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Original Message
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| RE: Mostly correct on the TL but not entirely |
| By Gerry Proctor - 10/19/2004 7:35:09 AM; IP 207.133.188.254 |
Here are the differences and possibilities:
Nearly all (terminology you have to use as a qualifier when discussing FoMoCo) small block Top Loaders were wide ratio units with the 2.78 1st gear ratio. They were 10-spline 1 1/8" input and 28-spline outputs. We're excluding the very early 25-spline units in this reference.
Most big block Top Loaders were also wide ratio units with the same in and out diameters and spline count as the small block unit. Big block, small input TLs were available in both close (2.32 1st gear) and wide ratio (2.78 1st) from the factory and what you got greatly depended on the final drive ratio but, again, most were wide ratio.
The primary difference between the big and small block Top Loaders is in the length of the input pilot length. The input shafts to the end of the splines are exactly the same length but the small block has 3/8" more length on the pilot. A small block Top Loader can be used in a big block application by trimming that 3/8" off the pilot. Obviously, you can't untrim a big block Top Loader to fit a small block car. There are some extended length pilot bushings that can be used to accommodate this transplant. You can also use a small block TL behind an FE if you use the truck FE bellhousing since this housing has about 3/8" greater depth. Though you may have to grind on the housing a bit depending on the style and diameter clutch you use. You can also just replace the input shaft with one of the correct pilot length.
Now not all big block Top Loaders are created equal. The 427 cars and the '68 and later high power cars like the 428 CJ/SCJ and the 429 cars were on tap for the big in and out Top Loaders. These transmissions, all close ratio from the factory, enjoyed an input diameter of 1 3/8" and 31-spline output shafts. From big block to big block, you can replace a small input TL with a big input TL but you'll be looking at a new clutch disc for the larger input and a corresponding throwout bearing for the larger input bearing collar. The output yoke will also have to be replaced with the 31-spline unit (same as the C6 yoke).
So it's entirely possible that what's behind the 289 is an FE toploader but, again, that's not saying much since there is no difference, strength-wise between a small input TL for either a small or big block.
And, through aftermarket support, while FoMoCo never offered a wide ratio big input TL, you can go that way if you wish. |
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