LT1 to LS1 T56 Conversion


This article describes my personal experiences and decisions while converting the T56 6-speed transmission in my 1995 Pontiac Formula to use an LS1-style McLeod Street Twin clutch.  If you wish to skip directly to the parts, click here.


When I started re-building my ’95 Formula in mid-2007, rather than putting the 4L60E automatic transmission back in, I decided to convert to a 6-speed T56 manual transmission figuring it would more for street duty. I came across a great deal from a friend and ended up with mildly-built T56 with a 300M output shaft and an almost new SPEC 3+ clutch kit. The SPEC 3+ is rated to nearly 800 lb-ft of torque and I figured that would be plenty to transfer power on my mild street car.

LT1 flywheel showing some signs of wear

Fast forward to May 2011. After some engine and nitrous system upgrades the car is now making around 750 lb-ft of torque and although the clutch has performed flawlessly to this point I decide to get smart an install an SFI approved bell housing from Quick Time Inc. which is now a part of Lakewood Industries. Upon installing the bell housing, I quickly found that over it’s 4 years of duty, the SPEC 3+ clutch was done. It had been a great clutch with many 6K+ launches on drag radials and slicks and I have no complaints. However, I now had to make plans for a new a clutch and not be near-sighted on what power levels it may need to hold.

QuickTime SFI Approved LS1 Bell Housing

Luckily, I was friends with a few guys that know a thing or two about 6-speeds: Taner Bosnali and Brady Matysek.  They both recommended the same clutch.  The only problem is that it wasn’t an LT1 clutch!  I was advised to undertake a transmission conversion which would allow me to run an LS1-style twin disc clutch. A McLeod LS1 Street Twin to be exact.  Not only for design and performance implications but also for safety.  I like my feet and legs and the ability to walk, drive and play with my kids.  I found out that the LS1-style street twin is much better suited to high RPM abuse over the LT1-style.  The LT1-style still uses a cast Valeo pressure plate whereas the LS1-style uses a billet pressure plate.  The cast design is more susceptible to weaken and fail and without an SFI approved bell housing the results of that scenario is something that Taner knew all too well and is the primary reason we have a McLeod LT1 bell housing today.

The Basics

LT1 T56 Input Shaft

In case you’re wondering what all this means.  It’s fairly simple.  In order to make your LT1 T56 use an LS1-style clutch you’ll need to do the following:

  1. Research and purchase the right clutch for you and your setup.  In this case, I went with a McLeod LS1 Street Twin.
  2. Purchase an SFI approved bell housing if you don’t have one yet.  McLeod and Quick Time Inc. have them.  The LS1 bell housings will bolt directly to the LT1 block.
  3. Purchase a stock or aftermarket internal release bearing.  I would recommend a stock GM slave cylinder.  My experiences with the McLeod unit have been be extremely frustrating and disappointing.  You will also need to get a shim kit from Tick Performance or make your own shim.  The shims are needed to get the clearance between the bearing surface and pressure plate into spec.  For the McLeod twin disc, they recommend between 0.100″ to 0.150″.
  4. Purchase an aftermarket clutch master cylinder from either McLeod or Tick Performance.  I went with the Tick unit based on recommendations from Taner and others.
  5. Replace the front case and input shaft of your LT1 transmission with an LS1 front case an input shaft.  The LS1 input shaft is longer and exposes more of the splines which is especially beneficial and even required for twin disc setups.  Make sure to set the correct amount of endplay on the input shaft.  I was advised to set endplay at 0.004″.
  6. Purchase or build an 0.50″ thick spacer to go between the transmission and bell housing.  McLeod makes these and calls them “scallop rings”.  Since the input shaft is longer, you need this to space the transmission back a little.
  7. Modify the transmission crossmember.  This conversion moves the transmission back a little over 1″.
  8. Check driveshaft length.  More than likely, you will need to have the driveshaft shortened.
  9. Closely follow the manufacturer’s instructions for assembling and installing the clutch!

What You’ll Need

I obtained parts from several different sources throughout this conversion, including McLeod Racing, Liberty’s Gears and RPM Transmissions. I’m sure there are other businesses out there that can get the same parts but I have to say that these three particular businesses provided me with execellent customer service and assistance during this process.

Description Part Number Price Qty
QuickTime Bell Housing (LS1 to T56)  RM-8020 463.95 1
Tremec LS1 T56 Input Shaft  1386-585-010 178.95 1
Tremec LS1 T56 Front Cover  TUEP2290 180.00 1
Tremec Shim Kit  TRS394225K 45.99 1
GM 2001 LS1 F-body Clutch Slave Cylinder  15046288 89.99 1
McLeod Scallop Ring  8703-12 154.95 1
Tick Performance Adj. Master Cylinder  TAMCKFB 299.99 1
Tick Performance Slave Cylinder Shim Kit (3 Pack)  TICKSHIMKIT 39.99 1
Tapered Roller Bearing Cup (for input shaft)  M88010 8.00 1
Tapered Roller Bearing (for input shaft)  M88048 12.00 1
Royal Purple Synchromax Manual Transmission Fluid  1 qt. 17.24 4
RTV  –  – 1
Non-synthetic DOT3 Brake Fluid  32 oz. 7.49  1



Mcleod Racing
1600 Sierra Madre Circle
Placentia,Ca 92870
(714) 630-2764
(714) 630-3668 – Tech Dept

Liberty’s Gears
6390 Pelham Rd.
Taylor, MI 48180
(313) 278-4040

RPM Transmissions
1426 West 53rd Street
Anderson, IN 46013
(800) 406-1109

Tick Performance
106 Performance Rd
Mooresville NC 28115-9590
(704) 660-5843


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One Response to LT1 to LS1 T56 Conversion

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