E4od
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
the sensor on the back is not a VSS. you can go to any autoparts store and ask for a VSS and they will hand you the incorrect part.
the sensor on the back diff is the abs sensor which talks to the abs computer and then sends signals to the PSOM (electronic speedo) in 92+ vehicles. the VSS in the tcase is no longer there. for the 87-91 models the VSS in the tcase turns the cable for the speedo and works with those years e4od (89-91). the sensor on the rear diff for those years controls rear abs unless it has the e4od which it also uses that pulse signal to work the shifting of that tranny electronicly but the vss in the tcase controls the speedo.
4wabs didnt arrive till 92+
the sensor on the back diff is the abs sensor which talks to the abs computer and then sends signals to the PSOM (electronic speedo) in 92+ vehicles. the VSS in the tcase is no longer there. for the 87-91 models the VSS in the tcase turns the cable for the speedo and works with those years e4od (89-91). the sensor on the rear diff for those years controls rear abs unless it has the e4od which it also uses that pulse signal to work the shifting of that tranny electronicly but the vss in the tcase controls the speedo.
4wabs didnt arrive till 92+
The sensor on the rear axle is a vehicle speed sensor. It's a magnet that sends a pulse to the ABS computer (and PSOM 92+) that it gets from the teeth on the exciter ring. The faster the vehicle goes, the more pulses it sends - sounds like a VSS to me. I don't care what someone who works at an auto parts store does or says - if you base your automotive knowledge on them you're in rough shape.
Saying that the VSS in the transfer case turns the speedometer cable says to me you don't really know what a VSS is. A VSS is an electronic part that sends an electronic signal to a computer. The cable is strictly a mechanical assembly. There are both VSS and cable outputs on my transfer case.
Another thing that you are confused on is that in an 87 to 91 truck with an E4OD, the VSS on the transfer case feeds speed data to the PCM for the tranny. It does not get its signal from the VSS in the rear differential. Check a wiring diagram, the signal from the rear axle doesn't even go to the PCM.
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Okay so, is the only way I am going to get the signal I need to the PCM for the trans and cruise control going to be a remote mounted VSS or will the VSS on the 89-91 interface with my PCM? Also do you know if the 89-91 mechanical speedo transfer case will interface with my speedometer cable on my 79? I don't even care if it is accurate as long as I have something.
I wish I had researched this better before I bought the 94 donor Bronco. There were others I could have looked at but I figured the newer the better. I wouldn't have thought a Bronco would be all electronic at that stage.
P.S. Thank you for your good information. I think I am a product of too much information that I have been incorporating into other information and coming out with some wrong information.
Helm's title page reads: Vehicle speed sensor at the top and I was confusing that with the rear axle sensor in fact I was even on the wrong page, Bronco is the one to the right.
I wish I had researched this better before I bought the 94 donor Bronco. There were others I could have looked at but I figured the newer the better. I wouldn't have thought a Bronco would be all electronic at that stage.
P.S. Thank you for your good information. I think I am a product of too much information that I have been incorporating into other information and coming out with some wrong information.
Helm's title page reads: Vehicle speed sensor at the top and I was confusing that with the rear axle sensor in fact I was even on the wrong page, Bronco is the one to the right.
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Okay can you tell me what the VSS on the transfer looks like so I know what I am looking for when I start shopping for another transfer case. My 94 doesn't have a VSS on the transfer case. Also does your speedo cable have a plastic gear on it? And does it have the pressure arm with one 1/4" bolt holding it into the case?
Thank you.
Thank you.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
The sensor on the rear axle is a VSS.
I forgot about the cruise when I first replied. If you want the cruise to work you will need either a rear axle with a VSS or a remote mounted one like Kem says. If you are keeping the 79 gauges then you will also need a transfer case with a mechanical speedo output.
And ALWAYS research before you buy.
I forgot about the cruise when I first replied. If you want the cruise to work you will need either a rear axle with a VSS or a remote mounted one like Kem says. If you are keeping the 79 gauges then you will also need a transfer case with a mechanical speedo output.
And ALWAYS research before you buy.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Here's what mine looks like:
The VSS basically piggy-backs on top of the cable and gets the signal from it. Which makes sense - because this way when you change the speedometer gear you get the corrected reading from the sensor. I've never seen the speedometer output cable on a transfer case prior to Ford using the VSS - so it may very well be the same hole, just with the sensor piggy-backed on top of it.
So your transfer case just has nothing in that spot?
The VSS basically piggy-backs on top of the cable and gets the signal from it. Which makes sense - because this way when you change the speedometer gear you get the corrected reading from the sensor. I've never seen the speedometer output cable on a transfer case prior to Ford using the VSS - so it may very well be the same hole, just with the sensor piggy-backed on top of it.
So your transfer case just has nothing in that spot?
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Okay I have found some mistakes in the Helm's EVTM. Once the prior replies have been read I started looking through there to find where the heck everything was. When I first was looking at it I was actually looking at the F-Series page. After digging I have found: The rear axle sensor goes to the 4WABS through there to the PSOM through there to the PCM and Cruise through there to the trans and maybe other places but that is all we need for now. Essentially I have to have the signal that the rear axle sensor produces to go to the PSOM, looks like I will need to mount the PSOM somewhere in my 79. Do either of you know if the VSS on the earlier transfer case produces the same signal that the rear axle sensor of the 94 produces?
Thanks in advance.
Thanks in advance.
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Thank you, that helps tremendously. That looks like if I have the cable for that transfer it will interface on the odometer end.
I actually have the 8.8 from the 94 I would rather stay with my 9" though. Plus the gearing isn't the same so I would have to change that and need a new ring toner too.
I actually have the 8.8 from the 94 I would rather stay with my 9" though. Plus the gearing isn't the same so I would have to change that and need a new ring toner too.
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Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
You would also have to relocate the spring pads and shock mounts. It's really a pretty involved job.
I have a site bookmarked, but the site is no longer valid. A guy put up a whole write-up on how he built a VSS for a 9" axle. He mounted the sensor and fabbed a ring with exciter teeth on it, and calculated the correct number of teeth and size of the gear. It was a really good write-up. If you use the gear ratio to figure out what the correct number of teeth are, you could do the same thing and make your own custom VSS.
I have a site bookmarked, but the site is no longer valid. A guy put up a whole write-up on how he built a VSS for a 9" axle. He mounted the sensor and fabbed a ring with exciter teeth on it, and calculated the correct number of teeth and size of the gear. It was a really good write-up. If you use the gear ratio to figure out what the correct number of teeth are, you could do the same thing and make your own custom VSS.
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Yeah I really don't want the 8.8. I guess I could tear it apart and see what the ring toner looks like. You don't think the VSS off the earlier transfer case will produce the same signal? I wish this Helm's book covered earlier Bronco's too.
I found an 89 transfer and hope to pick it up Friday. I am trying to get the speedo cable as well.
Thanks.
I found an 89 transfer and hope to pick it up Friday. I am trying to get the speedo cable as well.
Thanks.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
No, think about where the sensor is - on the driveshaft. The VSS on the axle reads off the ring gear, after the gear reduction in the differential. I'd guess the numbers are going to be about 3.5x off.
Hotshot
Joined: Jul 2002
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From: Bend,OR
a gear reduction in the diff will have no affect on the signal being sent to the computer. I installed 4.88 gears in my 8.8. the tone ring stays the same so nothing there changes. I did have to recalibrate my PSOM to the proper setting for my tire size so my shift points and speedo was accurate.
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
The original question was: will the VSS on the transfer case send the same signal that the VSS on the rear differential does - and the answer is no because of the gear reduction.
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