"Snap Ring" Failure
Service Bulletin Alert
See Technical Service Bulletin (TSB) #93-010, "Broken Countershaft Bearing Snap Ring"
What is the infamous "Snap Ring Failure"?
"Snap ring failure" refers to a small metal ring in the transmission that breaks (shatters) as a result of the stresses put on it by an improperly manufactured transmission case. The snap ring itself is not the cause of the problem, just the symptom. There is a groove in the case which is cut too wide on some transmission. This allows the snap ring to twist as the countershaft moves back and forth under load. The more load, the more twist. If the snap ring does twist (like rolling a rubber band inside-out) then it shatters in many pieces.
Which Cars Are Affected?
The snap ring failure is limited to transmission numbers J4A4-1003542 through J4A4-1005978. These transmission numbers are limited to 1991 and 1992 model year vehicles. You cannot determine whether a car is in the range for possible failure by VIN number, you MUST check the TRANSMISSION NUMBER because the transmissions were not installed in sequential order by VIN number. See Locating Engine and Transmission Numbers for instructions on locating the transmission number.
It is important to note, however, that the problem does not exist on all transmissions in this range. The range simply identifies transmissions which may have the problem.
OK... But what the heck is a "Snap Ring" anyway??
The snap ring is a very thin metal ring (pictured at right held between thumb and index finger) which holds the countershaft from moving in the transmission case. Since the transmission gears are not straight cut, when the main shaft gets power from the engine the cut in the gears makes the shafts want to move back and forth in relation to each other. The countershaft top bearing is held in place by the snap ring in the upper section of the transmission case.
The snap ring sits in a groove in the bearing and in a groove cut into the transmission case. It's purpose is to keep the countershaft from moving under load changes, such as when you get on and off the throttle. Without this snap ring, the shaft has approx. 6-7 mm of movement. If the groove in the transmission case is cut too wide, as with some of the cars in the range above, the snap ring can move back and forth a little. This causes it to flex which puts an enormous amount of stress on it and eventually leads to the whole ring shattering into several pieces.
Are all transmissions in the listed range defective?
No. Only some of the transmission case grooves in the range were cut too wide.
The snap ring sits in a groove-within-a-groove (actually more of a "shelf" within a groove) machined into the transmission case. In order to cut this complex part of the case the manufacturer used a 3-piece bit; one part to cut the main groove, one part to cut the "shelf" that holds the snap ring within the groove, and another piece to cut the outside of the groove.
During the process of machining a batch of transmission cases they would stop once in a while to measure tolerances. They found that the snap ring groove was cut too wide after the bit was used X number of times because the three pieces that made it up would spread apart a little (several thousandths of an inch make a big difference in transmissions). They kept replacing these multi-piece bits and finally redesigned it as one-piece bit to solve the problem.
So if a transmission is "in range" but was cut shortly after the bit was replaced, it will be just as good as one that isn't even in the range for failure. But they get progressively worse until the next time the bit was replaced during production. We as owners have not been able to find out how fast the multi-piece bits got out of spec or at what transmission numbers the bits were replaced. All we know is the range of potential problem transmissions. Honda may not have this information either; if they do, they have not made it available to us or to their dealer service centers. If you are wondering why the cases were used knowing these grooves were too big, it is probably because it was not known how big was too big until the snap rings started to fail.
So now you have a bunch of cases produced. Case number one is perfect, but the cut gets progressively more out of spec as things go along until number X, at which point the operator adjusts the machine. Then the cycle begins again, and as a result cases are produced anywhere from perfect (the first case cut after every adjustment) to way out of spec (the last case cut before an adjustment). This is why there are cars that have 90k miles and no failure despite being in range and cars that failed with 2 or 3 thousand miles on them.
How did they fix the manufacturing problem?
They fixed the manufacturing problem by making the machine tool one piece instead of two. That eliminated the possibility of the two parts moving out of spec.
There has been some confusion on this point, so just for the record: The snap ring material has never changed, they are made exactly the same way and from the same material today as in the very first NSX. It is one of Honda's most ironclad rules that if a part is changed, even the least detail, it gets a new part number. The part number on the snap ring has never changed because the actual ring was never the problem; the groove cut into the case was the problem.
I sent many private posts to people who asked if they should have the update (transmission case) done to their car. My answer was if there are a lot of hard miles on your car and you have not had a problem you probably won't have a problem. If you don't want someone opening your transmission then don't worry about it.
Again: Not all the transmissions in the range will have a problem.
Are all transmission outside the range OK?
No transmission outside the range should have an improperly cut transmission case groove. However, it is possible for almost any part in a car to fail. There have been reports of a couple snap rings breaking on cars not within the range, but there is nothing to indicate an abnormal number of failures. Sometimes things just break.
What are the symptoms of failure?
The giveaway for snap ring failure is the shifter moving fore and aft in first or second on deceleration or acceleration from slow speed. This happens because when the snap ring breaks (which holds the countershaft top bearing into the case) the whole countershaft moves back and forth in the case when the direction of load / torque changes. Since first and second selector are on the countershaft, and the selector hub hooks into the selector fork which hooks into the shifters.
Most people experience a loud crunch or mechanical grinding sound as the shattered fragments of the broken snap ring grind around in the transmission.
There are no warning signs prior to failure.
Will it hurt anything else when it fails?
If you experience a snap ring failure, stop driving the car as soon as it is reasonable to do so. If you continue driving the car with the snap ring shattered, there is a potential for broken bits of metal to start floating around in your transmission which is not particularly good and can damage other parts in the transmission. The transmission is a closed system so there is no risk of damage to the clutch or other components.
The problem will also get progressively worse as you drive the car, so you are at danger of getting stuck out in the middle of nowhere with a long tow to a qualified repair facility.
Will Acura repair this failure for free?
First, understand that if there were an across the board offering to fix every transmission regardless of failure, it would be a recall. Car manufacturers do not like the "R" word. There is no recall on the snap ring issue.
Goodwill decisions must be made by the local Acura District Service Manager (DSM). Acura has a very good goodwill policy compared to any other auto manufacturer. They usually covered most or all of the cost of snap ring repairs for years. However, now that the affected cars are over a decade old, goodwill coverage is pretty much unheard of. It started to taper off sharply starting in 1999 and was pretty much a thing of the past by 2000. Some owners with very strong relationships with their dealer have been able to get partial goodwill, but that is very uncommon now.
As far as goodwilled preventive work, Acura's official line was that it will only be fixed if it fails. While it's no fun to play the "wait and wonder if mine will blow up" game, Acura's reason for that policy is that it is expensive to fix since they tell their dealers to replace the entire transmission assembly, and only certain transmissions within the range of ones that can experience the problem will be affected. Despite the official line, a number of owners with good dealer relationships did get partial or complete preventive repairs paid for by Acura.
HELP! My snap ring broke! / How much does repair cost?
Acura tells their dealers that the only way to repair a snap ring failure is to replace the entire transmission assembly. That is because Acura simply doesn't want their dealer service technicians working on transmissions (even their master service techs which are the only ones who are supposed to work on NSXs). The reason for that is simply that transmissions are complex and require extremely tight tolerances which means they present many opportunities for problems. A problem means the customer has to come back multiple times for the same repair which is something car manufacturers very much DO NOT want because it results in irate customers. The only problem with the replace-the-whole-transmission policy from a customer's perspective is that it is very expensive - around $7000 - $7500 parts and labor, give or take.
But the fact is that a qualified mechanic can repair an NSX transmission. While it's opened up, it's a good idea to replace any worn synchros or other parts showing wear. The entire process of removing, rebuilding to factory spec, and re-installing an NSX transmission can be done for around $2500 or less by a truly qualified mechanic. The only problem is that there are not many mechanics in the country who have much experience opening up an NSX transmission to work on since Acura tells the dealers they should only replace the entire assembly.
One of the most experience mechanics in this area is Mark Basch at Basch Acura Service in Phoenix, AZ. His shop works on all kinds of Acuras but Mark himself works almost exclusively on NSXs and has done dozens of transmission rebuilds. Since not everyone lives near Phoenix, he also keeps "spares" that he can rebuild to factory specs and ship to your local dealer, so all they have to do is replace the entire assembly and then ship your bad one back to him. This is by far the best way to go if you need your failed snap-ring transmission repaired and Acura has declined to goodwill the job. Even with the cost of shipping it is well over $4000 cheaper than replacing the entire assembly from Acura.
For a PREVENTIVE repair (replacing the upper transmission case) by the book it is 10 hours of labor and about $700 in parts. Again, in the early years some owners with good dealer relationships received partial or complete goodwill on this preventive repair, even though the official Acura line was that they would only work with you after it had broken. Sometimes the owner was installing short gears or R&P anyway and Acura would give them the new transmission case since the owner was already paying for the labor to do their gear changes. However, again many dealers are unwilling to open an NSX transmission and work on the internals and will not do it even if you are willing to pay the entire cost.
What should I do if my car is in the range?
Obviously if your transmission falls within the range then you must make the decision if you want the transmission opened up. If you have many miles including some hard shifting then your transmission case may be cut properly and may never have the problem. If you have a low-mile garage queen and don't drive it hard you simply don't know. There is no right answer - it is really an individual decision. Some owners decide they do not want to have it break on them while they are out driving their car and simply pay to replace the case before anything fails. Most of the rest decide to just drive it and wait to replace the case when they are having other transmission or clutch work done so they save on the labor.
Should I buy a car in snap ring range?
Sure! It shouldn't be a deal-breaker for most people as long as you go into it with a plan. If a car has a transmission in range for potential failure, you might negotiate a little on the price. You can use the extra money to either do a preventive repair or just wait and see if it fails. If it doesn't you saved some money for taking the risk. If it does, you can use that money to pay for the repair.
What about owners outside North America?
The Technical Service bulletin was issued by American Honda. Several owners in Europe have reported that Honda does not acknowledge the problem over there and has not provided any kind of goodwill in any case thus far.
How many miles does it take to fail?
It varies widely. There are several factors which likely contribute to this. First, driving styles differ. If you baby the car it will take longer to fail vs. the same car driven hard. The other reason is the nature of the manufacturing problem which causes the failure (explained in detail above). Here's what some owners have reported.