Reaction valve issue

As long as I’ve owned my E coupe, 2018, I’ve had a sticky reaction valve problem. The master is a repro. I’ve probably removed and cleaned the piston and bore 3 times. Works fine for a bit, then starts hanging up again. The symptom is, press the pedal, engage the brakes, release the pedal, brakes release somewhat and fully release after 2-3 seconds. It’s better at startup when the engine bay is cold, gets worse as the engine bay heats up.

Since I have the original master, would a professional rebuild, resleeve solve my issue?

This is the same problem I have had John…… I initially solved the issue by putting a slightly heavier spring in the return area…. But after 2500 miles it’s returned…I’m about to do a clean and see if that works ok

Yeah, the fix for that is to put a slightly stronger return spring in the reaction valve.

Have you experimented with the free play in the brake pedal connection to the m/c plunger? Needs some to make sure pressure gets released.

I’ll check that …usually I adjust to get the least amount of slop in any linkage…what do you recommend 40 thou?

Just to throw another cog in the works … have you replaced ALL the brake flex hoses? Over time they age and have a tendency to collapse internally. When that happens the fluid is restricted and the brakes stay engaged. Just something to check and rule out if you haven’t changed the flex lines (3) in the last few years.
Also there is a threaded screw (pedal stop) on the pedal box for adjustment. When released If the stop is out of adjustment fluid may be trapped in the valve causing brakes to not fully release. As far as I know adjustment is NOT covered in the Bentley’s or S3 ROM! This also could be your problem of brakes not releasing.

My 2 cents worth.

Happy Trails,

Dick

I don’t know if it even needs that much, just so the pedal is free to come back to fully retracted plunger. I would just loosen the stop nut/bolt and see if the pedal moves back some more. I have had the clutch pedal return spring break but not the brack pedal return spring. Replacing those springs is a man sized job.

The “free travel of the pedal pushrods” is described on page L.13 of Bentley. 1/16" free play is specified. This is in the 3.8 brake section but I would assume that the same level of pedal free play would be applicable to the 4.2 brake system.

David,
Thanks… (Re)-Learn something every day!!! Just referenced my old Bentley book, page 268 (Page L.13) and, sure enough, found the “Free Travel of Master Cylinder Push-rods”. write-up! Amazing what one may overlook for all these years!!! Ha Ha
Further investigation for S3 models, procedure 70.35.01, item #39 indicates a pedal free play of 3.17mm but an incorrect 1.25 inch clearance. The 1.25 inch should read "0.125 " inch! Old dog relearning!!! Ha Ha Tanks for pointing me in the right direction.

Happy Trails,

Dick

Dick;
This has nothing to do with brakes but I am interested in the action related to the rotisserie that I gave you several years ago… You were having it powered coated, re assemble your car then ship it to the JCNA folks. I have looked from time to time but have not seen any mention. The last I knew you were tussling with making a front mount.
Thans, Joel

Exactly which spring are you changing?


Should I assume you mean spring 38?
Tom

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I suspect that this is not an error in the manual. The 1.25 inches is intended to be measured at the pedal, not at the pedal stop. This translates to a much smaller free play at the pedal stop due to the multiplier of the length of the pedal arm. Jaguar sometimes measured free play this way - for example, in the XK120 workshop manual, they specify 1" free play at the clutch pedal.

I think so. Coincidentally, I accidentally knocked the filter cover off the reaction valve of my S2 OTS yesterday while messing with the horn relay. It has never been removed since I installed the new servo in 2010-11. Inside, there were two nested springs, so clearly the manufacturer felt the needed to beef up the spring force.

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Hi, I had a similar problem with my sticking reaction valve on both of my E types. I used a round gold polishing wheel that matches the bore (I am a retired dentist) we used these when we polished gold crowns. Then I used my dremel with the correct mandrill and very slightly opened the bore, polished it then used rubber grease. Problem solved, whether new or rebuilt this works. EBays sell the polishing kit
Shofu gold polishing kit is the item.

Regards,
Allen

Hummmmm… Will investigate further… A Challenge Ha Ha.

In a message dated 4/8/2023 9:40:10 AM Eastern Standard Time, noreply@jag-lovers.com writes:

From what I see of the kit, these look like grinding mandrills? Are you saying you picked one of the piston shaped mandrills and opened and polished bore with that?

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David, does spring 38 ultimately push on 33 to return the piston?

David, I do not see how increased spring pressure would make a difference. I am, of course, assuming the small piston is not going back in far enough to reopen the vacuum valve and that is the issue. Spring 38 pushes the air valve/vacuum valve only until the air valve closes. Then the vacuum valve must reopen by the diaphragm pushing the small piston back further. It seems to me the spring is now out of the sequence. But if it does help, then it does.
Tom

I think many reaction valve issues are really problems with the small piston at the front of the master. If that gets sticky, more spring may help retract it.

Michael, yes as said i believe the issue is often a sticky small piston. My question is as i stated above. I do not see how a stronger spring will push the sticky small piston back. I see more spring only holding the armospheric air valve closed tighter. Am i missing something?
Tom

I’ve cleaned/polished it every time. This was the first time in 6/2020 Two years later I did it again, twice, but it was not rusty or varnished like the 1st time and the brake fluid was flushed after the 1st time.

What is a good way to clean the bore? Allen suggested gold polishing mandrills.