test mine. The guy had to dig for it a little though, mine was the first time they used it.

08-22-2004, 12:46 AM
Gosh, it's great to be regarded as if I knew what I was talking about,but scary when I have to come up with something concrete.
Here goes. Sometimes the light seems to work correctly and go completly out, in daylight at least. Other times it will glow brightly 'til the RPM is up around 4 grand then it will fade back. Turning on the lights will cause it to glow brighter as will the heater motor. Still, even with the lights on it will sometimes go nearly out. The battery stays up nicely and the voltmeter usually stays to the right of center, but sometimes with lights and stuff on will drop to the left for a time then come back up. Haven't been able to establish a correlation between the meter and the light. There are indications that there may be a relationship between the alternator light and the cycle of the moon, but have not been able to confirm that. I have no radio installed in the car. If I were to take my radio on an extension cord to the car would the "whine test" still be diagnostic? Thanks a bunch for the encouragement. I will stay in touch.

08-22-2004, 01:05 AM
Tupelo, MS neat! The name rolls off the tongue such that one wants to say it over and over again. What does Tupelo mean and what is it's derivation. I'm not writing a book or anything, just curious.
You're right that the wiring should be pretty straight forward and my friend with the 6 confirms it. Maybe even easier on my 7 as the later 25 amp alternator has eye connectors for two of the three wires already. My friend said that mounting was the bugaboo, but it appears on the 7 at least to be deceptively easy. The GM alternator looks to be a little smaller than the Lucas which should help matters. The flowmeter and aircleaner cramp the alternator some but only in getting it in and out of position. The Lucas unit has two brown wires, one large from the battery and one small also from the battery. I'm not sure of the function of the smaller one. The third wire is n/y or brown with a yellow tracer. This one goes to the "flashy thing" on the dash. Thanks for your kind response and I will let you know what developes.

08-22-2004, 01:18 AM
I did have the alternator checked on the car at Checker. And they said it was putting out over 13 volts. No idea about amperage. This might explain why the battery seems to be maintaining a charge, but variations in load cause the "flashy thing" symptoms. I suppose having the Lucas unit repared would be OK, but I sure don't want to spend $180.00 on a rebuilt one with the reputation that rebuilds have. I would expect to pay less than $100.00 for a new GM unit. Would having the unit tested on the bench be more illuminating? (sorry about the poor choice of words, we are talking about Lucas here /ubbthreads/images/graemlins/blush.gif)Thank You for your post. I will keep you enlightened. (oops)

08-22-2004, 09:52 AM
but I sure don't want to spend $180.00 on a rebuilt one with the reputation that rebuilds have.

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When I bought my car last year, that was the first repair that I had to do...the alternator was shot. It cost me about $120 at a local armature shop to get it done, and they had it done in a day (couldn't believe they had parts onhand for a Lucas ACR25). One other idea...have you checked/changed the drive belt, since the alternator is Ok according to the tests? Symptoms like these could be caused by a badly slipping belt.

08-22-2004, 10:41 AM
Tupelo, MS was named after the stand of Tupelo gum trees that grew here when the railroad came thru . It is also the name given to the region by the Chickasaw indians. Our claim to fame is Tupelo is the birthplace of Elvis. We also have one of the largest car museums in the southeast. If your ever in the area, stop on by, set a spell, take your shoes off. /ubbthreads/images/graemlins/grin.gif

08-22-2004, 11:49 AM
Dale, you should not be afraid of this swap at all, since the delco nearly bolts onto the tr3/4 with only minor mods it should be the slice of cake you need.It comes in many amp ratings so you can get a real horse if you want. I would think that you might want to take the old unit to a salvage yard and compare it to some of the toyota/honda units, they are more compact and very reliable.
MD(mad dog)

08-22-2004, 09:25 PM
One other idea...have you checked/changed the drive belt, since the alternator is Ok according to the tests? Symptoms like these could be caused by a badly slipping belt.

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You sure could be on to something Obi. I had not considered it, as the last time the belt needed adjustment it squealed to let me know. Have not gotten a squeal this time.

09-05-2004, 06:17 PM
Just had to replace the alternator on my '80 TR-7 Spider and found that the latest rebuild from Victoria British came incorrectly remanufactured on two units. After the second replacement and the second day of a rental car because of the goof, the mechanic took it to a starter rebuild shop in Maine. They checked their reference books and found the mistake, fixed one, and it's run fine since then.

I'd avoid the GM switch. If we all stop buying the rebuilds, no one will rebuild them for us. Moss doesn't even list an AC-installed alternator in their latest catalogue.

Best wishes,