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Old 11-22-2017, 10:45 AM   #1
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1983 31' Airstream310
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Gear Vendors Overdrive is toast

Well, I had a brand new Gear Vendors Overdrive installed in April 2015 in my 1983 Airstream 310 MH. The MH has the Isuzu Turbo Diesel Engine that was installed by Airstream when it was new that replaced the 454 that all Chevy P-30's had when they were delivered.

Back in March of 2015, I had researched the idea of installing an overdrive, since that little Isuzu straight 6 Turbo Diesel screams at 3,000 RPM at around 60 MPH. The gearing in the rear of the MH by the way is either a 5.38 or a 4.56. So, by putting an overdrive unit in seemed like a great option. I paid $3,300 to Gear Vendors and had it delivered to my local mechanic where he installed it for $630 labor.

Skip to a month ago when I was driving on I-84 between Boise, Idaho and Pendleton, Oregon, when the Gear Vendors overdrive kicked out of the overdrive gear and would not go back in. After arriving home, I made plans to take it back to the garage for repairs. The mechanic, after phoning Gear Vendors, was told the electronic module went south, so I bought another one at around $200. The new module was installed, plus a new speedo gear on the tranny side was installed too. They thought the problem was solved, until I got to the shop to pick up the MH. After driving it down the street, I did notice the green light indicating the OD unit had kicked in, but the overdrive unit itself did not kick into overdrive. I took it back to the shop where my mechanic, once again got on the phone with Gear Vendors. They led him through several other tests, but nothing has helped. I called Gear Vendors also, and they told me that my unit was out of warranty and the problem was most likely the overdrive unit itself. So, the rep at GV also told me that their unit does not like certain diesels, especially straight, inline six cylinder diesel engines. As of now, I have poured almost $5,000 into this and it only worked a little over 2 years and around 24,000 miles of occassional use. GVendors rep also said that I might not have operated the overdrive correctly. As of right now, I don't have a clue as to what to do about this other than just changing out the rear drive gear ratio to something like 3.73's

So, has anyone experienced any of these problems, or has a Gear Vendors Overdrive? I will accept all comments.

Thank you,

Russell, in Olympia, WA.
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Old 11-22-2017, 11:01 AM   #2
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My first impression is Gear Vendor is blowing smoke. It has been over 10 years since I had a GV in one of my older TV but the comment that they don't like certain diesels sounds like smoke to me.

The GV is after the transmission and isolated from the engine by the convertor so how can they claim the engine is a cause.

I do remember the speedo, they used Ford speedos when I had mine, was a common problem with erratic issues. The GV itself is expensive part but it is almost a completely mechanical device and short of exploding I would assume rebuildable.
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Old 11-22-2017, 11:11 AM   #3
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I hope all this can be resolved without a loss of $5000.

I have a 280 diesel and have considered the overdrive myself. This is an upgrade out of my budget for some time but am anxiously curious if things can turn in your favour with perhaps inexperienced representatives or mechanic
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Old 11-22-2017, 11:24 AM   #4
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To be honest I was less than pleased after getting mine installed to read the small print in manual and find out they have a 3000mile/12month suggested oil change/service frequency!
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Old 11-22-2017, 11:25 AM   #5
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I would get a hold of Smartstream as he lives in the Seattle area and has a 280 turbo diesel with a gear vendors. Maybe he could help.

A very knowledgable fellow is Dan aka Smartstream.
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Old 11-22-2017, 12:03 PM   #6
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Well that whole situation stinks! The GV rep sounds full of it but what to do? I would second Tony's suggestion of communicating with Dan, he's got mad skills and knowledge.
I don't recall seeing very many of the CLASSIC TDs equipped with the GV unit here on the forums. A handful if that, so resources may be few. I'm guessing that motorhomes are a significant % of GV sales so keeping us happy should be important to their bottom line. Hang in there and bird dog it, they can do better than that at GV.

Mike
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Old 11-22-2017, 01:02 PM   #7
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The only possible reason I can think of as to why it "doesn't like certain engines" is the amount of torque that some engine can generate. I assume the Isuzu diesel engines have a fair amount of torque so I wonder if the gear vendors unit just couldn't handle the Isuzu engine's torque.

Sure seem's far fetched to me.

Brad
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Old 11-22-2017, 02:06 PM   #8
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We found out early in the Cummins Dodge community that the GV wouldn't live long.

Many of us -- myself included -- wanted a second overdrive with the NV-5600 six speed manual. Solo cruising, or an empty open cargo trailer. Lowest reasonable rpm for fuel economy. I'd have changed rear gearing and tire height. Shot for 30+ Mpg at 58-mph.

The one by US Gear was said to have been better, but production stopped some time ago. OD automatics were pretty good by early 2000's and sales had dropped. Far more diesels, and far fewer big block gasoline.

Guys with my truck and interest have shifted to 7 & 9 speed Eaton-Fuller Roadranger non-synchro manuals. Won't break (unlike 5600 when towing heavy; 30-35k combined), but needs fabrication help to install and use. From 16, 17 and 18" tires to 19.5 commercial. And re-geared. Well above five grand parts cost with careful used buying and DIY.

Goes without saying there's no pleasure in reciting this.

.
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Old 11-22-2017, 05:01 PM   #9
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Personally I think the Gear Vendor is a POS. I believe that it is also used in VOLVO cars or was.....enough said. A rear end ratio change is by far the least expensive option, but will suffer on the low end. The best option in my opinion for what it is worth is the investment in a transmission change with overdrive.....actually about the same money (investment) but much better results.....just saying, Regards, Bob
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Old 11-22-2017, 09:24 PM   #10
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Quote:
Originally Posted by bobmiller1 View Post
Personally I think the Gear Vendor is a POS. I believe that it is also used in VOLVO cars or was.....enough said. A rear end ratio change is by far the least expensive option, but will suffer on the low end. The best option in my opinion for what it is worth is the investment in a transmission change with overdrive.....actually about the same money (investment) but much better results.....just saying, Regards, Bob
There was a lot of talk on more than a few forums questioning the durability of Gear Vendors for a few years. That talk has diminished over the past couple of years, so maybe their quality is getting better. It is unfortunate that Gear vendors isn't helping out with parts or advice, but that's what you can expect from a company with a checkered past.

As for changing your 4.56 to a higher ratio or adding an overdrive transmission, it's kinda tough with our diesel powered beasts; too high an overdrive and they'll bog down and you're shifting down like crazy all the time. Touch the diesel and down the transmission goes, which means a rebuilt transmission, sooner than later.

It would be real nice to put a 7.8L 300 hp 6 speed Allison instead of the band-aids that we add, like Gear Vendors, or my U.S Gear, but that's a pipe dream.

I do love dreaming though..........

Cheers
Tony
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Old 11-22-2017, 10:54 PM   #11
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Sorry for chiming in a bit late but I had to run into Seattle today to pick up a new double oven set so I could have turkey tomorrow. The old one kind of smoked itself on Saturday, put on quite a light show.

Speaking of smoke I think Tony and Mike might spreading a bit around also.
That being said I do have a GV behind my Isuzu and I probably put close to 60,000 miles on it before I smoked a clutch and had to send it in for a overhaul. I should add that I bought the unit used so I have no idea how many miles it has seen. The overhaul/exchange was about $1200 but I don't remember for sure and I'm too tired to walk out to the moho to look it up.

The unit was designed and sold by Laycock DeNormanville and used in Jags, Volvos, Austin Healy, Triumph and many other cars. GV bought the name and rights to manufacture. This is a simple explanation of how it works that I came across some time ago. "In the Laycock overdrive unit, the annulus was mounted on the output shaft of the unit and drove the propeller shaft and the planet carrier was splined on to the output shaft of the main gearbox. The sun gear was mounted on a sleeve which slid over the gearbox output shaft and splined to the sun gear was a cone clutch. The cone clutch was used to engage or disengage the overdrive." There is an eccentric washer on the front of the unit that drives a oil pump that provides pressure to engage the cone clutch.

The unit does have angle cut gears that help hold it in overdrive and GV recommends disengaging overdrive going down grades as the gear cut pushes the sliding unit the wrong way causing excessive wear. The Sprague clutch can be damaged if you try to back up in overdrive.

As to Russell's unit I wonder what the oil looked like. If the clutch was burned, it would be obvious in the oil. I also wonder if a pressure test was done to verify pump function. The guys at GV have always been helpful to me but I have no idea what went on between GV and Russell's mechanic. It would be interesting to have more details.

I don't believe the Isuzu has anything to do with the situation. And Brad, the hp and torque numbers are not very impressive, it is not much of a powerhouse and the BAE turbo only puts out 10 psi of boost so as not to harm the normally aspirated engine.

If Russell is interested I have a couple of Laycocks in my shop if he would like to see what is inside.
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Old 11-23-2017, 11:52 AM   #12
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Quote:
Originally Posted by bobmiller1 View Post
Personally I think the Gear Vendor is a POS. I believe that it is also used in VOLVO cars or was.....enough said. A rear end ratio change is by far the least expensive option, but will suffer on the low end. The best option in my opinion for what it is worth is the investment in a transmission change with overdrive.....actually about the same money (investment) but much better results.....just saying, Regards, Bob
Totally agree with this guy! The probable reason that the Gear Vendors doesnít like ďsome dieselsĒ is that the power impulses from them is much stronger. I remember when GM first produced the 350 diesel. I believe every one of them had to have the flex plate replaced with an updated/much stronger one before about 40,000 miles. This is also the issue of why diesels in aircraft have not caught on. They are or were having problems with the props holding up to the sharp power impulses. A GM 4L80E with a after market controller I believe would be the best way to go. GM used these for years in the diesel pickups. Maybe a beefed up 700R4 but you may have to do some research to see if they have proven. Motor On!!!!
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Old 11-23-2017, 01:41 PM   #13
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There is no doubt a lot to be said about diesel power impulse. In the case of our little Isuzu's, they still have the original very heavy flywheel in addition to the GMC flex plate that helps to absorb some of that impulse. I don't recall anybody here having a flex plate fail other than myself but mine was due to mis-alignment. Also the TH 450/475 doesn't have a lock up torque converter so I would doubt the GV sees much of the impulse at the rear of the trans.

It would be interesting if somebody came up with a flex plate with a spring loaded center dampener like a clutch disc. It would be easy because the Isuzu starter ring gear is on the flywheel not the flex plate so a clutch disc with holes to bolt to the torque converter is all that is needed.
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Old 11-23-2017, 02:01 PM   #14
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poor performance of the 4L80e with a TCI controller behind my 12 valve Cummins is why I bit the big $$$$$ bullet and put a Allison T1000 6 speed in. Works like a charm. Was not cheap, but what's $10G here and there.
My big problem with the 4L80e was heat and TCI. Had a cooler in front of the radiator, one behind the right headlight, and one under the radiator before it would stay cool.
The TCI controller was obsolete when I bought new from TCI. Only one guy at TCI know anything about the unit I had. Tried for over a year to get hold of him. He never was there and him voice mail box was always full. Their new unit may be fine, but I'd never buy anything TCI.
Just my personal experience with the company.
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