In the process of building my V8, 77 Mustang II coupe I decided that I wanted to convert from the C4 to a manual transmission (preferably an overdrive unit).

While the original style RAD 4 speeds are still out there, they are becoming rather scarce and demand a premium price. They also have a rather bad reputation of not lasting too long under sever use. Additionally there was no OD version of this transmission offered.

I also discounted the T5 units. The early non-world class T5s (1983-85) units are not known as being a strong piece, and the WC units generally demand a very high price and require a unique bellhousing. Additionally from What I’ve read, a fair amount of fabrication for the Cross member, drive shaft etc is required for this swap. (Don’t get me wrong, some of the articles I’ve read spell the T5 swaps out very well, and they are within the capability of most people).

What I finally decided to go with was the Toploader 4 speed from a 79-83 V8 Mustang/Capri. This transmission goes under various designations; RUG, Single Rail Over Drive (SROD), and T170FS. Like the RADs in the Mustang IIs, there were several different versions of this transmission offered, with the strongest unit being found behind the V8 engines. They are also an overdrive unit with either a .81 or .70 4^th gear. As the demand for these transmissions is not very high, and the cars they came from are now 20 Years old, I’ve been able to find them at a very reasonable price.

In my case (I did not have any original Mustang II manual transmission pieces), I used the entire set up from an 83 Mustang GT. This included the bellhousing, Flywheel, clutch assembly, throwout arm and of course transmission. This is a strictly bolt in operation. The bellhousing and flywheel is larger than the stock Mustang II unit, but fits with adequate clearance (though this car has stock manifolds I believe that it will also clear most headers). A stock clutch cable fits perfectly. The transmission bolts to the original unmodified cross member with a stock tranny mount. Overall length is the same and the original driveshaft is simply put back in place.

There were only 2 modifications I needed to do for this swap. The first involved having the flywheel rebalanced from 50 to 28 Oz (this would not have been required with a 79-80 Flywheel, or if I had been using a latter engine). The second was enlarging the hole in the floor a little for the shifter to fit thru (the shifter on the RUG transmission is a couple inches further forward and slightly to the left of the stock hole). After bending the shifter handle I was able to retain the stock console.

In the process of doing this swap I came across a couple of things that fall into the "I didn’t know that category".

1. Pinto Pedals do not interchange with Mustang II.
2. Manual brake and power brake pedals are different.
3. Early (at least the 74s) clutch pedals are different than later pedals (the clutch cable connects differently requiring a different cable).

Admittedly this swap may not be for everyone. One of the big complaints with this transmission was the large jump in ratio between 2^nd and 3^rd gear (3^rd gear is 1:1). The up side is overdrive 4^th gear will allow for deeper rear end ratios and still allow the car to comfortably drive at freeway speeds. If you can live with that, this is a very cost effective and simple swap for the Mustang IIs.

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