Inboard brake master cylinders take more travel

[N14ND]

Hope everyone is staying healthy. Taking this quarantine time to do more work on the Kiftox.
Here's my head scratcher: Series V, Cleveland setup: calipers and dual brakes, (4) master cylinders,(no parking brake), remote reservoir. Bled the brakes for the first time yesterday and have a puzzling outcome. Pressure bled from the caliper up to the reservoir. No problems there. Both sets of toe brakes actuate the calipers correctly. No spunginess. But the LH pilot-inboard pedal (right brake master cylinder) and the RH pilot- inboard pedal (left brake master cylinder) require more plunging distance than the outboard pedals for the same braking effect, about 1/4" more. The static measurements are the same for all of the master cylinders. So, I have been scratching my head as to why the inboard master cylinders are like that. All four pedals actuate the calipers just fine. Nice and firm. But it will be irritating to have the left pedal go down more when in the right seat and the right pedal to go down more when in the left.

I have consider moving the the two outboard master cylinders to the same side, but I don't think that will solve the issue. But I will if I have to.

[Delta Whisky]

For what it is worth, I've never been satisfied with my first attempt at bleeding brakes on an aircraft and my first time success on cars is only about 50% but I'll offer this for what it is worth. For the first time ever I bled the brakes on the KF using a hand held vacuum pump (pulling up from the caliper assembly) and was fairly pleased with the results except my results were somewhat similar to yours. I noticed after about 5 or 6 days that a few air bubbles started forming in the lines at high points. Not large bubbles but bubbles non-the-less. So a couple of days ago I ran the procedure again and - viola - all is well now. I don't have a picture of the pump at the reservoir but here's one of the capacity at the caliper assembly.
24501

The "syringe" approach helped keep track of how much was being used by each side.

[PapuaPilot]

Like DW said, you probably have some air in the system. The only other thing I can think of is bad O-rings in the master cylinder.

[N14ND]

Thanks guys. I have thought about the orings. Actually, all of them. These are original kit components (ala 1995) so there is probably quite a set to the orings. I lubed everything and plastic baggied them 20 yrs ago, but they probably have permanent flat sides. They may relax some with the oil and repeated pressure pulses, but probably worth the time to replace the orings. Would hate to have the brake fail at an inopportune time because the orings aged out.

[N14ND]

Thought I would give an update. Spent a couple of hours back bleeding the brakes again. This time I worked each pair of pedals/cylinders through their full travel numerous times and gave each rapid taps as I pushed fluid up from the caliper. Was amazed at the amount of air that was still in the system. Got numerous large slugs of air and a large volume of micro bubbles up into the overflow jar. Probably put a 1.5 quarts through each brake line before it ran clear. Now each brake has the same travel, firm and no leaks.

[PapuaPilot]

Glad to hear that you got it done. The Kitfox brake system is very challenging to bleed with all of the loops and multiple high spots. This was as I suspected. You will be glad you spent the time to get this right.

[efwd]

And even then you might find another bubble develop. Those micro bubbles you described, may still precipitate out. That's how it happened to me. But, I seemed to have a pretty easy time of bleeding somehow. I vacuumed fluid down from the top using a brake bleading system I got at HF. That said, I still had a bubble develop and I believed it to be the micro bubbles that coalesced. I know it feels good that its done.