Clutch replacement and other modifications?

Dear all,

The clutch on my 54 XK120 FHC almost failed during a rally last week. I managed to come home safely but it is clear that the thing needs replacement.

I intend to start next week, getting the Moss from inside the car and in the process I will do a few more things as a matter of course.

Can anyone help me decide of modifications that make sense, now that all the gearbox will have to come out:

  • open up the cover and check the forks and general state of the gears, consider butt-welding new first gear stops to avoid jamming (has happeded to me a couple of times)
  • new bushings (pedal mechanism)
  • check the fork for small cracks, perhaps with penetrating fluid?
  • Install new clutch and pressure plate → I like the feel of the Borg and Beck and Limora has new stock

Anything else I am forgetting: I was also considering lightening the flywheel or installing a new lightened flywheel alltogether. Any thoughts or recommendations on this?

Best regards,

Lluís

A heavier flywheel has many benefits, have yours machined if required and balanced with the pressure plate, and keep it unless it is a race car. It won‘t make the car faster or easier to drive. Just my opinion.

1 Like

Hi Louis,
What was the nature of the clutch failure, slipping, run out of adjustment, mechanical linkage worn out, etc? I have the same car so would like to have that info in my data bank.

I would certainly take the time to address leaks in the transmission, as much as that is possible. Mine is now leaking profusely and I need to take my own advice.

Best regards,
Tom Brady

Hi Tom,

Rest assured I will post pictures. I can only report that mid-rally, when pressed, the mechanism made grinding noises and the clutch would not fully disengage. Makes me think it could be the thrust bearing or any of the pressure plate mechanisms.

When fully depressed there were no undue noises.

I made it home, so no complaints. These will come when I need to remove the Moss from inside the FHC.

Best,

Ll.

Sounds like the fork pin is beginning to shear or has sheared.

Thanks: is there any particular heavy duty replacement that you would recommend? There are several available.

The original fork pin holds up well in saloons. I suspect, but probably can’t prove, that the incidence of shearing pins is related to the use of stronger pressure plate springs in the XK series.

LLuis:

Unfortunately, I have had both the tapered pin on the clutch operating shaft that holds the lever and the pin that secures the operating fork shear, on different occasions. I drilled out the operating shaft and secured the lever with a grade 8 bolt and with the fork I purchased the reinforced item from Coventry Auto Components and drilled that and, in addition to the tapered pin, secured it with a high tensile pin (see photos). Interestingly, the originals had held up for some 70 years, but unfortunately both sheared when I removed them when I got the gearbox out for a rebuild. It was the replacements that subsequently let go. All told I had to pull the gearbox no less than 3 times over a 2 year period!

From the number of times this issue with tapered pins has arisen on the Forum it definitely appears to be an Achilles heel with respect to XK120s and has resulted in folks welding the clutch fork to the shaft etc. The idea of drilling the fork and inserting the high tensile pin came from a friend who has had Triumph TR6s which experience the same problem apparently. It is also critical that there is no lateral movement in the mechanism and that all is correctly aligned. After installation the final time I noticed that my clutch operating shaft was moving forward slightly when the pedal was depressed, despite new spherical bearings. this turned out to be wear in the insert that houses the bearing in the frame which, after countless thousands of shifts had worn on the forward edge. I built this up with JB Weld and, so far touch wood, things have been fine.

Chris.



Thanks: is it true that one can convert to a direct action hydraulic sleeve in the bell-housing? This would basically solve the issue, right?

Of course option 2, would be to soften the spring setting, by using a 9.5" disk → would this solve the issues?

LLuis:

I seem to recall reading a post on the Forum back when I was in the throes of this hassle where the person had made the switch to the 9.5" disc and claimed that it didn’t seem to make the clutch operation feel lighter? Unfortunately, after treating myself to a Father’s Day cruise on Sunday I returned to town and joined the end of a horrendous traffic jam. One of my alternate routes home is currently not an option due to major sewer and road work, plus, to add to the mix, an accident on the four lane highway that bypasses my location had the police closing one lane. The two issues combined meant many folks leaving the bypass and channeling through town increased the flow created by the other road closure. After spending 40 minutes in a stop and go, first and second crawl, my left leg muscles are now in superb condition! Luckily, the car’s running temperature didn’t exceed 90C, the only positive outcome!

Again, if memory serves, some have made the conversions you refer to and you could probably find some information if you check back in the archives.

Chris.

Last year I broke the clutch fork. This turned into pulling the transmission out (3) times due to bad parts. First (2) times it was defective throw out bearings and the third time a (miss boxed) disk that was just off enough to keep from releasing.
Bad luck and Bad parts.
Please, if you have to replace the carbon throw out bearing ask a lot of questions to the supplier and do a scratch test to make sure it is quite hard. I had two fail in under 50 miles (simply wore down to the metal housing, and yes, everything was adjust correctly) They were from Borg and Beck kits. I hope they have corrected this problem.
Best of luck

Hi all,

The works have started, without much drama (so far): interior out, floors out, pedals out and there seems to be sufficient room to remove the gearbox.

I now have some questions, since we are at it: In the next message I will post a pic of how the stops for the 1-2 shaft look like: I was thinking (@Rob_Reilly ) to butt weld as you suggest, or alternatively, machine thread and use hardened, round headed screws. Would the second option work? I do not want to disassemble the gear box entire, and though I could do the second in-situ.

The on the Clutch: Limora supplied a Borg and Beck, as per original equipment with balance marks. Would you recommend sending it to a shop with the flywheel to balance the assembly?

THANKS,

Lluís

What is you opinion I think the gears look in good shape, as well as the synchros. The way I see the stops, a short screw, fixem with Loctite cement could work?

Hi all:

Updates from my end: here is the culprit of my cluch issues

The graphite bushing imploded, i was lucky to get home. Since i am at it anyway i will replace everything, but to be honest the clutch and flywheel were like new.

My quesion: would you Loctite the bolts attachinh the pressure plate assembly to the flywheel? Mine were not, but I find it odd.

MANY THANKS

LLUIS

Ps: so far the most annoying bit of this job has been removing the floors. I was totally surprised at how easily the rest happenned. The box is not that heavy.

Hi, Louis,
The old and replacement release bearings don’t look equivalent. I’d check that before you attempt reassembly.
Iain

Thanks Iain: They are… the graphite of the old one disintegarted to the point that the metal chewed through the carrier. No further damaged to the fork apparently.

Wow. That must have been making a lot of noise. I recently changed my replacement XK clutch (extremely heavy pedal pressure) for an E-Type, diaphragm clutch which is much more acceptable. The release bearings looked very similar but would not have been interchangeable. Good luck with your rebuild.

It happened during a long rally very quickly: my guess is that the graphite ring has at the end, disintegrated, exposing the metal. I made it home in direct gear using very little the clutch pedal, that was indeed noisy.