A few year's ago I started a thread about possible drivetrain mods/alterations for the P-32 short chassis. My 24'/12k GVWR Barth has the same 454/TH400 drivetrain as other P-32's of the day going all the way up to 36' and almost twice the weight. (If my unit was 2' shorter, it would have come with a 350)
Consequently, this gives me an abundance of off-the-line & low speed power. It also gives me what I consider some surplus cruise speed power (EX: able to accelerate up 4-5% grades,etc). I've always thought that I was wasting some fuel, but more importantly, the higher rpm's were creating unneccessary cabin noise, in spite of various soundproofing projects I had completed.

During the thread discussion, I got a lot of great advice, most of it centered on the possibilities of changing the rear end ratio to slow things down a little. After crunching all sorts of numbers, I felt a ratio change in the diffy would be too much of a compromise, and that any high speed benefits obtained would be equally countered by low speed/torque issues.

A Gearvendors installation would be ideal, were it not for the $$. At best, I've got a $6k Barth, making it hard to justify a $3k upgrade new and even $2k+ for a good used unit. Plus, the Gearvendor has underdrive capabilities that seemed overkill for me. All I really need is a two-speed rear end.
(Older farmboy troops here will probably remember the 2-speed rears that came on REO's, Diamond T's, IH and other farm trucks - step on the gas, pull up on the button on the shifter stalk, let up on the gas, the diffy changed ratios and away you went in 15-20% overdrive....

After a couple year's searching, I finally located a Doug Nash Engineering dual range auxiliary transmission w/ low miles. It's essentially a two speed rear end system that's mounted in the driveline right behind the TH400 and electrically controlled via a switch installed on the gear shift lever.
At 1/4th the cost of a GV, I figure it's definately worth a try.......






The unit has two ratios: either 1:1 straight through or 20% overdrive (.80). Generally, this means that 60mph cruise speeds (flatland)should produce engine/drivetrain noise levels approximating my previous levels at 48mph - hopefully, a noticeable difference. (Not an engineer, so I've excluded any significant changes in torque converter slippage.)

Some misc. thoughts:

1. It's already set-up for the TH400, i.e.: remove 4" tailpiece of TH400, bolt unit into place and shorten driveshaft about 12". Rather than shorten existing shaft, I'm thinking an all new short shaft, carrying original shaft & tailpiece under sofa. This way, an on-the-road unit failure still allows ERS to swap-out and get me home

2. No benefit is "free". In this case, I'm asking the TH400 to work harder. Since the TH400 doesn't have a converter lockup, increased fluid temps can be expected. I already have an extra deep (+5qt)tranny pan with cooling fins, plus the standard P-32 radiator cooler - hopefully that's sufficient.

3. The pan mounted tranny temp gauge shows me ready-to-work fluid temps. Maybe I should consider another sender immediately after the TC to show me immediate temp spikes to avoid the red-zone. (use same gauge with SPDT switch for 2nd sender?)

The Downside: Doug Nash Engineering sold tooling to US Gear a few years ago and they sold tooling to another company. It has since been taken off market (mainly because new OEM trannies incl. an OD ratio.)
Rumor has it that tooling has been scrapped, resulting in zero product support from now on. On the plus side, the unit was designed for 32k GVWR & 700 lbs torque, so I think my short Barth is going to run it in loafing-mode most of the time. The most vulnerable part is probably the electric motor that preloads the springs for gear sliding, but that's still a commonly available part from others.

Sorry for the long post, but this mod is gonna be all new territory for me and I'm kinda of a Nervous Nelly here Thoughts/comments/observations/suggestions/warnings would be greatly appreciated!

quote:

Originally posted by Lee:
The pan mounted tranny temp gauge shows me ready-to-work fluid temps. Maybe I should consider another sender immediately after the TC to show me immediate temp spikes to avoid the red-zone. (use same gauge with SPDT switch for 2nd sender?)

Good idea.

1. On hot uphills, it will warn you much earlier to back off the throttle, shift, turn off dash air, slow down, activate cooler fan, turn on water spray on TQ, etc.

2. It will warn you of fluid overheating to guide you on change intervals.

quote:

turn on water spray on TQ

Hmmmmm, Bill.....interesting concept How 'bout expanding on that a little?.....

Sidebar: Since the OD unit doesn't know or care what gear the TH400 is in, I'm thinking that
2nd gear tranny & OD are gonna give me a gear split that should do a lot to keep me
out of temp trouble on modest grades and still within reasonable rpm/torque/speed ranges...

The TH400 (from which the 4L80E/4L85E/6L85E were derived) is a sturdy unit; you'll not overstress it with what you propose. I think you'll find only minor temp increase on a climb.

My opinion on TQ heat is perhaps overkill for most folks, as my poor TQ is between a torque monster 502 and a 30 tag Barth pulling a heavy 4WD toad, and we climb a lot in 100+ temps.

With your smaller coach and stock 454, you are likely to have less trouble than I.

Having said that, I believe it is good to know trans temps, at least on a couple of trips so you know what is what. You have doubtless seen the chart that shows the relation between fluid temp and transmission life.

quote:

Originally posted by Lee:

quote:

turn on water spray on TQ

Hmmmmm, Bill.....interesting concept How 'bout expanding on that a little?.....

Just a yard sprinkler head that sprays on the TQ. Runs off the coach pump. Same logic and effect as a radiator spray.

quote:

Since the OD unit doesn't know or care what gear the TH400 is in, I'm thinking that
2nd gear tranny & OD are gonna give me a gear split that should do a lot to keep me
out of temp trouble on modest grades and still within reasonable rpm/torque/speed ranges...

You'll love it.

I'd go with a bigger tranny cooler - since the spray only hits one side, ir could lead to warpage. The stock TH400/4LxxE TC is not famous for being robust.

quote:

Originally posted by Rusty:
I'd go with a bigger tranny cooler

Yeah, I use two huge ones from Long now. When I put in the 502, they were not available.

quote:

- since the spray only hits one side, it could lead to warpage.

Caution--do not spray a non-rotating TC.

quote:

The stock TH400/4LxxE TC is not famous for being robust.

Sadly. The earlier electronic ones were quite weak, but the non-electronic ones weren't too bad. Mine is a HD unit used on Allisons. I got it from the outfit that did all the airline's truck, bus and tow tractor tranny work.

I had a brazed TC and machined spline (Suncoast Converters) installed with the tranny rebuild.

Update: The Good News: Overdrive is installed, works great and I'm really looking forward to reduced rpm noise on the flatlands! Maybe even a tad better mileage, but I'm not counting on it......Had driveshaft shortened, balanced, replaced all U-joints and carrier bearing for $210.00 - a pleasant surprize.

The Bad News: During OD installation, I had a chance to really look over drivetrain. Discovered that 2 of the 6 flex plate-to-TC bolts had issues - one broken off flush, another missing with elongated hole. Only way to fix is to split the engine from tranny - ugh!!

Question: If I need to drill & tap TC/flex plate holes, will oversize bolts cause any sort of balance problems? (hopefully, going from 7/16 to 1/2, but maybe 9/16, depending on damage) Bolts are only about
1 inch long.....At best, only the elongated hole needs to be oversized....

What-da-ya-think?

With all the weight of the TC and fluid I don't think it would be noticed, but you could Gun Drill the new bolts to match the weight of the existing ones.

Doorman

Update: Noise reduction from the overdrive installation is apparently better than I thought. Past weekend's trip out to MD's Eastern Shore for a fly-in got me a speeding ticket! A first-ever in the Barth.
Now that my speedo is out-of-sync in OD, guess I'll need to watch my GPS speeds a little closer.......

So far, tranny temps haven't budged when in OD....still in 170's - low-80's. If anyone w/ a TH400 runs across a low time U.S.Gear./Doug Nash overdrive unit at the right price, I'd encourage you to consider it.
Caveats: 1) NO mfg support, but fairly common parts 2) I'm at 12k GVWR, and power-wise the OD is quasi gutless on anything but dead level flatlands...it may be super gutless on heavier units.
3) Do it for the noise reduction only - mpg increases haven't been noticed yet. My unit, shaft mods and shop install came to about $1200......Payback, if any, ought to be about the year 2047 But still better than $3k+ for a GearVendor still in-the-box

Dude, you rock! A speeding ticket! You'll have to frame that. The only way my Regal would do it would be in a long free fall.
I don't think OD would work for the 33 ft since it is heavy and working fairly hard even on the level. Nice mod for lighter units for sure.
This weekend I'll check out the fly-in at Lake City in my "other Barth (C172)"

And here I thought the whole reason you polished it was to make it radar reflective

quote:

Originally posted by Moonbeam-Express:
And here I thought the whole reason you polished it was to make it radar reflective

that's the problem. It was too reflective and bounced back such a strong signal that the radar gun dang near overloaded.

The original Black Barth, raced in the Cannonball Baker events by Bart Markel, had a black finish that was capable of absorbing a radar signal, thus preventing a signal being returned to the radar gun. Some of you may recall previous posts on this Barth. It was the first "stealth technology" vehicle.

In fact, the seeming disappearance of the MH can be explained by the initiation of the stealth project right after the Barth disappeared, although there have been sightings form some of the ridges surrounding Area 51. The feddle gummint was going to release it to the owners after the technology had been studied and duplicated, but the various state gummints feared the loss of revenue from speeding tickets that would be the result of motor homes with radar absorbing finishes.