Converting early gas MH to Duramax? Possible?

[Dakster]

BigRabbitMan,

Have you made any decisions or started on the project?

[journeyman]

My dad has the 2900 R (1974) and quite possibly I will be inheriting it someday.

We have the 454/4L80e in it and got 8 MPG with the TH400 and yet to get enough driving data with the 4L80e.

I also would like to consider the LMM/Allison 6 speed. Weight on the engine is comparable. 1000 should be similar to the 545.

Jim Black told me that vibration was a problem with diesels in the 2900R and it would need significant body (structural) strengthening that he does. the Duramax may not have those vibration issues (that would be my hope).

I am impressed with the 454, and possibly will keep it in favor of diesel... But may inject it to improve efficiency

[journeyman]

Specifics:

The Marine Ind. 440: Weight: Long block as shipped: 670#
With accessories and manifolds it will easily be over 700

The Duramax (when introduced) was touted at 835 Lbs.

165 Lbs heavier seems like a safe ball park figure for weight.
Moving the exhaust (massive muffler) out of the engine bay will save you another good bit of weight.

[BigRabbitMan]

My dad has the 2900 R (1974) and quite possibly I will be inheriting it someday.

Jim Black told me that vibration was a problem with diesels in the 2900R and it would need significant body (structural) strengthening that he does. the Duramax may not have those vibration issues (that would be my hope).

Jim Black (of RVS, FMC authorized repair facility - Morgan Hill, CA) and Leslie Hoagland of Motor Coach Restoration in Illinois have only dealt with older diesels: the 8.2L detroit and 6 cyl in line Cummins. Either of those engines will have vibration issues, but more importantly weight issues and a narrow torque curve that do in fact force structual strenghtening. That is why I eliminated them upfront. I know both Jim and Lesle,and respect them both but in this case they are both still thinking old school.

As Journeyman indicated, in the case of the FMC pounds are important and the difference between the Duramax and other modern light weight diesels eliminated all others on that factor alone.

Since my last posting, I was able to make contact with the current owner [he did not do the conversion] of the FMC that was converted a few of years ago and written up on The Diesel Page. He surfaced at an FMC rally held in Colorado last month. While I wasn't able to be at that rally, I have received some very complete descriptions of how the conversion altered the fuctioning of the coach. Those descriptions were all good!

Here are a few:
"The coach has a 5-speed model 1000 transmission. It turns about 1700 rpm at 65 mph." [note: In my opinion that is too slow.]
"When we started up La Veta pass, Jim Evans [440 carb powered] (in the lead) said over the radio that he wouldn't be insulted if anyone passed him, so I [440 fuel injection powered] pulled out and stormed up the hill past everyone [This included a turbo inline 6 cyl Cummins]. Dave Jacobs followed in the Duramax coach, and when I waved him to come on by, he passed us like we were nearly going backwards! It was very impressive - and sounded great, too."
"Coach #735 performed perfectly, getting 11.2 mpg pulling the Bimmer (left in Colo. Sprgs for A/C repair) and 13.8 mpg empty including going over 3 mountain passes over 10,000 feet including Wolf Creek Pass (10,550 ft) which is the curviest and steepest I've ever seen."
"Several miles out from Pagosa Springs, we started the long climb up Wolf Creek Pass (10,857 ft). I suggest that Dave proceed ahead, and they proceeded to disappear again ;-) I didn't push it [440 fuel injected]: we stayed near the 35 mph speed limit at 3500 rpm in 2nd gear (Allison AT545 4-speed) all the way up the climb."

It should be noted that no frame issues were evident with the Duramax converted coach even though it still had the stock frame.

As all of you can understand, having read the above plus additional comments any thoughts of an 8.1 vortec disappeared. It also encouraged me as to the thoughts of converting to a Duramax. I came to two conclusions: for this conversion, it needs to use the 6 speed double overdrive transmission so that the stock 4.62:1 differential can still be used as that combination gives a good transfer of torque to the ground with 65 mph at about 1900 rpm, and that if it would be possible to locate an LBZ it would be best. An LLY would also be fine. The above coach has an LB7.

I then made the mistake last week of typing in Duramax LBZ in the search window of eBay! To shorten the story, I am now the proud owner of a used LBZ that was obtained at an attractive price! I guess I am now commited.

The following is the body of an email I wrote to a fellow FMC owner:
"What this purchase did was commit me to a methodology in that I can no longer look for a matched engine/transmission set. It is now piecemeal and just do the stuff that has to be done to make the pieces work together. That will take awhile. One of the reasons I went ahead is that a matched Duramax LBZ and Allison MH (Motor Home) transmission doesn’t exist. No motor home manufacturer has used the Duramax to this date so they aren’t matched to a MH transmission. Motor home manufactures have either used a gas engine or Cummins or Powerstroke. I already had eliminated those engines so I had effectively eliminated a matched set with the MH transmission. That left the possibility of a matched LBZ with a 6 spd Allison, but one that would have to be converted from a standard arrangement to the MH version with the driveline parking brake. Given the attractive price I paid for this LBZ, I went ahead and set pattern.

"Now the game plan is to obtain a matched ECM (engine control module) and TCM (transmission control module) from a Duramax LBZ / 6 spd Allison equipped wreck including wiring harness(s) if possible. That will be used to control a used Allison 1000MH 6 speed. This will be a challenge to obtain as the 6 speed is 2006 or newer, but this is why the year or more timeline to complete the conversion. In my dreams, I would prefer to use the Allison 2500MH with the lower first and second gear, but the population of those is so small I can most likely forget it. Which ever model Allison (1000, 2200, 2500) I do end up using, I do want it to have a parking pawl. Not all of them have one. [Note: the 2550 has the pawl.]

"Then comes the question of how to control the transmission. One possibility would be to obtain the push button, paddle controller found in some newer motor homes. It is 100% electrical I believe. This could most likely be mounted on the inside of the drivers door (or left side of the drivers seat stand) and, therefore, not be involved with the dashboard or driver/passenger area. Whether or not it could be mounted into the dash in the area of the existing shifter is not known.

"So the “you” part of the “we” is to start looking for the pieces and parts needed to complete the job. Start crawling through the junkyards looking for donor vehicles for the above items.

"Understand that I am not committed to the actual conversion until all component parts have been secured. The Duramax LBZ that is now on the way can be resold if all other components are not located at a reasonable price or if some other issue prevents the conversion."

Who am I kidding!! I am now fully addicted to the conversion of my coach to a Duramax LBZ with an Allison 6 speed behind it and ALL issues will be surmounted.

You now have the current status and know what some of the additional parts
needed include. I am going to try very hard to get hold of a 2550MH transmisson. The lower gearing of the first two gears may over time prove to help alleviate any frame issues as the torque is then easily transfered to the wheels when starting out without needing a stiff frame to hold the engine back from rotating.

Wish me luck and if any of you come across any of the items I need (everythng!) please give me an email at Stephen at Heinrichs dot com.

I will post updates as major events happen.

[Dakster]

Nice... Glad you decided to try it. Good luck with locating all of the parts to do it. In the MH's I've driven all where 2003 and Newer, 40' with either cummins or cat motors and the allision tranny. They had the shifter you are talking about. It appears to be all electrical and I have seen them mounted on the arm rest, on the dash to the left AND right of the steering wheel. One had it in the center console area which was still reachable by the driver. They seem to be fairly flexible for mounting.

You may want to look in a MH junkyard to get the tranny and controller you need?

I look forward to updates!

[BigRabbitMan]

You may want to look in a MH junkyard to get the tranny and controller you need?
I look forward to updates!

One of the questions that I need to get answered is what trans controllers are compatible with the Duramax's ECM. Will a TCM that originally was used with a Cummins or International also work with a Duramax (GM) ECM or will GM's propietory programing also require a GM TCM to be compatable. Are the plugs compatable? I expect the transmissions to all be the same, just different controllers so I should be able to plug a GM TCM into any Allison transmission regarless of source.

Everyone's thoughts are welcome.

[BigRabbitMan]

Here is a link to where pictues of the engine I purchased are posted. The first couple of pictures are what I purchased and the last three are what greated me at the trucking terminal.
http://www.fmcowners.com/mbbs22/phot...asp?albumid=29

I have just secured an engine stand and will now attach the engine to it where I can assess the shipping damage so that a claim can be submitted and so that the engiine will be properly stored and ready to be worked on when the time arrives.