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transmission information for Chev truck

1

1946 BN IHC

Member
We recently bought a 1983 winidago class C BUILT on a 1983 Chev chassis with a 350 ,5.7 engine. We took two "short" trips with it. The engine is carberated, with a form of electronic ignition, cap and rotor with no points.
The thought is to replace the 3 gear transmission with a 4,5, or 6 with overdrive.
I was just talking with our mechanic; his comment was that there would be a lot of gear shifting as one drove along the highway.
HERE ARE THE PARTICULRS FOR THE UNIT.
TOTAL FULL POUNDAGE, 8000
STANDING POUNDAGE 3 TO 50000
ALUMINUM MAIN BODY SOME WHAT ARODYNAMIC WEDGE SHAPED FRONT.
Present fuel milage about 11 mpg.
Rear end 3:37
TIRES 950 X 16.5 SINGLE REAR.

QUESTION
For those who know auto mechanics, power and transmition what would be our best or better choises?
Wm.(email open)
 
Is it presently a stick or an automatic? We had a 350 in a '71 Chev pickup, and it seemed to get 10 MPG no matter what we did- empty or loaded, fast or slow, level or hilly. I don't think you'll see much change in mileage, if that's what you're looking for. Even if you get 2 more MPG (which would be optimistic, I think), do some math and see how many miles you would have to drive to pay for the thousands you will spend to have it converted.
 
In my thinking I would leave it alone.
The chassis most likely has the Turbo 400 3 speed Trans.
Which is bullet proof.
The gear ratio is fast enough allowing it to cruse comfortably.

If you were to try a od unit or trans. you will have to change the Rear ratio to a slower one.

I also think your weights are a little lite in reality.
Not to mention the wind resistance.

Your MPG is already decent for what your doing.

Now the 350 is a Good engine but small for that application.
If it was a big block(454) then I would go for a OD and gear change.
Just what Me thinks
Tom
 
(quoted from post at 00:14:45 11/07/18) We recently bought a 1983 winidago class C BUILT on a 1983 Chev chassis with a 350 ,5.7 engine. We took two "short" trips with it. The engine is carberated, with a form of electronic ignition, cap and rotor with no points.
The thought is to replace the 3 gear transmission with a 4,5, or 6 with overdrive.
I was just talking with our mechanic; his comment was that there would be a lot of gear shifting as one drove along the highway.
HERE ARE THE PARTICULRS FOR THE UNIT.
TOTAL FULL POUNDAGE, 8000
STANDING POUNDAGE 3 TO 50000
ALUMINUM MAIN BODY SOME WHAT ARODYNAMIC WEDGE SHAPED FRONT.
Present fuel milage about 11 mpg.
Rear end 3:37
TIRES 950 X 16.5 SINGLE REAR.

QUESTION
For those who know auto mechanics, power and transmition what would be our best or better choises?
Wm.(email open)
Click to expand...
The 700R4 would be the easiest and cheapest to adapt to your application. The 4L80E is heavier duty (like a TH400), but would require an aftermarket controller. I'd bet the money involved with either of these would scare ya.
 
I also would leave it alone,if you change any part of the drive line,like the gear ratio your power will suffer and your gas mileage will probably get worse,you probably have the best gear ratio for mileage in it right now,if you try a over drive trans.you will lack power when going up hills and it will be down shifting more and your mileage will suffer.If it ain't broke-and in your case it isn't-don't fix it!
 
3.37 is high for a class c.. 3.52 would be better in my opinion.

There is a tailshaft" overdirve that is popular with motorhomes and rv's as most come with very very low ratio rear ends... like 4.11 or 3.73... Your rear end could actually be too high ESPECIALLY with a 350 cu in engine... I would be looking at long trips, low power, and running hot in the summer time before moving forward as you may be lowering ratio to get more power.
 
I know of a little larger motor home that had a Mopar engine and a torqueflite. It had 19" (?)rears and the owner put a 2 speed truck rear axle with 20" tires. I have ridden in it and it worked great. Get to a hill and just downshift the 2 speed. I also know of a chevy 1 ton automatic that had 16" rears and the owner put a 2 speed under it with 17"rubber. The 2 speed came out of a D-500 Dodge truck IIRC. He pulled a gooseneck hauling tractors and machinery. With a little digging, 2 speed rears can be found for fairly reasonable price.
 
Leave it alone. I have a 97 GMC 2500 4x4 with 4:11 rear ends It can get 15 mpg with babying it along put my camper on it and its 9-11 mpg. If you changed anything it will cost big $$$ and the truck will be 0ld before its paid back.
 
. Have a full manual shift TH700R4 built with a HD lockup torque converter. The torque converter could be manual operated but wired to pressure switches that block operation in 1st and maybe 2nd gear . And maybe a position switch on the throttle that unlocks the TC at 3/4 foot pedal .
Is there a functional cruise control ?
 
If you're looking for more lower gears you'd have to change the rearend gears. If your looking to lower crusing rpms to save fuel. I think your not going to get it. Those gears with those tires is pretty steep as it is. What is it running now for rpms at crusing speed like 70mph.
 
My 8,300 gvw Pu will get 10 or 12 mph pulling a trailer. There is no way to pull a trailer(about the same weight as your MH) and use the overdrive. You will just burn up the transmission,they do not like it when they shift in and out of OD(heat) The exception in my mind is a Gear Venders OD unit,not cheap, but a great reputation.
 
A 700R4 is about the poorest choice you could make. It is simply too weak for the weight and profile of the vehicle.
A 4L80E would be a better choice, but you will be getting into some money there. Even if you get a core transmission from a salvage yard, have it reconditioned, and get the controller to operate it, you will spend a lot of money. Not hundreds, but thousands.
Anything with more gears will get even more expensive - like an Allison.
And, the end result may not be satisfactory. Spend a ton of money, get about the same fuel economy, and be totally disappointed in the bargain.
Keep in mind that a vehicle with a large frontal area like an RV will benefit more from driving slower than it ever will with changing the transmission. Also note that a 5.7 liter engine is a bit marginal for an 8000 pound vehicle. It might turn out to be afraid of hills.
 
Thank you to each of you for your words of direction. I may inquire about a 2 speed rear end and do more research, if or if not it would be of assistance.
Thank you again.
Wm.
 
(quoted from post at 21:55:31 11/06/18) A 700R4 is about the poorest choice you could make. It is simply too weak for the weight and profile of the vehicle.
A 4L80E would be a better choice, but you will be getting into some money there. Even if you get a core transmission from a salvage yard, have it reconditioned, and get the controller to operate it, you will spend a lot of money. Not hundreds, but thousands.
Anything with more gears will get even more expensive - like an Allison.
And, the end result may not be satisfactory. Spend a ton of money, get about the same fuel economy, and be totally disappointed in the bargain.
Keep in mind that a vehicle with a large frontal area like an RV will benefit more from driving slower than it ever will with changing the transmission. Also note that a 5.7 liter engine is a bit marginal for an 8000 pound vehicle. It might turn out to be afraid of hills.
Click to expand...

The later versions of the TH700R4 with the updated shaft size and improved clutch drum is perfectly satisfactory.
A deep low gear, over drive and the biggie, a lockup torque .
 

That's a good combination no reason to mess with it unless you need/want more power. A 350 are a 400 trans will be all it needs no need to lug it I don't think you would be happy otherwise...
Enjoy it feeding it is just part of the deal...
 
I have a e3500 chevy van 5.7 4l80e trans 3.55 rear. I get 16 mpg it's not even a raised roof. So 11 mpg with yours is good. You can buy a lot of gas for what it would cost to replace the trans
 
What fuel mileage are you hoping to achieve?

A 35 year old RV does not have much resale value. Upgrading the power train may not change that value and may not improve the fuel mileage by enough to matter. I would drive it a year to be sure you actually like this RV before sticking any money into it. If you need to store it outside in the off-season, are you sure there are no roof leaks?
 
With a carbed engine I doubt going to an overdrive is going to help your mileage at all. Carbed engines lose a lot of power when the RPMs drop off - to really gain anything you need to go to at least a multiport fuel injection system and an overdrive transmission. Then your mileage will probably get to 13-14 MPG at best. If its running good I wouldn't touch it - to be honest 11 MPG isn't bad for the size of vehicle you are running down the road. Keep changing the transmission fluid every 30K and save your money.
 
I'd leave it alone. If you get one of the below suggested overdrive autos they recommend you do not use the overdrive if towing. Running that big rig down the road will be like towing with a pick up.
 

Your not going to gain much with a two speed axle other than hill pulling power. Most all two speed truck axles have low gearing which will require you to run big tires to get the overall ratio anywhere close to what you have now. Does the RV have wheel wells big enough to allow tires several inches taller to fit, then you'll need taller front tires to level out the rig as well.
The thing that would help you the most is a lockup convertor, but they only came in OD transmissions and you'r gearing is to high for a OD trans.
That rig should have a Turbo 400 trans, the OD version of a Turbo 400 is the 4L80E. A good 4L80E with stand along controller and regeared axle will cost thousands.
A 700R4 and it's replacement the 4L60E are light weight car and 1/2 ton pickup transmissions, they are short lived in heavy rigs or towing.

My advice is to leave it alone and enjoy it, you never save enough in fuel cost to justify the price of the conversion, if you plan to tow with it you need to upgrade to a more powerful RV, that 350 engine is going to be over worked.
 
(quoted from post at 22:58:31 11/06/18) Thank you to each of you for your words of direction. I may inquire about a 2 speed rear end and do more research, if or if not it would be of assistance.
Thank you again.
Wm.
Click to expand...

Do what YOU want.

I bet most of naysayers paid a hefty premium to buy their new diesel powered 4x4 dually pickups.
And then drive it less than 10k per year, have never towed with it and have never had a use for the 4x4.
 
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