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Clutch self-adjust?

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SteveHall64Healey

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Gents, when I bought my BJ8 last year, the clutch was engaging quite high in the pedal, suggesting that a new clutch was going the be needed in the near future. The 75 year-old BMC mechanic who saftied the car last fall, drove the car into his shop and told me that the clutch was on its last legs, I might get another month or two out of it, and as the clutch is self-adjusting, the high clutch pedal is severe wear and not an adjustment issue. I have some of the service records for the car, but could not determine when/if the clutch had ever been replaced.

Yesterday, I removed the exiting clutch and it was virtually brand new. The thickness was 5/16"-same as the new one. The pressure plate and flywheels each had a depression of less then 1mm, so clearly the clutch was done recently.

The shop manual also states the clutch throw is self-adjusting, so I am trying to figure out why I get no engagement of the clutch until the last 1-2" of the pedal's throw. Has anyone encountered this issue before?

thanks,
steve
 
It's possible that there's a mis-match with the throw-out bearing__pretty sure there's a different one (and "face to pivot height") for each of the three (3) different 6-cylinder clutches used.

You'd think the hydraulics would equalize the operating height of the pedal, but maybe there's not enough range to do so. I'd first make sure that I have all the right matching parts, before putting it all back together.
 
SteveHall64Healey said:
The pressure plate and flywheels each had a depression of less then 1mm
Click to expand...

What does this mean? The face of the flywheel and pressure plate should be flat. If the flywheel is worn 1mm then that would cause a high pedal for sure.

You can usually find out of the flywheel has been machined because it will be missing the alignment mark "1" stamped near the outer edge of the face. If you do need to machine it then mark this on the outer diameter so that you'll be able to put the flywheel back on in the correct orientation.

As Randy says, check all the parts match each other. BJ8 used a diaphragm clutch I believe which would look like this
390.jpg

The early spring clutches with three levers in the centre have some adjustment for the lever heights which the factory manual details reasonably well.

Andy.
 
If it's a diaphragm clutch take a close look at the diaphragm for a radial crack between one of the ears. Such a crack can cause what you are seeing and the clutch will still "work" and look, and measure, very normal both assembled and disassembled.
 
Gents, sorry for taking so long to reply - I had to step away from the project for a bit.

As suggested in this thread, something must be dimensionally incorrect. Does anyone have any literature or web resource that specifies the dimensions of these parts?

Although I don't have all of the receipts for the car, it is clear that the clutch has been done recently, as the flywheel has been machined flat within the last few years. I am advised that wear on the flywheel is normal and after many years of use, it is common to machine the flywheel flat again. The wear on the recently-machined flywheel is very low (much less than 1 mm). I wonder if too much was machined from the flywheel and this is contributing to the problem?

The pressure plate assembly is quite new looking, and bears the markings: 'MADE IN GREAT BRITAIN QY93036' (Q could be an O). The pressure plate is highly polished and does not appear to have undue wear. The diaphragm springs appear to be in good condition, with no cracks or blemishes visible and no weird flexing when depressed. One of the diaphragm springs has the marking 'KC769'.

The throw out bearing also looks new, with the graphite ring standing proud of the cup in which it sits by approximately 0.271". This is about the same as a new one. If my suspicion is correct, the speciality shop that did the clutch does many of them and they likely haven't used the wrong part. According to Moss, there is only one part number for late BJ7 and all BJ8 throwout bearings.

Lastly, the clutch disk is 5/16" thick - the same as the new one, and it is as depicted in the photo posted by 57_BN4, except that the posted photo does not show the other side. When viewed from the side, the clutch disk is assymetrical, with the side facing the flywheel being the same as in the photo posted by 57_BN4, and the side facing the pressure plate being as in the photo in this posting. This clutch disc can only go in one way, and it appears to have been installed correctly before I got the car.

So, any info on the dimensions of these parts would be very helpful!

One last (hopefully stupid) question: am I right in expecting that the clucth will engage earlier in the throw of the clutch pedal, as opposed to engaging in the last 1-2 inches as it now does?

thanks,
steve


image.jpg
 
Try Bleeding the clutch slave clyn. ??
 
You may want to check out your master cylinder location. If the clutch was virtually brand new, it is a safe bet that the previous owner also rebuilt the master cylinder. Healey M/C s don't use an adjustable pushrod to connect to the pedals. Instead there are split aluminum spacers that distance the M/C from the firewall. These spacers are sometimes stacked. Not sure if this is the cause but those spacers will change the pedal height. Is it possible they were left out?
 
Did the engine revs slow down when the pedal was depressed at idle? It's possible that the clutch was not fully releasing if the slave cylinder had retracted as far as it would go but the pushrod was still not fully released. You'd have noticed this when taking off the slave cylinder or removing the bellhousing bolts as they'd be under tension. It should be possible to manually push the clutch lever forward towards the slave cylinder half an inch or so when all is correct.

Another possibility is that the clutch cover is defective somehow. How far did the cover lift off the flywheel before the periphery bolts became free? Should be something like 1/4"-5/16" of spring compression (never done a diaphragm Healey clutch so not sure). If it only lifted a small amount then the bolts came free then there is something wrong with the clutch cover. A clutch shop will have a press type tool for testing clutch operation so you could verify it by taking the disc and cover in and having it tested.

Andy.
 
Thanks Richard, I rebuilt the master cylinder, and as I recall there were two metallic spacers that I removed, cleaned and reinstalled as part of the rebuild.
steve
 
Thanks Andy,

When the clutch pedal is fully depressed, the engine speed goes to idle and the car rolls freely. There was no impact on engine speed as the pedal was released until the clutch actually begins to engage high in the pedal's motion.

During disassembly, when I removed the clutch cover, it came away from the flywheel under spring for about 1/4 to 1/2 inch. Thanks for the suggestion re the clutch shop - I will give it some thought.
steve
 
Steve, it sounds like your slave cylinder might not be allowing the clutch to release fully. This gives the effect you describe of a high release point because the clutch is permanently semi-depressed by the slave cylinder and pushrod.

When the car is hot and idling stationary in neutral, the engine revs should drop about 100 when the clutch is depressed and the engine note change a little due to the increased friction of the carbon bearing. If it stays the same regardless of whether the clutch is in or out it may well because the clutch isn't releasing. Can you refit the clutch to the flywheel and measure the distance from the engine back plate to the release bearing thrust plate, then measure the bellhousing back to the release bearing when pushed fully in?

Andy.
 
You can rule out the flywheel being too thin; I had 1/8" cut from the face of mine when I fitted an MGC trans back in the 80s. I'm still using the same flywheel now, albeit with a hybrid clutch package (10" MKI friction disc and 365GTB/4 diaphragm pressure plate).

With BMWs__also hydraulic actuation__bleeding the system (properly, but BMWs are weird in their placement of the bleed screw...) can make quite a difference in the engagement point of pedal travel, as does the condition of the master and slave cylinders.

If everything looks good with the mechanical bits, might be time to look at the wet stuff...
 
Thanks for all the input. I reinstalled the clutch disk and cover plate assembly, and noted that clutch disk was held practically immovable between the driven plate and the flywheel when all 6 blots were torqued to 40 ft-lbs. (does anyone know the correct torque to be used for these 6 bolts?).

I then took a few measurements:

1) distance from rear engine back plate to release bearing thrust plate (flat face upon which the release bearing makes contact): 3.875"

2) distance from front of bellhousing to thrust bearing in forward-most position: 2.960"

3) distance from front of bellhousing to thrust bearing in rear-most position: 4.410"

4) when all 6 cover plate bolts fully loosened, cove plate assembly separated from the flywheel under its own spring force by 0.125". This separation was pretty even all the way around the clutch cover assembly.

Also, I am readily able to move the piston of the slave cylinder in and out by 1".

Lastly, when I fully loosen the 6 bolts, the release bearing thrust plate moves away (rearward) relative to the clutch cover housing by approximately 0.6", i.e. approximately 0.6" of spring travel in the diaphragm.

Any thoughts?

thanks,
steve
 
Looks ok on the measurements but the 0.125" spring compression sounds a too little. A clutch shop should be able to tell if that is normal for your clutch in a few minutes.

Andy.
 
SteveHall64Healey said:
Regarding the alignment of the TDC timing mark and the "1" stamped on the flywheel, why is this necessary?
steve
Click to expand...

The factory balanced the entire crank, flywheel and front pulley as one unit. If you put the flywheel on in any other position you'll most likely end up with vibration.

Andy.
 
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