Pedal Pusher: How to measure and adjust your Clutch Pedal Ratio

So you just converted your clanky old manual clutch to a hydraulic release bearing setup and you thought the pedal would be easier to operate than before. While that should be the case, it isn’t always, and that is due to geometry. Much like a brake pedal, there is a specific ratio that you need to achieve in order for the pedal to be easy to operate. For hydraulic clutch systems, that ratio is 6:1.

Manual clutches are different from hydraulics, they use a bell-crank system that increases the effectiveness of your clutch pedal. With a hydraulic system, it is all in the placement of the master cylinder push rod on the clutch pedal. The higher the pickup point is on the pedal (closer to the fulcrum of the lever), the easier it is to push the pedal. There are three key factors to this equation: pedal length, pick up point to fulcrum length, and master cylinder bore.

The bore of the clutch master cylinder is the smallest part of the equation because most clutch masters are in the 7/8” range. The bigger you go, the more effort is required to operate the master cylinder. Provided you have a 7/8” bore or smaller, the 6:1 standard is used.

To determine the ratio of the pedal, you need to do some measuring. There are two measurements you need to take: the length from the pivot (fulcrum) of the pedal to the pushrod hole (Y), and from the fulcrum to the center of the brake pedal (X). The formula is X/Y=Ratio. For example, your stock clutch pedal is 14 inches long (X), with a pickup point measuring 4 inches from the center of the fulcrum (Y). 14/4=3.5, which is 3.5:1. While this may have worked for the factory manual linkage, it is about half of what it needs to be for a hydraulic set up. In this situation, 100 pounds of foot pressure yields 350 pounds of pressure to the master cylinder. Move the pickup point up 1.75 inches, (Y measurement of 2.25”), and that same 100 pounds of foot pressure yields 600 pounds at the master cylinder.

For most applications, you can raise the pickup point by simply drilling a new hole in the pedal arm, but some cars, like GM A-bodies, use a convolute pedal design that requires welding if you want to raise the pickup point. This can be done with a ¼” tab of steel welded to the pedal in the location you want it. This process can become more complicated when you are trying to use a factory firewall hole for the master cylinder.

The sharper the angle is on the master cylinder, you run the risk of creating a bind, which no amount of pedal ratio can overcome. There are a couple of solutions for this scenario. The first is to move the master cylinder up on the firewall, decreasing the angle. This is not always possible, as the brake booster or other items that cannot be easily moved are in the way. The other option is the American Powertrain adjustable firewall mount.

The patented firewall mount allows the master cylinder to accommodate the clutch pushrod angle while being mounted above or below the pickup point on the pedal itself. Because the master cylinder is a sealed system, the angle itself does not affect the operation of the master cylinder. If you have this mount and the angle is still too great, then you have to move the master cylinder.

Here is the diagram for measuring pedal ratio. Always measure to the center of the fulcrum, pickup point, and to the center of the pedal.

This is a brake pedal, but the math is the same. On this pedal, the pickup point is 5 5/8” from the fulcrum.

The pedal measures 14 inches from the fulcrum to the center of the pedal. The math reveals this is a 2.48:1 ratio, which is ludicrously low.

To make this pedal match the 6:1 (which is also the optimum ratio for brake pedals), we drilled a new pickup point. All better.

On this 1965 Mustang, the factory clutch pedal is very close to the fulcrum, yielding a suitable ratio for the master cylinder. We were even able to use the original firewall hole.

GM A-body cars (Chevelle, Skylark/GS, 442, etc) have funky clutch pedal as shown here. If you have to change the ratio, fabrication and welding is required.


Written By: Jefferson Bryant


Red Dirt Rodz
4518 Braxton Ln
Stillwater, OK 74074
405-880- 5343

American Powertrain
2199 Summerfield Rd
Cookeville, TN 38501
1-931- 646-4836

Heil Hydra(Max)! Setting up your hydraulic release bearing

High-performance engine installed- Check. Close-ratio Tremec T56 installed- check. Clutch fully operational- nope. Well that isn’t good, it is kind of hard to put 650hp to the ground when your clutch won’t engage or disengage when you operate the clutch pedal. Unlike a mechanically-operated clutch, most modern manual transmissions require hydraulic release bearings, and if you are not close enough, you may as well be a mile off. Installing the American Powertrain Hydramax hydraulic release is not difficult, in fact it is pretty easy, but it does require some math.

The relationship between the clutch diaphragm and the release bearing is the key to a properly adjusted hydraulic set up. The release bearing should ride the diaphragm without putting pressure on the fingers, but also should not be too far away. It is pretty easy to install the bearing where it is either too close (clutch is always disengaged) or too far (clutch won’t disengage). Because these installations are not stock, you have to figure out this relationship on your own. Don’t worry, it isn’t difficult.

What you need:

  • Pen
  • Scratch paper
  • Straight edge
  • Calipers or ruler that reads to .001
  • Partially-assembled drivetrain.

To start the process, the engine must be assembled with the flywheel and pressure plate. The clutch does not have to be installed at this point, because it doesn’t matter; but if you want to do everything at once, install the clutch with an alignment tool in place. Additionally, the bellhousing must be installed on the engine as well. Begin by placing the straight edge across the center of the opening in the bell housing. Use a ruler or measuring tape to determine the resting depth of the diaphragm, this measurement is taken off of the fingers themselves where the release bearing rides. Take this measurement in three places and write the results down on the scratch paper.

Moving on to the transmission, the center alignment dowel must be installed, along with the Hydramax bearing with the notch locked onto the dowel in the fully seated position. Use a straight edge on the transmission, running across mounting surface for the bellhousing. Measure from the transmission mating surface to the face of the bearing where it rides on the diaphragm. Measure in three places and record the results.

The two sets of measurements provide the variables needed for the final calculation using the following formula. This equation will tell you how many shims are needed to achieve the proper air gap between the bearing and the diaphragm. The recommended air gap is .150-.200”, you can have as little as .100” (absolute minimum), but try to stay inside the recommended range. It is possible on some GM applications to not have enough room to get to even the .100”. If this is the case, you may have to shim the actual transmission from the bell housing using washers or spacer. This is due to the shallow nature of the GM bell housing design. There are 3 shim thicknesses for the big 3. Mopar uses .063, GM uses .090 and Ford uses .057. The conical shape of the GM shims creates the .090 thickness, even though the metal used to create the shim is not that thick.


Bell facing to clutch diaphragm – minus Bearing Face to Trans bell face – minus .150 / .090 = Number of shims 


For example: Bell to diaphragm= 2.450, bearing to trans mount face= 2.125

2.450 – 2.125 – .150 / .090 = 1.94

This means your application needs 2 shims, which yields an air gap of .180”, which is perfectly acceptable.

For GM T56, Tremec Magnum, and Viper 6-speeds, American Powertrain recommends the following procedure for measurements:

Install the clutch and pressure plate to the flywheel on the engine. Place the straight edge across the fingers of the diaphragm and measure from the inside edge to the block mating surface. Record this measurement as A.

Next, install the Hydramax bearing retainer base with guide pin to the transmission and load the bearing onto the retainer, with the guide pin in position on the bearing. Install the bellhousing to the transmission. Place a straight edge across the bellhousing and measure to the bearing face. Record this measurement as B.

Using the formula below, calculate the number of shims. A block plate for a scattershield can be factored in by adding the thickness to measurement B.


B-A-.150 / .090 = # of shims


Once you have determined the number of shims, count them up and stack them behind the release bearing on the transmission shaft, install the bearing, and mate the engine to the transmission. It is that simple. Before you mate the trans to the engine, lube the o-ring on the inside of the bearing base with a little DOT 3 brake fluid.

To demonstrate the process, we installed a HydraMax hydraulic release bearing system on a GM LS- series engine with a Muncie 4-speed (mechanical linkage with an LS is not a simple proposition) which was being installed into a 1969 Chevelle. Setting up the bearing was simple, and the results yielded a smooth clutch without any hiccups.

The process begins by mounting the flywheel to the engine. We torqued the bolts to spec.

The clutch does not have to be installed if this is a mockup, but if it is the final install, make sure it is in there. Be sure to put the clutch in using the correct orientation.

Use an alignment tool to keep the clutch in position.

Next, the diaphragm is installed to the flywheel. There may be multiple bolt patterns on the flywheel, so you might have to find the right holes and line it up.

Use a couple of bolts to secure the bellhousing and then use a straight edge and ruler or caliper to measure the depth of the transmission mounting pad to the diaphragm fingers. Measure in 3 different places and note each measurement. This is measurement A.

The hydraulic release bearing mounts on a stud in the transmission. The American Powertrain kit comes with several studs to match the threads from the front bearing cover. Remove one bolt and match the threads.

Then the stud is installed into the transmission. Don’t forget to use medium threadlocker on the threads and bend the retaining tabs back over the hex on the stud.

The Hydramax bearing slides over the input shaft and locks in place on the stud, this is a free-floating unit, it does get bolted down.

Now measure the height of the release bearing to the transmission mounting flange. Make sure
that you measure to the top of the bearing. This is measurement B.

Using the formula, we determined we need 2 shims: (A – B)-.150”/.090 will determine the number of shims required. For example, 2.45-2.125- .150/.090 = 1.9 shims, so you use 2 shims. You can run as little gap as .100”, but .150 to .200 is optimum. Stack up the shims and install them behind the bearing.

At this point, the bellhousing is removed from the engine and bolted to the transmission using new grade 8 bolts.

Each hydraulic line threads onto the bearing and the line ran out of the bellhousing through the clutch fork hole. The lines are secured with a wire clamp.

Finally, the engine and trans are mated together and ready for installation in the vehicle.

Written By: Jefferson Bryant


Red Dirt Rodz
4518 Braxton Ln
Stillwater, OK 74074
405-880- 5343

American Powertrain
350 Transport Dr
Cookeville, TN 38506
1-931- 646-4836

Shifter stuck in gear after your new transmission shows up? Here is the cure…

American Powertrain TKO Shift Assembly Re-alignment Procedure.

Background: Your brand new TREMEC TKO shows up in at your shop or house…You rush out to open it up get it in the shop and it will not shift through the gears! Sometimes your new transmission may get jostled during shipping, causing a misalignment of the shift mechanism. You should shift your transmission through all the gears before putting it in the car and rotate the input shaft to make sure it moves freely.

Note that reverse must be engaged from the neutral position. The transmission has a mechanical reverse lock-out that will not allow a straight shift from 5th to reverse.

If your transmission shifts into all gear positions and the input rotates freely you may proceed with installation.

Should you have a transmission that is locked up due to misalignment you can easily correct the problem with a few simple tools in about fifteen minutes.

Correction Procedure:

Step 1: If you have a clutch disc handy, place it on the input shaft and attempt to turn the disc like a steering wheel. If the alignment issue is minor this will often correct the problem.

If that fails, move on to step 2

Step 2: Remove the four bolts that secure the mid-plate on top of the transmission. This is the flat five-sided plate in the center of the gearbox. See image:


Step 3:  Gently pry the cover off with a flat blade screwdriver or small pry bar.  Work slowly around the periphery of the plate and do not bend the cover.  A chisel punch can be used with a small hammer if used carefully.

Step 4: Under the cover you will find three shift lugs. These lugs should be aligned in neutral position as shown in the image.

Step 5: If they are not aligned use a large screwdriver or small pry bar to move the lugs back to neutral

Note the arrow pointing to the right lug in an incorrect forward position. You may need to move more than one lug. There will be an audible click when each lug is in neutral and you will feel the neutral detent.

Once the lugs are re-aligned the shifter should move freely through the gears and the input shaft should rotate freely. You can test this with the cover off.

Step 5: Now that the transmission is operating properly, remove the gasket sealer from the case and cover plate using solvent and a rag. You may use a razor blade on the case, but do not use a razor on the cover. The sealant will rub away with a rag and solvent. Run a continuous 1/8” bead of grey gasket sealer on the top of the case and around the bolt holes. Then reaffix the cover.

NOTE: Don’t go crazy with the gasket sealer. You don’t want chunks of it dropping off and gumming up the linkage.

If these steps do not correct your problem you will need to contact us for help at 931.646.4836. If your transmission was damaged in shipping we will need images of the transmission and the original shipping carton inside and out. This will allow us to make a claim with the shipping company. Our tech support folks can walk you through this procedure.

Thank you for working through this simple issue. Enjoy your TREMEC TKO.


Swapping a 5-speed into an F-100

Driving a classic truck is fun. It’s even more fun with a stick.

American Powertrain had an F-100 project built by their IT guy Barry. It’s a “pro-touring” like project he has been slowly and meticulously building at home. The truck has good handling and old school looks with a modern EFI 351W under the hood. The parts are a go-to play list for F-100 builds: Panther front end swap, FITech and disc brakes. He knew the final cherry on top would be a TREMEC TKO 5-speed swap. Follow along on the install.


Barry’s 1972 F-100 short bed. 351W with Fitech EFI, Trick Flow heads and mild cam. Even has Vintage Air


The truck came in with no transmission so this gave us a nice clean place to start. The Crown Vic Panther front end swap puts the engine pretty close to stock location so transmission placement was no issue.


The heart of it all is the American Powertrain F-100 Pro-Fit 5-speed kit, using a TREMEC TKO-600. This kit has everything you need to install a 5-speed in a classic Ford truck: crossmember, hydraulic clutch, pressure plate clutch, bell and flywheel.  A custom built driveshaft is also included in the kit. Once you do the install, fill out the driveshaft order form to send in the measurements and your new, custom made shaft will be on its way a couple of days.


The first thing we did was slap the bell housing on with no flywheel or clutch. We hoisted up the trans to see what kind of clearances we had to work with on the tunnel. Turns out we had to do a little hammering just at the vent tube (a common clearance issue on TKO’s). One of the ways American Powertrain gets these larger transmissions to fit into older cars is case minimizing on the transmission. They also offer a fiberglass tunnel hump for F-100. 6-speeds will need a larger tunnel opening.


The trans on the left is a stock out of the box TREMEC TKO. The trans on the right has been “minimized” by American Powertrain. You can see the corners on the top cover of the trans were CNC milled and new cover plates installed for better tunnel clearance. Doing these mods yourself will void the TREMEC warranty. APT works with TREMEC on approving these mods and offers a two-year warranty. The shifter has been replaced with a White Lightning short throw shifter that also serves as forward shift position to clear a bench seat.


Once the tunnel clearance’s was checked and shifter location set up, we installed the X-Factor universal adjustable crossmember. American Powertrain has these in 3 sizes that adjust to fit frame widths from 20” to 34”. We used the widest one that adjusts from 32”-34”. This allows you to set height for the right driveline angle, and uses a standard GM transmission isolator. The crossmember also allows adequate exhaust clearance for lowered trucks. Simply slide the plates to the frame, mark your holes and drill, using the supplied grade 8 hardware



Set the crossmember to the right driveline angle. Plus or minus 3 degrees are the specs that TREMEC calls for to avoid vibration.  A cheap angle finder makes this pretty easy.



Now the real fun begins.  Once we did the mock up and took out the trans, it was time to start the install. One of the critical procedures is to dial indicate your bell housing. This is very important to make sure the bell is centered on the engine so the input shaft lines up straight with the crank. This is critical for transmission longevity. American Powertrain has videos and instructions on how to get this right. 


Once the bell is checked, take it off and start installing the flywheel and clutch. Make sure to torque everything down to spec!


Now its time for more math! This time it’s for the hydraulic clutch bearing. Once the bell and clutch were installed, we had to measure the distance from the pressure plate fingers to the back of the bell. Then from the face of the trans to the face of the bearing. This difference tells us how far the bearing is sitting back from the clutch fingers.


The Hydramax Hydraulic Clutch Kit allows many different clutch combinations. The key to this is making some measurements and setting the depth correctly for the set up you have. The specs are .150” air gap between the bearing and the pressure plate fingers. Once you get the measurements this will determine the number of shims you need to set it correctly for long clutch and bearing life. Once again, American Powertrain has all the instructions and videos to make this pretty easy.  A digital caliper is all you need.


Install the trans and the bearing together. Make sure to run your lines out of the bell and away from the exhaust.



Barry’s truck already had a clutch pedal. These are fairly easy to find for Fords in a junk yard or any of the restoration catalogs.


Next up mount the patented Hydramax master cylinder bracket on the fire wall. This requires a about four holes to be drilled. The bracket has a backing plate to prevent firewall flex. You may have to drill an additional hole higher up on the pedal to get the clutch rod ratio set correctly. We had to lengthen out the mounting point using a piece of flat stock to get the correct angle. American Powertrain will have this added in to the kit for F-100’s as soon as research & development approve the new component.


Finished install is now ready for a new drive shaft. Do a few simple measurements on the included driveshaft measurement form then send it in to American Powertrain. In a couple of days your new driveshaft will show up, ready to install.


We had plenty of room for a bench seat with a double bend 18” shifter handle. APT has tons of shifter handles, shifter knobs and boots to finish up your install. We finished it off with one of their gunmetal gray billet shift knobs to match the wheels of the truck. No more boring automatic!



American Powertrain also now offers an F-100 fiberglass high hump tunnel replacement for F-100s. TKOs and T-5s fit the truck with slight massaging. Magnum 6-speeds will need more clearance. But if you want all the room you can get grab one of these to finish it out.

TREMEC discontinues production of all Magnum 6-speeds with a .50 overdrive gear.

If you want a .50 6th gear call now because when they’re gone … they’re  gone

We still have a few in stock. If you want one give us a call!

Tremec will still offer the 2.97 first gear option previously offered with the .50 6th, but it will now only be available with the .63 6th .

YES – that is correct you have 2 choices of 1st gear that are only .31 apart but no factory option for the .50

After the supply of factory built .50 6th gear  Magnums is gone American Powertrain will be able to custom build a new Magnum with the .50 6th gear for an additional charge. Call for details and pricing.

931-646-4836 or shoot us an email

TUET11009 MAGNUM for GM   2.66/.63
TUET11010 MAGNUM for Ford  2.66/.63
TUET11011 MAGNUM for Ford  2.97/.50  Discontinued
TUET16884 MAGNUM for Ford  2.97/.63  NEW MODEL
TUET11012 MAGNUM for GM   2.97/.50  Discontinued
TUET16885 MAGNUM for GM   2.97/.63  NEW MODEL
TUET11430 MAGNUM XL for Ford 2.66/.50  Discontinued
TUET16886 MAGNUM XL for Ford 2.66/.63  NEW MODEL
TUET11940 MAGNUM XL for Ford 2.97/.63
TUKT12019 MAGNUM XL + Mustang install kit 2.66/.50  Discontinued
TUKT16901 MAGNUM XL + Mustang install kit 2.66/.63  NEW
TUKT12021 MAGNUM XL + Mustang install kit 2.97/.63