6BT in a GMC motorhome
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Thread: 6BT in a GMC motorhome

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    Default 6BT in a GMC motorhome

    I have a 1974 GMC motor home that needs engine work and a completly rebuilt 6BT from a 93 Dodge with all of the accessories.

    GMC motorhomes used the Olds Toronado front drive set up. Basicly a turbo 400 (BOP bolt pattern) split behind the torque converter. The TC mounted to the engine and the engine mounted front to back in the normal way. The balance of the transmission mounted back to front and connected to the TC by a monster chain drive. The "rear" center section coupled to the end of the trans. and the passenger side independant axle passing under the engine.

    I know 4BT engines have been adapted to turbo 400s with the Chevrolet bolt pattern and I know there are adaptors from Chevrolet to BOP.

    Assuming the trans is "built" and the final ratio is changed to a taller gear, the question is... is this practical?

    I would much appreciate your thoughts.
    Thanks,
    Grammabud

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    I'm familiar with the tranny, and my first impression is that it is an interesting idea, but not likely to be successful. My guess is that the engine and oil pan would be too deep, and that the differential and passenger side axle would be in the way. It might fit, with a front sump pan, but the only way to know for sure would be to come up with some measurements.

    All things considered, It would be cool if it worked, but not sure how the chain would like living behind the Cummins.

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    Poke around on the www, google etc. I seem to recall Winnebago using a diesel front drive set-up in a utility vehicle (panel van). Report back if you find something, I am curious if I remember correctly or not...
    1989 D250 CTD, 727HD, D70/3.07, BHAF, DIY Cold air, Tuned VE, 4" exhaust

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    Quote Originally Posted by sdstriper View Post
    Poke around on the www, google etc. I seem to recall Winnebago using a diesel front drive set-up in a utility vehicle (panel van). Report back if you find something, I am curious if I remember correctly or not...

    You are remembering correctly. I have looked, trying to find it, no luck so far. It has literally been 20 years ago, but I considered buying one once, and poked around under the hood. Given the amount of time that has passed, I am somewhat fuzzy on the details, but I seem to recall that the engine was built by Volvo, and was transversely mounted. I may well be mistaken on the mounting arrangement, but the engine was definitely not domestic.

    The TH400 transfer case is an interesting approach, I'm just not sure that it can reasonably be pursued, without having the t-case, the engine and adapter available. The Cummins is a deep block with the skirts dropping almost 4" below the crank center line. On top of that, the tilt in the GM adapter could help to alleviate any interference, or it could create more. My guess, is that it would create a problem, as it would tilt the bottom of the block, towards the transfer case and differential in this particular setup.

    In short the only way to iron out the details, is to have everything in hand and mock it up. I'm sure that isn't what Grammabud wants to hear, but this one is thinking so far out of the box, that he is breaking new ground.

    As far as gearing changes, I'm not even sure that is possible. Again, it has been years ago, but I saw the break down of those once, and I believe the ring and pinion are non standard.

    Here is a link to a photo of the transmission, for those who are unfamiliar with it.

    http://www.charlietranny.com/425THMdswdiff.JPG

    From the photo, it looks like it just might work, but it is going to be close. Would require a front sump pan, and would almost certainly require some clearancing around the passenger side axle.

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    I found an adaptor with both bolt patterns (Chevy and BOP) on eBay. I'm looking into it. I know Cummins made different oil pans for marine, industrial equip. and farm tractors. I'm looking into that also.

    I completly rebuilt the 6BT almost two years ago for a project that I decided not to do. Believe it or not, I got the RV for FREE. I answered ad for it priced at $7500, called and the number was disconnected. I followed a lead and found it 20 miles from my house. The owner had died several months ago and the Exec. of the estate wanted it gone. I have all of the paper work and keys. For starters, it needs brakes and air bags. The ad said the engine (500 Cadillac) needed work. Don't know the engine condition yet.

    Given the circumstances and the total expenses to date, it seems like a natural.

    I appreciate your comments, Thanks...Keep'em comming.

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    Quote Originally Posted by Grammabud View Post
    I found an adaptor with both bolt patterns (Chevy and BOP) on eBay. I'm looking into it. I know Cummins made different oil pans for marine, industrial equip. and farm tractors. I'm looking into that also.

    I completly rebuilt the 6BT almost two years ago for a project that I decided not to do. Believe it or not, I got the RV for FREE. I answered ad for it priced at $7500, called and the number was disconnected. I followed a lead and found it 20 miles from my house. The owner had died several months ago and the Exec. of the estate wanted it gone. I have all of the paper work and keys. For starters, it needs brakes and air bags. The ad said the engine (500 Cadillac) needed work. Don't know the engine condition yet.

    Given the circumstances and the total expenses to date, it seems like a natural.

    I appreciate your comments, Thanks...Keep'em comming.
    Oh yeah.. there are a number of sources for nearly every part for these things encluding various ring and pinion sets.

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    Found a site while searching gearing options. Seems that there are, or were at some time, some gearing options, including gears in the diff, as well as different chain/sprocket assemblies.

    I didn't spend much time looking thru there, but there seems to be some good info about gearing, the differences between the GMC versions and the BOP version, and converting to the old switch pitch front housings. Seems like a good mod to look into, given the load that it has to drag around.

    http://gmcmotorhome.info/

    Have fun with it. Would be really cool if you could get that tranny bolted up. Has me thinking about a rear engine 4bt buggy/coup.

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    Default GMC motorhome cummins repower

    Hi I am new to this site. Have you carried out the motorhome repower I are looking to purchase one of these motorhomes and because petrol is $2.05 a litre here diesel is a must.
    Steve

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    Default 6BT in motor home.

    I hate to say it, but perhaps a 6.5T would be easier to adapt, and get better fuel mileage than the 500 Cad. Some have worked the 6.5T up to be reliable, not, however, up to the reliability of a 6BT.

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