Classic Motorcycle Build

Ironhead Transmission Remove And Install

Text and Pictures by Mark Trotta

Recently a viewer emailed me about a shifting problem he was having with his 1969 Sportster. One of his questions was how to remove the transmission assembly without the specialty tool listed in the factory manual.

Ironhead-transmission remove and install

To remove an Ironhead transmission from the cases, you first have to remove the primary cover, then remove the clutch, primary chain, and gears.

When the access door (trap door) is clear, remove the four bolts, then slowly and carefully, pry the access cover with a right-angle screwdriver or something similar.

remove Ironhead transmission

Loosen one spot a little, then loosen another spot opposite that one, etc. It will take a few minutes, but this method works without damaging anything.

I have seen videos of mechanics smacking the transmission mainshaft from the other side with a hammer. This is the "quick and dirty" way and not recommended.

Trap Door Removal Tool

The factory service tool is currently available in the aftermarket. It allows removal of the transmission unit with minimal effort.

Ironhead-transmission remove trap door

Remove Ironhead Transmission

With your left hand on the sprocket-shaft side, and your right hand on the primary (mainshaft) side, remove the transmission assembly as slowly as you can. Gears, washers, and roller bearings will fall every which way.

ironhead-transmission remove and install

No matter how careful you are, the transmission will not come out in one piece.

Sometimes when removing, the counter-shaft will stay in the case and the rest will come out with the access door. Other times, the gears on the counter-shaft will fall off when pulled out of the cases.

There are 23 small roller bearings on the pinion side of the motor. These rollers will fall out as you pull the transmission out, so prop some rags around the motor and try not to lose any of them.

Ironhead transmission roller bearings

It's a good idea to round up all 23 roller bearings immediately after removing the transmission to make sure you haven't lost one.

Keep track of the thrust washers at the ends of both shafts. The shafts are two different I.D. sizes, so you can't mix them up.

Ironhead transmission remove and install

Mainshaft vs Countershaft

Since it may be weeks or even months before the transmission is re-installed, note the order that things come out so you can reassemble it correctly. Write things out in a notebook, or take pictures.

Ironhead transmission removal

If you mix up the transmission gears, remember that mainshaft gears have five dogs, and countershaft gears have four dogs.

The mainshaft gears are installed "big-small-big-small", so countershaft gears will install "small-big-small-big".

Install Ironhead Transmission

Install the transmission assembly back into the engine case, aligning the the two dowel pins in their respective holes. Washers are not recommended or needed with the four mounting bolts.

When installing the transmission assembly, the mainshaft and countershaft end play needs to be checked and adjusted. You'll need a dial indicator to correctly measure end play.

Mainshaft End Play

Ironhead transmission mainshaft play

The factory manual states that main-shaft end play should be between .015"to .025". Mainshaft thrust washers are available in assorted sizes.

Countershaft End Play

Ironhead Sportster countershaft end-play

The factory manual recommends countershaft end play should be between .004"to .009". Countershaft thrust washers are available in assorted sizes.

Mainshaft Roller Bearings

The standard width for the 23 loose mainshaft rollers is .1562" O.D. They are available in several oversizes to compensate for wear.

Shifter Shaft

After the mainshaft and countershaft play are checked and corrected, it's time to install the shifter shaft. The shifter shaft is also referred to as the shift shaft, shift lever, inner gear shaft, or lever arm shaft.

ironhead transmission remove and install

There are two kinds of shifter-shafts used on Ironheads. Early models (like the one shown) have smooth splines, and later Ironheads (1977-1985) have shaft ends that are splined. The two styles will interchange.

To me, the early design seems to make more sense--if the bike fell on it's side, a splined shifter would break or bend. This would mean removing the primary cover, primary chain, gears, clutch, and transmission. A smooth shaft would merely be pushed up, which could loosened, spun back, and re-tightened.

Before the transmission assembly goes back in, install the shifter shaft into the right-side engine case. For proper shifting, the shift lever arm needs to be centered. I use a dab of wheel bearing grease to hold it in place. If you mark the shaft at the 12 o'clock position with a felt-tip marker, you can tell if the arm position changes when installing the transmission.

Install Roller Bearings

First, install the flat washer that sits between the rollers and the spring circlip on the outside. I use a dab of wheel bearing grease to hold the 23 roller bearings into the bearing race. The grease dissolves into the engine oil upon start up.

ironhead transmission install

Once the transmission is back in the engine cases, check that the shifter shaft is correctly engaged with the shifter pawl.

Bench-Check All Gears

Check all four gears (including neutral) by shifting the transmission by hand. I go through the gears with a pair of Vice-grips attached to the shifter-shaft, or you could temporarily install the foot shift lever. You should feel a slight resistance and hear a solid "clunk" when the gears engage.

install ironhead transmission
ironhead transmission install

Read: Ironhead Transmission Basics