The floor cut for the T56 Magnum. The trans transmission sits approximately 2" higher than the A Body standard tunnel.
Pilot bushing time. Measuring the ID (inside diameter) of the crank revealed a 1.090" diameter with a tiny step bore at the back of 1.070". All bushings for GM's that I looked at measured out at 1.094 0r 5. This was too much of an interference fit and would distort the ID when installed. I wanted a .001 oversize as maximum. Also the concentricity had to be good. Some of the sintered bushings measured .002" out ID to OD. I'm a firm believer of dialing in the input shaft as close to ideal as possible and strived for something around .0005"concentricity. With a dialed in bell housing, you get better shifts at high rpm, lower chatter and longer transmission life. I ended up making a tool, suitable for machining between centers, to modify pilot bushings and needle bearings. Just chucking a bushing in a 3 jaw chuck with a filing technique is not going to give you ultimate accuracy and concentricity that this small but important component needs.
The only real way to ensure the transmission is truly aligned is at the front bearing race cavity. There are some adaptor methods, but this way accounts for tolerance of a non parallel block, bellhousing manufacture, dowel pin placements, and input bearing race machining. For this, I had to remove the transmission front cover from the gear box and will be bolting it to the Quick time bellhousing to dial indicate, through the input shaft hole, 1st for the parallelism of where the front bearing resides to the crank flange and 2nd the radial runout at the bearing. It is important to first check parallelism to a max of .002" so that we won't be dial indicating the circular runout of otherwise an ellipse, giving us an erroneous reading. The spec for max radial offset of the input shaft is .005" or .010 TIR (true indicator reading at the total circumference) To correct for out of tolerance I will be shimming the bellhousing to the block first (if required) and second shift the runout to spec. with the use of offset dowel pins. (if required) Some pics of the disassembled cover & The internals of the Mighty T56 magnum.
In dial indicating the T56 magnum front bearing surface, a parallel measurement of .0017"( on a .002" tolerance) to the block was revealed, so I proceeded to indicate the concentric runout measurement to the crank, which turned out to be .006" on a .005" max limit. Just slightly over. I expected something out due to a couple of previous line hones on the bottom end work. So now I'm waiting for a set of Robb Mac .007" eccentric dowel pins that should correct things to .001" (.007-.006) on the .005 limit. Meanwhile I'll be cleaning up the surfaces of the bell & backplate by chamfering all the holes.
Having just done a 4 speed swap last winter I can appreciate all your work and attention to detail. Good stuff. Will be worth it when you finally drive the stick! Does the McLeod dual disc require a thinner flywheel or other mods to accommodate its depth?
Thanks. I'm looking forward to rowing gears again. The Macleod RST and RXT dual disc clutches are a retrofit kit with an adaptor ring and intermediate ring to use stock flywheels. The actual finger placement in the pressure plate itself is supposed to be a changeout to a stock clutch. I'll post pics of the install, which will be coming up. I have now finished installing the adjustable dowel pins, pilot bushing, and re indicated the runout. There are 3 ways to build a better clutch: Increased surface area More clamping pressure Different friction compound The RST uses increased surface area with a street driveable stock type compound. (rated for 800 HP) The RXT also uses the same with a grabbier friction compound (rated 1000 Hp, but some feedback I got, was it was tougher to drive in city type traffic) Tom
With the front trans cover reassembled and alignment completed I checked the installed pilot bearing ID to find it had ever so slightly crushed, so out came a 15mm reamer which measures .5955". The trans input shaft mic'd out at .5895", so using the metric reamer left a pilot bearing to input shaft clearance of a touch over .001" Here's a pic of a mm 3 point inside mic set that I used. Tip. If you use a reamer, always back it out in the direction of turning into the work. Reversing rotation will dull it.
Splitting hairs, but I get .006" if the reamer is .5955" and the input shaft is .5895", not 1 thou as mentioned (which is still darn good fwiw!). What am I missing math-wise? Can I assume you mean the reamer was .5905 (which would be 15mm)?
My bad. It was a typo error. I did use a 15mm reamer. It measured .59055 not .5955. I do have about 1 thou. clearance. Why a 15mm reamer, because it was closest to the input shaft diameter. The next closest English system reamer would have been 19/32" (.5938) less input shaft diameter of .5895 for about .0043" clearance. Some people have used this with success, I just wanted it to be as close as possible. If we think about how much any error is amplified over 7 inches of input shaft sticking out, the closer to perfect, the better the transmission input bearing longevity and high rpm shift will be. Thanks Shawn. P.S. Here's a pick of one of the installed RobbMc adjustable dowel pin that was used for lining up the input bearing to the crank
Another look at the T56 Magnum inside. I took these while assembling the front cover and resealing the tail section. Top shaft is the front portion of the single rail shift mechanism. The original shims and mainshaft bearing race were 1st reassembled into the front cover. Then assembly of the cover to main case. Finally the detent roller, spring and plug were installed through the top of the front cover after it was torqued down. Bottom of the shifter plate with ball end lever that assembles into one of the single rail shifter cups. Output shaft with conventional speedo drive gear and electronic multi tooth reluctor underneath it. Single rail shifter shaft with multiposition cups for different shifter locations. Inside view of tail section. Tail flange for shifter plate showing the area the shifter rail resides in. The plunger at the center of the rectangular opening depicts the electronic reverse gear lockout solenoid tip.
A Bad Flywheel Bolt. I previously bought a Mr Gasket's Chevy/ Ford flywheel bolt set that was a touch less than an 1", only to discover one stretched on me and would not torque up to spec. In retrospect I should have gone with ARP in the first place. Their NASCAR 351 Ford set #350-2802 measures .925" in length, fits well with way better clamping force and quality. At very left, the Mr. G flywheel bolt that began to yield at only 58 ft/lbs. ARP on right
Wow, good catch on the bolt. I very much appreciate your attention to detail on the finite element side of things, nicely done.
The McLeod RST Twin Disc Clutch install. Layout of the Unassembled RST clutch. (Right to Left) bottom disc, red adaptor ring with the attached floater ring, top disc & pressure plate. The top & bottom clutch discs are specific and are identified for installation. View of bottom disc (against flywheel) in it's adaptor plate Top disc between adaptor/floater plate and pressure plate On the flywheel. The RST adaptor plate is assembly is assembled to the flywheel's 11" clutch bolt holes. Special supplied bolts are torqued to 35 ft/lbs. At this point the bottom disc between the adaptor and flywheel has to spin freely without drag to be correct. Next the top disc installed on top of the adaptor ring/ floater plate. The alignment tool locates through both discs into pilot bushing. Finally the Pressure Plate aligns onto 6 threaded adaptor plate studs. When fasteners are torqued to spec., the pressure plate sandwiches top disc, floater & bottom disc tight. The pressure plate diaphragm fingers are at or below the pressure plate housing surface if the install is correct. The benefit of the smaller pressure plate, with two discs, is a low rotating mass clutch that is capable of better capacity, lighter than stock pedal and good release.
Some Clutch math before we assemble the trans into the car. Throwout Bearing (TB) check The Tilton hydraulic TB has the ability to achieve a maximum travel of .700", however a modern diaphragm style clutch only needs up to 7/16" or .4375" of travel to operate. McLeod states that their RST dual disc will function at .450" movement. After setting the initial TB to clutch finger clearance of .125" (for clutch wear since the clutch fingers rise as they wear) we have .700- .125= .575" left before the TB will be out of its bore. Since we only need .450" for proper clutch actuation, there is still another .125" of travel left (.575-.450") in the bearing. Check ok. Master Cylinder Selection check Tilton's advertised volume displacements for their 6000 series TB's are as follows: For a travel of .400" Displacement volume = .483 cubic inch For a travel of .450" Displacement volume = .543 cubic inch For a travel of .500" Displacement volume = .604 cubic inch Calculating our clutch master cylinder supply capacity (.7" bore with a 1.4" stroke) we get a touch under .540 cubic inches of volume with the pedal adjusted to stroke to the floor. Pretty well on the money for a the required .450" stroke. I just want to clarify, the Tilton hydraulic TB does not retract every time we release the pedal. The preset .125" set up clearance allows the pressure plate fingers to rise as it wears in and stays in pretty close contact with the clutch fingers, like a disc brake pad after it is pressed. So there is a full .450" travel in every pedal stroke. From the above, it can be concluded, there should not be any danger in over centering the clutch assembly or over travelling the TB that can cause a potential a hydraulic leak.
It's in and bolted up. Still on the trans jack for now until I get the crossmember in. Once I aligned the input spines with the clutch discs, by putting it in 1st gear and turning the output yoke, it slipped in relatively easy. I made two bellhousing guide pins by cutting off some longer bolt heads. The most difficult part was getting the trans on the trans jack, as I had to slide the gearbox under the car due to limited working height. I left out two bottom scattershield block plate bolts due to an interference with my custom made oil pan. The clearance for the bottom two bolts just wasn't there due to the additional reinforcement corners that Stef's put on the oil pan. Some pan manufacturers put their drain plugs in the back, so check your clearances before bolting up your bellhousing. The final position of Tilton throwout bearing with the additional .125 clearance adjusted in. I used some flat vice grips and a bodywork hammer with dolly to open up the sheet metal a bit.
The G force crossmember for GM A bodies, that I bought years ago, doesn't fit above the frame rails with the new trans, however with a modification of the tabs (that normally sit on the frame) to 1.0" or so higher, it can be made to work. Actually the old TH400 frame rail holes line up well. It's just the height doesn't work. Others have had this issue also. In experimenting, by bolting the member to the bottom side of the frame (effectively raising the tabs), the problem is solved. It solves the height issue, centers up with the trans mounting, still clears my 3" exhaust and measures a 3ish degree negative angle for geometry. I just want to do it with tabs on the frame without having the member weight also hanging on the bolts. My options are, I could also order a custom made member from the Tin Man or Hooker/Holley etc., or modify the tabs on the G force. Decision time...
