Denman Overdrive

[Gordon Maney]

Your first link is bad.

[maineSS]

Yes, you'll have to Google maximum-overdrive auto transmission parts...

[Doc Dave]

Have you got the overdrive operational yet? If so how do you like it?
I really like mine; have had zero trouble once I got the ground issue solved as well as running it on greater than 8 volts (it prefers 12!).
Much more drivable now on the highway as now I have a "5th gear", but I still have my lower gearing which I have found the 230 really needs. I wanted my truck to be close to original, but now I know why people say the 230 is "gutless" haha.

[maineSS]

I went up to the vintage salvage yard today and found a pile of NP 205 T-cases from various years of Ford, Chevy, and Dodge. Two of the Chevy and Dodge units had some parts taken off, and better yet, the Chevy had the fine spline output needed for the Maximum Overdrive adapter shaft, while the Dodge had the coarse 10 spline shafts which hopefully mate with the PW yoke for the front output- got to check shaft dia.

The T cases also had the 8-bolt retainers that bolt up to the NP 200 case. The yard owner was willing to let them go quite reasonably, so we'll be able to see fairly quickly whether my mix n' match plan for using the Maximum Overdrive casting will work out. This would be the factory way of doing an OD conversion, hopefully it doesn't hit some nasty little snag.

As far as the 230 being "gutless" is concerned, some induction, valve, and cam work might surprise certain people. The biggest challenge is getting the gearing to work with the 230's torque curve, and bringing that curve up to the 1800-2000 rpm level.

[maineSS]

Well, I have some good news and some bad news. I found that the 10 spline input on the married 205 T-case fits the PW Yoke. However, after spending most of the day dropping a divorced case from a '68 Dodge truck, I found that the front output splines on the yoke were fine- didn't count them, but they look in the 30-32 range.

If I end up using the entire input/output assembly in the NP 200, I'll have to see if the slip yoke in that Dodge will mate with the PW front driveshaft. If our world is perfect, the 205 rear gear cluster will mate up with the NP 200 front cluster- but that's probably asking too much.

When BrightRanch did his 201 swap into the 205, he ended up losing Neutral in the T-case. I'm wondering if I use the entire 205 cluster and shift rod/fork if I'll lose- or possibly gain Front Drive without having to drop the rear shaft.
The 205 T-case options are 4 Lo, Neutral, 2 Low, 2 Hi, with 4 Lo being all the way forward, according to the diagram on the shift knob (as I remember).

[maineSS]

A correction to the 205 T-case shift options in the last post- it goes 4 Lo, Neutral, 4 Hi, 2 Hi. Now for a look at the rear output shaft & bearing retainer of the NP 205, one of the world's toughest T-cases. I took this one off another unit instead of the divorced case to see if some other ideas would work. If they do, then using both shaft assemblies of a divorced case wouldn't be required, which would cut down the parts search tremendously.

Pic #10 shows the 205 retainer/yoke assy- it weighs 25 lbs, real steel here. Pic #12 shows the retainer top with the yoke removed, notice the big ball bearing that supports the shaft. The 205 uses a this bearing retained by a circlip, and a race of needle bearings at the other end to support the shaft instead of two tapered roller bearings like the NP 200. It seems to work OK, and doesn't need shimming. Pic #13 shows the other end of the retainer, you can see some of the needles in the race, and some more on the paper. Also visible inside is the speedo drive gear. (Continued).

[maineSS]

Pics # 13 & 14 show the 205 and 200 U-joint yokes. In pic #13, the 200 yoke on the right appears longer, but the splined section is not (2"). In pic #14, the 205 fine spline yoke on the left appears to have greater shaft dia, both shafts are actually 1 3/8" OD. The 205 32 spline is stronger and doesn't wear as rapidly as the 10 spline 200, however.

Pic # 15 shows a side view of the 205 rear shaft. What I'm going to look at is seeing if it can mate with the 200 front output shaft, or if the 200 rear output shaft can be modified to work in the 205 retainer. The 1st possibility would give the best of all worlds, as it would allow use of the Maximum Overdrive sleeve coupling for the OD. The 2nd possibility would require getting a partially splined coupling broached to fit the 10 spline 200 shaft. If none of these work out, then it's on to transplanting the entire 205 input/output assy. This would require a slip yoke for the front driveshaft that can accept the 205 U-joint. I brought home one of these yokes to compare to the PW shaft, we'll see if it fits...

[Gordon Maney]

You are doing great and fascinating work.

[Matthew Ziegler]

idea

the overdrive is a great idea, but has anyone thought about mounting it between the trans and transfer? seems like a lot less work even if you have to move the case back and get the driveshafts cut otherwise it's 3 rods and a speedometer cable

[Doc Dave]

Matthew,
The problem is that there is not enough room with the flatfender power wagon or M37, the overdrive is maybe 18 or 20 inches long. You could not move the t.c. back enough for it to work.
I agree that placed there would be ideal, then you would have overdrive in aLL situations if desired. But, with lockout hubs inactivating the front axle, I use the overdrive in high 2WD, which is really the only time I need it. So behind the tc works o.k.

[maineSS]

The primary advantage of mounting behind the T-case is in keeping T-case temp and gear wear down by not overdriving the gearset. The NP 200 has real heat problems in many (but not all) cases when shaft speeds get over 2500 rpm under load.

[maineSS]

After travelling 555 miles in journeys to the Vintage Yard, I thought I'd do a progress update.

(1) It's not possible to mate NP 200 driveshafts with NP 205 driven shafts-
the shaft pilots and clutch gears are completely different.

(2) It's not possible to substitute the NP 205 input shaft assembly into the
driveshaft side of the NP 200 case. Even though it will fit, and the gears mate, the fixed gear on the NP 205 input shaft would engage the front axle all the time. Also, the large gear on the driven shaft is free to rotate unless locked up, unlike the NP 200 gear, which is fixed. To get selectable 2/4WD in the 200 case, you'd have to grind the teeth off the 205 input shaft, permanently lock up the 205 driven shaft gear, and use the 205 shift arm and clutch collar. This is doable, but the early model divorced 205 input shaft is very rare, and costs around $400 NOS and $300 for an import version. It does have the 10 spline end used by the PW yoke, however, and the 32 end spline on the output shaft required for the coupler used in the Maxiumum Overdrive conversion. Probably not an option for too many people, but I'm keeping it in reserve if all else fails.

(3) I ran across the NP 202 T-case used mainly in International 3/4-1 ton 4WD trucks. This t-case had a PTO port on the driver side, and was the direct ancestor of the 205. It's a direct-drive version of the 200- if you had to build a 205 with 200 parts, this is how you'd do it. The early version (1950's) had a weird spring-loaded gear on the driven side, the later version (60's-early 70's) had a fixed gear like the 200, and used the 205's ball/roller bearing retainer casting.

Pic #16 shows the spring-loaded gear of a '54 202. I can't figure out what advantage such an intricate gear confers- apparently it didn't work out in real life. Pic #17 is a closeup of the spring feature. Pic #18 shows the face of the early 202 gear vs the later 202 gear. If something looks "different" about the two- you're right. New Process decided for some odd reason to cut the teeth on the new gear in the reverse direction and at a 15 deg vs the 30 deg pitch used in the 200 t-case. Then, in the 205, they went back to the 200 style gear- go figure. To be continued...

[maineSS]

Moving on with t-case history, Pic #17 shows a side comparison of the early/late 202 gearshafts. The early shaft uses the thrust roller bearing retainer of the NP 200 case, while the late shaft shown in pic #18 uses the ball/Torrington needle bearing retainer of the NP 205. Both shafts have the 10 spline pattern of the PW yoke, which is a problem for the Maximum Overdrive sleeve.The retainer castings are slightly different (pic #19), but have the same bolt pattern and shaft dia/lengths to fit either 200, late 202, or 205 gearshafts, provided bearing types are accomodated. The perfect part would be 200 gearshaft with the ground boss for the 205 Torrington bearing and a 32 spline end- which is forbidden to exist, of course. The late 202 gearshaft has the wrong cut and pitch, so it's not an option.

It may be possible to grind the boss of the 200 gearshaft for the Torrington bearing- I'm presently looking at that, since New Process likely did the same for their late 202 shaft. That still leaves the question of the 10 spline end.

It would be possible to use the NP 200 retainer if a way to preload the thrust bearings can be found. Otherwise, the NP 205 retainer has to be used. The NP 200 yoke is used for bearing preload, which means either the coupler or the seal retainer would have to substitute. One way would be an adapter splined internally for 10 splines, and also splined externally, which would serve the preload function of the yoke. The coupler would have to accept the external splines and then neck down to the 32 spline dia of the overdrive unit. Another coupler would have to be made as a tightening tool for the adapter. Lots of machine work here. to be continued...

[Matthew Welcher PWA]

I am wondering how this is going? Is it still proceeding?

Is the Overdrive unit Installed now?

[Dodgekcl1935]

very interesting thread. would be great to know how it all went.

Cheers