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| final drive [message #361122] |
Fri, 25 December 2020 08:36  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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For the gurus - JimK especially. Would it be possible to either turn the final drive upside down, or flip the ring gear from side to side? Either would allow a regular turning transmission to be chain driven, therefore giving some choices to the transmission used. I used to do this with VW transaxles when they were changed from a bus to a bug or vice versa.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: final drive [message #361134 is a reply to message #361122] |
Fri, 25 December 2020 21:08  |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Johnny,
The THM425 IS a "regular" transmission, ie a THM400, as used in millions of larger GM vehicles from mid '60s to the '80s. The only significant difference is the chain drive, and the 2 overrunning clutches which are installed "backward" when the tranny is assembled. Yes it turns "backwards", but so would any transmission driven by a chain off a normal clockwise-rotating engine. (Extra credit: What are the two cars whose engines turned counter-clockwise? Hint, they both begin, or began, with a "C" and I owned one of each.  )
Flipping the ring gear is done in a VW when you install one of those engines. In a GMC, it would only be necessary if you installed a conventional engine mounted backward back near the dinette.
HTH
Merry Christmas and Happy Solstice to all!
Rick Staples
Sorry Johhny, I reread your post and realized what you were suggesting. It's an interesting idea, but I doubt there's room to flip the ring gear. Also, the THM425 was a pretty short version of the THM family. Still, if someone makes iit happen I'd like to see it.
BTW, you must have worked on some really old VW busses, the ones with reduction gears out at the rear wheels. Almost forgot about those.
Rick
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
[Updated on: Fri, 25 December 2020 21:16] Report message to a moderator |
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| Re: [GMCnet] final drive [message #361136 is a reply to message #361134] |
Fri, 25 December 2020 21:43 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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I have built a bunch of Dune buggies. With VW engines, when you make a mid
engine configuration, the ring gear needs to be flipped over inside the
case. I usually included a "beef-a-diff" carrier when I did this, along
with a 1-1 top gear to replace the .890 -1 top gear, along with 1st and
second gears that made it a close ratio gear set. Then, when you built the
air cooled engine up to about 175-200 hp, you had enough beans to make the
thing fly.
If the VW engine was replaced with a Corvair engine, the ring gear
swap was required, as the Corvair turns the opposite direction from the VW.
The VW transaxle is none too strong with tall final drive gears or huge
paddle tires that load the transaxle up. They will live with up to 200 hp,
but not much more than that. But, the sand usually destroys the engine
before the transaxle gives up the ghost. You want to go fast, you have to
pay the cost. Speed costs money, how fast can you afford to go?
Jim Hupy
Salem, Oregon
On Fri, Dec 25, 2020, 7:09 PM Richard H Staples via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Johnny,
> The THM425 IS a "regular" transmission, ie a THM400, as used in millions
> of larger GM vehicles from mid '60s to the '80s. The only significant
> difference is the chain drive, and the 2 overrunning clutches which are
> installed "backward" when the tranny is assembled. Yes it turns
> "backwards",
> but so would any transmission driven by a chain off a normal
> clockwise-rotating engine. (Extra credit: What are the two cars whose
> engines turned
> counter-clockwise? Hint, they both begin, or began, with a "C" and I
> owned one of each. ;) )
>
> Flipping the ring gear is done in a VW when you install one of those
> engines. In a GMC, it would only be necessary if you installed a
> conventional
> engine mounted backward back near the dinette.
>
> HTH
> Merry Christmas and Happy Solstice to all!
> Rick Staples
> --
> Rick Staples, '75 Eleganza, Johnstown, CO
>
> "Advice is a dangerous gift, even from the Wise to the Wise, and all paths
> may run ill." -Tolkien
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: [GMCnet] final drive [message #361137 is a reply to message #361136] |
Sat, 26 December 2020 02:23 |
mghamms
Messages: 466
Registered: March 2016
Location: Ware, Massachusetts
Karma: 2
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Senior Member |
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pre-2000 Honda 4-cylinder engines
rear-mounted Chevrolet Corvair engine from the 1960s
Voisin and Citroen front-wheel drive French car engines from the 1920s and 1930s.
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
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| Re: final drive [message #361138 is a reply to message #361122] |
Sat, 26 December 2020 08:11 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Wasn't thinking it through. You'd need to gear drive it so it turns correctly and then reverse the differential. It may well be though, the transmissions now are too long to do this without surgery to the steps and such.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
[Updated on: Sat, 26 December 2020 08:12] Report message to a moderator |
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