There are 8 main symptoms to look out for when diagnosing an automatic gearbox:
- Stuck in one Gear
- Limp Mode
- No Gears
- Harsh Gear Changes
- Harsh Engage into Drive or Reverse
Seeing as we have not discussed the internals of an automatic gearbox, let us first discuss how it works before we discuss each of the above symptoms…
An automatic gearbox works with clutch packs, bands & planetary gears rather than gears/cogs in a typical manual gearbox. Let’s look at this…
Now let’s discuss the symptoms of a faulty gearbox…
SLIPPAGE – The clutches in the clutch pack have a friction material on both sides. A clutch pack is made up of a set of clutches and a set of steel plates as shown in the picture above. A piston is then activated by the valve body to bind/lock the clutches. This friction material can start to wear away due to the following reasons: Overheating, Getting water in the Gearbox, Running low on oil, piston seals worn, etc.
When we say “the clutches start to slip”, basically the steel plates and clutch discs slip and rub against one another causing the clutches to burn, this burning breaks down the friction material and contaminates the oil. Remember that the oil in the gearbox circulates through all its components… the valve body, gearbox and torque converter. Once there is oil contamination, it affects all the clutches in the gearbox, torque converter and damages many parts in the valve body. A full reconditioning of the gearbox is required: Torque converter, Mechanical gearbox & Valve body.
How to feel for a slip? – Normally a slip is felt in the middle of a gear where suddenly the RPM will jump and there will be no power but the RPM will increase. This may happen intermittently.
FLAIR – Similar to slippage, a flair happens when changing gear and is most likely to be caused by a worn piston seal on the clutch pack. We can justify this by saying that when the piston is engaged and the gear is changed, there is a slight flair, but this can also be due to many other reasons, like: oil contamination worn clutches etc. Normally this will need to be brought into Sparklight for a second opinion and for the gearbox to be stripped if necessary. Remember, once there is oil contamination, it affects all the clutches in the gearbox, torque converter and damages many parts in the valve body. A full reconditioning of the gearbox is required: Torque converter, Mechanical gearbox & Valve body.
How to feel a flair? –When the vehicle automatically changes gear the RPM will jump before dropping to the next gear. It is important to note which gear change is flairing in order to help diagnose the cause of the problem.