OD Transmission for a Small Block 318

[sneke_eyez]

My A-904 is working decently, but I can't help but wish I had that fourth gear for highway cruising and better gas mileage.

I've read magazine after magazine where they tell you what tranny to use to easily add OD to your old muscle car to achieve exactly what I'd like to do.

I figure Ma Mopar was probably using an OD-equipped version of the A904 behind the ever-reliable and well-used 318 SB at some point during the mid 80s, and if so, what did they use it in?

If not, is there another tranny I can use to add OD to my car?

I'm well versed in junkyard searching, and if someone can just tell me what it is I need to look for, I can probably find it and for a pretty decent price.

The only additional issue I might have to contend with is my center console shifter, I don't know how the linkage would work on a newer tranny.

Thanks in advance.

 

[70aarcuda]

the od version of the 904 is the a-500...you will need the 42rh version...

42rh is the hydraulic control od and lockup...

you will need to cut the floor board to get the trans to fit the tunnel....

you will need to fabricate a new trans mount.....

also you will need to some way of engaging the od and lockup with a switch...

 

[sneke_eyez]

Thanks for the info.
Sounds like a pretty detailed modification.
Maybe I'll just stick with my A904 but add a shift kit...

 

[MopaR&D]

Thanks for the info.
Sounds like a pretty detailed modification.
Maybe I'll just stick with my A904 but add a shift kit...

That's the problem with Mopar transmissions. The 727 is fantastic and the 904 is not bad performance-wise but if you want overdrive you either have to reinvent the wheel or pay $3000 for a new OD trans that bolts up to your old engine. In fact the easiest way to get overdrive is to swap to a post-1976 A-833 four-speed manual OD trans but that still involves all the mods necessary to convert to a manual transmission.

What are your rear gears and typical cruising speed on the highway?

 

[375inStroke]

You can get more torque, and run higher gears. You can run a low gear trans. The first 904 and 727 transmissions used a 2.45 first, and 1.45 second gear ratio. The newer 904 (a998 or A999 maybe) used a 2.74 and 1.54 gear ratio. This, combined with higher gears would get you similar acceleration off the line, and lower RPMs at cruise. There is also the Gearvendors, but that is pricey, like $2500 I think. If you want a 500 or 518, you should get a '94 or earlier hydraulic controlled version. I think in '95 they switched to computer control, and you want to stay away from that. There are ways to make OD shifting automatic, and there is at least one company that makes a kit. Here are a bunch of links on this subject:

A500 in a 1970 A Body
A518 OD shifting kit from PA&CT
If this is for a big block--Ultrabell
Identification and measurement info
Big block with Ultrabell, but you can see the crossmember mods
Automatic OD in a 68 Dart GT
GearVendors OD installed in '73 b-body
Low First Gear Set

 

[375inStroke]

Here are some more links:

This shows the ground clearance This is an A-body, and the floor was not cut. Only the upper torsion crossmember was cut, then reinforced.
Trimming the trans for clearance at torsion bar crossmember
Crappy Hot Rod article
More OD talk
4 page OD post with pics

Is this enough reading yet?

 

[sneke_eyez]

Wow, thanks a lot for all of the reading!

Its something for me to think about.
Either way, I want to do something with the tranny, we'll see if this is it.