M1152 Low Top Speed

[blutow]

OK what if he does not have a Tech II to read it with? BTW that is an inductive pickup and it runs 4X crankshaft speed.
All he needs is a pulley to fix his tach issue easy pleasy fix, RWH has pointed that out,, then he can tell if the trans is acting correctly or not.

Is there any way to get an accurate rpm using the existing sensor (or any other approach) if I don’t have a tach? I see the $25 tool and might go that route, but wondering if there is a free approach using a multimeter or something. I feel like my truck may be idling a bit high, but I don’t know how to measure it.

 

[Mogman]

Is there any way to get an accurate rpm using the existing sensor (or any other approach) if I don’t have a tach? I see the $25 tool and might go that route, but wondering if there is a free approach using a multimeter or something. I feel like my truck may be idling a bit high, but I don’t know how to measure it.

Yes just get a "photo tachometer" over 1000 on fleabay alone, you stick a piece of reflective tape on the crank pulley and presto it gives you the RPM.
I should not have to say this, nothing to do with you but this is America so BE CAREFUL do NOT do anything STUPID, do not put the tach in your mouth or try to swallow the reflective tape............

 

[Mogman]

If you do have the crank sensor, and wanted something permanent you could look for a programmable tach, one that would work with an inductive pickup and can be programmed for 4 pulses per crankshaft revolution.

 

[TOBASH]

Just borrow a Diesel tach and measure true ROM at idle. Then again at 2000 ROM. Then again at 3000 RPM. Compare to RPM on the alternator driven unit. Then divide the alternator driven ROM result by the appropriate number to get the true RPM.

 

[Mogman]

There is no reason not to get the larger pulley, no need to have to calculate in your head while driving.
There is no need to have that much current at idle and driving the alternator at it's "correct" speed will save wear on the belt, the alternator AND consume less power,,, WIN, WIN, WIN!!!

 

[01GRANDER]

There is no reason not to get the larger pulley, no need to have to calculate in your head while driving.
There is no need to have that much current at idle and driving the alternator at it's "correct" speed will save wear on the belt, the alternator AND consume less power,,, WIN, WIN, WIN!!!

Only problem is the larger pulley is $175 I think, it’s not horrible but not cheap either.

I did find someone that had one of the laser tachs and put a piece of that tape on my harmonic balancer and got:

855 when the tach was saying 1100
1425 when the tach was saying 1900

assuming it is correct, it does appear the smaller pulley causes a readout of higher rpm’s. Can’t say that the larger one would be accurate without testing it.

 

[Mogman]

One thing to consider is when they put that alternator in OD they did not intend for someone to be driving that truck at highway speeds, when you are driving at 3000RPM that alternator is turning as if you were driving at around 4000RPM, the alternator was not designed for that type of operation, someone just decided to jury rig it because they needed more amps in stationary operation.
I would think if you put a want out in the classifieds you could do much better than $175, but even at $175 I it would be a wise thing to do IMHO.
Actually if it were me I would source a 200A and get that beast out of there....

 

[Retiredwarhorses]

One thing to consider is when they put that alternator in OD they did not intend for someone to be driving that truck at highway speeds, when you are driving at 3000RPM that alternator is turning as if you were driving at around 4000RPM, the alternator was not designed for that type of operation, someone just decided to jury rig it because they needed more amps in stationary operation.
I would think if you put a want out in the classifieds you could do much better than $175, but even at $175 I it would be a wise thing to do IMHO.
Actually if it were me I would source a 200A and get that beast out of there....

you only have to go to our company FB page to see over a year ago the write I did on this very issue, that and the other
numerous 400’s removed and replaced with 200amp. Ive posted many photos of the damage these 400’s can cause and have caused…
unfortunately folks don’t like my answer’s when I give them the alternatives because it’s expensive. You are right on as well about the gen and it’s application, these were for C&C trucks and Shelter trucks, the 400 produces at idle what the 200 puts out at full rpm, they were as the documents I have for “Heavy comms and IED threat equipment“

 

[01GRANDER]

you only have to go to our company FB page to see over a year ago the write I did on this very issue, that and the other
numerous 400’s removed and replaced with 200amp. Ive posted many photos of the damage these 400’s can cause and have caused…
unfortunately folks don’t like my answer’s when I give them the alternatives because it’s expensive. You are right on as well about the gen and it’s application, these were for C&C trucks and Shelter trucks, the 400 produces at idle what the 200 puts out at full rpm, they were as the documents I have for “Heavy comms and IED threat equipment“

Did they make a serpentine pulley for the 60a generators? Reid has a few older ones lying around, they have the v belt so I’d have to get that pulley(assuming they exist). I’ve just never seen a serpentine on a 60a.

 

[Retiredwarhorses]

Did they make a serpentine pulley for the 60a generators? Reid has a few older ones lying around, they have the v belt so I’d have to get that pulley(assuming they exist). I’ve just never seen a serpentine on a 60a.

Huh? Where did I mention 60amp serpentine?
as I’ve previously stated “unsuccessfully it appears“ you have 2 options for your pulley, the current small pulley or the larger clutch pulley.

 

[01GRANDER]

Huh? Where did I mention 60amp serpentine?
as I’ve previously stated “unsuccessfully it appears“ you have 2 options for your pulley, the current small pulley or the larger clutch pulley.

You didn’t, I was asking about getting rid of the 400a and switching to a 60a instead of the 200a because I have access to some. I am talking about I have access to multiple 60a generators, I am asking if they have serpentine pulleys for the 60a generator since I’ve only seen v belt setups on 60a generators.

 

[TOBASH]

You didn’t, I was asking about getting rid of the 400a and switching to a 60a instead of the 200a because I have access to some. I am talking about I have access to multiple 60a generators, I am asking if they have serpentine pulleys for the 60a generator since I’ve only seen v belt setups on 60a generators.

I think replacing a 400 amp with a 60 amp is way off the RADAR. It is a serious downgrade that makes no sense. If it is a money issue, save up the money and purchase a proper replacement, and then sell the 400 amp unit to recoup some cash.

IMHO

 

[01GRANDER]

I think replacing a 400 amp with a 60 amp is way off the RADAR. It is a serious downgrade that makes no sense. If it is a money issue, save up the money and purchase a proper replacement, and then sell the 400 amp unit to recoup some cash.

IMHO

I don’t see how it’s a downgrade, I don’t use 200a. I run a basic radio and occasionally some lights. It’s not a money issue in this situation, it’s literally just that I don’t need the 200a.

 

[SmartDrug]

I don’t see how it’s a downgrade, I don’t use 200a. I run a basic radio and occasionally some lights. It’s not a money issue in this situation, it’s literally just that I don’t need the 200a.

That's fair, but I thought the 200a was substantially more stout than the 60a. The dual voltage aspect of the 200a is a benefit as well. I'm no expert, though.

 

[TOBASH]

If you are not interested in placing a 200 amp, consider purchasing a GM 24 V alternator, (which is easily sourced and easily rebuilt), and make custom brackets and hook it up to your unit. There is no reason that you must use stock military items.

Given that you wish to swap out a 400 amp unit, you would need to purchase brackets anyway. You might as well just customize the brackets that you have and put in any alternator you are comfortable with if cost is an issue.

If you are not comfortable making your own brackets, then purchase the 200 amp brackets and you will have an easy fit with a dependable unit.

From my discussions with Steve/RWH, the 60 amp alternators are not as good as 200 amp units. Steve seems to dislike the 60 amp units. I hate speaking for other people so I’ll let him explain.

No one is forcing you to go in any single direction. However, you should really take the advice of RWH because HMMWV’s are his bread and butter . He has tremendous experience that he is willing to share with all of us. There’s no sense in reinventing the wheel.

IMHO.

 

[Coug]

One other thing, your truck does require a 12V feed to power the transmission control module.
The 60 amp gen and aftermarket 24V alternators do NOT have a 12V feed.
If you try to go that route you will have to figure out some way to feed 12V to the rear battery to keep the TCM functional and not kill your batteries. Usually a battery balancer of some type, though other people have come up with some more inventive/less conventional ways of accomplishing this.

 

[blutow]

I don’t see how it’s a downgrade, I don’t use 200a. I run a basic radio and occasionally some lights. It’s not a money issue in this situation, it’s literally just that I don’t need the 200a.

I don't know anything about the reliability of the 60a unit, but your logic makes sense to me if they are reliable. The 200a generators are extreme overkill for what many people are using their trucks for. I'm sure there are exceptions for folks running a ton of electronics, but even modern vehicles with lots of electronics (electric steering racks, heated seats, etc.) don't have alternators anywhere near the output of a 200a 24v unit. 200a doesn't sound extreme until you consider that it's 24v (so it's the same as a 400a at 12v). Your current 400a 24v unit is just plain nuts (9,600 watts). You could literally power a decent sized house with that kind of output.

 

[Mogman]

The 60a is not considered as dependable because it has brushes and a regulator that has a high failure rate, if you go with the custom install as TOBASH recommends the tack will not work.
Also the 12V issue for the trans.