Tilton master cylinder question

[DaveW]

I'm using a Tilton 78-Series Master Cylinder # 78-625 (front pivot MC) for the clutch.

Anyone have issues with its internal check valve? I'm getting inconsistent clutch release (both at the track and in the shop).

I've bled the clutch system and set the MC stroke multiple times. Sometimes the clutch releases fine, sometimes it won't release at all.

I have a new spare, and I will replace the one that's now in the car. I'll report back after I do this.

[DanW]

No issue for my master cyls.

[Garey Guzman]

I had bought some of those but still haven't gotten them installed.

With the price of them, I would just disassemble, make sure the seals look ok, lube and reassemble!

[DaveW]

I had bought some of those but still haven't gotten them installed.

With the price of them, I would just disassemble, make sure the seals look ok, lube and reassemble!

I'll change it since I have 2 new spares. I'll then disassemble the removed one to diagnose, and if it looks OK inside, I'll rebuild it.

[Hardingfv32]

I have always wondered about the adjustment to the cutoff port travel on these cylinders. Why is such an adjustment not normally found on other brands of cylinders.

I do not appreciate the need for this adjustment. What issue does the cutoff port travel adjustment remedy? How would it present during brake/clutch operation?

Brian

[Phil Creighton]

Generally the cutoff port adjustment prevents the fluid going back into the reservoir and that small adjustment can mean the difference with the hardness of the pedal. On AP cylinders this is done by pushrod shimming to quickly cover the port in the bore - not recommended once done by the OE. I thought that Tilton/Wilwood and Girling were 'foot valve' type where the piston movement closes the valve in the end of the cylinder. Not something generally adjustable.
We have had issues with rubber grease affecting this seal on girling cylinders if new - the spring is very light.

[DaveW]

...Not something generally adjustable.
We have had issues with rubber grease affecting this seal on girling cylinders if new - the spring is very light.

The MC in question has been in the car since 2019, so it's definitely not new. It acted OK in the shop when I first bled and set up the clutch system after engine R&R this spring, but then at the track I had issues getting the car in gear 1st time out. It then worked OK when I came off the track, but was screwed up again before 2nd practice. We reset the pedal throw a few times, but that did no good - it was still alternating between releasing and not.

In the shop afterward, same issue - worked then didn't, then worked, then didn't, etc. after multiple adjustments and bleedings, with no evidence of fluid leakage or air in the system.

As I said, I'll replace it with a new one, and report the results.

[Phil Creighton]

Other thing we had once was that the pedal bottomed out in bleeding and was never quite the same. I think we attributed it to distortion of the valve seal and it sealed sometimes

[DaveW]

Contrary to my initial thoughts, a dedicated check valve was not the issue. In this MC, the check valve is the pressure seal movement, which Phil mentioned. See post #12 below.

This AM I replaced the MC with a new spare, ordered a couple of rebuild kits, and will repair the removed one.

After bleeding the new one, and re-setting the pedal travel, things seem to be back in order.

Thanks, everyone, for your help.

[DaveW]

Other thing we had once was that the pedal bottomed out in bleeding and was never quite the same. I think we attributed it to distortion of the valve seal and it sealed sometimes

That could also have been my issue, but I think mine was as I described above. That also might have been acerbated when I bled it this spring.

[DaveW]

Contrary to my initial thoughts, I don't think the check valve was the issue.

When I replaced the MC, there was a tiny bit of dampness and dirt accumulated under it. There had been no sign of fluid loss, except for this dampness which I couldn't see previously...

I pulled back the rubber boot on the Tilton MC, and there was NO FLUID inside it. So either it was sucking air w/o leakage or the check valve function is somehow screwed up, and the dampness I saw must have been left from when I spilled a bit of brake fluid this spring - the reservoirs are above the pedal area.

More to come when I totally disassemble it prior to rebuilding.

[DaveW]

Similar to what Phil said in post 6 about AP MC's...
Movement of the piston and the pressure-seal during MC (clutch or brake) actuation opens and closes the port to the reservoir (the ~1/32" vertical hole just to the left of the pressure seal in the attached diagram). At full retraction, it's open and a few 0.001's of motion closes it.

Evidently, the pressure seal wore just enough (it still looks OK, but I use the clutch for every shift) to make sealing/opening/closing the port to the reservoir inconsistent, leading to the issues I described previously. So rebuilding with new rubber components should correct the issue.

I just rebuilt it (4/6/23), so we'll see how it works when I need it.

MC cross-section:

[DaveW]

I had bought some of those but still haven't gotten them installed.

With the price of them, I would just disassemble, make sure the seals look ok, lube and reassemble!

That would have led me down the wrong path, since minor, almost invisible, wear on the pressure seal was apparently the culprit, and I would have been right back where I started.

[DaveW]

...Movement of the piston and the pressure-seal during MC (clutch or brake) actuation opens and closes the port to the reservoir (the ~1/32" vertical hole just to the left of the pressure seal in the attached diagram). At full retraction, it's open and a few 0.001's of motion closes it.

Evidently, the pressure seal wore just enough (it still looks OK, but I use the clutch for every shift) to make sealing/opening/closing the port to the reservoir inconsistent, leading to the issues I described previously. So rebuilding with new rubber components should correct the issue...

Another thought on this subject:
Last winter, QS rebuilt my engine and replaced the entire clutch assembly. That included a lighter clutch spring than what I had previously been using.

The heavier spring likely made the pressure seal wear a bit, but because the initial stroke was against a higher hydraulic pressure as a result of that spring, it was forced against the cylinder bore more firmly than the lighter spring could do, and the check function worked OK.

With the lighter spring and less hydraulic pressure, the slightly worn pressure seal could not completely seal until more pressure/stroke was applied, leading to the inconsistent behavior.

Since seal wear should be a bit slower now with the lighter spring, I think I should have no more issues for several years, and if I do, I'll know what to look for.

[DaveW]

The new MC worked perfectly at Mid-Ohio. And the softer clutch spring that QS installed makes moving around the paddock and getting underway a lot easier.