I have just completed my first trip in a RV that I bought in August,2014, I drove from NE Indiana to NW Florida about 1700 mile round trip. The RV is a 26 and a half foot Class C on a 2000 Chevy Express 3500. I knew that I should not expect much in the way of MPG, less than 10 mpg, and I was willing to accept that as “the cost of RVing” ,but the noise of the transmission dropping into 3rd every time I had to Speed up on the highway, is something I Would like to figure out how to avoid. Anybody know how to get an Overdrive transmission retrofitted into a 15 year old RV? Any thoughts on a reasonable budget? I would also love to put an airbag suspension on this beast. I live in Indiana and am positively ashamed of the State of our (IN) highways! I drove thru 5 states-Indiana had the Most expensive gasoline and the worst, by far, highways. Rock19
Welcome to the SDMB. There are a few professional mechanics who frequent this board, but I’m not sure if they have the expertise you’re looking for.
Good luck!
I don’t see how an overdrive transmission will stop the vehicle from shifting down a gear when accelerating or climbing a hill. A modern 6 speed overdrive transmission downshifts frequently when on the highway when you encounter things like hills or passing. That’s the way they are designed to work.
It’s my unprofessional understanding that cars drop into 2nd/passing gear when the accelerator is pushed to the floor due to a cable that links the throttle body to the transmission. I don’t know anything about your transmission, but there may be an actual cable that you could remove that would prevent it from shifting when you accelerate. However, you’re going to have a helluva time speeding up when you need to if you disable that.
If you do some googling for ‘kickdown cable’ or ‘kickdown rod’ or just kickdown you may find what you’re looking for.
you already have an overdrive transmission, likely it’s the 4L80E. 4th gear is overdrive.
As my friends have pointed out, any thoughts on retrofitting a modern 6 Speed transmission to a Chevy 454 engine?
I’m not sure how the ratios would behave in an RV bit this is an 4L80E 6 speed automatic tranny for big/small blocks up to 850 hp.
6 speed auto 4L80E that can handle up to 1000 hp.
It can be done, it all depends on how much you want to spend.
I don’t think changing to a newer 6 speed transmission is going to accomplish what you want. To help prevent the transmission from downshifting on grades or accelerating you should look at the gear ratio of the rear differential.
Some RV’s put too high (lower numerically) of gearing in to try and scratch out every mile per gallon possible on the road. This higher ratio forces the tranny to downshift upon acceleration or climbing a grade.
The good news is that it is much easier to change the differential gears than to retro fit a new transmission. First thing is to determine what the gear ratio you have. If you have any factory literature from when the RV was new this info is no doubt listed with the engine and transmission specs. I’m showing you could have the 3:42, 3:72 or 4:10 gearing depending on how it was set up when ordered. I’m guessing you may have the 3:42 set up. Changing to the much lower gearing of the 4:10 would be an easy retro fit using factory parts. You could go even lower to 4:88 by using some aftermarket gears.
But understand there is no free ride in physics. Lowering the gears is going to result in higher engine revolutions per minute (RPM’s) which will lower your fuel mileage.
To me, happy motoring in a RV means not fighting the equipment all day. Pulling our fifth wheel trailer could be done with a lot less pickup than what I use. But I like the power and control that a powerful engine/ transmission/ rear end gearing combination gives you.
A change to the factory available 4:10 gears will make your rig much more drivable at the expense of one or two miles per gallon. You don’t get into RV’ing for fuel mileage. Most any Chevy dealer or good indy mechanic could change the gears for not a whole lot of cost. Especially when compared to retro fitting a new tranny.
nope. they’re all electronically controlled and you’re going to have to do a lot of custom electronics hardware and software to make such a thing work.
not that it helps you now, but for future reference, vehicles this size are really meant to have diesel engines.
I agree with the others that this could well just be normal behavior for a vehicle this size with a gas drivetrain, but a really touchy kickdown could also be something like a vacuum leak or simply the engine needing a tune-up. Is there any indication this rig is current on plugs, filters, etc?
Generally, early automatics had a kickdown cable or rod, then most of them went to a vacuum-controlled system (which had the advantage of working off engine load, not just throttle position), but now most transmissions are electronically-controlled, so the computer decides when to shift down depending on the input from various sensors. I would guess the transmission on the OP’s RV is vacuum-controlled.
There is absolutely no question that a diesel would handle towing better and get better mileage, but… diesels are way more expensive to buy, maintain, and repair. For an RV that’s only being used for weekend getaways instead of getting crazy mileage put on it, a big gas engine is probably the more economical choice.
it would make more sense than buying a gas-powered beast, then look into spending thousands on changing the transmission.
That is true, and a big part of the reason why people pay the big premium for diesel RVs and tow vehicles is because they don’t like how hard it feels like a big gas engine has to work, which seems to be the issue the OP is having. But the idea that you “need” a diesel to pull a big vehicle isn’t really true, nor that the diesel will be cheaper to run (at least with US fuel prices.)
One option is a GearVendor’s overdrive/underdrive unit. It’s basically a small planetary 3-speed transmission that bolts up to your regular tranny in place of the tailshaft. While it is almost the price of a transmission, it’s much easier to instal.
It’s a bit unclear what the OP has and wants.
If the transmission is making noise when it’s down shifting; that is something only a professional transmission shop can deal with - and you’ll have to find one that can accommodate an RV.
If you (OP) don’t like the engine noise when the RV downshifts… I think you need to adjust both your driving style and expectations when driving the RV.
I also second the nomination of ensuring the vehicle is ‘in tune’.
I think you’ll get more specific answers by asking an RV forum.
I once had a similar problem with a new truck. This was just a standard 12 tonne truck with two axles and a manual six speed gearbox. The driver complained that “It wouldn’t pull the skin off a rice pudding”. I took it out and I found that I had to downshift at the slightest incline, and even when diving into a moderate wind.
The supplier had a look and they discovered that the manufacturer had put a differential meant for a bus on it. Once that was swapped, it was fine.
Yes if the differential is wrong, the gears can be too far apart and so when you are forced to change up, you find its stuck at a really low RPM with no pickup from that and you drop back on the hill.