Jeff Smith Senior Technical Editor
April 1, 1999

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T5 Trans Trickery
The Borg-Warner T5 trans is the hot ticket for budget Ford street heroes, butthe proliferation of those transmissions can lead to problems. Before you step up to buy a used T5, be aware that not all T5s are the same. Later-model Mustang T5s, beginning with '90 Mustangs, are upgraded transmissions that offer much stronger nickel-steel gears and superior synchros and are highly prized by knowledgeable Ford fans. They can be identified by a B-W tag listing either a 1352-208 or 1352-199 serial number.

If you are junkyard or swap-meet hunting, keep in mind that the four-cylinder T5 transmission looks the same but actually has a longer input shaft and slightly smaller-diameter pilot shaft. If you bolt the four-cylinder T5 into a V-8 application, the clutch will chatter on engagement, because the pilot shaft is loose inside the pilot bushing. Worse yet, the longer input shaft presses forward into the crankshaft, placing pressure on the thrust surface of the main bearing, which will quickly destroy the bearing and cause major engine damage.

If that isn't enough, four-cylinder transmissions have deeper 4:1 First-gear ratios that are substantially weaker than the V-8 boxes. Borg-Warner engineer Steve Whitaker advises that you steer clear of pre-'85 V-8 T5s, as well, since they are a little weaker than the post-'85 models. Furthermore, the new '94 Mustang T5 is different from either of the previous T5s and will not interchange. Hey, nobody said it was easy! The bottom line is that there's no reason to buy a four-cylinder T5, even if it's dirt cheap.

The head on the left has the Ford-supplied insert (1) that also blocks off the exhaust port. The head on the right is open (2). You need to look carefully to ensure that the plugs are in place, or you'll have a noisy exhaust leak.

All Ford small-block heads since the 1975 are configured to accept smog-pump input into a hole in the back of the right cylinder head that is plumbed to the exhaust ports. The hole is drilled and tapped in both heads for a 5/8-inch national coarse (N.C.) thread. Ford inserts an adapter plug that is internally drilled and tapped for a 3/8-inch N.C. thread for the opposite end of the head in the front to mount the accessory-drive bracket. When an engine is rebuilt and bolted into an emissions-exempt vehicle, the rear hole may be left unplugged. Left open, the holes will generate a tremendous exhaust leak that may not be immediately apparent and could be blamed on leaky header gaskets. If the smog pump is not used, the O.E.M. Ford 5/8-inch blind hole insert (Ford PN 351418-S) is a simple and inexpensive fix to this problem.

Using a quality head gasket, such as Fel-Pro part No. 1011, line up the steam holes between the gasket, head and block. If you find the indicated passages (arrow) not drilled in either the head or the block, carefully drilling them could eliminate an overheating or detonation problem.

All Steamed Up
When mixing and matching Ford small-block cylinder heads and blocks, there is a great possibility of mismatching steam-pocket relief holes between the heads and the block. If the steam pockets are not vented properly, they can cause internal water-jacket hot spots that can lead to detonation and engine damage, especially in high-output, high-compression situations. The fix for this problem is to line up a head gasket such as a Fel-Pro PN 1011 on first the head and then the block to check for small holes located on the intake side of the cylinder deck surface. The holes should line up with holes in the cylinder heads. If there are holes in the block but not in the head, you should very carefully drill through the deck surface of the head or block to ensure that the steam-pocket points are open. Carbide drill bits work best, especially in high-nickel-content blocks. This mismatch can even occur on original factory engines and could account for engines with a sensitivity toward overheating or detonation problems.