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I agree but I wouldn't be complaining about 13mpg, that is my mileage pulling a trailer of any size with a frontal area, using my modern 16' RAM. Advantage comes when not towing 20 MPG.Hi Kevin
Thank you for the reply
Introducing computer controlled technology into my old Chevy sounds a little over the top
A six speed typically has at least one over-driven gear with 5th usually being 1:1, with some having two overdriven gears with 4th being 1:1. Since you already have 1:1 in third, and don’t want overdrive, swapping to a 6 speed (if its even possible) would really only net you one extra gear, closing up your ratios a bit which might improve performance under some conditions, but since you wouldn’t be using over-drive much, probably wouldn’t improve your MPG, which as Kevin said, isnt all that bad anyway. And if you did want to improve mpg a bit, an OD unit (such as a Gear Vender OD at around $3200) would do it for you and would be a fairly easy job.Hi Everyone
I have a 1979 351 G30 Coachmen Surrey, in the UK
I get about 14 mpg out of my 3 speed automatic gearbox, does anyone have experience of installing another one, say 6 speed?
I am aware of overdrive upgrades, but would like a lot more
Thank you
Tony
Thank you for thisIt would cost more but if it were me I'd be looking for a "4L80E". Not only will you gain a fourth overdrive gear but they are WAY tougher than a 700R. 700R's are pretty iffy in half ton trucks if you ask me. 4L80's can be found in 7.4 liter 20, 000 pound class A's over here. And they work fine I don't believe the factory put any 700R's or their electronic successor, the 4L60E in any truck or van that is rated as being a one ton like a G30. They evidently didn't think they were robust enough either.
To use a 4l80E, among the other changes, you would have to buy the standalone computer and harness that makes it work without a factory computer. Those run right at $500. Not a cheap undertaking all told and I doubt you save enough in fuel to pay for all that. Even knowing your petrol is a LOT higher in price than ours.
Part of my shopping criteria when I was looking for my older coach (1993 model) was that I wanted it to have overdrive. It does. Spends a disappointingly small amount of time actually in it, but it's there.
Whatever you get you will need to make sure it is not computer controlled. That of course is unless you have the ability to program the controller.Thank you Kevin, Rich
The more I investigate this, the more I am learning
Currently I have a TH350 gearbox, the later generation of Chevy has the 700R4 gearbox, which will bolt straight on with a reduced prop shaft
This will give a top ratio of 1:07 which is equal to 6 speed boxes that I have seen
Now I need to find one and get it shipped to the UK