Johnny71dusty
Well-Known Member
Do all a904 small block trans bolt right up to the 90s 3.9 v6 ? If so what years ? I want to help a guy put one of these motors in his old mopar
90s 3.9 v6
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As long as you use the "old" flex plate. I would use the 68 and newer to avoid the odd ball convertor hub and input spline.
Johnny71dusty
Well-Known Member
What flex plate ? One from motor or one from trans ? Also I see no 3.9s came with 904s but see guys on here say they boot right up . I just can't verify any years or models .
No need to verify make and model of a donor car or for parts.
The bell housing pattern is the same on the back of the block and the crank is in the right spot. Any small block transmission will bolt right up. The flex plate from ether will work.
The V6 engines came with the overdrive trans which were the 904 variant. A-500, RH 42? I keep forgetting that number….
The early 904’s have an odd spline count of *I think* it was 18.
(I should remember this since I have one and it was a bear to find a converter for it.)
Just make sure the front of the converter fits the rear of the crank. It should be super close fitting.
Below is a picture of the hub on my 727 converter, the measurement may not be dead on as it was a bit of a pain to do where it sits. But that’s the idea…. That hub sits in the rear of the crank.
The stock flex plate uses small (*Again I think) 5/16 bolts. ES to source from Summit and other places. If you need to order a flex plate, just say it’s for a 904.
The bell housing pattern is the same on the back of the block and the crank is in the right spot. Any small block transmission will bolt right up. The flex plate from ether will work.
The V6 engines came with the overdrive trans which were the 904 variant. A-500, RH 42? I keep forgetting that number….
The early 904’s have an odd spline count of *I think* it was 18.
(I should remember this since I have one and it was a bear to find a converter for it.)
Just make sure the front of the converter fits the rear of the crank. It should be super close fitting.
Below is a picture of the hub on my 727 converter, the measurement may not be dead on as it was a bit of a pain to do where it sits. But that’s the idea…. That hub sits in the rear of the crank.
The stock flex plate uses small (*Again I think) 5/16 bolts. ES to source from Summit and other places. If you need to order a flex plate, just say it’s for a 904.
autopar3000
Well-Known Member
Is the V6 going to be running a carb or the factory EFI?
Johnny71dusty
Well-Known Member
Who knows lol . We not even looked if there is a carb/ intake for them aftermarket
Johnny71dusty
Well-Known Member
This is great thank you . I'd like to use that 904 variant I think. All the trans I see that went with them are in trucks but they don't list it as a 904 but some weird numbers
Right! Basically it’s an A-500 or that RH42, but someone please ether confirm or correct me on this.
I do know that you want the RH model and not the RE. The “E” stands for Electronic and “H” is Hydraulic. The H will hook up and run like the 70’s era transmission.
Dakota 2 wheel drive trucks had them. You can use that as a reference if you’re ordering one up. Whatever the first year Dakota was. See if you can’t order it with a 318 V8 Dakota.
I do know that you want the RH model and not the RE. The “E” stands for Electronic and “H” is Hydraulic. The H will hook up and run like the 70’s era transmission.
Dakota 2 wheel drive trucks had them. You can use that as a reference if you’re ordering one up. Whatever the first year Dakota was. See if you can’t order it with a 318 V8 Dakota.
At one time Mopar Performance did make a intake of the 3.9 V6.
I have a 1997 catalog and it shows P4452114 as the part number.
They even had cams,heads and other performance parts. Maybe find a dealer who specializes in NOS parts.
Johnny71dusty
Well-Known Member
Rad guys thanks
Johnny71dusty
Well-Known Member
42re it says aka a500 . But nowhere do I see a rh .
Earlier the better for the A-500 and its variants.
Keep looking.
Keep looking.
autopar3000
Well-Known Member
The 3 speed 904 or 727 will work fine behind that V6. If you're keeping the EFI you will have to notch the bellhousing for the crank sensor. Also, you'll have to elongate one of the torque converter mounting holes in the flexplate so it can bolt to the earlier style torque converter.
pishta
I know I'm right....
post 68 spline count changed from 67, iirc. so a 68 convertor wouldnt fit on a 67 trans.
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Johnny71dusty
Well-Known Member
So what year trans should I get ? If using a 2000 3.6 ?
If you want a basic 904, go for a 1973 or newer. If you want the overdrive variant, use 92(?) to 95.
I confused a 3.6 with the 3.9, my bad. At this point, I don’t know if it will fit.
3.6 or 3.9 ?
A 3.9 is basically a 318 with two cylinders chopped off.
Comes in magnum and la depending on year
Johnny71dusty
Well-Known Member
I'd heard people say this and other people say that isn't true. But either way if it bolts to a 904 I'm happy with that. I wish we had a carb intake to run that way but no signs of ones out there for sale
Johnny71dusty
Well-Known Member
Lol see lol
1) the 3.9 was carbureted 1 year only, '87 model with a 2bbl.
2) Mopar did offer 4bbl intakes, cams, & headers. Even HP heads iirc. Eddy also offered items for them. Pistons, valves, springs etc. all shared with the 318 as mentioned.
3) Magnums are the same as any other Magnum V-8 swap. 1st years were '92 MY
iirc
4) SB's changed to larger crank pocket in '67, Slantys in '68.
5) The 3.9 Daks came with L/U "904's" early on, even 7.25" rears, & 14" rims. By '89 they almost all came with A-500's, which were all 42RH with the L/U & O/D being the only electrical controls, and an 8.25" rear w/3.55's. I'm not sure if the switch to RE coincided with the sw to Magnum, but likely it did.
The upshot is, any '67 & newer SB trans will work on the 1st gen/LA 3.9, and Magnums are Magnums...so all Mag conversion steps apply there, as well as all A-500 swap steps if You go that route.
P.S. The "odd numbers" are A-998 & A-999, which are the V-8 & HD versions of the TF6, (904).
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autopar3000
Well-Known Member
The switch to the 42RE transmissions, from what was originally the 42RH (aka the A500), coincided with OBD2. So generally speaking, 1995 and back was the RH, 1996 forward was the RE.
For the OP, in case you're not familiar with them terminology when we talk about 42RH / 42RE:
4 - Number of forward gears
2 - Strength level (2 = kinda low, 4 a bit better, 6 even better, 7 or 8 you're into V10 or Cummins trans territory)
R - Rear wheel drive
H - H for hydraulically controlled, E for electronically controlled.
You can identify whether it's an RH or RE trans by looking at the connector on the driver's side of the trans, above the neutral safety switch connector. The most desirable hydraulic transmissions will have 3 pins; 1 for power, one for torque converter lockup, and one for the overdrive shift. The less desirable transmissions don't have a lockup converter so they will just have 2 pins; 1 for power and another for the overdrive shift. The RE transmissions will have an 8 pin connector. If you get one of these you you have to run the OBD2 computer or some other electronic controller/
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