1985 Chrysler 5th Avenue 2 questions

I did this swap in a '78 LeBaron, which is the same frame style as the late 70s - '80s Fifth Ave. / Diplomat / Volare.

The 904 transmission is the standard transmission used, but the 727 will bolt right in its place. They both use the same valve body, mount, shifter linkage, cooler lines, and universal joints.

There are a few things to be aware of. There are three bolt patterns where the case bolts to the engine. Big block V-8s (383, 400, 440), small block V-8s (273, 318, 340, and 360), and the six cylinders. Chances are you have the 318 c.I. So you need a transmission from a small block. The 360 c.I. (All years) and the 340 c.I. (Only in 1973) used cast crankshafts which are externally balanced. All that means is the vibration damper and the torque converter have balancing weights cast in or welded on to them. If you use a transmission from a 360, don't use the torque converter that comes with it or you will have a horrendous vibration.

You will need a drive shaft that is 4" shorter because the 727 tail shaft housing is 4" longer. I can't remember for sure but I think the tail shaft is larger diameter on the 727 so you will need the drive shaft yoke for a 727. The easiest way to find the right length drive shaft is to visit a salvage yard and dig through their pile. There were so many different combinations of axles, body styles, and transmissions in the '60s and '70s that drive shafts were not inventoried by application. You pick one by measuring the length from the centers of the loops where the u-joint cups are pressed in. Your installation will be perfect if the new shaft is 4" shorter, but an inch more or less will work fine. There is some leeway to make up for distance changes as the rear axle moves up and down. There are also different drive shaft diameters but you don't have to worry about that. Length is the only consideration.

As an alternative, you can have your drive shaft shortened and rebalanced at a drive shaft shop.

Another consideration is the use of the lockup torque converter. Chrysler started using them in 1977 with the big block engines and in 1978 with the small blocks. Lockup converters need to be used with the proper front pump in the transmission. Just use a converter and transmission from the same vehicle. You should be able to easily find a newer transmission from a 1980s truck. That will have the lockup converter for better fuel mileage.

For your application the 727 is kind of overkill but will work fine. I used one because I tried twice to rebuild my 904, but had trouble both times installing the front clutch piston seal without cutting it so it slipped in third gear under heavy acceleration. The rotating members are larger in the 727, and I don't have that problem installing the seals in those bigger units. The nice thing about these older Chrysler transmissions is that except for a two-dollar seal installer, no special tools are needed to rebuild them. Hundreds of dollars in special tools are needed for GM and Ford transmissions.

The 727 is really tough and reliable. In my opinion, it's the best transmission ever built.

Caradiodoc

That won't work. I'm 99 percent sure the 727 has a larger diameter output shaft and therefore a tail housing with a larger bushing. Besides, replacing the tail shaft involves pulling out the front pump, front clutch, rear clutch and over-running clutch. At that point you have everything out that gets new plates and seals so you might as well rebuild the 904.

What you might try, if you're extremely lucky, is finding a 727 from a 1970 - 1974 Challenger or Cuda. Whether it's a three speed, 4 speed, or automatic, they had a tail housing that was shorter than on the trannies of all the other models. Remember, you must find a transmission for a small block V-8, (273, 318, 340, 360). The 318 in the Challenger / Cudas probably used the 904. I have two Challengers. My daily driver has a 340, but it's a 4 speed car. The other car is a project car that had a 340 and automatic, but the drive train is gone so I don't know which transmission was in it. The 727 would probably have been used to handle the horsepower.

If you can find a Challenger or Cuda with a 340 and automatic at a car show, you can peek underneath to see which one is used. The 904 oil pan is basically a rectangle. The 727 has an extra bumpout on the right front corner of the pan. Once you see the two pans side-by-side, they're easy to tell apart.

I'm not sure how much shorter the 727 is in a Challenger. I think you're much better off just looking for a shorter drive shaft. That way the swap will be a simple bolt-in process.

Caradiodoc