• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Need some help with GearVendors OD unit behind 4L80E

dbrannon79

dbrannon79

I'm getting there!
Messages
6,159
Reaction score
13,273
Location
Seguin, TX
Hey guys, I figured I would start a new thread for this GV OD unit that was installed on this 93 truck. Now that I have the TCI TCU working properly I need to figure out how to get the "AutoDrive" portion of the GV unit to work. as it is now if I use the manual switch, the OD will kick in when I'm going a little over 40 MPH. when this happens the green light on the panel will turn on showing the OD is on. using the toggle on the panel doesn't change anything and the autodrive light does not come on.

From the information I was given, this unit was used when it was installed, but seems to be intact as I have been tracing the wiring according to the attached diagram I was given. I did find the operation / install book online but it's for a mopar 904 and 727 trans in an older vehicle. I would like to see if someone has a copy of the same manual specific to the 4L80E so that I can make sure it's all connected properly along with learning how it is supposed to operate.

Link to Mopar manual I found.
 

Attachments

  • Electric21.pdf
    182.8 KB · Views: 2
A little update after reading the manual I linked above. I saved 5 pages into a separate attachment as it seems to pertain to all GV units.

As it seems, the auto function is working as outlined in the "operation" on page 2 of the attachment here but... I do not have the red light on the dash panel while the switch is in auto mode, only the green light comes on when I reach about 40-45ish mph as the OD kicks in. this happens when both the panel switch is in auto mode and the other switch is turned on. I went back out and double checked the wiring to the dash panel, pulled the connector on the bulb in the panel and verified the red one is good. it's just not lighting up. this means ether something isn't connected properly or conditions are not met for it to light up.

The attachment shows this light is on when the auto is selected and the other switch is turned on when you are going too slow for the OD to engage. Interesting.
 

Attachments

  • GearVendors Operation.pdf
    156.3 KB · Views: 2
Well I had something happen today on the way home that made me think about the speeds at which this GC OD unit turns on and off on it's own. so far it's been working fine, but today while on the freeway I had to slow down due to another truck in front slowing down. the GV OD will turn on at around 40-42 mph and will turn off at about 25 mph or so. I think this is hard programed into the brain box but not sure.

what happened was when I had slowed down my speed wasn't quite enough for the OD unit to turn off, when I started accelerating again the RPM was too low and the engine began clattering really ugly. as soon as I heard the noise I let off the pedal. what happened is the engine was out of it's power band range and couldn't accelerate due to two reasons. the trans didn't down shift and the OD stayed on.

I would like to find a way to adjust the GV OD so it will turn on and off at a higher speed. just cruising at 45-47 the RPM is below 1500. everything happened too quick for me to look at what speed and RPM I was at when all this happened.
 
the unit has it's own drac or VSSB which the speedo is also connected to. the truck uses the factory one for what, idk, but I was wondering if I were to adjust that vssb so the OD unit thinks I'm going slower it might allow it to shift later into OD. I would need to move the speedo to use the factory VSSB to have it read accurately though.

has anyone dealt with this kind of thing? I have attempted to contact gearvendors directly when I was trying to figure out the wiring but they never responded.
 
Here is my vote: Get larger diameter tires to mimic the desireable final OD ratio and ditch the GV. Or, re-gear the rear and still yank the GV.

I looked into those things a while ago. Could not really determine the flud change interval were at max it looked like 5K miles IF it had an optional sump type thingey. After towing with a NV4500 and 3.42 rear, it demonstrated that an aux overdrive was not necessary. I really wanted something like a Spicer with actual gears and a long fluid life, but that was just too much headache for me to find one and then fabbing the install.

On the upside, at least somebody else paid the premium for that GV :)
 
I’ve no laptop or desktop currently - just phone, and can’t open those pdf for some reason.
Can you screenshot the 5 pages and post as full size pics?
ON EDIT- never mind- figured it out

I would keep the GV, the downsides of them from all I’ve seen is price and learning them.
I’ve seen several rigs with them on it and the only person I heard have major issues was @THEFERMANATOR here had issues on 4wd truck and a vibration iirc.

The other owners I spoke to that had them all were happy with their purchase.
A friend of my folks had one on an old dodge and ran that rig into the ground. iirc his had the 727 trans. I say fight through it and learn how it’s supposed to work and how you can set in up for your application.
Coming in at 45 mph sounds like the p.o. did a lot of 45-50mph cruising.
 
Last edited:
Yeah, for it's purpose it works fine, but its under those odd situations were it makes things worse, like what happened to me yesterday. I think if I can get it to come in at around 55 60 and turn off around 35-40 it would be fine. the way GV designs them is a one size fits all as far as the programming. every engine from different makes and models all have different power and torque bands.

not to mention I don't think they or anyone intended to have an aftermarket trans controller and a GV OD unit too LOL.

for the TCI TCU, one think I have noticed is when cruising or accelerating slower, by the time you hit 30 mph your in 4th gear. it's shifts fast like the older TV operated trans. my 95 won't hit 4th till your at least up to 45-50 no matter how fast or slow your accelerating.
 
Yeah, I have the switch to turn it off. didn't use it LOL I need to look but I didn't see any way to change the shift points for each gear on the TCI. only the aggressiveness and how long it holds the gear. I can probably play with those two setting more and see what difference it makes.
 
today after work I decided to look at the schematic diagrams for both the GV unit and the TCI controller. I think I have two issues I need to work out. the first one is to get both the TCI controller and the GV unit to use the same speed sensor rather than the TCI using the rear trans speed sensor and the GV unit using it's sensor further back on the trans. the reason is when the GV unit turns on, the TCI controller thinks I am going 30 mph while I am really going 40mph. I have already witnessed this by watching the TCI display live data while on the road. if they both read from the same sensor then they both would see the same speed all the time.

The second issue is once the first one it worked out, I need to readjust the shift points for when the trans shifts and enters TCC lockup.

Here is some snips of the diagrams for both along with a page from the factory truck diagram. looking at them, I think I can disconnect the speed sensor for the TCI controller and then connect pin 7 from the VSSB to pin 29 on the TCI controller. If you all would have a look at this and tell me if I am correct. basically I need to split the output of the speed sensor on the GV unit to send a signal to both the GV controller and to the TCI controller. I also attached the full pages in PDF form.

1709859066573.png

1709859102298.png

1709859139219.png
 

Attachments

  • TCI Diagram.pdf
    631.8 KB · Views: 2
  • Gear Vendors 94-94 diagram.pdf
    182.8 KB · Views: 1
  • 1994 VSSB Diagram.pdf
    1.1 MB · Views: 1
The gear endors unit was originally setup to shift in at 45 and out at 25 in auto mode as they were meant to be used behind 3 speed non OD autos. That is hard set into the box and not adjustable. You must have the trans controller using the speed sensor in the output of the trans so it knows the teans shaft speed and then the gear vendor and speedo use the speed sensor after the gearvendor as your speedo needs to know the speed pf the shaft going to the diff. I know many trans controllers have an extra programmable output that can be used to turn the gear vendors on and off so they can shift it on at a more desireable speed, but most just use the manual mode, and shift them in once you're up over 60.

The gear vendor is good for hwy driving, but not for in town. And yes, they should have the oil changed every 5k miles with the deep sump, and gear vendors reccomends using 12346190, not atf like they used to recommend.
 
Thanks Ferm, and it's good to hear from you. hope your doing well.

right now the trans controller is using the output sensor in the trans and the GV unit and speedo is using the sensor on the rear if the GV unit. Changing the oil is next on the list. I did check it by pulling the fill plug and some came out that looked clean and clear. I figure I will do both the rear axle and GV oil change at the same time since when I did the sniff test on the axle oil, it stunk like oil gear oil LOL.

center support bearing is starting to make some noise too so that just got added to the list. I might end up taking the driveshaft to get checked and balanced since the PO shortened it them selves. the support bearing cross member is slotted where it bolts up and it's slid fully towards the trans side with the slip yolk looking like it's almost fully compressed. I need to check the travel and see if the shaft needs to be shortened another 1/2 inch or so too.
 
Well I figured I would post here and see if anyone out there knows just how hot these GV units are supposed to run after a long trip. Or at least what is acceptable. this weekend I drove the 93 out to the coast for a weekend on the beach. the trip was about 150 miles out there and another coming back. we arrived home this afternoon and while I was unloading the truck, I noticed the floorboard of my truck between the front seats was quite warm, felt like clothes that had just came out of the dryer! the truck was not pulling anything, only hauling the 4 of us plus one 65lb fur baby. the bed has a fiberglass camper and was loaded with the usual weekend luggage and fishing gear.

I slid under the truck to see what was making the floor so warm. felt the driveshaft, front u-joint, and then the OD unit. the gearvendors overdrive housing was very warm to the touch. hot enough that you wouldn't want to leave your hand on it very long. this unit has the oil sump installed and is filled with synthetic gear oil, not atf fluid. I plan on changing the oil soon. during the trip there was no noises or any indication of an issue. Even as our trip was ending (rolling into our home town) stopping at traffic lights and then going back up to speed the GV unit would kick in normally. So no functioning issues at all, it just alarmed me that it was so warm along with the carpet on the floor of the cab.

I have the center console removed and had a blanket there for our pooch to lay during the trip. I felt so bad after I found that the floor was so warm and this was her spot to ride in the cab. If this is normal for the OD unit to warm up like this I am going to need to make a heat shield along with build an insulating platform for her to ride on and be comfortable.

If anyone has any info on the operating temp of these things please let me know. I'm also wondering about finding a way to mount a temp gauge for it as well.
 
I finally got to talk to someone at Gearvenors about this unit. I asked the question about what the normal operating temp was for them and explained what happened on the trip. the guy was very nice, he first asked me what transmission I was running. after telling him it was a 4L80E, he immediately said " I assume you were running in double overdrive". I said yes. he proceeded to tell me that these units were not designed to be ran this way and that running my trans in OD with the GV OD on puts a lot of strain on the GV unit. He told me that they normally run about 200 degrees and I most likely got it hot running in double OD for that long of a trip.

I asked him what I should do about this, and he again explained that they weren't really meant for a trans that has OD, that I was running the trans in OD which gave a 26% OD ratio compounded by GV OD at another 22%. Then I asked about the oil. he said they only recommend Lucas synthetic 75W90.

I looked and no one in town carries this brand so I settled for the house branded synthetic 75-90, same stuff I used in the diff. Just got finished changing the oil in the GC unit along with topping off the diff at the same time. upon first glance watching the oil lube drain, it looked dark golden and I could see though it like it was fairly clean. After finishing up and pulling the drain pan out where I could see what came out, the sun hit the oil and I could see lots of copper-ish color glitter swirls. nothing at the bottom collecting though. I poured what came out into the bottle I used to fill it with, it filled a quart bottle up to the brim. I'm sure that is clutch material, but I also don't know when it was last changed.
 
What I didn't understand is if there not made for a trans with OD, why do they offer them specifically for this trans? from what I have read online they say otherwise and they should be capable of handling trailers too. I did run across another forum where the guy did the same thing calling them worried about towing with it even installed. they informed him that they can tow up to 14k, of course I wouldn't want to try with it on.

we were just cruising the freeway only bearing the weight of 4 people and some fishing gear, no trailer. I wonder if there is a way to strap a temp probe on it and have a gauge in the cab. maybe later, add a cooler with a inline pump connected between the drain and the fill ports. The threads in the fill and drain look unique so that might not be feasible.
 
You must log in or register to reply here.
Back
Top