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CHAPTER 2

FUNCTION OF THE A-833

The A-833 4-speed, like practically all muscle car–era 4-speed transmissions, is what is known as a constant mesh transmission. This simply means that all forward gears are in constant contact with the cluster gear in the case at all times. Even in reverse, the forward gears are in mesh, but since none of them are locked to the mainshaft while the unit is in reverse, the direction of gear travel can be reversed without damage.

Let’s begin by reviewing terminology. There are several terms that are used regarding the components of the A-833 transmission, as described in the image here.

A synchronizer is made up of several components. In addition, there were three different main designs as described in Chapter 1.

“A” is the synchronizer clutch gear. This is also known as a synchronizer hub. This is the part that attaches to the mainshaft via splines and is retained by a snap ring. The splines around the outer circumference match the splines on the inside of component B.“B” is the clutch sleeve. This is also known as a synchronizer slider. This, too, is splined on the inside, which mates with the outer splines of component A.“C” shows the three strut keys. These are sometimes called “dogs” or “shift struts.” They are retained in a slot in component A and held in by component B.“D” shows two strut key springs. These provide outward pressure to stabilize and retain the components in C.“E” is a synchronizer stop ring. Sometimes called synchronizer rings, these are sandwiched between the synchronizer assembly and the gear cone.

General operation of a synchronizer during a gear change starts at the shifter handle. Movement of the handle transfers to the synchronizer via rods, levers, shafts, shift forks, sliders, strut keys, and synchronizer stop ring to the appropriate gear.

While first through fourth gears are fully synchronized in the A-833, reverse is not. This makes it necessary to be fully stopped before attempting to engage reverse. Otherwise, a “grind” will occur. This is not the case with putting the vehicle into first gear; you can be rolling forward slowly and put it in first gear and it typically will not grind. This is because the 1-2 synchronizer is engaged when the shift fork moves the clutch sleeve.

During a shift, the shift fork moves the slider. The slider is splined to the inner hub. Keep in mind that the inner hub is splined to the mainshaft. Therefore, the synchronizer assemblies always spin at mainshaft speed. Continuing on, the slider moves the three spring-loaded strut keys, which move the brass synchronizer stop ring onto the gear cone. As pressure is applied to the stop ring via the strut keys, the ring matches the speed of the gear to the speed of the mainshaft. This entire action is a “synchronized shift” and happens as quickly as you move your hand.

Power Flow and Layout

1 This is the power flow of the A-833 in neutral. All gears are in constant mesh. However, because the 1-2 and 3-4 synchronizer sliders are in the neutral position, no power is going through the output shaft. Power comes in through the input shaft and runs the entire geartrain at engine speed.

2 In first gear, power enters the geartrain through the input shaft and travels down through the cluster gear. It is then transferred up through first gear. The power is transmitted through the 1-2 synchronizer assembly by moving the slider to the first gear position. This locks first gear to the output shaft. (The red arrow shows the direction the slider is moved, and the blue arrows show the direction of power flow.)

3 In second gear, the power enters through the input shaft and is transferred down through the cluster gear. It is then transmitted up through second gear. Again, this power is transmitted through the 1-2 synchronizer assembly by moving the slider to the second gear position. This locks second gear to the output shaft. (The red arrow shows the direction the slider is moved, and the blue arrows show the direction of power flow.)

4 Third gear power comes in through the input shaft and travels down through the cluster gear. It is then transmitted up through third gear. This time, the power is transferred through the 3-4 synchronizer assembly by moving the slider toward third gear. This locks third gear to the output shaft. (The red arrow shows the direction the slider is moved, and the blue arrows show the direction of power flow.)

5 In fourth gear, power comes in through the input shaft. The cluster gear is not in use at this time and just spins along. The power goes through the 3-4 synchronizer assembly by moving the slider onto fourth gear, effectively running power straight through the upper geartrain and output shaft. (The red arrow shows the direction the slider is moved, and the blue arrow shows the direction of power flow.)

6 Reverse gear is a different arrangement than most other manual transmissions of this era. To reverse, the lower reverse idler gear moves back and meshes with the teeth present on the circumference of the 1-2 slider and the reverse teeth on the cluster gear. This idler gear rides on an idler shaft and is not in mesh, except when in reverse. (The red arrow shows the direction the idler is moved, and the blue arrows show the direction of power flow.)

As stated earlier, first through fourth gears are fully synchronized. However, reverse gear is not synchronized and relies on the geartrain not being in motion to cleanly engage without grinding. The reverse gear arrangement is unlike any other passenger-car transmission of the muscle car era. It relies on a row of spur teeth in the outside circumference of the 1-2 slider. In the neutral position, this is splined to the mainshaft and is not engaged with any other gears. When the operator moves the shifter into reverse, this moves the reverse gear selector arm and this, in turn, engages the reverse idler gear between the teeth on the cluster gear and the teeth on the 1-2 slider. By doing this, it reverses the direction of the mainshaft, making the vehicle back up. This is a good compact design because most other transmissions of this era dragged the reverse idler assemblies along at speed all the time, which required using rollers and thrust washers. Consequently, it makes rebuilding this part of the A-833 easier than others due to the lack of roller bearings and thrust washers.

Malfunctions and Fixes

The A-833’s most popular claim to fame, is that it rarely broke. Most often, these transmissions needed a rebuild because they were worn out. The strength factor causes you to see an A-833 modified to fit into many GM cars. Using an adapter plate and shortening the input shaft tip accomplishes this. One must also decrease the diameter of the tip to 5/8 inch.

This plate manufactured by Passon Performance adapts the A-833 to the standard Muncie bellhousing. The four threaded holes are where the A-833 attaches to the mount plate. The four larger holes that are generally equidistant from each other are where the adapter plate is bolted to the GM bellhousing.

The upper input shaft pictured is modified for use with a 1-inch-thick adapter plate. The typical GM pilot tip diameter is 5/8 inch. The lower input shaft is a stock untouched Chrysler input shaft. Notice how much longer the pilot tip is. Also, the diameter is 3/4 inch.

Popping Out of Gear

The most common misdiagnosis is how to fix an A-833 that is popping out of gear. When we get a call that this is happening, I will ask some specific questions and the customer will often say, “I just had synchros put in, and that didn’t fix it!” Replacing the brass synchronizer rings will not fix a pop-out condition. Synchronizer rings get the transmission into gear. They do nothing to keep it in gear.

Popping out of gear can happen for a myriad of reasons:

This is an example of how an operating lever in the shifter mechanism itself can become worn, causing the transmission to pop out of gear. The lever on the left has the correct diameter hole. The lever on the right exhibits significant wear. This allows the arm to “run out of travel” before moving the shift fork the correct distance.

• A slider that is not fully engaging onto the synchronizer teeth of the gear. This can happen due to a worn shift fork; the forks are in constant contact with the slider and can become worn in the area of contact.

• A bad rear bearing or broken snap ring groove in the bearing pocket.

• A missing snap ring. We have seen this after some inexperienced people have been in an A-833. The reason that this is important is because, by its design (helical drive tooth), there is forward and backward thrust on the bearings whether accelerating or decelerating. When a rear bearing is allowed to move forward and backward (for whatever reason), the entire mainshaft moves. This will affect staying in gear because the sliders (which are attached to the stationary housing via the forks) will try to stay stationary while the mainshaft moves independently.

• The drive-side of the synchronizer teeth is worn. This can cause pop out under power.

• Misalignment of the bellhousing.

• Worn synchronizer teeth. This is by far the most common thing that causes a transmission to pop out of gear. This can happen in a couple different ways. As a synchronizer ring becomes worn and eventually fails, a grind occurs during shifting into that particular gear. This grind is the result of the splines on the slider being at a different speed than the gear. When this grind occurs, it wears the synchronizer teeth. As the teeth recede back and the slider wears, they will no longer stay in gear when not under power. Another action that will cause worn synchronizer teeth is sloppy driving. This is when the driver drags the shifter out of gear instead of pushing the clutch in and shifting. All of the weight of the car is stacked up against the side of the synchronizer tooth of whatever gear the transmission is in. When the slider is dragged off the gear, it wears the side of the synchronizer teeth. After thousands of times, the teeth will show wear and the unit will pop out.

• The gear selector shafts are worn. This can cause a pop-out condition because the shifter is completing the allowable travel and the slider is not moving far enough because of the worn shaft.

• A worn or misadjusted shifter. This will be covered in the shifter section, later.

This gear shows excessive wear on the synchronizer teeth. Note how they have receded. If installed into a transmission, this gear will almost definitely pop out of gear when the driver lets up the accelerator. Once a gear is this worn, it must be discarded, unfortunately, because there is no fix for these.

Grinding During Shift

When a transmission grinds during a shift, it means that the brass synchronizer rings are not functioning correctly. Synchronizer rings can malfunction for reasons ranging from a broken or spread synchronizer ring to a bad gear cone and many things in between. Incorrect clutch adjustments can also have an adverse effect on the function of the rings. If the clutch is not completely releasing, the engine is still transmitting power through the transmission. This will require the synchronizer rings to undergo extra abuse to get the gear speed matched to the slider. After extended periods like this, they will fail prematurely. The harder a transmission is driven, the more wear is to be expected on the synchronizer rings.

A grind typically shows up in reverse initially if there is a clutch problem and you are not getting complete release. Since reverse is the only gear that is unsynchronized, the geartrain must be stopped to engage it. The old trick back in the day was to put it in first gear to briefly stop the geartrain and then quickly put it into reverse before the gears start spinning inside the case.

Notice that the stretched, worn synchronizer ring (top) is darker in color than the new ring (bottom). Also notice the fine grooves that are in each ring. The worn ring shows much more space between the grooves. Essentially, the material between the grooves is worn and it makes the grooves shallow, appearing as if there is more material between them.

The marks on the synchronizer ring to the left indicate that it was bottoming out on the face of the gear instead of applying braking pressure to the gear itself. The ring to the right is a new, unused ring. Notice the lack of marks.

The fitment of a brass synchronizer ring on the cone of the gear is shown here. Notice that there is almost no clearance between the ring and the gear. This ring is both worn and stretched. When pressure is applied to the brass ring via the synchronizer strut keys, the ring will bottom out before the inner part of the brass ring applies braking to the cone of the gear. The end result will be a grind when shifting into that gear.

Bad Bearings

It helps if you can properly diagnose the problem with the transmission before tearing into it. Since some parts for the A-833 are difficult to obtain, it may take some time to acquire them. Typically, a bad bearing will make a growling sound. Usually, there are two main bearings, with the exception of the 1964–1965 flange-type output. They have a bearing at the extreme end of the tailhousing as well. A bad input shaft bearing will make noise with the unit sitting in neutral or in all the gears. A bad mainshaft bearing will only make noise when the output shaft is turning (driving condition).

Whining Noise

A whine is usually caused by a problem with the gear teeth themselves. These can be caused by a lack of proper lubrication or improper bearings being used. Since the A-833 uses an application-specific 308 SG8 bearing, this tolerance is important. We have taken apart units in the past that have had 308 LOE bearings in them and have observed improper wear on the helical teeth because of it. These 308 LOE bearings are too thin. This moves the mainshaft forward and the input shaft back, which causes a misalignment with the cluster gear. This can create a whining noise and will eventually wear the gears irregularly. Mishandling or a catastrophic event, such as an internal part failure, cause dings that result in gear tooth irregularities. If the ding makes a high spot on the side of the gear tooth, it can cause a whine. If on the drive side, the whine will be noisy under power. If it’s on the coast side, it will be noisy when the driver lets off the accelerator pedal.

Visualize the face of this bearing as a clock; look at the eight o’clock position. You will notice that the cage that retains the correct spacing of the balls has broken. This will completely destroy the bearing in short order. As the cage breaks up, it will go through the transmission, likely causing significant damage. This bearing was caught before any of the cage broke free and destroyed the transmission.

If you focus on the inner race of this ball bearing, you will see significant brinelling. The surface hardening has left this area of the bearing. This will cause a growl and, eventually, the bearing will fail completely. This will get louder as the surface keeps getting worse and worse.

Banging Noise

This is typically an easy noise to diagnose. Very often, a jarring feeling in the vehicle is associated with the noise. It is caused by one or more teeth being knocked off either the mainshaft speed gear or the cluster gear. The transmission should not be driven when this happens. When pieces are floating around inside, they can get caught between other teeth and do further damage.

Typically, loss of teeth happens from overpowering a transmission. The usual weak point of the 23-spline A-833 is the input shaft. They will generally twist before something breaks inside. In order to take care of this issue, Chrysler engineers increased the input shaft diameter from 1 inch to 1 inches. They also made the splines more coarse and fewer in number. This transferred the weak point to the inside of the transmission. Usually, third gear is the first gear to fail because it is the least supported gear.

Many of the transmissions that end up in people’s hands now have led a tough life. The stress that this puts on the gears is incredibly high. Also, everyone did burnouts in third gear. This was to allow the most tire speed to heat the tires up faster. However, this is very hard on the transmission. We sell a 2.65 ratio third gear that is manufactured from 9310 alloy, which is notably stronger than the standard 8620 material assembly line gears. We have had good results with this improved material gear and have had almost no breakage.

Vibrations

Most times, vibrations are caused by something outside the transmission. These can range from driveshaft balance issues to universal joint wear issues to a bent driveshaft. Even axle bearings or tire/wheel issues can resonate up through the transmission and shifter.

The A-833 was designed to be used with a pilot bushing in the rear of the crankshaft. This supports the pilot tip of the input shaft to keep the mainshaft aligned. The driveshaft slip yoke keeps the mainshaft aligned as well. When these become worn, vibrations can develop.

In some instances, if a solid mount is used, it can transfer vibrations. There are 16 loose rollers present inside the bore of the input shaft. They support the front of the mainshaft. They do not have a super tight fit because assembly would be nearly impossible. This is an area of deflection under very high power loads. In addition, if a polyurethane mount with a high durometer is used, it can also transfer vibrations.

This gear shows just two teeth knocked off. This would still move the car, but every time the bad spot in the gear comes around and meshes with the cluster gear, you would get a bang and likely a loss of forward movement until the gear rolled past the bad spot. (Photo Courtesy Sawmill Garage-Sweden)

The catastrophic failure of third gear seen here likely happened at high speed in a racing situation. The gear made many revolutions, which caused all of the teeth to be wiped off. This would make a great amount of noise in a transmission and would likely not move the car in third gear. (Photo Courtesy Sawmill Garage-Sweden)