Overdrive questions for a 152/D18

[Toby Dahl]

I've read some talk about overdrives lately and it sparked my interest. I found a link to Herm's Overdrive and found that I can still use my PTO if I installed an overdrive. Until now I didn't know that. I also did some searching to find out more about how they operate and perform. I found a lot of advocates for them, but no real figures on MPG, top speed, etc... Here are my questions:
1. How much will it improve my MPG (152, T90, D18, w/4.27 diff)?
2. Will it increase the top speed? Currently most people don't like to take their 80 over 55 with the stock set-up of gears and such. Will the overdrive allow for 60 or 65?
3. What are some opinions about cost v. reward? Is this thing really worth a thousand bucks?
4. Are there any known obvious obstacles for the installation?

I think that's enough for now. I can't wait to see what your guys' experiences have been. Thanks.

Toby

[Scott L]

Toby, I can't speak on the Scouts, but I did have the Warn OD in my 1960 Willys CJ-3B w/ D18.

I bought the Warn OD unit new, in order to make the Jeep more road friendly. The gear ratios in the pumpkins was a stout 5.38:1, great for off road crawling, but the thing was dang near topped out at 45-50 mph! The 25% OD dropped the effective gear ratio to 4.04, which made highway travel much more acceptable. The Jeep had the original equipment 134 cid Hurricane 4 banger and T-90 3 speed.

Have no recollection with regards to fuel economy change. Obviously, it had to have helped some.

Reward...in my case a definite yes. Although I did battle my Dad on it, as I was living at home at the time and I think he had qualms about seeing me spend $700 (this was in 1980) on the Jeep. His argument was I was trying to make it something it was not. He had a point, but it was my only vehicle, and I hated getting passed by everyone.

I would kinda wonder about how effective it would be in a Scout 80 with 152. I guess my thought is that if the 80 had a gear ratio of 4.27, it would effectively change that to 3.20. Just wonder if that would be a good gear with any kind of decent sized tires and the 152. Hopefully someone with hands on experience with the exact specs can chime in.

I'd say go for it. I thought it was the coolest thing having 4 gear levers sticking out of the floor of that Jeep. If your PTO unit is lever operated, that would be 5!

[racerboy9]

I have one on my Jeep FC150 and it makes it a much nicer ride. When you are in overdrive the gearbox quiets down a lot. Great on a long flat stretch and around town. I am putting one on my '64 S80 very soon. I am putting in a 196 in the not too distant future and the added horsepower will help. I think it is a wise investment if you would like your Scout to be a little more user friendly. Gas mileage will probably improve a little on a long trip but I wouldn't get too excited about big improvements. The Scout was made when you could get gas for $.17 a gallon which seemed ridiculously cheap even then.

[TBD]

Jensers probably knows better on the 152 and the O/D. But I have heard that making 65mph is a long wind up. But 20 mpg is suppose to be in the zone of reality.
My 196 is slightly modefied, In O/D the engine is ticking over at 2500 rpm and I get 16-17 mpg at 70 mph on a flat freeway. Around town I get 13-14.

I have 32" tall tires and the 4.27 gears.

[Jensers]

Well - when I still had the 152 in my rig I didnt have the OD. With 4.27's and 31's I had no problem at 60-65... I now have the 196 and so I am not much help.

Jamie in the club has a 152 and an overdrive. He really loves it... Just remember that the power of the 152 is limited and the OD will not do you any good if you are building a big rig with big tires. So it depends on your rig and the desired outcome. Bigger tires are like adding an OD. You are not currently driving the scout correct? An OD is something that you can always add later if you find that you are unhappy.

Hope that helps...

[Toby Dahl]

Thanks for the help guys. Although my scout is in pieces, I'm always looking for ways to improve it once it's done. I plan on having 31's so I guess 60-65 is already within reason. I know with the 235/75s, 65 MPH was pushing the little guy pretty hard. I wonder if 31's, 4.27, and an OD would make it realistic to cruise at 70? Jensers, you are correct that my scout is not on the road, and I don't plan on doing anything with an OD until after everything else is in working order. I don't need to add to my list of things to complete. The only reason I would add the OD in the future would be to increase my top speed for freeway cruising.

[MJL]

I had a 152/t90/d18 in my Scout, geared with 4.27s and 27 inch tires. I could do 65 on the flats, give or take on the hills. Later I went to a 35 inch tire. Never figured out the effective ratio, but the top speed dropped considerably to around 40. Never figured my mileage, either.

With my experience, I always wonder why guys ask how they can get to 60mph? Will it just not do it, or what?

[Toby Dahl]

It will do 60, but the engine will be revving pretty high. I'm more interested in how it would perform with an overdrive.

[TBD]

This is a website that I like to play with gear ratios to tire size to RPM to MPH.

They have it set up really well and easy to utilize to compare the relationship to each above.

I used this extensively to determine what tire size would be optimum with what I had planned to do.

www.4lo.com/

[TDemarco]

I had 31" swampers with the 152, 4.27's and O/D. Cruising at 70 is a stretch. I always found it was hard to get up to a good cruising speed because my 152 didnt have enough guts. Going downhill was fine, but Scouts have a LOT of wind resistance. Also remember that these things werent designed to go over 55 mph. Ill try to avoid sounding like the crazy old man preaching at the parts store, but remember that you should also consider how stable a 40+ year old vehicle will be at 70 mph. I know stock brakes aren't the best even at low speeds.

[Toby Dahl]

Originally Posted by TDemarco

I had 31" swampers with the 152, 4.27's and O/D. Cruising at 70 is a stretch. I always found it was hard to get up to a good cruising speed because my 152 didnt have enough guts. Going downhill was fine, but Scouts have a LOT of wind resistance. Also remember that these things werent designed to go over 55 mph. Ill try to avoid sounding like the crazy old man preaching at the parts store, but remember that you should also consider how stable a 40+ year old vehicle will be at 70 mph. I know stock brakes aren't the best even at low speeds.

I don't really want to cruise at 70. I was just reading up on O/Ds and it sounded intreging. Do you think the O/D was worth having? What did you like/dislike about it?

[pondscum]

Originally Posted by Toby Dahl

I've read some talk about overdrives lately and it sparked my interest. I found a link to Herm's Overdrive and found that I can still use my PTO if I installed an overdrive. Until now I didn't know that. I also did some searching to find out more about how they operate and perform. I found a lot of advocates for them, but no real figures on MPG, top speed, etc... Here are my questions:
1. How much will it improve my MPG (152, T90, D18, w/4.27 diff)?
2. Will it increase the top speed? Currently most people don't like to take their 80 over 55 with the stock set-up of gears and such. Will the overdrive allow for 60 or 65?
3. What are some opinions about cost v. reward? Is this thing really worth a thousand bucks?
4. Are there any known obvious obstacles for the installation?

I think that's enough for now. I can't wait to see what your guys' experiences have been. Thanks.

Toby

1. Yes. My mpg is 16 around town and over 20 on flat highway driving. It is about 1 mpg less each in my turbo equipped 152 with the warn. The turbo has the same rears...4.27

2. Yes 60-65 is likely with a good running rig and it won't sound like it is about to explode. The T152 will go 70mph easy but it sucks down gas and likes to overheat as they are want to do.

3. No not worth a thousand but if you can get one for 300-400 and have Herm rebuild it for a couple hundred go for it. he guarantees his work.

4. The biggest issue for installation is the proper spacing between the OD gear (essentially the bullgear...the OD gear drives the case) and the transmission. The tolerances are in the thousandths between nominal operation and grenading it. Herm will hold your hand and walk you through it like he did with me.

4a. The other obstacle is if you are removing it from another gearbox/tc setup to put into your rig...you must follow the proper steps for removal or you will pull the guts out of your T90 or whatever donor it is hooked up to.

[TDemarco]

One thing I like most about my O/D is when Im wheeling. I know a lot of guys want it for road driving, but being able to split between 1st and 2nd in 4lo has advantages. I found I could always find a perfect gear with the use of the O/D.

[charlesa]

Just saw your post regarding OD. I have a warn in a 62 scout/152/4.88s/31's. I also like it more for off road as you can split all the gears. Don't like it on the highway as my setup seems to run out of power real quick in OD. Haven't noticed any change in gas millage.........still uses a lot on the highway.

[kingkonger708]

"The other obstacle is if you are removing it from another gearbox/tc setup to put into your rig...you must follow the proper steps for removal or you will pull the guts out of your T90 or whatever donor it is hooked up to."

My transmission is shot (152/D18), but it had the Warn OD which I really liked. I've got a replacement and am swapping the Warn OD into my new D18, and had trouble taking it off. Definitely not a "bolt-in" - my Warn OD is on the floor of my garage completely dissassembled...

Anyone have a schematic or advice on how to swap it into my "new" D18 from the old one?

MUCH APPRECIATED!

[Oregon80]

Call Herm.

[71mtnscout]

I live in the mountains and 2nd/OD is more useable than 3rd. 25-35 mph is the norm around here and in 2nd it screams and 3rd is to low of rpm to be any help. I have 4.88's and really havent done any highway so I cant help you there, but it gives you alot more gear choices with the mismatched T-90 ratios.

[pondscum]

Originally Posted by kingkonger708

"The other obstacle is if you are removing it from another gearbox/tc setup to put into your rig...you must follow the proper steps for removal or you will pull the guts out of your T90 or whatever donor it is hooked up to."

My transmission is shot (152/D18), but it had the Warn OD which I really liked. I've got a replacement and am swapping the Warn OD into my new D18, and had trouble taking it off. Definitely not a "bolt-in" - my Warn OD is on the floor of my garage completely dissassembled...

Anyone have a schematic or advice on how to swap it into my "new" D18 from the old one?

MUCH APPRECIATED!

http://www.hermtheoverdriveguy.com/id21.htm

hope this helps, it worked for me