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Unread 04-30-2007, 07:17 AM   #1
byrdman73
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Chevrolet V8 Conversion-1977 CJ7 304/TH400

I've just bought my first Jeep, a 1977 CJ7 with a 304 and an automatic. From what I can gather the trans is a TH400. I see that there is a spacer bewteen the engine and the trans. Is this also an adapter from the Chevy bolt pattern to the AMC? If that is the case, it should be reletively easy to change over to a Chevrolet V8. I would like to find out without having to pull the engine.

Ultimately, I want to convert to a mid 80's Chevrolet Diesel.

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Unread 04-30-2007, 07:37 AM   #2
jpfaris
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Yes thats an adapter. You have an early version. They layer started using AMC cases.
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Unread 04-30-2007, 08:30 AM   #3
byrdman73
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The spacer/adapter is about 2 inches thick. Without it ,the chevy V8 replacement will be up against the firewall. What is the best way to compensate?

Should I do fab work on the firewall to make a recess?
Should I shift the trans and transfer case forward and modify the drive shafts?
Can I put a spacer bewteen the trans and transfer case to shift only the trans forward?

This is a 30yo vehicle, I'm thinking someone has to have been down this road before. Whatever did we do before internet forums?

Experience is something to don't get until after you need it.
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Unread 04-30-2007, 09:13 AM   #4
BESRK
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If it were mine, I'd mount the engine where I want it, move the drivetrain up and lengthen/shorten the shafts as required. That saves a bunch of sheetmetal hacking, makes working on the distributor easier, makes pulling the valve covers easier..etc.
Granted, I have a lathe so it's easy for me to shorten/lengthen shafts.. I do it all the time.
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Unread 04-30-2007, 11:03 AM   #5
jpfaris
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^x2 .....
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Unread 04-30-2007, 12:49 PM   #6
byrdman73
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That sounds like a plan.

I also have a lathe, Nardini 1560 with a removable gap bed up to 24". It sits nex to to my Supermax mill with dual power feeds and a varable speed head. They both sit in my 1260 sqaure foot climate controlled garage cooled by a 2.5 ton geothermal heat pump. OK, now I'm just bragging, sorry.
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Unread 04-30-2007, 12:56 PM   #7
thenubsterman
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hmm i wonder if i could do driveshafts with just a lil ol cnc fadal.
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Unread 04-30-2007, 01:11 PM   #8
byrdman73
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Back to the transmission question.

Would the later model TH400 transmission with the AMC bellhousing be in the same relative position as my version or would it be shifted forward in the absense of the spacer?

If it is shifted, then a set of standard drive shafts might fit in place without modification.
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Unread 05-01-2007, 05:52 PM   #9
BESRK
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Hmm... not sure. I would be willing to bet it would be moved forward a bit though. I'd imagine the GM 400 and the AMC 400 are pretty close in the bellhousing "length" measurement.. could be wrong though. Even so.. check the tranny skid and the frame rails. There are probably bolt holes to accomodate movement.. if not, there's always the drill..

There are also dozens of stock CJ driveshaft lengths.. many fit different applications.
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Unread 05-01-2007, 09:16 PM   #10
jfwireless
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I have seen this discussion before, why not just put in a 360 or 401, they should mount and bolt right up?? Other than just having to be a Chevy?

Jim
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Unread 05-02-2007, 07:17 AM   #11
byrdman73
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The motivation for changing to a chevrolet is that I want to convert to diesel. The 304 has enough power, but no gas engine will have the power AND fuel economy that I want. A mid 80's chevy V8 diesel will bolt in as easily a 350. I used to own an 85 chevy truck with a 6.2 diesel and a 4 speed. I would normally get 24 mpg. I never lacked for power and I could tow anything with ease.

I'm in the process of setting up to make biodiesel. My other car is an 87' Mercedes 300SDL turbo diesel that gets 30mpg. My truck is a 96' GMC 6.2turbo diesel 4x4 crew cab dually that gets 19mpg. I just like diesel.
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Unread 05-02-2007, 07:41 AM   #12
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that adapter will not fit a chevy it is a B/O/P adapter from a early jeep before they went to the AMC tranny case
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Unread 05-02-2007, 08:08 AM   #13
byrdman73
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The adapter is presently bolted to a 304AMC, I wouldn't expect it to bolt to a chevrolet. The transmission is a GMC TH400 automatic. The question is if a chevrolet engine will bolt to the transmission bellhousing once the 304 and adapter are removed.
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Unread 05-02-2007, 10:48 AM   #14
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OK, I understand your conversion to Diesel and it makes alot of sense. Lots of torque and great fuel mileage. A biodiesle project would really be great.

You may have to beef up the TH400 to handle that amount of torque, althought the TH400 is a strong transmission.

As the 304 is using the adaptor to mate to the TH400, I believe your GM engine should bolt right up without the adaptor plate. You will most like need to move the entire drive train forward to have room for the engine.

Is the Diesel longer than the 304?? That should help determine how to address the drivetrain issue. First you have to fit the Diesel into the engine compartment, than determine how to mate up to the trany. Than see how to work it all out. I am sure someone can make you a custom GM to GM adaptor plate if needed.

Jim
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