Transmission Shaft Alignment


Aligning and Balancing the Model T Ford Engine and Transmission

 Fred Houston and Mike Bender 

Updated April 2008  

The Model T Ford engine and transmission differs from others because the transmission is bolted solidly to the crankshaft. This means that the 4th main shaft or tail shaft must be in near perfect alignment to eliminate vibration, performance degradation and damage to the transmission and crankshaft. The alignment of the 4th main bearing has been covered in the literature, but this is only one small part of the problem. Murray Fahnestock discussed the problem in a rather obscure article, but the issue of shaft alignment has not been discussed in any modern publication.

THE CAREFUL ALIGNMENT AND BALANCING OF THE MODEL T FORD ENGINE AND TRANSMISSION will significantly improve the life of the engine, transmission bearings and the crankshaft.  Over the past 30 years or more, we have been besieged with broken Model T Ford crankshafts. Why not, the Model T crankshaft is small for the work it does and some are approaching 100 years in age.  Having said that, it is our belief that much of the problem has to do with the lack of good alignment and balancing techniques used in the rebuilding process.  Further, we believe if one starts with a magnafluxed crankshaft and properly aligns and balances the Model T engine, that the crankshaft and bearings will be long lived.  Also there has been considerable interest recently on the MTFCA Forum in new light weight bolt-on counter weights similar to the bolt-on counter weights available in the Model T era.  Since “all” Ford four cylinder engines had counterweights starting in 1931, we believe that a carefully designed set of counter weights could also help eliminate the possibility of a broken crankshaft. 


The basic design of the Model T Ford engine/transmission “demands” careful alignment and balancing.  Differing from most others, the Model T Ford engine has an 85-pound rotating mass transmission bolted on the rear of the crankshaft that must be aligned and balanced.  Since there are four different ways the transmission may be assembled to the engine (both the transmission main shaft and crankshaft flanges may be turned 180 degrees); any time the Model T transmission is removed from the engine for maintenance, an opportunity for misalignment is introduced.  Over the life of an engine, several such opportunities may have occurred perhaps accumulating and resulting in severe misalignment.  Crankshaft regrinding, re-babbiting, parts used from other transmissions, and/or assembly errors may unknowingly introduce misalignment.  For example, a rather common occurrence in the crank shaft re-grinding process is grinding the main bearings off center from the alignment pins.  These problems must be resolved during engine/transmission reassembly procedure.  Also, a common practice is to have one craftsman rebuild the transmission and another rebuild the engine and the two simply bolted together upon return; completely skipping the alignment process!  Misalignment will severely drain horsepower from the engine.  We only have 20 horsepower or so and we need all of it.


A good foundation is required.  The photo above shows all the components that affect the alignment: crankshaft, mainshaft, brake drum and drive plate/output shaft. The path to a correct running fit on the tail shaft starts with the crankshaft.  Concentricity must then be maintained starting with the crankshaft and carried through the transmission main shaft, flywheel, brake drum and sleeve and drive plate and sleeve (tail shaft).  The distance from the back of the crankshaft flange to the rear-most tip of the tail shaft sleeve is approximately 11½ inches; thus even a slight tilt or off-set will introduce a wobble at the end of the tail shaft.


Crankshaft Grinding


The alignment procedure is greatly simplified if the crankshaft bearings are reground aligned with the alignment pins.


Alignment is Critical – We believe it was Ford’s intention that the crankshaft crank pin bearings and main bearings be ground at the factory aligned with the alignment pin holes in the crankshaft flange.  These alignment pins have a snug fit in the crankshaft and the transmission main shaft flanges and are a press fit into the flywheel, all well designed to carry an accurate alignment to the rear.


Indexing a crankshaft grinder on the alignment pins requires a special fixture – Crankshaft grinding machines have lathe chucks on either side, plus the capability of using the lathe centers on either side.  For example, the front end of the Model T crank may be chucked on the left side of the grinder, with the surface under the crank gear providing an accurate attachment surface. Since all surfaces on the used flange end are suspect, a fixture (see photo below) made from an extra transmission main shaft will assure the bearings will be reground aligned with the alignment pins as the factory originally intended.


Making the Fixture – Select a transmission main shaft in nice condition and cut about 3 inches off the shaft leaving the flange with about a 3 inch stub shaft.  Drill out and thread the four bolt holes in the flange to ½ by 20.  Prepare four ½ by 20 thread bolts, short enough so they will not protrude beyond the crankshaft inner flange surface when the fixture is attached (this to allow grinding on the front surface of the crankshaft flange).


Preparing the crankshaft to be groundBolt the fixture to the rear surface of the crankshaft flange with the alignment pins inserted.   Next, the fixture shaft is chucked into the left 4 – jaw chuck and centered by indexing on the shaft of the new fixture.  This procedure will provide a very accurately ground crankshaft…….UNLESS…the crankshaft was not correctly ground at the factory (aligned with the alignment pins).  In this instance, if you choose to use this crankshaft, the crankshaft may be ground aligned on the least worn main bearing and the transmission alignment procedure (described below) used to align the transmission, plus your crankshaft, transmission main shaft and flywheel must be dynamically balanced as a unit.  Note: If you are grinding a Model A shaft to be installed in a Model T block, the exact crankshaft grinding procedures would be used as the alignment pins and bolt holes are essentially the same size and location, the only difference being the Model T pin hole is push fit and the Model A is a press fit.  Also, if you are using the full length rear main, the model A flange has 7/16 by 20 threaded bolt holes. 

 Alignment Procedure


Alignment tasks are accomplished by placing the engine block with the installed crankshaft nose down on an engine stand.  The transmission is then assembled piece by piece onto the engine. This method removes the gravity component from all measurements, plus all measurements are made with a dial indicator mounted on the block allowing concentricity to be measured by turning the engine and transmission components in exactly the same manner as when the engine is running.


Step 1 - It is critical that the transmission main shaft be aligned with the crankshaft main bearings to a high degree of accuracy.   Usually the crankshaft is freshly reground, but any time the engine is removed, alignment and balancing should be considered.  Remove the crankshaft from the engine and use V blocks with a surface plate and dial indicator to check if the crankshaft is straight. 


The crankshaft may be straightened on a press protected by wood blocks on both top and bottom. A bent crank shaft will have a flange that is not perpendicular to the crankshaft main bearings (tilted).  Model T Ford crank shafts are very tough, flexible steel forgings so don’t worry about harming the crankshaft by straightening it.  Carefully measure the amount you push the crankshaft each time, as some over-compensation will be required.  It is important to take your time and straighten the crankshaft to within .001".   Place the straightened crankshaft in the lathe, centered on the main bearings (not the crankshaft centers). Check the run out on the rear flange surface and true if run out is greater than .001.  Next turn .008 off the flange circumference to make absolutely sure there will be no interference between the crankshaft flange and the flywheel during assembly.  The alignment procedure changes the relative positions of parts and may   introduce interference.   


Prepare the transmission main shaft.  Center the transmission main shaft in the four-jaw chuck using a light half-inch grip along with the steady rest.  True the outer flange surface to remove “cupping” on this surface.  Note:  All outer flange surfaces of transmission main shafts we have checked to date have been cupped, that is, the outer edge of the flange surface is higher than the center.  This “cup” must be removed to allow an accurate fit to the crankshaft flange (see left photo below).   As with the crankshaft, turn .008 from the circumference of the main shaft flange (right photo below). 



Then, as shown in the photo at left, use the drill press to bore the main shaft alignment pin holes with a 31/64 drill bit (increasing the diameter of the hole from 15/32” to 31/64” or 1/64”).  Caution, relieve only the main shaft alignment pin holes.  This allows movement of the main shaft in the alignment process. 


Trial fit the transmission main shaft to the crankshaft –Begin by carefully cleaning and oiling all the main bearing surfaces on the crankshaft and block. Next, snug fit the crankshaft in the block so the crank may be turned easily by hand. With the engine block nose down on the engine stand, trial fit the transmission main shaft flange to the crankshaft flange using bolts, nuts and loose alignment pins (photo at right).  Carefully center the main shaft to the crankshaft to within .0005” at the top and bottom of the large bearing surfaces.  After achieving acceptable run out, tighten the nuts and bolts and verify that the run out does not change.  This step is to verify the run out without the flywheel, and the same tolerance will be duplicated in the next step when the flywheel is added to the mix.  Mark the main shaft and crankshaft for proper orientation and then disassemble.


Add the flywheel to the properly oriented crankshaft/main shaft assembly. With the engine nose down on the engine stand, place the dial indicator’s magnetic base on a short piece of angle iron or square tubing bolted to the top block surface (see photo below left).


Install the flywheel and main shaft using four 7/16-20-grade 8 bolts 1 1/4 inches in length.  At this time, you may prepare six of these bolts by cross drilling the heads for safety wire as used on the original bolts.  The extra two bolts will be used to pin the main shaft in place after alignment to center.  Install the crankshaft flange bolts and tighten just snug.  Using the dial indicator on the block and turning the flywheel, main shaft dial indicator readings are taken near the top of the upper large diameter bushing area and near the bottom of the lower bushing area (not on the bearing surface of drive plate bushing).  The goal here is to center align the main shaft perfectly straight with dial indicator readings to within .0005” at the upper and lower large diameter bushings areas.  Only the main shaft will be moved.  The original alignment pins remain pressed into the flywheel and passing through the main shaft flange to a snug fit in the crankshaft flange to preserve the integrity of the crankshaft to flywheel fit.  These unique pins are three-diameter with the larger diameter in middle (main shaft flange).  Only the main shaft flange alignment pin holes have been relieved 1/64” to allow movement for centering.  Since the crankshaft bolts are just snug, the main shaft may be gently moved to center with a small pry bar (between the main shaft and flywheel) while turning the flywheel and observing the readings on the dial indicator. Once the main shaft is centered, the bolts should be tightened while observing the dial indicator reading and always tightening the bolt with the lowest reading. DO NOT PROCEED UNTIL THE SHAFT IS STRAIGHT AND CENTERED TO WITHIN .0005”.  Note – If you are unable to achieve the same reading as the previous trial fit without the flywheel, then the flywheel is the culprit.  First, make sure the alignment pins are completely seated in the flywheel.  Next, try bumping the flywheel in the direction needed with a small block of wood and a hammer.  Then, use a feeler gauge to check for flange perimeter interference with the flywheel on both the transmission main shaft and the crankshaft flanges.   If necessary, disassemble and turn the flange circumferences as needed to remove any interference with the flywheel.


Lock the transmission main shaft in the aligned location.  To lock the main shaft in the newly centered location, two holes are drilled from the top at 90 degrees from the original alignment pins, and then the holes are threaded 7/16-20.  The placement of these two extra holes is not critical and an obvious offset will force a correct re-assembly at some later date.  Two of the previously prepared 7/16” grade 8 bolts are now installed in these threaded holes.  Thus the next person who opens this engine will simply see six crankshaft bolts rather than the normal four.   Note: Some have suggested that alignment be achieved by replacing the original alignment pins with new bolts or pins.  We prefer to maintain the integrity of the original alignment of the flywheel with the crankshaft and move only the main shaft.  Our reasoning is that we want to retain to the greatest extent possible, the original engineering and alignment afforded by the complex, original three-diameter alignment pins. 


Step 2 - Balancing the crankshaft/flywheel Assembly - Remove the crankshaft/main shaft/flywheel assembly from engine by way of the main caps (one of the crankshaft flywheel bolts will need to be removed).  First, static balance this assembly on knife-edges. Next, have this same assembly spin balanced.  Return balanced assembly to block and snug the main bearings.



Step 3 – Centering the brake drum and sleeve and the drive plate and sleeve assembly - Remove the bushing and soft plug from drive plate sleeve and the two bushings from the brake drum sleeve.  We have determined that Ford was not too concerned with the accuracy of the internal bore of these sleeves, apparently relying on the accuracy of the final bore of the bronze bushings.  Thus, our procedure does the same. We have made a special run of the brake drum sleeve bushings (two each required) and the drive plate sleeve bushing (one each).  These bushings are the same outside diameter and length as the original bushings but leaving .010” additional material inside to bore accurate holes inside.  These bushings also have the internal oil grooves, which are the same as the originals.  Press these bushings into the brake drum sleeve and the drive plate sleeve.  Don’t forget that the brake drum sleeve bushing which meets the transmission main shaft flange must be pressed about 3/8” deep because of the main shaft radius.


First, chuck the brake drum surface in an independent four-jaw chuck.  Index the sleeve near the drum and below the key slots to within .0005”. zero run out is ideal, but the wear of the sleeve makes this difficult to attain.  We use a steady rest to support the sleeve during the boring process (see left photo below). Bore bushings to .996”.  Remove the brake drum and use the four-jaw clamp on the surface of the sleeve in the key area. Using the steady rest index the sleeve as before and take a truing cut on the bolt-hole flange surface (right photo below).  (Note: we have found that the bolt flange surfaces of both the brake drum and drive plate to have run out.)  For the pre-26/27 early type brake drum, remove the same amount off the relieved area that the drive plate fits over.  Great care must be used to assure the bolt surfaces will fully seat.  Provide a .005” diameter clearance on the drive plate flange.  Provide a small 45 degree interference cut on the 26/27 inner perimeter bolt surface.  



Place the drive plate in the lathe with the sleeve in the four-jaw clamp on the first ½” or so. Using a steady rest, index on both ends of the sleeve with the dial indicator.   An old shifter collar with a set screw in the center may be used to hold the clutch fingers in place.  Bore the bushing to .933” (left photo below) and then true the flange bolt surface (right photo below). 


The early type requires the bolt hole flange to be trued and the lip should be cleaned the same amount that was removed from the flange surface.  Failure to do so will not allow the flange surface to make full contact with the brake drum (not necessary on 26/27 models).


Our next step is to bolt the brake drum to the drive plate using a mandrel.  The mandrel is 12 inches in length and is  designed to hold the brake drum and sleeve on the left and the drive plate and sleeve on the right with the bolt surfaces together in the center.  We turned this mandrel from a discarded rear axle.  Lathe centers were placed in each end.   The left 5¾ inches of the mandrel was turned to .995” to give a .001” fit to our oversized brake sleeve bushings at .996”.  The next 1½ inches should be turned to .932” for a .001” fit on the oversized drive plate sleeve bushing .993”, with the balance of the shaft turned to .925” for clearance


This mandrel is used as a center for the final bolt pattern fit between the brake drum and the drive plate.  Place the mandrel on centers in the lathe with the brake drum on the left and the drive plate on the right (left photo below), bolt surfaces together in center.   Using dial indicators, on the sleeve surfaces, do a trial fit of all six bolt positions to find a position that (a) does not lock up on the bushing, and (b) has the least run out on the tail shaft sleeve.  Note: it appears that some run out to .001” will not cause any problems here.  Install and tighten all fasteners.  Do not take apart until the following procedures are completed.



It is now time to turn the tail shaft to the final fit of the 4th main bearing (right photo above).  A steady rest should be used to better support the tail shaft for turning.  Either the four-jaw or a lathe dog may be used to turn the assembly.  Whether using babbitt or ball type 4th main bearing, turning may or may not be required. Some ball bearing types require turning the drive plate down to 1½” outside diameter.  After your decision as to the 4th main configuration, the drive plate/brake drum assembly may be removed from the lathe and remove the mandrel from the assembly.


Reamers are now used to make the final fit of the brake drum and drive plate bushings on the transmission main shaft.  This is done as an assembly from the mandrel operation. The drive plate bushing is reamed first with a 10” long by 15/16” reamer fitted with a .995” pilot sleeve to align ream through the brake drum bushings.  


Finally, a standard Model T Ford 1” tapered reamer is used to ream the brake drum bushings (Note: ream to fit transmission main shaft). 


Check the final results by cleaning, oiling and assembling to the transmission main shaft.  Our final run out result at the tail shaft has been found to be something in the .004” to .006” range.  Remember, we have bearing clearance on all three main shaft bushings; therefore, there will be run out.  If your readings are outside this range, carefully review all the above procedures.


We need to address “total” run out.  Just turning the brake/drive plate on the main shaft is not total run out, you will need to index the brake/drive assembly 90 degrees (four times) and rotate the flywheel 360 degrees each time.  If you are happy with the results, place reference marks to indicate the aligned location of the drive plate and brake drum bolt surfaces.  


The brake drum and drive plate may now be separated. 


Next, static balance, on knife edges, the brake drum, drive plate, low and reverse drums.  Refer to the MTFCA transmission manual.


Carefully clean, oil and reassemble the completed engine.  Don’t forget to install the soft plug in the tail shaft sealed with a liberal amount of RTV.  Complete the assembly of the transmission and install engine pan and transmission cover.  Final fit the 4th main bearing by bumping (bending the pan) with a block of wood and small sledgehammer until the 4th main slips easily into place.  On the 26/27 models, alignment can usually be achieved by adjusting the shims between the hogshead and block.


Addendum:  Fellow Model T Ford engine re-builders; these procedures are not chiseled in stone; they represent our best efforts to date.  We have about 8 engines in the field using these procedures.  These procedures are difficult; and, require a lathe and a fairly sophisticated machinist.  We want these procedures to continue to evolve; to simplify, and improve the accuracy; and we need your input to make that happen.  If you have an idea how to improve these procedures in any way, please share your ideas with Mike Bender at or Fred Houston at .


We are now able to perform this procedure in 4 to 6 hours depending on the condition of the transmission. 


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