4L80E speed sensors

[Nasty-Z]

Have an unknown vintage 4L80E , I am assuming though it is a 94-later because there is no reluctor ring on the rear drum for the rear speed sensor on the side of the case , it was installed into a K3500 running a BBC and the '7060 PCM . Because it has the '7060 it needs a signal from the rear speed sensor inputted to B5 and B6 to function properly . There is no signal now as there is no reluctor ring for the sensor to pick up .

Does anyone know a work around to give the PCM the correct signal from what would be the rear speed sensor ? Does the speed sensor on the transfer case feeding the DRAC/VSSB module have the correct signal or is there an output on the DRAC/VSSB that can be used .

I know on the later '7427 PCM's the output speed sensor is omitted as the DRAC/VSSB provides the signal.

I really don't want to remove this trans to install the reluctor wheel nor do I feel like repining to the later PCM.

Any help or advice is appreciated.

Thanks

TOM

[1BadAction]

Does anyone know a work around to give the PCM the correct signal from what would be the rear speed sensor ? Does the speed sensor on the transfer case feeding the DRAC/VSSB module have the correct signal or is there an output on the DRAC/VSSB that can be used .
No workaround necessary, the T-Case speed sensor sends the same signal as it does when it is mounted on the transmission. I believe there needs to be a grounded switch when in 4-lo pinned in also. I'll check real quick...

[1BadAction]

This is all I can find at the moment, it's for a 1991 R/V Series. All it says is "to the pcm" on the purple wire. You know that input may also be the key to getting our "performance mode" shift table in the 7060. :innocent2: I guess now all we need to do is figure out which pin it goes to.

http://i.imgur.com/T4GTmUX.jpg

[Nasty-Z]

8254

Jim , thanks for the response ,

I suppose I was unclear in my first post , the front sensor (TISS or transmission input speed sensor) and the sensor on the tailshaft of the T-case (VSS or vehicle speed sensor) are there and functional, the rear most sensor on the transmission case itself (TOSS or transmission output speed sensor) is what is missing the reluctor ring. This is common on later 4L80E's as the '7427 and later PCM's do not use it.

At the top of this page , the Transmission output speed sensor is what the '7060 needs to see , on the trans I am working with the reluctor ring in not installed on the rear planet assembly , therefor there is nothing for the TOSS to gain a signal from . Aside from removing the trans and having the ring pressed on (disassembling the trans is needed to do this) I was looking for another option to get an input of the correct signal to B6 and B5 .

I do not know what signal the TOSS produces , I believe it to be a 40 tooth reluctor wheel , much like the VSS on the tailshaft , so I was unsure if the VSS on the tailshaft could provide the correct signal and /or if it was acceptable to use it for two inputs by piggybacking the signal.

I hope this all makes sense .

Thanks

TOM

[brian617]

Are you saying the 7060 has to have three speed sensors? The reluctor wheel is on the output shaft if I remember correctly.

[1BadAction]

I do not know what signal the TOSS produces , I believe it to be a 40 tooth reluctor wheel , much like the VSS on the tailshaft , so I was unsure if the VSS on the tailshaft could provide the correct signal and /or if it was acceptable to use it for two inputs by piggybacking the signal.

I hope this all makes sense .

Thanks

TOM
Yes, the output signals are the same between the trans case and transmission, however, you'll need to tell the PCM the truck is in 4WD LO with an input switch if you want it to not shit the bed in Lo Range. I do not know if it is acceptable to split the VSS Signal... I did it on my 88 IROC/T56 and the speedo dropped out over 120mph, not sure if the signal split was the reason why but I think it probably was.

[Nasty-Z]

Are you saying the 7060 has to have three speed sensors? The reluctor wheel is on the output shaft if I remember correctly.

Yes , as far as I can see, its use in 4x4 applications is how the PCM calculates which range the T case is in (4 low or 4 high) as well as shift timing (how long the trans takes to complete a shift) , on the 2wd models it is used only for calculating shift timing .

There is a reluctor ring on the input drum (for the TISS) as well as the output planet assembly (for the TOSS) , the reluctor ring on the rear planet was only there until the switch to later model PCMs , whereas it was not needed anymore , there is also a reluctor ring on the output shaft for the VSS.

With the later model PCM's such as the '7427 there is an input to the PCM relaying when the vehicle is in 4 low as well as another input from the DRAC indicating output shaft speed , so the TOSS is not needed.


Yes, the output signals are the same between the trans case and transmission, however, you'll need to tell the PCM the truck is in 4WD LO with an input switch if you want it to not shit the bed in Lo Range. I do not know if it is acceptable to split the VSS Signal... I did it on my 88 IROC/T56 and the speedo dropped out over 120mph, not sure if the signal split was the reason why but I think it probably was.

Well , I suppose i'll give it a shot , saves the guy from removing the trans ....... I'll see if it'll work or not .

Thanks again

TOM

[brian617]

Depending on how many of the outputs are currently used you might be able to find a 1:1 output from the DRAC?

[myburb]

My understanding is with a 7060 in the early years they installed the reluctor at back of trans whether 2 or 4 wd and just plugged the rear speed sensor hole on 4wd and sent the transfer case output to b5 and b6. If it was 2wd the signal went to a drac and was then sent to b11. I think the signals are the same so probably could sent the tcase signal to a drac and as long as you weren't using 4wd the 7060 wouldn't know the difference.

[1BadAction]

My understanding is with a 7060 in the early years they installed the reluctor at back of trans whether 2 or 4 wd and just plugged the rear speed sensor hole on 4wd and sent the transfer case output to b5 and b6. If it was 2wd the signal went to a drac and was then sent to b11.
This is correct according to the schematics, and a switch (in the schematic I posted for an early 7060 truck) would tell the PCM when the T-case is in low range so it would shift correctly. I've never seen a 4L80/205 combo out of a 91 square with 3 speed sensors, the couple I've seen had an extension harness to the VSS in the tailshaft of the transfer case.

[Nasty-Z]

Depending on how many of the outputs are currently used you might be able to find a 1:1 output from the DRAC?

The only 1:1 on the DRAC is at C13 , it is already used to input to B11 on the '7060. I don't think there are any others .

Maybe i'll try to piggyback the VSS and input to B5 and B6 , whats the worst that can happen.............



This is correct according to the schematics, and a switch (in the schematic I posted for an early 7060 truck) would tell the PCM when the T-case is in low range so it would shift correctly.

Where would this be inputted to the '7060 ? I have never seen a schematic that correlated to a pin on the '7060 such a switch would be inputted to.

FWIW , the '91 V3500 Ex railroad truck that my 4L80E/205 combo came from was a 3 speed sensor truck , It was a '7060 PCM also. That combo was supposed to go in my S10 Blazer , but I used the 700R4 / 205 instead.

TOM

[1BadAction]

FWIW , the '91 V3500 Ex railroad truck that my 4L80E/205 combo came from was a 3 speed sensor truck , It was a '7060 PCM also. That combo was supposed to go in my S10 Blazer , but I used the 700R4 / 205 instead.

TOM
Intredesting. The 7060 is slow, yet they are doing that extra calculation, makes sense that it would work though.

I can't find pinouts online, other than the "to ecm" on that above. I think it may be time to fire up my old hard drive with the GM SI software so I can pull some schematics.

[Nasty-Z]

Intredesting. The 7060 is slow, yet they are doing that extra calculation, makes sense that it would work though.

I can't find pinouts online, other than the "to ecm" on that above. I think it may be time to fire up my old hard drive with the GM SI software so I can pull some schematics.

I went through my old (key word there , "old") books last night with the early square body wiring diagrams in them , no mention in '91 R/V books of an input to the PCM for 4 low.

I'll have to look at my old PC also , I have the old fiche (sp) copies from GM for the 73-87 (and 88-91 R/V) trucks , maybe something will pop up.

TOM

[Nasty-Z]

Well,

FWIW , and for anyone who might search for the same topics that I did , splitting the output of the VSS on the tailshaft of the T case to feed both the DRAC and the TOSS input at B5 and B6 works fine , no problems in 2WD , 4WD or 4WD low range . Rock solid output and accurate to 75+ mph which was all we ran it up to.

Thanks for all that responded , I appreciate the help

TOM

[billygraves]

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[Nasty-Z]

If you have a 91-93 L80 4WD truck and PCM, and you are trying to use an aprox 94 with the OSS ring missing. If this is the case, you should consider a few facts. I know of no work around for a 95 4L80-E with no OSS ring in a 91-93 where the PCM needs the OSS signal.

The work around is in post #14 above , use the VSS on the T case for both the input to the DRAC and for the TOSS input into the '7060. Works flawlessly.

For the record , I did not know this would work and was hesitant to try it , but it sure beat removing the trans and tearing it apart to install the reluctor ring. Glad I tried and verified that it could and would work.

Just because I am so curious though , can you explain in terms that I can understand why we cannot (or should I say should not) interchange the early (91-93) and the later 94 and up 4L80E transmissions ? I ran a 1995 model 4L80E in my '92 454SS for years with the '7060 with no problems whatsoever before I switched over to the '7427 , my 93 K3500 has a 96 model 4L80E , again with many many miles and no indication of a problem with the '7060 controlling it before I switched to the '7427. This truck that the original post was about is a 1992 model year also , again with a 1995 model 4L80E in it now with a '7060 controlling it.

I would just like to understand why this is frowned on if all works as intended . I am at a loss as to what would be so drastically different that the model years should not be interchanged .

Thanks

TOM

[billygraves]

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