Looks like I will be swapping out the alternator on my 1974 40 series. Engine shuts off when jumper cables are removed. Would appreciate any tips/suggestions as I am still learning the ropes on this machine. Searched the forums but could not find threads for an older fj on the subject. Thanks in advance.
'74 FJ 40 Alternator Replacement (1 Viewer)
- Thread starter JDragon
- Start date
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Alternator for '58 to '74 US Spec Land Cruiser FJ40 FJ55
Aftermarket remanufactured alternator for '58 to '74 US Spec Toyota Land Cruiser FJ40, FJ55 equipped with external voltage regulator. Upgraded to 50 amp. Note: Your existing alternator must have the same type of plug on the back as shown. You must either reuse your existing pulley or purchase...
www.cityracerllc.com
cstav86
SILVER Star
City racer is great, and the upgraded 50 amp is helpful if you have any modern electronics. Fuel injection, lights, compressor, stereo, that kinda thing.
Pretty simple deal to replace. Unplug the electrical connection. Loosen the tensioner bracket that comes off the water pump and loosen long bolt that holds it to the bottom of the block. May be smart to replace the belt now too. Will have to fish that around the fan blade if I recall correctly. Remove the old and reverse the sequence to install the new one. May want to replace the voltage regulator too. An inexpensive part and now you have a completely fresh power feed.
Pretty simple deal to replace. Unplug the electrical connection. Loosen the tensioner bracket that comes off the water pump and loosen long bolt that holds it to the bottom of the block. May be smart to replace the belt now too. Will have to fish that around the fan blade if I recall correctly. Remove the old and reverse the sequence to install the new one. May want to replace the voltage regulator too. An inexpensive part and now you have a completely fresh power feed.
I second that - Cityracer has been excellent. I have a question about the 50 amp upgrade. Will the 30 amp gauge on the cluster still operate properly without mods? Does this require a new 50 amp voltage regulator?
That is a good question. I think if you want the meter to read correctly you will need to change the shunt. I suspect the meter would just read pegged at anything above 30 A.
POTATO LAUNCHER
TLCA #6928
I've never noticed the amp gauge pegged running a 90 amp GM alternator for years.
cstav86
SILVER Star
Same. I run a 55 amp and the needle is toward the + side but not pegged out.
Coolerman
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The 1974 FJ40 Amp Meter shunt would be dificult to replace as it's part of the meter itself, not external like the 1979 and up amp meters.
Great read: all things gauges
Here is why you can run a high amp replacement alternator and not burn up the 30 A amp meter: with a couple of cautions... and a quick beginners lesson on Amp Meters
What the Amp Meter is measuring: The Amp Meter measures the CURRENT or amperage being pulled FROM, or sent TO, the BATTERY. The Amp Meter has two wires: The White+ wire connects straight to the battery usually though a fusible link. The White/Blue - wire has splices in it that connects to the key switch, fuse box always on circuits, the separate hazard switch fuse, and finally to the B+ terminal of the alternator. So the amp meter measures current from the alternator into the battery as + on the meter and current from all the loads connected to the fuse block as - on the meter. Note: Any loads connected straight to the battery will not register on the amp meter.
For the following, assume the alternator is running at the rpm needed to output the current required.
Quick statement about alternators in general. Contrary to what seems logical, alternators are not meant to charge dead batteries. They are designed to keep a battery topped off. Their FULL time job is to supply eletrical power to the vehicles loads. Keeping the battery charged is secondary.
Using a stock 1974 FJ40 as the example, lets turn on everything in the truck that is electrical including the ignition. This will pull about 35-40 amps from the battery. The Amp Meter will be pegged full negative. Start the truck. The OEM alternator, which is conservatively rated at 35 Amps, would provide 35 amps to the loads connected to the fuse panel, and the battery would provde the other 5 amps.
So what is the Amp Meter doing in these two cases? When the truck is not running the Amp Meter will be pegged full negative since all the current is being pulled from the battery, and flows through the amp meter towards the loads . Here is where it gets interesting and confusing. When the truck is running, the Amp Meter will only read 5 amps negative! The needle just barely moves off center. Why is it not reading the full 40 amps? Because the alternator is providing a lower resistance path to ground than the internal resistance of the battery, most of the current flows through the alternator down through the fuse panel, through the loads to ground and therfore cannot be measured by the Amp Meter.
So now you install a 90 amp alternator, again turn on everything in the truck, truck not running. How many amps will it pull? 40 amps from the battery. The Amp Meter will be pegged full negative. Now start the truck. With the truck running, the 90 amp alternator will easily supply the full 40 amps to the loads, drawing nothing from the battery. The Amp Meter will be reading close to 0 amps.
The Cautions
Now all the above was assuming a fully charged battery and little time was spent with everything on draining it. In the real world just starting the truck will draw 100-200 amps for a couple of seconds requiring it to be topped off. The top off currents are low like 4-10 amps for a few minutes.
Now think about this case. You leave the radio on draining the batttery down to say 8 volts, the temps fall into the thirties and you come out the next morning and of course the truck is dead. What do you do? Same as always. You grab the jumper cables, pull your wifes car in front, connect the jumper cables and hit the truck key. What do you think is about to happen? Let me explain...
Lets say you have a starting battery with a rating of 100 amp hours storage capacity. The ideal charge rate for that battery is no more than 10-20 amps. Any more than that and the battery will be damaged. The problem you are now facing is this: This discharged battery is cabable of drawing way more than the ideal charge rate if it is connected to a high output alternator. The alternator is stupid, all it sees is the low internal resiatance of the discharged battery and it dumps as much current into the battery as the battery will take. This could be 50 or 60 amps for a standard lead acid battery. If your battery is an AGM or some other newer chemistry, some of those can accept charges rates as high as the FULL AMP HOUR RATING of 100 amps for a 100 amp hour battery!
So you hit the key, the trucks cranks for a few seconds and roars to life just about the same time as a small puff of smoke comes out of the dash. Depending on the alternator, the truck may or may not die instantly. If it doesn't die it won't be charging the battery any longer and if you shut the truck off nothing will be working electrically as the battery is now effectly disconnected. So what happened? When the truck started the alternator saw the low resistnace of the discharged battery, and dumped as much current as the battery could take... through the 30 amp rated amp meter. Now the amp meter can take possibly up to 40 amps for a very short time but the wires inside it can only take so much and go up in smoke when their current rating is exceeded. If you are wondering why the fusible link didn't blow? It's a slow blow device allowing for large amounts of overcurrent over long periods of time. The amp meter was the weak link and it blew.
So to sum this way overly long post up. Yes you can run a higher amp alternator with your 30 A amp meter. Just don't let your battery get low and if it does charge it with a charger before driving it. If you get caught out and the only solution is to jump it. Disconnect the battery and remove the gauge cluster. Take the white wire off the Amp Meter+ terminal. Remove the nut from the Amp Meter - terminal. Place the White wire on top of the White/Blue wire and put the nut back on and firmly tighen it. This bypasses the Amp Meter and allows you to jump the truck safely without frying the amp meter.
So whats the point of the higher amp alternator? To provide added current for any added loads like off road lights, heated seats, sniper fuel injection, high power audio and such. However you should install an aux fuse panel connected to a fused lead straight to the battery to power them. This will keep those added loads out of the 30A amp meter and the undersized wiring in the main harness. Sorry but the added loads will not show up as current draw on the amp meter.
Great read: all things gauges
Here is why you can run a high amp replacement alternator and not burn up the 30 A amp meter: with a couple of cautions... and a quick beginners lesson on Amp Meters
What the Amp Meter is measuring: The Amp Meter measures the CURRENT or amperage being pulled FROM, or sent TO, the BATTERY. The Amp Meter has two wires: The White+ wire connects straight to the battery usually though a fusible link. The White/Blue - wire has splices in it that connects to the key switch, fuse box always on circuits, the separate hazard switch fuse, and finally to the B+ terminal of the alternator. So the amp meter measures current from the alternator into the battery as + on the meter and current from all the loads connected to the fuse block as - on the meter. Note: Any loads connected straight to the battery will not register on the amp meter.
For the following, assume the alternator is running at the rpm needed to output the current required.
Quick statement about alternators in general. Contrary to what seems logical, alternators are not meant to charge dead batteries. They are designed to keep a battery topped off. Their FULL time job is to supply eletrical power to the vehicles loads. Keeping the battery charged is secondary.
Using a stock 1974 FJ40 as the example, lets turn on everything in the truck that is electrical including the ignition. This will pull about 35-40 amps from the battery. The Amp Meter will be pegged full negative. Start the truck. The OEM alternator, which is conservatively rated at 35 Amps, would provide 35 amps to the loads connected to the fuse panel, and the battery would provde the other 5 amps.
So what is the Amp Meter doing in these two cases? When the truck is not running the Amp Meter will be pegged full negative since all the current is being pulled from the battery, and flows through the amp meter towards the loads . Here is where it gets interesting and confusing. When the truck is running, the Amp Meter will only read 5 amps negative! The needle just barely moves off center. Why is it not reading the full 40 amps? Because the alternator is providing a lower resistance path to ground than the internal resistance of the battery, most of the current flows through the alternator down through the fuse panel, through the loads to ground and therfore cannot be measured by the Amp Meter.
So now you install a 90 amp alternator, again turn on everything in the truck, truck not running. How many amps will it pull? 40 amps from the battery. The Amp Meter will be pegged full negative. Now start the truck. With the truck running, the 90 amp alternator will easily supply the full 40 amps to the loads, drawing nothing from the battery. The Amp Meter will be reading close to 0 amps.
The Cautions
Now all the above was assuming a fully charged battery and little time was spent with everything on draining it. In the real world just starting the truck will draw 100-200 amps for a couple of seconds requiring it to be topped off. The top off currents are low like 4-10 amps for a few minutes.
Now think about this case. You leave the radio on draining the batttery down to say 8 volts, the temps fall into the thirties and you come out the next morning and of course the truck is dead. What do you do? Same as always. You grab the jumper cables, pull your wifes car in front, connect the jumper cables and hit the truck key. What do you think is about to happen? Let me explain...
Lets say you have a starting battery with a rating of 100 amp hours storage capacity. The ideal charge rate for that battery is no more than 10-20 amps. Any more than that and the battery will be damaged. The problem you are now facing is this: This discharged battery is cabable of drawing way more than the ideal charge rate if it is connected to a high output alternator. The alternator is stupid, all it sees is the low internal resiatance of the discharged battery and it dumps as much current into the battery as the battery will take. This could be 50 or 60 amps for a standard lead acid battery. If your battery is an AGM or some other newer chemistry, some of those can accept charges rates as high as the FULL AMP HOUR RATING of 100 amps for a 100 amp hour battery!
So you hit the key, the trucks cranks for a few seconds and roars to life just about the same time as a small puff of smoke comes out of the dash. Depending on the alternator, the truck may or may not die instantly. If it doesn't die it won't be charging the battery any longer and if you shut the truck off nothing will be working electrically as the battery is now effectly disconnected. So what happened? When the truck started the alternator saw the low resistnace of the discharged battery, and dumped as much current as the battery could take... through the 30 amp rated amp meter. Now the amp meter can take possibly up to 40 amps for a very short time but the wires inside it can only take so much and go up in smoke when their current rating is exceeded. If you are wondering why the fusible link didn't blow? It's a slow blow device allowing for large amounts of overcurrent over long periods of time. The amp meter was the weak link and it blew.
So to sum this way overly long post up. Yes you can run a higher amp alternator with your 30 A amp meter. Just don't let your battery get low and if it does charge it with a charger before driving it. If you get caught out and the only solution is to jump it. Disconnect the battery and remove the gauge cluster. Take the white wire off the Amp Meter+ terminal. Remove the nut from the Amp Meter - terminal. Place the White wire on top of the White/Blue wire and put the nut back on and firmly tighen it. This bypasses the Amp Meter and allows you to jump the truck safely without frying the amp meter.
So whats the point of the higher amp alternator? To provide added current for any added loads like off road lights, heated seats, sniper fuel injection, high power audio and such. However you should install an aux fuse panel connected to a fused lead straight to the battery to power them. This will keep those added loads out of the 30A amp meter and the undersized wiring in the main harness. Sorry but the added loads will not show up as current draw on the amp meter.
Last edited:
rkymtnflyfisher
Trout Bum
Excellent explanation, solid tech.
The most important thing is to not over tension the belt. If you make it too tight it will ruin the bearing
A bit more work, but faced with a similar question, I went with path of the GM alternator run directly to battery (to bypass amp gauge). I use a voltmeter to monitor the battery state of charge and alternator state of health. This does require a small amount of fabrication for a new bracket, a wider pulley, and a new set of wires going to the alternator.
DeskJock
SILVER Star
I think it boils down to what you pull thru the amp meter. I know that on my rig, fuel injection and electric pump are outside the wiring that passes thru into the fuse box / amp meter.
DeskJock
SILVER Star
Fantastic reply and great information! Thank you!
