Clutch rattle and slowing engine

[DCMVan70]

Hi All

I have an issue with my clutch - some history… The engine is an A+ 1275, the gearbox is a standard ribbed case, refurbished and fitted about 1500 mile ago. At the time of fitting the GB I also changed the clutch, release bearing and rebushed the clutch release are and fitted a new bolt.

I have an intermittent (well kind of) issue with a bad vibration when engaging the clutch. Normally the car start up fine, but after a couple of uses the peddle vibrates when the clutch is engaged and the engine RPM drops quite a lot. Seems to be less of an issue at higher engine speeds, so is more noticeable in traffic or when manoeuvring.

The video below (hope it works, and shame we can’t post videos directly here?), show what I mean through the bell housing.

https://youtube.com/shorts/p4pJt7525w0?feature=share

I have now removed the engine and gear box and see that the clutch and release bearing look brand new, but there is quite a lot of lateral play on the clutch release fork. There are scratches on the bolt and the new bush seems worn.

Do you think I can just rebush and reboot the release fork - bad new parts again, or there is something else going on?

There is a little bit of movement on the GB input shaft, but not worse than when I received it, and the little bearing on the end of the shaft seems fine - it is a roller type due to the A+ engine and is new (about 5000 or 6000 miles). I cannot see/feel any crankshaft movement, so think that the thrust bearings are OK.

Regards
David

[philthehill]

The biggest problem with the Minor clutch release arm/clutch is that the release carbon thrust moves in an arc which is not concentric to the clutch cover release pad i.e. when you push the pedal down the thrust bearing moves off centre relative to the clutch cover release pad - the more you press the pedal down the carbon thrust goes further off centre. That causes the thrust bearing to oscillate on the clutch cover release pad. The oscillation can be seen in the video. The only way to mitigate the problem is not to have everything so well fitted. One supplier of modification kits has the clutch release lever mount pivot hole slotted so that the thrust pad can find its own centre. The turning clutch release pad pulls the carbon thrust to naturally centralise itself so getting rid of and cancelling the oscillations. My own modified clutch release lever and roller release bearing is fitted with sufficient play to allow the roller release bearing to find its own centre so cancelling out the oscillations and and any vibrations that may have formed.
The first motion shaft and bearings are not effected by the oscillation and will be ok. The first motion shaft on the gearbox fitted to my Minor is supported by a roller bearing in the rear of the crankshaft and I have not experienced any problems with the bearing.

[DCMVan70]

Hi Phil

Thanks for that, certainly makes sense.
The rattle or vibration is one thing, but probably the more worrying issue is how much the engine slows when the clutch is dipped.
The reduction seems related to the vibration - when starting no vibration, very small reduction in RPM. When the rattle starts the RPM drops to such an extent that the engine will stall - probably a drop of 300 rpm.

It has not always been like this, so wonder where that issue is?

I will try and take a quick video of the play in the release fork - just to check it’s not excessive.

Regards
David

[philthehill]

The engine revs will normally reduce when the clutch pedal is pressed as you are pressing an immovable object i.e. the carbon thrust against a moving object the i.e. clutch. Something has to give and what gives is the engine revs.

[Edward1949]

The engine revs will normally reduce when the clutch pedal is pressed as you are pressing an immovable object i.e. the carbon thrust against a moving object the i.e. clutch. Something has to give and what gives is the engine revs.

As an old-timer I still instinctively start cars in neutral with clutch released for this very reason (even though with moderns it doesn't really matter). Tickover is smoother. Also any end-float on crankshaft is exaggerated by dipping the clutch.

[svenedin]

The engine revs will normally reduce when the clutch pedal is pressed as you are pressing an immovable object i.e. the carbon thrust against a moving object the i.e. clutch. Something has to give and what gives is the engine revs.

As an old-timer I still instinctively start cars in neutral with clutch released for this very reason (even though with moderns it doesn't really matter). Tickover is smoother. Also any end-float on crankshaft is exaggerated by dipping the clutch.

Yes. I never depress the clutch pedal when starting the engine but I was caught out when I hired a modern car that would not start unless the clutch pedal was depressed. Most odd! I check every time that the car is in neutral because I often don't trust the handbrake on hills and leave the car in gear.

Stephen

[myoldjalopy]

On very steep hills it is also worth positioning the front wheels so that, if the handbrake fails, the car will roll into the kerb/hedge and stop, rather than rolling across the road into traffic, or down the hill.

[svenedin]

On very steep hills it is also worth positioning the front wheels so that, if the handbrake fails, the car will roll into the kerb/hedge and stop, rather than rolling across the road into traffic, or down the hill.

Good advice!

[svenedin]

Looking at the OP's video there seems to be a lot of wobble going on when the clutch pedal is depressed. I assume this is related to the lateral play he has found at the clutch fork. The clutch fork does have a bush and a special bolt (clutch operating fork pivot bolt 2A3289). When I re-fitted my engine I also changed the gearbox front cover that the clutch fork attaches to. The fork was a pretty tight fit in the jaws of the gearbox end cover. I wonder whether the gearbox end cover is worn where the fork sits and that allows excessive lateral play? Another thing I found is that when the clutch pedal free play was set to the workshop manual figures the clutch would "overthrow" with full pedal depression and make a nasty noise. I adjusted the clutch a little bit and the noise was eliminated. I presume this is due to differences between the original clutches and what is available today. I recommend Precision Clutch Components in Somerset. They sell reconditioned original clutch components (not modern stuff that just uses the original manufacturer's name). This is expensive compared to off the shelf stuff of course.

Stephen

IMG_1591.jpeg (4.3 MiB) Viewed 72 times

[oliver90owner]

The OP is disengaging the clutch, surely? Clutch is engaged when the transmission is transferring power from one side to the other? While some understand the error, it carries on to other newbies who know no better and then describe it AaF.

At tick-over engine speed the engine is providing just enough power to drive itself - no more. Adding a small extra load at tick-over will slow it by some amount. Extra loads, like this one, are parasites - so definitely need to be minimised.

[Bill_qaz]

My modern, a mitsubishi, actually increases its idle speed, via the ecm when you press the clutch pedal. You also have to press the clutch to make the start work instead of a neutral start inhibitor.
As oliver90 says if you apply engine load, by disengaging the clutch, when you have a fixed idle and no electronics it will slow.