Clutch Master Cylinder behaves differently when hot

[Philk]

Having now got my 3.8 OTS car on the road, unsurprisingly, a few gremlins have cropped up (one cured with a new coil being fitted). I have, however, got a bit of a strange issue with the clutch (which was replaced alongwith the slave cylinder during the recommissioning). When the car is cold, everything works fine. When the car is hot and has been running for around 20-30 mins, the clutch is intermittently only biting on the bottom inch or so of travel with the pedal being a bit floppy above that). There is no leakage from the master cylinder (which was not replaced) and, as I said, when the car is cold all works fine again. Has anyone else experienced this? Could this be something sticking in the master cylinder? If so, is a replacement or a repair recommended?

Many thanks!

Regards

Phil

[Robbiee]

Could it be a very small air bubble which expands when hot??
Having just bled the clutch on my wife’s frogeye I can vouch for the fact that a soft pedal can be due to a very small amount of air!
Robbie

[politeperson]

I would try re-bleeding the clutch, maybe using a pressurised system.

[christopher storey]

Phil : this is a very common problem , and although I cannot explain to you the logic, the solution which usually works is to lengthen the pushrod , either by adjustment if it is one of the adjustable type, or if it is a fixed one, by welding a further length - IIRC something of the order of 6 to 9mm onto it, and then re-bleeding

[Philk]

Phil : this is a very common problem , and although I cannot explain to you the logic, the solution which usually works is to lengthen the pushrod , either by adjustment if it is one of the adjustable type, or if it is a fixed one, by welding a further length - IIRC something of the order of 6 to 9mm onto it, and then re-bleeding

Hi Christopher - that's great advice - many thanks. Whilst I don't have easy access under the car myself, I can see from photographs taking during the restoration that there is an adjustable pushrod fitted from the slave cylinder. I'll have a word with them (the car needs to go back for some other snagging items to be addressed) so we can look into that then. It would still be good to understand why the symptoms happen but if there's an easy fix that is good news.

[Philk]

Having investigated the issue, the restorers found firstly a very slight leak from the master cylinder. The car's history shows it had new seals fitted back in 1989. We're fitting an aftermarket master cylinder as a temporary measure whilst we get the original item completely refurbished. This will then be re-fitted later in the year.

[Philk]

Having investigated the issue, the restorers found firstly a very slight leak from the master cylinder. The car's history shows it had new seals fitted back in 1989. We're fitting an aftermarket master cylinder as a temporary measure whilst we get the original item completely refurbished. This will then be re-fitted later in the year.

As a further quick update (and as a few people saw at Thursday's Surrey JEC evening), the replacement clutch master cylinder (sourced from "one of the normal" suppliers) lasted all of four hours prior to a seal giving way and fluid coming back up the clutch pushrod! Our restorer has now managed to trace an OE master cylinder which will be going onto the car early next week. We'll still get our original re-sleeved and refurbished.

This issue followed a replacement fuel tank sump seal also failing (from the same supplier) earlier in the week. That was replaced with the old fashioned fibre type at the same time as the (now faulty) master cylinder was fitted. Being somewhat new to all of this, I am somewhat surprised at the low quality of some of the items being sold in the after-market. Given the inconvenience that re-fitting involves, I would willingly pay 50% more for some of these cheaper mass-produced items if they were made to a high quality and therefore did not fail so rapidly after installation.

[mgcjag]

Hi Phil...have you reported these problems back to the supplier......the only way they will know there is a problem is if we all report it and seek an answer.....As an example SNGB now have a quailty control department....i recently raised issues with two of their products.....one item was being reccomended as an upgrade has now been withdrawn from sale and the other has had added information put on their website about the product......Steve

[Philk]

Hi Phil...have you reported these problems back to the supplier......the only way they will know there is a problem is if we all report it and seek an answer.....As an example SNGB now have a quailty control department....i recently raised issues with two of their products.....one item was being reccomended as an upgrade has now been withdrawn from sale and the other has had added information put on their website about the product......Steve

Hi Steve

Yes, my restorer (who sourced the items) has provided this feedback.

Regards

Phil

[mgcjag]

Hi Phil....thats good that they have contacted the supplier....too often people mention on the forum about faluty parts but when questioned they have done no follow up... Steve

[Philk]

Hi Phil....thats good that they have contacted the supplier....too often people mention on the forum about faluty parts but when questioned they have done no follow up... Steve

The supplier is a well known name and I believe (from my restorer) that they have taken the pro-active step of taking the after-market items off the shelves. We have now fitted an OE item (which had to be sourced from elsewhere due to lack of stock) and, I'm happy to report, it's working perfectly.

[Tom W]

I had a similar problem with my clutch, with the pedal behaving differently hot and cold, though mine worked better hot than cold. In my case the cause turned out to be the flexi hose between the reservoir and the master cylinder breaking up internally. The bits got into the valve at the end of the master cylinder, and rather than sealing off as soon as the pedal is pressed, the path to the reservoir remained open. The pedal would just push fluid back and forth to the reservoir.