McLeod GM Auto Muncie M23 2.50in-2.99in Hydraulic Bearing
Putting an Auto Gear Muncie M23 four-speed behind a big-block Chevelle, a first-gen Camaro or a GM-powered hot rod, and want to lose the clutch fork, Z-bar and linkage? The McLeod 1300-AG is the hydraulic throwout bearing McLeod catalogs specifically for the Auto Gear Muncie M23. It bolts on where the Muncie's front bearing retainer goes and turns the clutch release into a single hydraulic unit. Most people looking for it are dealing with linkage that binds against headers, a clutch that drags at stoplights, or a swap into a chassis that never had four-speed linkage mounts.
On a stock Muncie setup, the pedal moves a rod and Z-bar that swing a fork, and the fork pushes a release bearing riding on the front retainer collar. Every pivot adds slop and every engine-to-frame movement changes the adjustment. The 1300-AG replaces the retainer itself with a hard-anodized billet aluminum housing that holds a piston and a constant running bearing. Fluid from a clutch master cylinder enters through braided AN-4 lines on swivel fittings, the piston extends, and the bearing pushes the pressure plate fingers. McLeod notes that the bearing stays lightly in contact with the fingers without loading them, so it takes up wear on its own and the engagement point does not drift. The AG version uses the adjustable piston, for an A dimension of 2.50 to 2.99 in. A fixed-piston Auto Gear version for 2.31 to 2.50 in. is cataloged separately as the 1300-1AG.
If shifts still grind on the move after the clutch releases cleanly, the Muncie itself likely needs synchros and bearings. Our Yukon 1966-74 Muncie bearing and synchro kit covers the original GM boxes.
McLeod's FAQ is direct about this: establish your A dimension before you buy, because a wrong-height piston means downtime and an exchange. Bolt the clutch and pressure plate to the flywheel, torque it, install the bellhousing, then measure with a two-decimal caliper from the bellhousing's outer mating flange, where the transmission face seats, to the tips of the pressure plate fingers. McLeod clarifies that the reference is that outside flange, even though an arrow on its older chart pointed inside the bellhousing. A reading between 2.50 and 2.99 in. calls for this 1300-AG; 2.31 to 2.49 in. calls for the 1300-1AG. Final running clearance after install should be .100 to .250 in. If the decision is really about whether to rebuild the drivetrain or replace it, our manual vs. automatic repair cost guide gives a realistic picture of manual gearbox work.
McLeod lists two 1300 series bearings for Muncie gearboxes, and they are not interchangeable in the catalog. The plain 1300 is listed for GM Muncie and Jeffco transmissions with a 4.680 in. register. The 1300-AG on this page is listed for the Auto Gear Muncie M23 with the adjustable piston. If you have an original GM M20, M21 or M22 rather than an Auto Gear unit, tell us before ordering. Send the case casting, the transmission maker and your measured A dimension and we will confirm the right version. The bearing will not work with counterweighted diaphragm pressure plates unless the weights are removed, or with self-adjusting pressure plates. A matching GM 621 Muncie bellhousing for an 11 in. clutch and our full manual transmission hard parts are here too.
Install a new pilot bearing while you are in there; the OTC 1172 slide hammer pilot bearing puller pulls the old one out of the crank without damage.
| Brand | McLeod Racing |
| Part number | 1300-AG |
| Fits | McLeod GM Auto Muncie M23 2.50in-2.99in Hydraulic Bearing |
| Type | Release Bearings |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
McLeod lists the 1300-AG for the Auto Gear Muncie M23. For original GM Muncie and Jeffco boxes with a 4.680 in. register, McLeod lists the plain 1300. Send us your transmission details and A dimension if you are unsure which you have.
It is the distance from the bellhousing's outer mating flange, where the transmission seats, to the tips of the pressure plate fingers with the clutch installed and torqued. Use a caliper that reads to two decimals. The 1300-AG fits 2.50 to 2.99 in.
Only if the input shaft has a slinger nut under the bearing collar. McLeod says the slinger flange has to be ground or machined off, bringing the OD from 2.00 in. to 1.800 in. The nut is left-hand thread.
DOT 3 or DOT 4. Silicone-based DOT 5 fluid attacks the seals and will cause leaks.
No. The constant running bearing follows the fingers as the disc wears. You will actually see the reservoir level rise over time, so leave about 1/4 to 1/2 in. of room at the top when you fill it.
