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GM T56 Installation Overview Print E-mail

Installation Overview

(reprinted from Car Craft Jan 1994)

Tremec's GM aftermarket replacement T56 assembly uses a 26 spline input shaft that mates with the existing GM clutch assembly. Also included is a special adapter plate that bolts the transmission to the stock T5 bellhousing. Borg Warner developed the kit using a ' 92 Camaro equipped with the optional '89-92 dual-catalyst exhaust system. Although the exhaust pipes remain unmodified, the hanger that previously attached the pipes to the transmission mount is discarded. Most GM F-cars (Camaros, Firebirds, and Trans Ams) use only a single catalyst, which, if anything, should provide even more clearance for the transmission. The kit moves the '90-92' T5 mount 1.9 inches rearward to mate with a sectioned and rewelded '93' GM F-car transmission crossmember. This in turn requires correspondingly shortening the rear differential torque arm by 1.9 inches. Retain the stock 27-spline skip-yoke, but shorten the driveshaft by 2 inches.

Bellhousing and Clutch Linkage

The '93 F car uses a "pull-type" clutch assembly, and the T56's front face is different from traditional GM manual transmissions. Tremecs's adapter plate provides the solution -- it bolts the new trans to the earlier T5 bellhousing and permits retention of the existing T5 V8 clutch system without alteration.   gmtrannie1_large.jpg
Stock T5 V8 bellhousings rotate the T5 trans 18 degrees counterclockwise from "straight up." Borg-Warner's adapter plate returns the T56's orientation to "straight up". Old Muncie/T10/Saginaw transmission also mount "straight up." Use of the old four-speed bellhousing with the T56 adapter would thus rotate the new trans clockwise from the vertical (leaving the mounting pad nonparallel to the crossmember). Instead, use a T5 bellhousing when replacing an old four-speed with a T56. The '83 F-car T5 V8 bellhousing is the best choice for old musclecar retrofit application, as it still uses mechanical clutch linkage. This unit is no longer available from GM, so ask the salvage yards. Lakewood offers an equivalent scattershield. The '84 - '92 Camaros use a bellhousing set up for hydraulic linkage.  

Cross members Modification

No detailed drawings of the modification required to mate a '93 F-car T56 crossmember to the earlier F-car T56 crossmember exist, so it's a cut and try proposition. The '83 and later F-car installation uses the original T5 mount. For earlier conversions, use the stock 3.75 inch bolt spacing (non-Turbo 400) mount for the chassis in question, but attach it to the trans using metric M10x1.5x30 mounting bolts.

Use four countersunk sockethead capscrews (arrows) to attach the adapter plate to the bellhousing. Note that the palate corrects the trans orientation to "straight up." Carefully align the clutch disc splines with the input shaft splines, then bolt the trans to the adapter plate. The orginal flat T5 crossmember (left) won't fit the T56. Instead, get a '93 T56 crossmember (center). Modify it so it looks lite the one on the right. This involves drilling a new hole (A), cutting the right side off to chane its angle (B), and adding new material (C). Details follow:

  Start with the left-hand side. The new crossmember attaches to the rearmost two threaded factory mounting holes. This requires drilling one new hole in the crssmember that corresponds to the location of the rear most subframe hole. To find the proper hole location, scribe an easily visible line on the subframe through the rear bolt hole that is parallel to the vehicle's longitudinal axis. Scribe a second line at a right angle to the first line through the rear bolt hole. Make the lines long enough so they extend beyond the cross member when it is in position. Bolt the crossmember and mount to the T56 trans. Install the forward left-hand cross member to subframe bolt (A). Using the ends of the previously scribed lines as a baseline, extend them across the crossmember. Remove the crossmember and drill a 10mm hole at their intersection point (B).


Remount the crossmember to the trans and left-hand subframe. Cut off the crossmember to the right of the mounting pad (A). Bolt the cut-off section's front hole to the rearmost existing tapped hole in the frame channel (B). Section and add new pieces of material (C) to make the crossmember's existing rear hole flush with the frame rail kick-up. Drill a new hole into the frame rail that corresponds to the rear hole in the crossmember (D).


  A blind Rivnut or Nutsert is the "elegant" solution for suppling the female threads required by the newly drilled bolt lole. The low-buck solution is a 2x3x1/2 inch-thick stel or aluminum block. Shove it into position through the large existing hole in the frame as shown so it lines up with the newly drilled crossmember mounting hole (see arrow above), then drill and tap it for metric M10x1.5 threads. Adding a second (but countersunk) bolt hole to the frame and block will keep the block from twisting out of position. Finally, bolt the crossmember solidly into position using all four bolts, and final-weld all joints.  


T56 Electric Reverse Lockout

Unlike the T5 or traditional four-speed transmissions, the T56 uses an electrically actuated reverse-lockout solenoid system to prevent inadvertent shifts into Reverse gear. In production applications, the vehicle's computer will power up the solenoid only if vehicle speed is less than 5 mph. For retrofit use, use a monetary switch to operate the lockout solenoid. B&M, Hurst, and even nitrous oxide companies offer shifter handles with these switches built in (normally, they're used for controlling nitrous or the Roll Control). Connection with the lockout solenoid at the trans requires a GM Metipack connector assembly. If it is not desired to enable the solenoid, the Neutral to Reverse shift can still be completed at the vehicle speeds less than 5 mph by overriding the lockout assembly with the emergency "crash-through" feature. The lockout assembly plunger is spring-loaded and a high side effort on the shift lever compress the spring, overcoming the lockout.

Shorten the rear differential torque arm 1.9 inches by sectioning and rewelding in the area shown.  







Production GM T56s accept only a fully electronic speedometer connector (A) In both above photos, (B) indicates the location of the electric reverse-lockout connector receptacle, a common feature on all current T56 transmissions. Tremec machines the aftermarket version's extension housing for the traditional GM speedo cable connections (A), which accepts both full-machinical cables and the hybrid '90-'92 magnetic pickup. Use GM T5 drive and driven gears for speedo calibration. Although the speedo hookup is 2.6 inches farther rearward, the existing cable should still hook up. Shifter location is also revised to conform to the T5 location, eliminating the need for any floorpan modifications.



The completed T56 transmission shows the new adapter plate, relocated and modified cross member, and shortened torque arm.


Critical Dimensions

Listed below are the critical dimensions of the T56 in comparison to T5 and traditional four-speeds. Metric dimensions are converted to inches and rounded off to the nearest 0.1 inch.
Trans Model







GM Super T10 Muncie







GM T5 V8







GM T56 F-car Prod







GM T56 F-car After- market








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