I need information about over/under add on units for trans.

Mr. D · 08-28-2007, 02:38 PM

I have my rig ('88 345) in the shop at Jackson Center, Oh. I'm having them repair the damage from a blown right front tire to the aluminum skin(see earlier thread for pictures) while its in the shop I'm having them check out the electric brakes in my tag axle and what they referred to as an over/under add to the transmission ... what many people refer to as a gear vender. I need to find out from those with brakes working in their tag axle if they have ever had an occasion to notice the difference between having tag brakes and not having. Mine are currently disconnected ... I'm not sure if they would make a big difference .. particularly in the mountains. On another note I have something the mechanics at Airstream called an over/under add on unit(maybe a gearvender?). I don't think it is working completely. It may be stuck off or in over drive all the time... is there a way to test those units? I have a new trans but the guys at that shop did not know much about the unit ... they thought it had been disconnect from the controls. It seems like my rig has plenty of top end ..I can cruise at 70 and not go over 3000 rpms... the guys at Airstream thought a normal trans would be over 4000 at that speed ... is there anyone with experience (a 454 Banks power pack system 3 speed trans) ... with or without a gearvender add on ... that could give me some feedback on what the operation of rigs with and without these over/under units should be? Mr. D.

swebster · 09-01-2007, 06:46 PM

My 345 with the TH475 tranny runs at 3000 rpm at 65 mph. A few other members have installed the CV over under and it drops about 400 - 500 rps at highway speeds.

Have you contacted Gear Vendors about this unit? They might have the manuals and troublshooting guides to help you check everything out.

str8strm · 09-01-2007, 06:52 PM

I would guess that if you are running at 3000 rpm's your over under is stuck in the off postion. I've got the Gear Vendor unit and we never get close to 3000 unless I forget to engage it. Ron

Mr. D · 09-04-2007, 12:59 PM

It sounds like I may be stuck in overdrive? As I excellerate, I may get to 2800 but never over 3000 rpms while going through the gears ... seldom do I go over 2500 rpms while cruising... I normally run at 63 mph ... but on the rare occasion that I push 70 mph or beyond I don't notice any limits and my rpms at the most may reach 2700 rpms ... Question? When you drop your gear vender into low for a hard climb does it add another gear range below the standard 1st gear? Does that low range make as big a difference as overdrive does at the high end? I guess since my rig has been running great I don't know how to measure the benefits ... but than again I have never driven it out West. I just made a short 500 mile run from Jackson Center, OH. through and around Michigan ... and pulling my Tracker I felt no difficulty at all during the worst climbs. Thanks for the feed back I need to make sure my Over/under add-on is actually a gearvender and not some other unit ... from that point I can researching my specific unit. Mr. D.

GlenCoombe · 09-13-2007, 08:17 AM

If your over / under, maybe Gearvendor, unit is working you should be getting progressive shifting through the gears when the unit is on. That means you'd get six gears. The unis give you in effect 1st, 1st over, 2nd, 2nd over.. and so on. This keeps you in the sweet spot for climbing but does not give you an underdrive on 1st gear with a GV.

Lido&Linda · 10-23-2007, 03:15 PM

I use my tag brakes going down hill and on ocation when have to stop quick,I find it helpfull.