A Tale of Two Transmissions?

[blackf3504dr]

Originally Posted by Carl Bice

Do you know where or who to check with on an overdrive unit? being an ex semi driver, I keep thinking about a splitter on the rear axle? but not sure if that is even possible on a motorhome? Or Feesible.... Just a thought?

The two speed rear ends I have driven were a low and lower gear, haven't seen any that employ an overdrive type gear.

[Burban]

Blackf2504dr, gearvender.com just to let you know they start around 2 grand!

[Mr_D]

Originally Posted by lonestarace

Replaces the tailshaft housing.
Gear Vendors under/overdrive transmissions the most awarded auxiliary transmissions.

We installed one in a 17' Type B MH. It had the 460 and towing package. Didn't make any noticeable improvment in mileage but the lower rpm at cruise was nice.
My guess is that it wouldn't make much if any improvment as the OP would be overgeared and it wouldn't pull it easily. Might even lose mileage unless you changed the axle ratio too.

[fleamarketer]

Whaooo.STOP THE PRESSES!!!If you talking about a stock 700R4 behind a 454,the answer is no.BUT if your talking about one that is modified for use for a RV and a 454 it is every bit as tough as a 400 with the bonus of a o/d.That is the facts.And if you want something that is even tougher you move on to the 4L60E with stand alone wiring and programmer and one step beyond that a 4L80E.There are options.The old school would lead to believe there isn't and that is just not true.

Read my ref thread and link supplied for 700R4's.

[Burban]

Flea marketer, I under stand that some may say a 700r4 built would hold up but in the long run it would not keeping it cool and not hunting back and forth between 4 and 3 would also be an issue. The 700r4 became the 4l60e the 400 became the 4l80e, the 400 was developed when a heavier duty unit was needed for the large GM cars and trucks of the mid to late sixties and ( with big blocks such as the 500's used in the caddy's) throw the sevenths and used up till the early 90's so as it goes metric 250=200r4 small cars 350=700r4=4l60e mid size cars and 1/2 ton pick ups 400=4l80e large cars and trucks over 1/2 ton also GM gave heavy duty units a different number 4l80e standard 4l85e heavy duty same with the smaller 4l60e. As I have read and bought built units from monster I would never recommend to someone to under size a transmission. So hope fully we can help our fellow R/V's out with their choice and guide each other with our experience.

[pwf16129]

before you get excited over an overdrive no pun intended you need to ck into the gear ratios, most cars and trucks that run a 700r4 use a higher gear in the rear end and the trans has a lower first gear and a small overdrive for the final gear. to give you a clearer idea with a turbo 400 the rear gear would be a 3.73 he same rig with a 700r4 it came with 2.73. if you put a 700r4 in you would have the take off like a 4.73 and the top end just a slight over drive.
unless you change your rearend gear you won't gain enough to ever pay for it.
i looked into a gear vender over drive they are $3000 plus so unless you drive a lot it would only make the rv easier to drive due to better gear splits but be hard to justify.love to have one just would never pay for it's self in my application.
good luck with your mh

[Mr_D]

Originally Posted by pwf16129

before you get excited over an overdrive no pun intended you need to ck into the gear ratios, most cars and trucks that run a 700r4 use a higher gear in the rear end and the trans has a lower first gear and a small overdrive for the final gear. to give you a clearer idea with a turbo 400 the rear gear would be a 3.73 he same rig with a 700r4 it came with 2.73. if you put a 700r4 in you would have the take off like a 4.73 and the top end just a slight over drive.
unless you change your rearend gear you won't gain enough to ever pay for it.
i looked into a gear vender over drive they are $3000 plus so unless you drive a lot it would only make the rv easier to drive due to better gear splits but be hard to justify.love to have one just would never pay for it's self in my application.
good luck with your mh

Yep, you just validated what I said earlier.

[Burban]

Pwf16129, you ring& pinion idea is not right, I own and 87 pick up 454&400 R&P 4:10 , 91 sub with 350&700r4 R&P 3:73 ,92 sub 454&4l85e R&P 4:10, 03 Tahoe 4l65e&3:73 had Astros with 4.3 and 700r4' and with 4l60e's all with 3:73 so having a taller first gear does not indicate lower ring and pinion gearing, most new truck with six speed autos come with 3:08's or 3:42's first gear is 4:02:1

[bcbrowne]

What you will find out without changing your rear end gearing that the 700r4 will be geared to high to use overdrive with stock rear end gears from t400. I built a kit car an H1 hummer on a suburban frame and running gear that had a t400. Installed a striker motor a a 700r4. Could barley get into overdrive except on very flat highway and down hill. This from experiance

[Burban]

bcbrowne, looked in to that truck kit as well, what size tires to you have on it, that would have been one issue. If you put anything over 36's changeling R&P to 4:56 or so would put all back in the right power band and rpm, I'm a wheeler as well. Most Motorhomes have 4:56 or higher R&P gearing it's the only way to get them moving so depending on the weight and size so adding an overdrive trams would help to some point. So if you could gain 1 to 1 1/2 mpg over long term use would pay off when moving a brick down the road at 65 mph.

[fleamarketer]

A 4.56 R&P with the small port/peanut valve 454 grunt(torque) and a 700R4 O/D will be fine.Built enough of them to know that.Can supply the rpm formula if needed.It's right at the beginning of the torque curve.

[Burban]

I understand all of that but why not just start out with a trans that is already stout to begin with, also knowing that every one drives differently trans life will very, just like the statement their no replacement for displacement!

[Phobos]

Well, the 700r is most strong enough if built properly, and any truck equipped with one would have a lower rear end ratio than one with a 3 speed.
Take it from a guy who has done this swap in older vehicles and just go with the THM400 you already have. It's a lot of work to swap them over and when you go modifying things like that you lose the reliability of the vehicle.
With that said, I decided to change my 4.10 ratio out with a 3.73 mated to a thm400. In the end I am pleased with the small but noticeable fuel mileage gain, and no real big loss of power.
If I where you, I'd rebuild the 400 and consider a one-step higher rear end gear ratio.
I would think that 454 would do ok with a taller gear, it didn't seem to hurt my little 350 all that much. Or you could just fix the 400, and drive a little slower and forgo the whole thing!

[Carl Bice]

Originally Posted by Burban

there's no replacement for displacement!

This statement is where all this research has been leading me, it looks like more HP is what i am looking for after all, IF I ever get the money to do it, I think a larger displacement motor is what I need, to get what I am looking for. The reason I am researching this is not just for fun, as it stands the DW is wanting to travel an extreme amount... and putting a lot of miles under us.. we are basically taking our part time hobby, and doing it fulltime, not sure if many of you know about it, but We go Geocaching alot, the entire family loves it, and this is why we got the MH we got, Size, and mobility.. We were doing it in a tent set up, and we needed more room, so now we are here with a MH. And the Kids are finally all out of school, so we are going fulltime, and I just want the MH set up as best I can get it, with both reliability, and fuel economy, I have most of the exterior done, and now I am working on the interior, and drive train, and after reading all of these responses to my original question, I am leaning toward just rebuilding the 400 in it, and just using it as is, well aside from already lined out improvements, such as electronic ignition, and exhaust upgrades, and Tire size changes, I think I might be good for a bit anyway, at least till we come into a boat load of cash to spend on it.. Thanks everyone for the great advice..