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SpiceStream 01-18-2019 10:07 AM

Gear Vendors Experience
I purchased our 1984 310 with a 6bt Cummins, Allison 545 / Gear Vendors, 3.54:1 Gears in Diff, Stock Tires.

This setup has served us well, but I wanted to discuss my experience with this set-up over several years and tens of thousands of hard miles so others can make an informed decision if they decide to head down this road so to say.

First off, the gearing, power, and fuel efficiency of our rig is fantastic, I would not change a thing as far as gearing and power goes.

We use our 310, we have been to some of the most desolate corners of our county and Canada, these machines are built tough as nails. I would guess that we have logged over 5000 miles of unpaved roads including the entire AlCan, the entire Haines highway, Many Many miles through the road-less portions of the Theodore Roosevelt National Grassland and many other two tracks and road-less areas in the western parts of the US along with countless miles down logging roads in Michigan's Upper Peninsula.

So in all of this we have never been stranded...but.

On our way out to Utah last spring dragging our Jeep, our Gear Vendors Overdrive gave up.

We were not stranded, just had to turn off the overdrive which meant slowing down a bit, getting less fuel economy, and going skiing rather than Jeeping...Tough life, I know.

I have gone through all the scenarios of what I could or should do and I decided that I would have the overdrive rebuilt by Gear Vendors and keep things the way they are since they work so well and are integrated into my rig and move on. Gear Vendors has been very easy to deal with in this process, during the breakdown, and during the overhaul, the Overdrive is currently in transit back to me.

That being said, if I did a fresh swap, I would definitely without question put the 6 speed in out of the gate.

Just my two cents.


Magnet18 01-18-2019 11:01 AM

Glad you've had a good experience with yours, I like mine as well :)

How often did you change it's oil? I think it's supposed to be changed every 3-5 thousand. Just curious

Smartstream 01-18-2019 11:10 AM

Interesting, did you change the rear end gearing? You must be idling down the highway in OD. My 280 does 62 mph at about 2200 rpm in OD with 4.56 rear end. With 3.54 you must barely be doing a fast idle.

I agree the Gear Vendors is great and they also have treated me well. A 6 speed would be great but changes with the old Isuzu gets more interesting.

SpiceStream 01-18-2019 01:12 PM

The previous owner did the drive-train swap, and yes, he did put the taller gear set in the diff, and you are correct, I will have to double check but I believe at 70MPH I am running below 2000 rpm which really helps with cabin noise and fuel economy on the flats. As far as oil changes, I definitely did them every 5000 miles, it is super easy and very low cost so I change the fluid almost every trip out.

Gear Vendors had two thoughts on the matter.

-I told them how much grunting around at low speeds we do which coupled with the 6BT and its nasty torque pulse is a recipe for disaster in the drive-line.

-Also, and more importantly in Reverse, the Gear Vendor is essentially relying on spring pressure to keep the Vertex Cone Clutch engaged. Over the years, during said plugging around at slow speeds on sometimes very muddy two tracks, I have been temporarily without traction at which time I for sure tried to dislodge myself by using the reverse gear available to me. This is almost for sure how I damaged the Gear Vendor, all my fault and if I have a chance to do it all over again, I will do the same thing again with 100% certainty.

One other side note on this subject is that Gear Vendor suggests that we disengage the overdrive when descending hills, I am normally in this habit because I rely heavily on engine braking downhill whenever possible and the gear vendor is the first thing I shut off when going down any hill.

Again, this is a great unit, I do not want anyone to think this is a substandard product, it is super tough in fact. and the company has been great to deal with, I am just saying if I had a clean slate and I was starting over I would go for the 6 speed...although you are then stuck with another computer who knows but one thing is for sure, we will be running the Gear Vendor as long as the Cummins/545 keeps chugging along.

Again, most of you would be appalled at what I have put this poor old girl through, but I can tell you they are the best built, most capable motor home I have ever seen, do not be afraid to enjoy them, they can take you places you cant even imagine, they were built for it.


tevake 01-18-2019 05:49 PM

Curt, it's so nice to hear of folks actively using their classic motorhomes. They certianly are very capible machines. And it sounds like you have fully used yours abilities.

My 345 also has a gear vender overdrive installed.
It's a great piece of kit. Nice keeping the revs down at highway speed.

I had done a few trips in the Rockies of Colo, and a trip up the west coast and the mountains of the PNW before learning that its not good using them while descending. Bummer, cause I really appreciated the ability of splitting gears to zero in on the right gearing for speed and revs while going down long descents.

So far I haven't seen any dire results, or excessive dirty fluid at change time and Im now based in Fla so wont be doing any big mountains for a while.

Your gearing change sounds great. Do you have very slow accelerating from a stop?

Am I understanding correctly that is good to disengage the unit for backing?
Thanks for the heads up on that. I think that mine shuts itself off at low speeds, so is unlikely to be on when shifting into reverse.
I'll have to watch more closely.

Cheers Richard

SpiceStream 01-21-2019 12:08 PM

Gear Vendor Operating Instructions
Richard, I have cut and pasted the official GV Instructions Below, it does go into the hill decent issue, and I will keep digging into the reverse complications. I do know that the GV is turned off in reverse, but there is a spring that engages a cone clutch issue, I have heard the story a few times but cant remember exactly how it works... if for some reason I forget or am run over by a bus before I get back to you, Michael McCarthy at GV is the guy that I have been dealing with, he has helped me through this issue, and he has mentioned several times that I should not back up steep grades if possible.
They have had issues with this in the past, and this is most likely how I toasted mine since I was pretty good about avoiding all of the other situations on the not recommended list.

My shiny new GV unit arrived on UPS this morning, I will sling it in tonight, but too much salt on the roads to give her a true test for the moment.

michael mccarthy

OPERATING INSTRUCTIONS DASH/FLOOR CONTROLS These instructions are for Trucks and Motorhomes with 3 speed automatic transmissions and the Gear Vendors Under/Overdrive.
Warning – Always set your park brake when parked. The Gear Vendors is a transmission and if something was wrong with it your vehicle could move even in park unexpectedly.
Prior to operating your vehicle, acquaint yourself with the location and feel of the two newly installed control switches, which operate your GEAR VENDORS UNDER/OVERDRIVE.
A floor button (similar to a dimmer switch) is positioned to the left of the steering column for convenient use by your left foot. Along with that, a control panel is located on or at the bottom of the dashboard. This panel consists of a rocker switch (MAN/AUTO), a red indicator light (AUTODRIVE), and a green indicator light (OVERDRIVE).
The two switches, in conjunction with the column shift lever, are all that is needed to operate and enjoy the economy of overdrive, and the performance of gear-splitting. Electronics
The electronic controls installed in your vehicle to operate the UNDER/OVERDRIVE provide several significant benefits.
(1) Regardless of which condition you set the dash control rocker switch, or floor switch, or any light – the UNDER/OVERDRIVE will automatically turn off at all stops. This means that when you take off from a stop, you will always have the lowest gear possible (1st). And this feature also prevents the accidental use of the UNDER/OVERDRIVE in reverse.
(2) The electronics also control certain automatic features of the UNDER/OVERDRIVE (AUTODRIVE) as follows: the MANUAL/AUTO switch sets two operating thresholds available within the electronics, which prevents the UNDER/OVERDRIVE from engaging until the selected threshold is reached. In the MANUAL position the in-shift threshold is between 15 and 20 miles per hour. In the AUTO position the in-shift threshold is between 45 and 50 miles per hour. You set the in-shift threshold by first activating the red (AUTO) dash light. The red light illuminates any time you have selected overdrive by pressing on the floor switch. It informs you that you have not yet reached the particular threshold for the dash switch setting. When your speed increases and you reach the in-shift threshold, the red light
will extinguish and the green light will illuminate, letting you know that you are in overdrive. (3) The electronics also include out-shift thresholds of 15 miles per hour on the MANUAL side, and 25 miles per hour on the AUTO side. This allows two other significant benefits when you are driving. First, the overdrive, once engaged, will not hunt (in and out-shift), because the in-shift thresholds are so far apart from the outshift thresholds, that once you engage the overdrive it will stay in overdrive, not dropping out if you slightly reduce speed or increase throttle pressure. These threshold differences also mean that if you have selected AUTODRIVE (automatic overdrive) and later you approach a hill where gear-splitting is needed, you do not need to manually switch ranges on your dash switch. You can operate the manual control button on the floor and gear-split all the way down to 25 miles per hour. We do recommend shutting off the overdrive when you are on the manual side no later than 25mph as it is hard to hold 700psi at very low speeds and this could cause clutch wear in the overdrive. Operation Normally you will leave the dash switch on AUTO and leave the floor switch on for all of your flat land cruising. With the column selector in drive, the vehicle will go through its normal three gears (first, second, and third), and then will shift into overdrive automatically between 45 and 50 miles per hour. When you come to a stop, you will notice that the overdrive will go off about 25 miles per hour, and the red light will come on – indicating that the electronics are on, controlling the system. Auto-off
When you park the vehicle, and turn off the ignition key, the electronics will automatically turn off. There is no need to turn off the AUTODRIVE when parking the vehicle. When you come back to the vehicle at a later time, and turn on the ignition key, the system will automatically return to the AUTODRIVE condition. You should always set your emergency brake when parked because the overdrive is a transmission and if it were to malfuntion it could slip and let the vehicle roll if the park brake is not set. Passing Performance
The GEAR VENDORS UNDER/OVERDRIVE greatly enhances passing performance. Typically without the UNDER/OVERDRIVE, passing gear, or second gear, is two low to be of value at highway speeds. With the UNDER/OVERDRIVE on, simply pressing the accelerator all the way to the floor, engages “second-over” (that gear right in between second and third).
As the vehicle’s speed increases, the transmission will automatically shift to “thirdover”. When that occurs, if you are still wanting to increase speed, depress the floor switch to turn off the UNDER/OVERDRIVE in order to return to third direct.
If you happen to be cruising with the UNDER/OVERDRIVE off, and want to pass, depress the floor switch and push the accelerator to the floor to engage second-over. Climbing Grades
For the best performance on grades, you will want to keep the engine rpm between 3000 and 3500 rpm (gas engines) at all times. To accomplish this, you will use the UNDER/OVERDRIVE as a gear-splitter. Most commonly, you will be approaching the grade at highway speed in third-over; simply move the gear shifter selector lever to second gear to engage second-over. If you were not in 3rd overdrive, turn the UNDER/OVERDRIVE on and move the gear shifter selector lever into second gear. If while climbing, your tachometer, or engine speed, drops below 3000 rpm, you will want to downshift a half-a-gear to second; so depress the floor switch to turn off the overdrive. This will bring our engine speed back up to 3500 rpm. If the grade were to steep and your engine speed again drops below 3000 rpm, the next half-gear down would be first over. Activate this gear by turning on the overdrive, and moving the gear shifter selector lever down to first (in that order). Gear splitting like this on grades is a great benefit to the life and reliability of your engine and your engine driven accessories, including the transmission. No longer are you lugging and over revving the engine, or trying to maintain speed through too few forward gears. Dash Control Panel – Manual
The only time you will find the need for the MANUAL setting on the dash control panel is when you want to gear split from a complete stop. This is a very useful feature when tackling a steep on-ramp to a freeway where you will want to come up to speed quickly, or virtually anytime you are pulling out on a grade from a stop.
To use this feature, set the dash control panel on MANUAL, turn the UNDER/OVERDRIVE floor switch on to illuminate the red light, and pull the gear shift selector to low. As you take off, your vehicle will go from first, to first over, automatically, at about 20 mph. Once your engine’s rpm is approximately 3500, move your shift lever into second gear. After you hear the transmission shift into second gear, turn off the UNDER/OVERDRIVE by depressing the floor switch, and this is second direct.
Once the engine again revs to 3500 rpm, press the floor switch for second over. For third direct, move the gear shift lever to drive, wait until you hear the transmission change gears, then turn off the UNDER/OVERDRIVE (this would be third direct). General Comments
It will take a day or two to become fully acquainted to the new gear selection capabilities of the GEARVENDORS UNDER/OVERDRIVE. The best way to learn is by doing. Do not be afraid to operate the buttons, as there isn’t anything you can do that
would hurt the UNDER/OVERDRIVE. The UNDER/OVERDRIVE is intended to shift under any throttle condition – including full throttle. It is designed with a mechanical helix aiding the hydraulically actuated clutch, so that firmness is automatically dictated by torque and load. For smoothest shifts you will let off the gas when shifting into overdrive and do the opposite (go on the gas) when shifting out of overdrive. But when you want speed you will shift under whatever throttle you are at without concern for shift firmness
On steep down grades where engine braking is beneficial, this helix assists the direct drive gearing. For this reason, is is recommended on all steep down grades the UNDER/OVERDRIVE be turned off. Use your brakes to reduce your vehicle speed, then select either second or low on your shift lever to help maintain that speed with only intermittent braking.
Drain and refill the overdrive with GM 12346190 or Mopar 04874459 or Lucas Oil 75-90 synthetic or Lucas Oil 80-90 non sythethic diff and manual trans lubricant. The drain plug is the half inch 6 point bolt on the bottom pointed rearward. The fill plug (fill until it runs out the hole is the also a 6 point half inch – it is on the rear case pointed rearward about half way up the passenger side of the overdrive. Drain and refill every 10,000 miles. The overdrive holds just about 1.3 quarts new and typically just at a quart (some fluid remains) on changes.
If you ever suspect you have a transmission problem (reverse, forward or park) call our tech line first and let us diagnose that it is not a problem with the overdrive before you take your vehicle in for service.
If you have any questions on the operation of the GEAR VENDORS UNDER/OVERDRIVE, call GEAR VENDORS Customer Service Department toll free at 1-800-999-9555.

SpiceStream 01-21-2019 12:16 PM

I forgot to answer your question about acceleration.

Since I purchased my 310 with this drive-train already installed, I do not know how fast she was off the line before the gears were swapped. I will tell you that I have never lost a motorhome race. I do not feel like I am lugging off the line, obviously she was snappier before the taller gears, but I do not hold up traffic. I am hoping to make a few get togethers this year, and we are contemplating a trip to the Gulf side of FL this spring, maybe you can give her a test before you make any changes.

Smartstream 01-21-2019 12:49 PM

Curt which Cummins do you have and do you know the HP rating? My 345 has an early 12 valve, pre Dodge Ram, rated at 160 HP with the 4:56 gear and Allison 545. I haven't had it out much but been thinking about a gear change.

SpiceStream 01-22-2019 10:20 AM

I have a 1988 12 Valve if memory serves me, Pre Dodge as well, no intercooler, I will check the HP rating tonight. I think mine has slightly higher pressure Injectors than stock, but nothing major, it is not a high output engine, I have the old school VE pump. I know these things can be cranked through the roof as far as HP goes, but the fact is you are stuck with a thermal dynamic problem, when you are tossing a ton of HP at your cooling system up a long grade, you lose, slow and steady wins the race. these things have plenty of torque to down shift a gear or two, take the slow lane, and avoid a meltdown, heat is not your friend.


Smartstream 01-22-2019 04:30 PM

Thanks Curt, that gives me hope. I only drove mine about 75 miles home from the auction and the tach was cutting out so don't have good numbers to work with. The wife followed me home in the 280 with an Isuzu and GV. She was keeping up with no problem even on the hills. I certainly wasn't pulling away from her. I never thought of the 280 as being quick but I thought the Cummins might do a little better. The 345 was empty and hit the scale at 15960 lbs. and the 280 is a little over 15000 lbs. fully loaded for camping.

The highest speed limit on the peninsula is 60 mph so I have to drive over 100 miles to find a 70 mph limit. I'm now replacing all the brake hoses and I need some fresh tires before I can get on the highway to see how it does. I have been thinking about some taller gearing but was wondering what the Cummins would handle.

Isuzusweet 01-22-2019 05:44 PM

Supposedly a diesel operates at peak efficiency at whatever rpm the engine developes its peak torque at.

Keep that in mind when considering gearing, metric tire swaps, or GV overdrives and rear end gearing swaps.

A Cummins will run lower rpm of course, but not be as efficient.

Sidekick Tony

Smartstream 01-22-2019 09:07 PM

This is true Tony however actual highway driving experience helps also. Our Isuzu's make max torque at 1800 rpm and max governed speed at 3400 rpm. My Isuzu seems much happier at 2200 to 2400 rpm then at 1800. The Cummins makes max torque at 1750 rpm and max governed speed at 2925 rpm. The Isuzu torque is about 235 lbs. ft. while the Cummins makes 400 lbs. ft. My pick up is very happy at 1700 rpm down the highway but it's not moving 16000 lbs. of Airstream down that highway. That's why I'm so interested in Curt's experience especially towing a jeep. That has to be about the closest example around here to my 345.

So far I have the front brake hoses on but had to quit working on the back because of rain. I have been arguing with Kwikee about an upgrade motor, gear box and controller for my step. They want me to buy an entire new step set up. Next is tires, do I drop $3200 for good tires or go $1500 for off brand? Then I can go play. :lol:

davejay 01-27-2019 10:04 AM

When you installed your GV how did you do that with the e brake drum there. Did you replace the cable? I know the driveshaft has to be cut, does GV make a stand alone overdrive unit? What kind of oil did use apron oil changes. DJ

SpiceStream 01-28-2019 08:27 AM

1 Attachment(s)
Gear Vendor does make a stand alone unit, that is what is in my 310.
the drive shaft is cut about midship. GV used to offer a unit for the Allison 545 that sat between the tail shaft and the e-brake, but they no longer do, they will rebuild one if you have one, but they are no longer making them.

I will try to get more pictures.

As far as tires, my 310 had some new Sampson tires on the steer wheels when I bought it, I swapped all 6 out with the good ones before we went on our first trip, and have not been disappointed in that decision.

As far as towing the jeep with my rig, I would rather not.

I would say the gearing I have is suited for just the 310, or towing a lighter car, I have a 2012 Jeep Wrangler Rubicon 4 door which is reportedly 5300lbs. And if my wife finds more space, she tosses in more stuff, so god only knows what I really weigh, I never was on a scale with the jeep, but I will say, I know it is back there when I take off.

I hope this helps,


jdalrymple 01-28-2019 10:48 AM

I just got my back from the GV install. I have the stock 1990 P30 drivetrain.

My coach is extremely low miles (25k) so considering all the alternatives, I decided to go with the GV against a swap.

I haven't driven it much, as the second time out a puddle of coolant showed up on the floor.

So I pulled the AC down and removed the radiator..

Radiator cleaned and repaired, replaced water pump, fan clutch, hoses, belts, and such while they were exposed.

Waiting on a new AC dryer and will finish up this week.

But, I really liked the GV so far. Looking forward to the quieter road trips.



SpiceStream 05-04-2020 12:05 PM

GearVendor Removal
We had a "Real American Road trip" with a french family that we are very close to last summer. Wisconsin to Michigan's Upper Peninsula, to Mackinac Island to Detroit, to Niagara Falls to Boston. We dropped the french Family off in Boston and struck out for the East Coast of Canada, no plans, first stop Quebec City.

Well, the Gear Vendor Overdrive gave up again, just West of Quebec City...we limped home.

If you are not following this thread, this is the second GV to go out in under 20,000 miles...this one did not even last 5000 miles.

Gear vendors said that this was not a good application for there product, they are writing me a check for the unit and I am having a new front driveshaft built as I write this. I will miss the overdrive, but it was not reliable for me. If I need overdrive, I will swap in a different transmission.

I just wanted to finish the end of this story if any of you are still contemplating a Gear Vendor Swap.


bobmiller1 05-04-2020 01:25 PM

Yeah Curt, the gear vendor might be good for an application below 5000 lbs. but not good for ours. Personally I think the unit is a POS. If you have ever had the chance to take one apart I think you would agree with me. I forget what your application is but if it’s a Chevy you’re best bet would be a 4L85E with a US shift controller. The 370LE that I own now sports a heavily modified E4ODE with a US shift controller. I was able to cruise at 75 MPH all last summer and use the transmission as a downhill brake with no issues. The shift controller made by US shift are second to none, and the ease of installation and customer support are awesome. Any questions send me a PM. Regards, Bob

bobmiller1 05-04-2020 01:35 PM

On another note, stay away from a company called Powertrain Control Solutions, although they attempt to use knock off factory components, their software sucks. Their customer service sucks. They pretty much suck at everything they do. How do I know this ???? I wasted 2 months of my time along with the transmission builders time (Diesel Site) in Florida trying to make their lousy system work in my 370LE. Kevin at US shift took hold of our problem and sent me what I needed within 1 week, most enjoyable summer I have ever had. It’s real nice to be able to stay with traffic at 75 MPH when you have to. So basically in a “Nutshell” PCS sucks and don’t use them......just my opinion, Regards, Bob

1987_345 05-05-2020 10:54 AM

I really wish I had put a Gear Vendors unit in my 345 back in 2009 instead of the unit made by US Gear. It worked fine but the module quit in 2018. I was able to find another one on ebay last year, but now it's gone out. Since the parts are no longer available, I'm left with it in low range....

jhenry 05-05-2020 10:59 AM

So the best would be to change tranny to a 4L85E was looking at gear vendor? thanks Jonathan

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