Fabulous Four Speeds - Manual Transmission Detailing Tips - Pontiac Enthusiast July/August 2009

When it comes to four speeds there are many different combinations of, year, shifters and shift plates. This is a 69 GTO Muncie M-21 4speed for a center console car. Transmissions are matched to rear end ratios so while the M-20 was the standard 4 speed it was matched to the rear gear ratio of 355. If you ordered the M-21 Close Ratio you had to have a 3.90-4.33 rear gear. It is not in the best interest of performance to have a M-21 with the 355 rear gear. In 69 there was no M-22 (Rock Crusher) available. Shifters handles also changed depending on if you got a center console, bench seat, or column shifter. The best way to know what transmission you have is to look for the 2 letter code painted on the top of the main case but these are usually covered in grime.  Next you can look at the main shaft at the front of the transmission if there is no rings on the shaft it is a M-22, one ring is M-21, two rings is M-20. To find the year of the trans there will be a production code Eg. (P9C05 B) P=Muncie Aluminum 4-speed for passenger, 9=model year, C=month March, 05=day 5th, B=Trans Identification ratio starting in early 69. A=M20, B=M21. There is also the main case number that can identify the year 3925660 – 1968-70 and side cover number 3950306 = 1969.  The transmission will also have the last 8 digits of the car serial number stamped in various locations. Much of this information can be found in Eric Whites 64-74 GTO identification guide to GTO’s

Overall you can see that the aluminum colors vary from part to part, the main case is light while the tail shaft is darker and the side cover is another shade. The trans was taken apart so the pieces could be soda blasted. Soda blasting is a very mild form of sand or glass beading to restore the original finish. Sand or more coarse blasting etches the metal and can change the color. Generally the rods are Gold Zinc and the shifter is silver zinc. Most of the bolts are black phosphate.

When you look closer the next level of detail starts to appear. The shifter levers are silver zinc and have a built in rubber washer that is coated in rubber causing the end to be black. The side cover bolts are black phosphate and the back drive bracket is black, but also seen is silver.  You can also see the green and purple inspection marks on the side cover.

The front bearing cover is cast, the bolts are black phosphate and the bearing cover locks are silver zinc. These special locks have tabs that fold over to ensure the bolts never loosen out. It is hard to see but the shaft has one ring and a coarse spline. Later transmissions have a fine spline. The turned down tip of the shaft is what rides in the bearing that is in the back of the crank. If adding a manual trans to an automatic engine the crank may have to be drilled for the bearing pocket.

The four speed rods are held in with a series of flat washers, spring washers, spring clips and cotter pins. Some use cotter pins and others use spring clips or a combination of both. The red sticker is a shipping guard. Hurst was having a problem with the center shifter sleeve pin falling out during delivery. This red sticker held the pin in place and when the shifter was installed the factory worker was to remove the sticker. In most cases the sticker did not go far, we have seen it stuck to the body like shown and also with the bolt inserted through the sticker. Today this sleeve is hard to get out with all the worn shifter plate grooves in it. To perfectly adjust the 4 speed shifter and linkage, a ¼” rod or piece of tube is inserted in the mouse hole at the bottom were all the levers are. Insert the rod through all three lever arms and the back of the shifter housing and snug up all the nuts and the shifter is adjusted.

This black bracket is part of the back drive linkage, that started in 1969, it was used to lock the steering column when the car was put into reverse so the key could be removed.  This is considered PARK on a manual transmission car. This bracket connects to a cross shaft and then to steering column rod that went to the column so when the column was locked so was the transmission. These back drives are disconnected and missing from many cars today.

This is a Hurst shifter and all the parts are Silver zinc. The shifter levers like the trans levers have a rubber washer and rubberized end where all the rods connect. To restore these ends they have been dipped in Plastic Dip available at any hardware store. If the rubber washers are badly deteriorated they will have to be replaced with a concave spring washer. The shifter is also tricky to get out. If you take 2 .020” shims or feeler gauges and insert them between the chrome handle and the metal surround the handle will slide out with ease. The shim forces the tab in the metal surround flat releasing the handle.

The shifter is mounted to an aluminum plate that is bolted to the tail shaft and has a special stop nut that allows the shifter to be tilted forward or back for perfect alignment in console cars. The bracket becomes steel starting in 1970 and the shifter rods go to a thicker diameter although the shape is the same. This trans has one drain plug and a prevision or flat for a second that is used on the M-22. The speedo cable fitting can also be on either side of the trans affecting the length of the cable. The yellow letters are the id code for the trans and are 1” tall.

This bell housing looks better than most because it has been bead blasted and all the flashing sanded down to look better than stock. Once all the unsightly flash is removed it is put back into the blast cabinet and gets another round to remove any grind or sanding marks. The back of the bell housing has 8 bolts to bolt the various manual transmissions to the bell housing. The unused holes had black plastic plugs to protect the holes. These are new bell housing to engine block bolts and a new clutch fork dust boot. The clutch fork has been bead blasted and phosphate. The hole in the end is for the clutch tension spring.  When putting this all back together there are many clutches on the market with different spring rates and tension so do not be surprised if the clutch threaded rod comes up short. It is typical to have to have a longer threaded rod to take the place of the original.

Inline tube manufactures all the parts to detail your trans to look like new. They make the shifter rebuild kits, housing stencils, bushings and levers and all the hardware for any rebuild.

There's always a problem  - Aluminum bolt hole fix

On assembly we run into a snag, one of our bell housing to transmission bolt holes is very weak and the bolt will not tighten up. The trans has to come out, so  the bell housing can be fixed. With Pontiac’s  this is common on the aluminum pieces such as the timing, chain cover, Ram Air 4 intakes and bell housings. At 3pm on a Saturday this install has hit a brick wall. Our options include getting a new bell housing, but we spend so much time making this one nice or heil coil the hole. After 5 calls I find the kit for the 1/2-13 bolt that luckily comes with the tap but more bad news comes soon after when looking for a 37/64 drill bit. We are prepared to use a ½ drill and tap hoping the soft metal will still tap but then I find a store with the correct size drill. After running around for a hour we are back in business. Ready to drill we soon find out the drill will only accept up to 3/8” drill and the bigger will not fit. A quick trip to the neighbors house secures the bigger chuck drill and we are back to getting work done. It takes a few minutes a piece and we are ready to install again. The heil coil kit was $68.00 the drill $15.00 so near $85 dollars later we go back to work. The heil-coil is a life saver and handy to know how to do.

We first drill out the hole to ½ inch and then the second operation is to drill to the final size of 37/64. The aluminum cuts with no problem. We test on the first hole and repeat on the remaining three.

Now that the hole is drilled, we are ready to tap, Since the tap is so big we do not have a holder and use 2 wrenches and some tape to hold this quick fix together. The tap is tapered to get it started and it is important to keep it as straight as possible. We apply a couple drops of oil and begin to spin. It cuts the aluminum easily.

Here is the heil coil ready to be installed. The concept is to thread the hole to the next size up and install the coil which uses the threaded hole for support and the inside of the coil for the existing bolt size. Once installed a Heil – Coil is stronger than the original thread. The coil is made of stainless steel so binding is not an issue and the thread is very smooth and consistent.

We put the coil on the supplied tool and apply lock tight to ensure it will bond in the housing. The coil has a tang on the bottom so the tool bottoms out and it is ready to be installed in the piece.

Installation is a matter of threading in the desired distance and the tool is unscrewed leaving the coil in place. The next step is to break the tang off so it does not stop the bolt. With a punch or a screw driver insert into the hold and apply pressure until the tang breaks off.

Once you are done the hole will look clean and have a brand new thread.  Repeat this process 3 more times and the housing is better than new. It is a good idea to inspect all aluminum threads before installing components on the piece. There is nothing more disappointing the striping a thread in the middle of an install. This could easily happen on the water pump, front of oil pan, fuel pump, water neck, carb bolt hole as well as the bell housing.