72 Wagoneer -- should I add overdrive?

[marmoset]

Hello,

I just picked up a 72 Wagoneer 360 + TH400 + (D20 i think), which is in excellent shape. Runs like a top, but on the highway it just does not sound right -- very high rpm's at 65+. I think all is shifting well (1st thru 3rd), and its in 2wd HI.

I do the majority of my driving on the pavement -- perhaps I should be looking into an overdrive to save wear and gas ? Or have I overlooked something -- the kickdown seems to be electric, which has me wondering.

Thanks,

Mark

[frozen]

Welcome to the board.

I am the proad owner of a 72 J4000 360+TH400+D20 and I can relate to the whole high RPM issue. I attribute my high RPMs at highway speeds to low gearing and small tires. I don't know what sort of gearing you have in your diffs but 4.11 gears and small tires will wind your truck right out. Nothing can beat you out of the hole though.

There are a couple ways to get an overdrive. There is a unit that bolts on behind the tranny I think (probably waaaay off her but I am sure someone will correct me) that will change your ratio. Another option is slapping new gears in your differential, or you can simply buy some beefy tires. If you are running 36's I bet you won't be winding your engine out at 65.

All TH400's that I know of have an electric kickdown. I think that the kickdown point as well as the shift points are adjustable, but if you can feel all 3 gears then the kickdown isn't a problem. Unless of course you have your foot to the floor at 65 because then you would be in a lower gear and that would most certainly wrap the ol engine up.

Anyway enough of my rambling. Welcome to the board, enjoy yourself, there are a great bunch of guys here.

-Frozen

[dharmabum]

Howdy and welcome to the board, I've got a 72 as well with the same tranny/transfer case. I would check what gears you are running in your rears. There should be a tag on the front and rear diff covers. I have 3.31s and 32 inch tires and can cruise pretty comfortably at 75-80mph. If you have 4.11s or so and stock tires this could be your problem. The cost of an add on overdrive is way too high to make it worthwhile. Are you planning on lifting it, bigger tires etc...? There may be other ways to lower your RPMs and build up your rig at the same time.
Oh yeah got any pics?

[letank]

make sure that your "D'" position is a real "D", may be the adjuster slipped..... and you are in 2.....

"D" should engage a about 25 mph

Michel
74 wag

[mark j]

I have a '72 as well- 360, T400, D20, D44 rear with 3.73's. Gas mileage is best when I stay under 55mph. I have a donor wag- '78 with 3.07's that I am thinking about swapping in but I like the low end pull of the 3.73's. Been considering a T700 4sp or even a 4L80E 4sp auto so that I will have the best of both worlds.

[Peter Matusov]

I drive a '68 with 350,TH400, D20, and 4.30 in the axles. the tach says 4000 rpm @ 65mph - so I never go over 70.

[Serious Johnson]

Mark:

Depending on your truck's final drive, you may not see better fuel mileage with an overdrive. Old-school non-lockup slushboxes like yours (great tranny, just not economical) can end up drinking MORE fuel at road speed due to converter losses at lower revs. You probably would benifit a touch if your axle is a 3.73, maybe not if it's a 3.31, and you would almost certainly lose some fuel economy if it's a 2.72.

:-

[The Anti-Chrysler]

You could drop in a GM TH-700R-4 with a bellhousing adaptor, and use a stand alone torque converter lock-up setup, but it would cost alot of money, and you would likely either have to swap your transfer case, or get an adaptor to fit it.

These rigs were just designed at a time where gas was cheap, so there wasn't a need to keep the revs down to get better fuel mileage. I think alot of speed limits were around 55 as well, as opposed to 65 nowadays. It adds up.

[marmoset]

Thanks for the welcome, and all the excellent suggestions. I'll check the rear end out this weekend -- if it ever stops raining...

I know the the tires will need to be replaced anyway, so I just as well consider lifting the body before I plunk down $$ for good tires.

If I did this I would not really want to get too far away from stock (for now!) -- so if I do decide to lift for 32" tires -- what is best kit with enough clearance that will still let me fit into the office parking garage ?

Thanks,

Mark