As you all know, the most difficult problem to diagnose is NOISE. When it comes to gearbox noise, one needs to be highly trained to diagnose where the noise is coming from as there are so many possibilities. The noise may be due to any of the following: Planetary gears worn/broken, torque converter, pump, bearings, blocked filter. Sparklight have various ways of testing for noises and would recommend that the vehicle be brought to our workshop.
Simple to diagnose, get into the car… Put Reverse, Put Foot… If the car is still by the lift… You’ve got no gears!!! Put Drive, Put Foot… Repeat the last check. There are three reasons why a vehicle will have no gears:
No Oil, Broken Pump, Torque Converter, Worn clutches inside the gearbox. If the torque converter is the problem, it may have contaminated the oil and circulated through the gearbox causing further damage. This will need to be towed into Sparklight for a second opinion.
A harsh gear change is normally caused by a stuck valve in the Valve body, A worn piston, Shift Valves and solenoids. Usually reconditioning the valve body will solve the problem, but once again if the vehicle is driven with this problem the harsh gear change can damage the mechanical parts in the gearbox. Once the valve body has been reconditioned it needs to be re-adapted with a special diagnostic tool which Sparklight Gearboxes are capable to do on almost all vehicle brands.
While this seems like a minor problem, and while most people tend to ignore it… The first thing to check is the gearbox mountings. If they are worn, replace them and see if the problem is still there. Secondly, check if the problem could be due to a lack of oil pressure. This can be caused by a damaged pump or a leaking /damaged drum. Over time, this harsh engaging slowly causes more and more damage until eventually the gearbox will fail completely. So hopefully by the time the vehicle reaches a workshop, the damage is not too bad. The main causes of this are: Valve body Malfunction & Mechanical Damage inside the gearbox.
Often diagnosticians mistake the vehicle being stuck in one gear with what is known as LIMP MODE. The gearbox computer has the capability of sensing a potential problem and it therefore puts the vehicle into a safety mode called limp mode to avoid damaging the gearbox further. DO NOT drive the vehicle unnecessarily in limp mode. You may drive the vehicle a short distance to your workshop but no more than that. Should the vehicle go into limp mode while driving. Pull over, switch off, switch on. The vehicle normally resets to normal mode but will store the fault code on the computer. Normally a vehicle will go into limp mode due to an electrical problem, computer problem, TCM (Transmission Control Module) or even engine problems.
A test drive may be done to record when the vehicle goes into limp mode.
STUCK IN ONE GEAR – When a vehicle is stuck in one gear, there is most likely a mechanical failure in the gearbox itself. There may be a chance that only the mechanical parts in the gearbox needs to be replaced. HOWEVER, if the vehicle is driven once this has happened it can cause damage to the other components and the car should be towed. Once the vehicle is at your workshop, a diagnostic machine will tell you exactly where the fault is and confirm that the problem is a mechanical fault. NO TEST DRIVE MUST BE PERFORMED!!!!
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.
Unlike an automatic gearbox, a manual gearbox can be repaired as opposed to reconditioned. For example, if there is a grating into 3rd gear, we can perform a repair on the 3rd gear only, which will be much cheaper than reconditioning the entire gearbox. The 3rd gear, 3rd gear syncro, 3rd gear sliding sleeve & 3rd cluster gear need to be replaced. Let’s look at this…
Do you notice any differences between gears 1 – 5 & the reverse gear?
You will notice that gears 1 – 5 have angled teeth and the reverse gear has a straight cut gear. The gears are angled to reduce the noise they create at higher rotational speeds. This is why all vehicles make a whining noise in reverse. Please do not try to test this at high speeds in reverse.
There are 3 main symptoms to look out for when diagnosing a manual gearbox:
– Jumping out of Gear
– Grating into Gear
Jumping out of gear – When a vehicle jumps out of gear, 99% of the time this is due to the gear being worn. In the diagram below you will see that the original gear tooth pattern meshes together with a perfect point of contact. Unfortunately over time this contact pattern wears down to the red line on the gear tooth and the 2 gears no longer mesh correctly. The most common cause of this symptom is high mileage and simple wear & tear.
This is the most basic symptom to diagnose because when you drive the vehicle, the gearbox will jump out of gear. We will discuss the different options for repair in the next section.
Grating into gear – This happens when the synchronizers or synchro rings are worn and they do not lock onto the gear. Let us have a look at a syncro and where exactly the wear occurs…
When trying to diagnose this fault, be aware that the clutch can also cause a grating into gear. We determine the difference by which gears grate when engaging. If the grating occurs when engaging 1st gear or reverse while the vehicle is stationary, the grating in usually caused by the clutch. If the grating occurs in any other gears while the vehicle is moving, this is usually caused by the syncromesh inside the gearbox.
Noise – Noise is by far the most difficult problem to diagnose. The main causes of noise can be: worn/noisy bearings; gear meshing (wear & tear); lack of oil (Burnt Gears) or Excessive play on the gears/shafts.
- Bearing Noise – Over time bearings tend to wear down which create an excess of play inside the gearbox allowing the gears and shafts to move around more than they should. This results in a whining noise.
- Gear Meshing – Once again, overtime the contact pattern on the gears slowly wears down causing the gears to mesh incorrectly resulting in noise. This can also be the result of a bearing wearing away giving the gear more play than it should have which in turn changes the contact pattern.
- Lack of oil – If a manual gearbox runs without oil the internals of the gearbox overheat and burn. Not visible to the naked eye, the gear itself and the teeth on the gear lose their shape which will create a noise from that particular gear. Even though the difference in shape is not visible, we are able to tell this very easily as the gear will turn blue in colour.
When diagnosing a noise in a gearbox, it is of absolute importance to test the noise in various states before coming to a conclusive diagnosis.
Normally, when a customer brings a vehicle in for a gearbox problem they will tell you what their concern is… Grating, Jumping or Noisy.
Steps to diagnosing – jumping out of gear
- Drive the vehicle and in all gears
- While driving in ALL gears you must do the following and a separate record should be made for each gear:
- Release and compress the clutch quickly and slowly
- With the clutch released, play with the throttle… full, release, full, release
- Make sure to record which gears are jumping out and when it occurred
Steps to diagnosing – grating into gear
- With the car stationary, try to select 1st gear and reverse while listening and feeling for a grating sound when engaging. Record your findings.
(Should there be grating into 1st or Reverse, it is most likely the clutch. HOWEVER, the other gears still need to be tested with the car in motion)
- Test each gear change for grating (Upshift and downshift)
- Make sure to record which gears are grating into gear
Steps to diagnosing – noise
- Before driving the vehicle, make sure that the customer has given precise details of when he/she can hear the noise.
- Begin driving the vehicle to replicate the noise and take note of when it happens.
- Test for the noise in all gears, especially in 4th
(If the noise is apparent in all gears but quiet in 4th gear, the fault is on the cluster and spigot shafts and they both need to be replaced. 4th gear is a direct drive @ a 1:1 ratio and does not run through the cluster gears)
- Replicate the noise at a constant speed and compress the clutch to see if the noise goes away or stays there. (If the noise goes away when the clutch is pressed in, the problem is most likely in the gearbox. If the noise does not go away with the clutch compressed, this can mean a bearing in the gearbox is noisy or that the noise is coming from the differential or another part of the vehicle. Eg. wheel bearings)
- Record the outcome
Most of the time a noise cannot be diagnosed easily and the recommended way to diagnose noise is to open the gearbox to inspect.
NOTE: The recorded information from the steps above is extremely important to establish what to look for when the gearbox is open for inspection.
A manual gearbox is made up of 4 main components, Namely:
– The Clutch – When the clutch is pressed in, the engine and gearbox are disconnected from one another and when the clutch is released the engine is reconnected to the gearbox. When the clutch is pressed in the driver is able to change from one gear to another. ie Neutral.
– The Mechanical Gearbox – The mechanical gearbox contains all of the different size gears which in turn give you different gear ratios and speed capabilities. The driver changes gears with a Gear-Lever. This is all shown in the picture below.
– The Driver & The Gear-Lever – In a vehicle with a manual gearbox, the driver needs to calculate the necessary gear and manually change the gearbox into the required gear by shifting the gear-lever.
The 4 main components of a Manual Gearbox are:
– Mechanical Gearbox
Now that we have discussed a manual gearbox let’s compare it to the components of an Automatic Gearbox:
|Mechanical Gearbox (Gears)||Mechanical Gearbox (Clutches)|
|Driver||Transmission Computer (TCM)|