3spd auto too revvy: Gear Vendors or 4spd auto?

[Nordby]

Hi Folks, My brother and I are considering options for his 3spd auto D250 (1989). He is on the highway a bunch, trying to do 75-80mph, and it just doesn't work with the 3spd. He has 3. 07 gears in it.





What is a reasonable approach to this, econmically of course, but to do it right as well. Are folks putting in 2nd gen autos and controlling the O/D manually?Do the US Gear and Gear Vendors units solve this problem and shift OK (no banging between gears, etc)? Seems this is the easiest, least intrusive solution.



Another obvious solution is an NV4500 or NV5600 I suppose, but that is a fair amount of cost and work.



Thanks guys,

jon

 

["Mad Max"]

Jon -



First off, good questions. Second, long answers, but I'll give you my perspectives, and the other choir members will chime in to give theirs.



There are several options, all good, and all not cheap. First off you could get a later 1st gen transmission (A518/46rh) with the non-lockup converter and the overdrive, or second upgrade to the 47RH or RE (A618) with the overdrive and a lock-up converter, or third bolt up a gearvendor (or other similar, US gear, etc) OD to the back of the transmission you already have.



There are several factors to consider, the biggest being weight, towing needs, and engine power. With the 3. 07's you'll already fighting the accelleration issue, and even with big power the transmission will suck up most of the abuse trying to get to speed. Once at speed you have great top end until the engine runs out of rpm's. If you're towing big weight you'll probably want to go to taller gears, either 3. 54's, 3. 73's or 4. 10's depending on your needs. Doing so however will lower your top end and you'll definitely want an overdrive. If your engine has good power either OD will work good providing it's in good shape and you have a very good (not stock) converter, regardless of lock up or not. Noone that has a stocxk converter, especially in the 1st gen transmission's, really likes the torque loss from the converter - it just bleeds away a bunch of the engine power and the rig just slows down. Most folks upgrade to an aftermarket converter, and there are a lot of options and previuous threads to search on.



I'll give you a description of what I'm doing and why, and you'll have some comparison data to consider. I'm building a big, and I mean LARGE rig, and it'll be between 7000 - 8000 lbs all by itself. I'm also going to be hauling 10,000 lbs worth of trailer/toys, so my combined gross vehicle weight is going to be between 18,000 - 20,000 lbs. That's a LOT, and it means I need a few particular things: Big power, bulletproof transmission with lockup converter, overdrive(s), tall gears, and without a doubt an exhaust brake. I took the worst case scenario for my travels and built backwards based on that. My truck is a 1st gen, but I am swapping to a 2nd gen (47RE) transmission that will be built bt DTT (read- bulletproof), a DTT overdrive, and 4. 10 gears to get it all moving. Now, I'm also adding a GearVendor OD to the back of the transfer case so I can split gears and get a double overdrive. This will give me a very good top end (I like to be able to go fast... ), and with the power upgrades the engine will be faster than me. So, that's about the meanest drivetrain setup I could design, and it will never break, won't get necessarily hot because I'll have lock up, and I can use the exhaust brake to keep it all from flying off the edge of the highway going downhill. I'm basically building an RV.



All that said, my opinion is if you're going to swap the transmission to a newer version, I think you'd be moneywise to go to a 2nd gen with lockup, do the mods necessary to accommode it, and you'll have a great transmission, especially if you swap out the gears. If you want to keep the gears, the gearvendor is about $2700, uninstalled. I think you could get a 2nd gen transmission in your truck for around $4k. A 1st gen A518 OD transmission isn't too bad, probably for around $1500 after a rebuild and good converter.



Most economical approach, prolly the A518, rebuilt and good converter. Second, GV od on the one you already have, and third go for the lock-up converter with a 2nd gen transmission. DTT may have a good price for a good transmission without the big dollar guts. Not sure what a rebuilt 2nd gen transmission costs, but someone else in the choir will know. With the second gen transmission you'll need an electronic control module to make it work, and again the guys at DTT will work you through it. Ask for Bill K - he's a good dude and knows his stuff.



Either way you're going to have at least $2000 for a good swap, but you will definitely not regret doing it.



Woah, I wrote a book.....



- Sam

 

[Nordby]

Thanks Sam, I really appreciate the insight!



18KGross is huge! Especially up and down the hills! Sounds like the exhaust brake will keep you lined up, and your transmission is going to get you up the hills. I tow horses and tractors around a bit, but rarely no more than 9K on the trailer so my gross is several tons less than that!



The truck in question is not a tow rig, though carries tile and tools to lay floor covering. Tows occasionly to bring material to the jobsite, but mostly just gets itself around. Thanks for the info!



jon

 

[TKingsbury]

The one drawback I see with the gearvendor is you can not compressoin brake with it. You must disengage it or use your brakes. If you try to go down a grade using the engine to hold you back you will burn up the clutch. You also can not start off in O/D, it wont engage until approx 35 mph. The US gear O/D seems better since it is gear driven and you can start with it engaged and you can compression brake with it. These are observations I've made looking at two friends trucks that had each.

Travis. .