Denman Overdrive

[maineSS]

I heard the Denman was available again, so I contacted Dennis Gronan and bought one. I took a pic before the battery died in my Sony, when it recharges I'll post more as I get the unit installed.

Pic #1 shows the unit with M37 flanges at each end. They appear to be out of phase, I'll have to see if the mount on the end can be re-indexed properly.
The manufacturer's tag shows this one was made under license by GKN, a large OEM supplier to car companies and various military forces. There appear to be several "J" type Laycock overdrives with different case configurations, Dennis uses the one found in Volvos (240 Series). I'm presently looking for a Tech Manual. More when my camera flash revives.

[JStinson]

Very nice!

I'm planning on posting a thread about my build, but I got a call today that my M37 engine was done with the first phase of the rebuild. All that's left is the short block rebuild and it's good to go!

Sorry to hijack, but I'm really excited.

[Tom Petroff]

There are manuals and a lot of tech. info on line.
Try google Laycock od.
Here's one that I use

http://www.odspares.com/

Also gearvendors uses a exact copy of the laycock.
some info on ter site as well.
They will never admit that there's is a copy.
TGP

[maineSS]

It's beginning to look like quite a bit of extra design and fabrication is going to be needed to get things up to speed. The biggest consideration is driveline phasing (or lack of it) between the t-case and diff when the unit is in the non-overdrive mode, since the two joints can move independently. More on this later. Also, the rear adapter was rather scary- definite redesign there.

[iranch]

driveline phasing

If the OD unit is mounted correctly, on the same plane as the transfer case, there is no need to worry about the phasing between the the input and the output. You have two separate drive lines and they are both in phase if they are installed correctly.

In OD the input and output turn at different speeds, in order to synch the in and out when you shift back direct you would have to have a gear setup that would only engage in one of two places, very complicated and not needed.

No divorced transfer case is set up this way. In fact they have three independent drive lines that are never in complete synch with each other, but phased to themselves. If phased and the angles are correct, the first u-joint puts an oscillation to the drive shaft, the second takes it out. the input into the next gear box is thus smooth and the out put is smooth, the next u-joint puts another oscillation in which it's mate takes out resulting in smooth input to the next gear box, you could go on and on into infinity with this and never have to worry about phasing the gear box in/outs to each other.

If your rear drive line is short and you want to mount the OD at an angle other the the same plane as the transfer case, then you have a problem. The input to the OD would not be smoothed and would cause problems.

[Tom Petroff]

It's beginning to look like quite a bit of extra design and fabrication is going to be needed to get things up to speed. The biggest consideration is driveline phasing (or lack of it) between the t-case and diff when the unit is in the non-overdrive mode, since the two joints can move independently. More on this later. Also, the rear adapter was rather scary- definite redesign there.

Iranch has it correct on the phase issue.
I missed that earlier.

No way you will ever keep them in phase and not needed.
Also I would not be too concerned about the U-Joint yoke either.

Of course if you can improve on it do so, but mine has been in service for over 6 years now without a problem of any kind.

When mounting the unit the OD must be straight L/R, and on the same plane as the T-case.

TGP

[maineSS]

It looks like the unit hangs at the same angle as the driveline, judging by the front mount. I haven't tried to figure yet what the driveline angle would be with the unit mounted parallel to the ground, but the resulting angle might be greater than recommended for a U-joint.

Right now it's looking like the idea is to use the front end u-joint as part of the driveline, and the rear as a shaft connector. This could work if it doesn't experience any angle changes, and is perfectly aligned with the diff/t-case driveshaft plane. The only downside would be shorter u-joint bearing life due to no bearing rotation, but this would be cheap compared to the alternatives.

It's not commonly known, but shaft vibration due two out of phase U-joints is twice as bad that on a shaft with a single joint. A shaft driven with a single joint must speed up and slow down twice per 360 deg revolution, even with a constant rpm input from the driving shaft, resulting in noticeable vibration. Two properly phased joints on a shaft cancel this effect out, resulting in a constant output to the driven unit.

Two improperly phased U-joints on a driveshaft beat seals, bearings, and gearbox internals up in a hurry. With the independent motion between both ends of the planetary gearbox, out-of-phase U-joints are guaranteed, so any deviation from perfect alignment of the "connector" U-joint will cause some effect. Normally, diff pinion angle changes on power application, the rear axle moves up and down to follow terrain, etc- and this overdrive doesn't float with the driveshaft, being frame-mounted- hence my concern.

Insofar as the rear flange adapter is concerned, I intend to get in touch with Dennis to see if he's changed fabricators- hopefully what I got is a one-time thing.

[MoparFreak69]

In OD the input and output turn at different speeds, in order to synch the in and out when you shift back direct you would have to have a gear setup that would only engage in one of two places, very complicated and not needed.

This is exactly what I was thinking. The only time the would be in phase in OD is maybe every 5th revolution or so? When in OD the driveline will be spinning the fastest (when you are trying to obtain a higher top speed -vs- just trying to lower engine RPM for the same speed) which would mean the problem would be more pronounced in OD. It just doesnt make sense to have them in sync because you would never be able to take advantage of the OD feature of the unit.

[maineSS]

I got in touch with Dennis and cleared up some things. It seems my flange was drilled incorrectly, which spaced the bolt holes too far out- the bolt pattern on the OD flange is rectangular, not square, and orienting it the other way allows more metal thickness. He's sending me a revised flange, so I'll post comparison photos so OD owners can check their units and see if they're correct. I may go ahead with my welded adapter ring, since I believe in wretched excess.

The U-joint between the T-case and the OD is meant to be a connector, so if it stays straight in both planes, phasing is necessary only for the rear OD U-joint and the diff U-joint. If the front OD joint angles, it will start acting like a U-joint again, and phasing will become a concern. A double cardan CV-type joint might help with flex-induced angularity here, I'm going to talk with some driveline shops to see what they suggest.

The unit is meant to angle down at the same degree as the T-case, so fitting the mount will have to conform to the individual truck. My front OD mount looks like 10 deg, my T-case appears to be 7 deg down...

[maineSS]

Here's a pic of the rear flange as originally received (pic #2). Not a whole lot of metal left to handle the 1152 lb-ft of torque 1st gear generates at 1:1 (2257 lb-ft @ 1:1.96). Although a reinforcing plate has been welded to the top, the hole is close to the edge also (pic#3). Part of the saddle has been ground away (pic #4) along with the Allen bolt head to hit the bolt circle on the Overdrive flange (pic#5). (Continued)

[maineSS]

When the drive shaft is turning, one pair of bolts is going to be acting on the "strong side" of the holes with lots of material thickness, and one pair is going to be acting on the "weak side" of the holes with no metal thickness (pic 6). The blue pen indicates the "strong" holes (diagonal axis), the black pen indicates the "weak" pair of holes.

Dennis sent me a redrilled flange which allows more metal around the bolts, and doesn't require metal removal on the saddles or boltheads (pic #7).The reinforcing plates wern't welded on, maybe that's optional? (to be continued)

[maineSS]

I see pic #6 & 7 didn't make it, here they are. The bolts along the axis of the blue pen are turning into solid metal, while the bolts along the axis of the black pen are turning against the weak area of the holes.

Pic 7 shows the redrilled flange, note the difference in metal thickness around the holes. No need to grind clearances for the allen bolt heads either(pic #8). (Continued).

[maineSS]

The reinforcing plates haven't been welded on, but that's ok, because I'm going to weld up the new holes and proceed with my weld-on ring plan for the rear flange. It will be the same dia as the front flange, and 5/8" thick to allow direct bolt up of an unmodified M37 companion flange. Pic #9 gives an idea of the dia size, and pic# 10 shows the difference in bolt sizes. One of my reasons for doing this is to avoid having nuts on the backside of the OD flange hit the OD mount- this interference on my unit is what started me looking closely at the rear M-37 flange mods. The supplied locknuts were too tall to clear the enginemount, even though it had been relieved by grinding.

I've also been looking at the front T-case coupling design. I spoke with Wood's Driveline and High Angle Driveline, both of whom recommended changes. I found another possibility in a casting offered by a West Coast firm that allows the OD to bolt up to an NP 205 with a custom input shaft and coupler- which is the way it was originally designed to do by Laycock. Now supposedly, the NP 200 gearset is the same as the 205's, and the retainers also bolt up. What I'd like to do is see if the 205's input/output shafts could be substituted for the 200's on the drive side of the T-case to allow this adapter to bolt up. If this works out, the adapter would replace the 1st housing, plate, and front shaft/flange of the present unit, and would likely shorten overall length by 5-6"(look at Pic #1 and imagine...). Cheap- No. Strong- absolutely.

[Gordon Maney]

Great thread.....

[maineSS]

Pics of the NP 205 adapter and connector/input shaft are at www.maximum-overdrive.com/products.html . Right now, none are available due to foundry problems- the one this guy uses is down due to furnace repairs, he's looking for another with some free time. You'll have to Google the link, try "maximum-overdrive transmission auto parts" or "maximum-overdrive underdrive/overdrive" when it comes up.

Here's a good inside look at the Laycock- it's in 4 parts, start with http://www.buckeyetriumphs.org/techn.../JOD1/JOD1.htm , and read parts 1-4.

I'm pursuing a two-track strategy in the event the 205 retainer switch doesn't work out. I'm looking at reworking the front end to better accomodate the stresses it's subjected to- stay tuned.