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8HP70 & 90 TRANSMISSIONS
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Heavycruzer
Posted 2018-11-11 12:11 PM (#573318)
Subject: 8HP70 & 90 TRANSMISSIONS


New User

Posts: 2

Location: Auburn, CA
I have an 8HP70 transmission that came out of a 2015 RAM truck running a 3rd gen 5.7 Hemi. I have checked every way I can to establish that the transmission bell housing has "essentially" a LA mounting pattern. I want to bolt this trans up to a 1956 354CU Hemi for installation in a 56 Chrysler. I think I can sort out the electrical/electronic interface but am having some heartburn with the mechanical bits. Has anyone on this board attempted this type of swap? I know I will need to fabricate a spacer for the crank flange but the late model flexplate is much smaller in diameter than the ring gear on the early stuff. Am I going to have issues with the starter interfering with the side of the early Block? Any comments, advice, observations would be appreciated............................
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mikes2nd
Posted 2018-11-11 12:45 PM (#573323 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS


Expert

Posts: 3173
200010001002525
I doubt anyones done that. Good idea though as you get overdrive and stuff. Sounds like youll need to be machining alot of parts though to make it work.

I would look at what Hot heads has.

For 435$ you can buy a chevy auto adapter and be done.

http://hothemiheads.com/transmission_adapters/index.html

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58coupe
Posted 2018-11-12 11:32 AM (#573379 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS



Expert

Posts: 1292
1000100100252525
Location: Alaska
The crankshaft is longer in the 354 than in the newer engines.You will have to make a bellhousing adapter/spacer and also a crank spacer for the smaller flex plate. I am not sure you can find these premade so you should talk to a machine shop.
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jboymechanic
Posted 2018-11-12 9:19 PM (#573421 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS



Expert

Posts: 1347
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Location: Muskego, WI
Yeah, that is a pretty radical update for the crowd on this page. I'd love to see such a conversion done, though, so if you do it please share with us.
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Heavycruzer
Posted 2018-11-13 1:32 PM (#573448 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS


New User

Posts: 2

Location: Auburn, CA
Appreciate the comments gents. I really wanted to keep all the drivetrain in the Chrysler family......funny that way. From what measures I could take, the mounting face on the back of a Gen III crank extends beyond the mounting surface on the back of the block by about .485-.500 inches. This suggests that the 8HP70 converter needs to locate just shy of .500 inches inside the bell housing mounting surface. I am using an old Wilcap adaptor plate (1 inch thick AL) with ears to mount the back of the engine in the car. Since the crank flange on the Gen I engine sits well inside the mounting surface on the back of the block, I should have enough room to locate a machined adaptor between the crank and converter. Much bigger issue will be starting the engine. The new trans flex plate is much smaller diameter than the 46 trans and converter currently behind the engine. It's going to be an interesting exercise, to say the least. I'll detail the parts/machine work needed to make all of this work, as well as the method used to get the new trans talking to the MegaSquirt ECU. I have arranged with a friend to borrow a Gen I block and crank to mock up this mashup. (My engine is already in the car) Don't expect to see anything on this string from me any time soon.....I've been on this project for 8 years now. If anyone can offer advice/insight on the mechanical or electrical interfaces, I would very much like to hear them. The challenge is to get the project on the road before I lose my license First road trip in this car will be to Wasilla, AK.........................
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goat19642004
Posted 2018-11-15 6:41 PM (#573625 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS



Member

Posts: 39
25
Location: Clifton Springs, NY
I’m following this. Very interested in a controller for these transmissions.
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59 in Calif
Posted 2018-11-16 8:10 PM (#573650 - in reply to #573318)
Subject: Re: 8HP70 & 90 TRANSMISSIONS


Elite Veteran

Posts: 1082
1000252525
Location: Hayward, Calif
COOL idea !! I hope you can make it work. Keep us updated on your progress. Not all of us are ' Purists ' . Jerry
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