Clutch judder in the morning is so annoying, especially when you’re in uphill traffic… Arrggh!!!
So what causes clutch judder when cold? The most common cause of clutch judder when the engine’s cold, is clutch contamination, but it’s not the only possible cause. Other causes include:
- Faulty clutch/pressure plate
- Engine mount fault
- Faulty flywheel/DMF
- Engine issue
In this post, we’ll outline the causes of each of these types of faults and what you can do to fix them. A clutch judder should not be ignored, it may be a symptom of a more serious failure on the horizon.
Clutch Plate Contamination
Clutch contamination is the most common cause of clutch judder in the morning. A clutch as you know is responsible for the smooth application of engine power to the gearbox. The clutch plate is sandwiched between the flywheel and pressure plate. Both flywheel and pressure plate are fixed to engine rotation and the clutch is fixed to the gearbox rotation.
The clutch works on the principle of friction, or slip. Pressing the clutch pedal causes the clutch disk to slip inside the flywheel pressure plate sandwich.
The clutch pedal controlled consistent slip of the clutch as the engine rotates causes a smooth application of power. Now imagine oil on one part of the clutch disk, the effect would change the consistent degree of slip and this is what causes the judder.
But what exactly is clutch contamination? Contamination is usually an engine fluid that leaks down onto the clutch plate.
The most common types of disk contamination include:
- Engine oil
- Gear oil
Moisture build-up on the clutch assembly is a common problem. The warm engine and the cold night air will cause moisture to gather on the clutch assembly overnight.
Using the clutch once or twice is usually enough to clear the moisture from the friction surfaces. This is a condition you can’t really avoid unless you have a warm garage to park your car.
Things you can check: Park your car in a warm garage overnight, if the clutch judder isn’t present on the next cold start, moisture contamination is the source of the judder.
Rear main crankshaft seal leaking
An engine oil leak is a very common cause of clutch contamination. Oil on the disk will cause it to slip inconsistently which causes the annoying judder. A small oil leak from the rear crankshaft seal is the usual culprit or an oil pan leak at the rear will allow the spinning flywheel, throw oil all over the clutch assembly.
Daily use will sometimes clean the disk and the judder disappears and you may find it worse in the morning as an oil mist settles on the disk.
Things you can check: Look under the gearbox and check the ground for oil drips. That’s a sure sign an oil leak is contaminating the clutch assembly. If oil contamination is diagnosed, it’s likely you’ll need a new clutch but only after the oil leak has been repaired.
A rear main seal will require the removal of the gearbox and so obviously you’ll replace the clutch then. An oil pan leak won’t require the removal of the gearbox and so repairing the leak and test for judder might be the best strategy.
Gearbox oil leak
A gearbox oil leak is not very common. But if it leaks at the input shaft seal it will affect the clutch in the same way as engine oil.
Things you can check: Check under the gearbox for an oil leak, gearbox oil has a distinctive smell and it’s quite thick unless your gearbox is running ATF, in that case, it’ll be red. Check the gearbox oil level, they don’t use oil, so if it’s low, it’s probably your leak. Running a gearbox low on oil will cause bearing damage.
The gearbox will need to be removed to replace the input shaft seal, and while you are there, best to replace the clutch disk.
A coolant leak isn’t very common, but I’ve met it a few times. Lots of coolant system plumbing pipes are positioned just above the gearbox. Leaking coolant can make its way to the clutch disk. Even a small drip overnight will create a judder in the morning.
Things you can check: Check under the car looking for a watery colored liquid like red, yellow, or green. Check on the top side of the gearbox for any wet staining. Check the coolant level, does it need constant top-ups? In this case, repairing the coolant leak should solve the problem.
Faulty Clutch Pressure Plate
The pressure plate has a machined face that mates with one side of the clutch face. Any high spots in the clutch or the pressure plate will cause the clutch to bite in one spot only, this can be experienced as a judder in the car.
A defective clutch is a pretty common problem, it’s not worn out but it’s warped. Similarly, a pressure plate can be distorted which will cause a judder. The clutch generates heat which can change its characteristics as it reaches operating temperatures.
It’s less likely this is your issue as it should give trouble all the time not just when it’s cold, but it can’t be ruled out.
Engine Mount Fault
The engine and gearbox mounts work really hard, they’re designed to keep the power plant fixed in the engine bay and absorb driveline vibrations. The engine and gearbox are torquing the mounts as you get on and off the gas pedal.
The mounts are made from blocks of rubber and steel, and when they start to fail they will often cause the engine and gearbox to vibrate, causing a judder feeling in the clutch pedal. What you can check: Check the engine mounts for loose bolts. Diagnosing a partially failed mount can be difficult.
In the workshop, I’ll have a helper simulate a first gear take-off with the hood open, I’m careful of my toes obviously but I’m also looking for excessive power-plant movement. If you feel it’s excessive, change the mount.
The flywheel is the other bread slice in the clutch sambo. It has a machined surface just like the pressure plate, that the clutch mates with.
The flywheels are made from pretty durable stuff, so don’t usually warp. But clutches can cause a lot of heat that can mark the machined face of the flywheel, which causes a judder.
A DMF (Dual Mass Flywheel) is a lube-filled flywheel assembly that dampens and prevents uneven engine torque from transmitting through to the gearbox.
Things you can check: DMF fail regularly, they’ll often be associated with juddering. Check for other symptoms of failure, they include:
- Rattling from the gearbox area
- Banging sensation in the clutch pedal
- Slight clutch slip
- Squeaks gearbox
The DMF can only be confirmed as a failure by measuring the side-to-side free-play. Replacing a DMF will require removing the gearbox.
An engine fault might seem unlikely, but it’s very possible. Your car’s engine, as you know is managed by the ECM (Engine Control Module). It controls many functions including responses to engine load and idle speed. Both are very important to standing starts.
Manufacturers are constantly releasing ECM software upgrades to combat know problems. Some manufacturers have successfully solved juddering by programming the ECM to raise the rpm at standing starts. Software updates are usually offered free with a tune-up.
Things you can check: Ask your local dealer about recalls and software updates.
Scan your vehicle for trouble codes, if there’s an engine issue, it could be the cause of the judder. Problems like faulty Idle speed control valve (older cars), turbocharger or dirty/faulty electronic throttle body, misfiring cylinders, etc will cause a lack of Oomph at standing starts.
If you need a new clutch kit, check out the Amazon link below.Amazon Clutch Kit
How do I know my clutch needs replacing? Your car needs a new clutch if the following symptoms are present:
- Won’t go into gear
- Difficult to get gears
- Burning smell and or smoke
- Engine revving high but car moving slowly
- About the Author
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.