As I know nothing at all about ABS brakes, please indulge me! If you have to loosen something in order for the pedal to return, and once you have loosened that something, the pedal does return; then logic suggests whatever needed to be loosened is at fault, or a system that feeds that something. So I would start by trying to understand what the something when functioning normally should do. If fluid is meant to return through it, and does not, then maybe a valve is stuck or some similar fault. Is the part something that can be taken apart?
Now I am I correct in assuming that this system does not have a normal master cylinder setup? As if it did, the M/C reservoir would automatically fill the M/C and the pedal would return, regardless of whatever was downstream of the M/C pedal setup.
Thus, is it possible that you have a problem with, or the fluid feed to, the M/C, and releasing a nipple on a caliper lets the fluid back up to allow the M/C to return?

 

OK, talking with Greg just now, more important things, and he mentioned these issues here, and asked if I knew anything about the operating of this Hydraulic Ram in lieu of a Vac booster.
Being as I had a couple of XJ40's.

That "ram" as I call it, it actuated by a the pedal push rod opening a Reaction Valve in the 1st 2mm of travel. That Valve allows Hi-Pressure to enter the ram, and PUSH the Master Cylinder, and the brakes do what brakes do. Just like a Vac Booster does on any other car.
When you "relax" your foot, as in release the brakes, that Reaction Valve closes, Hi-Pressure is ceased, the spring inside that "ram" returns the thing, including the pedal to the upper rest position.
Those Reaction valves can be Blonde, and NASTY. Pedal adjustment, as in FREE PLAY is MORE than critical here. Not enough free play, and the system can remain active, BUT you have issues AT the floor, so a stuck Reaction Valve is my 1st thoughts.

The Master Cylinder has been dismantled. NOT DOUBTING YOU AT ALL, but are the seals etc all in 100% condition, AND the right way round, coz you may be getting a by-pass inside that Master Cylinder, and that will do the same, especially if its the Hi side.

The rest I know zero about. We removed MANY of these "rams" on the XJ40 cars, and fitted X300 style Vac Boosters back in the day.
The "kit" was $1250 + fitting (memory, so dont quote me please). I doubt there are any kits these days, and that $$ would be miles off today's asking price.

I agree. it is a gremlin in the Hi side, and what I wrote is ALL I know of that bit.

 

Adam,

Greg and Grant raise an interesting point. I went back and read your thread from the beginning. It mad eme think about a couple of things:

- Yous started off by saying that you'd rebuilt the actuator. That makes you pretty unique in my experience! As in, the first person I've heard of who has needed to take one of these apart! But what was the reason? What was the fault you were experiencing with the brakes? Because it now does make me wonder if there's a problem with the fitment of the seals on the primary and boost chambers.

- the other thing was that you said the pedal went to the floor and styed there when you tried to bleed the rear brakes, and you had to open the bleed nipple valve to release the pedal. But that's a bit confusing because to bleed the rear brakes properly, you have to open the bleed nipple BEFORE you press the pedal.

If you have bled the LP side, then the rear brakes using the correct procedure (where you don't touch the pedal until after the bleed nipple is open), then if after that, the pedal can be pressed to the floor if the ignition is on, then it feels as if one of two things might be happening:

- the primary / boost seal is possibly failing allowing excessive pedal travel with pumped pressure behind it which then causes the pedal to jam. or
- the abs outlet valve is activated but somehow the inlet valve is deactivated, allowing both boost pressure but also reservoir return of the fluid. That situation should not be allowed to happen.

So have you checked the state of the abs valves when the ignition is turned on? Are they all deactivated? And which valves are pin 3 & 4? ( I don't have my diagrams to hand right now?)

Cheers

Paul

 

Sorry it’s taken me so long to reply! My father (74) and myself (23) run a car dealership/repair shop in the lake of the ozarks Missouri
I’m unfortunately busy on other cars and trucks too often so I haven’t messed the Jag in awhile

I see I’ve been to all around the place with my explanation of repairs/my thought processes so here’s what I did in what order

Day 1. Bought the car knowing the brakes didn’t work, pump would come on and build up in 60 sec and shut off with no dash lights. The pedal was a sponge and had no resistance. One press and the pump was back on and brake and abs lights on until pump shuts off. Pedal returns normally

Day 2. I removed the ABS valve block and tested all solenoids. Found one that was dead and cleaned it up with wd40 while tapping it with 12v to free it up. It clicks as loud as the others now. Reinstalled and still no fix. Pedal still spongy but returns as normal

Day 3. New Accumulator, still no change. Pedal still returns

Day 4. I removed the entire actuation unit because with the key off if you pumped the pedal with VERY short fast kicks it would get hard like it’s supposed to, but would sink to the floor within 5 seconds of normal holding pressure to bleed brakes.
This made me think their had to be a bad seal somewhere inside the master cylinder or the high pressure side of the unit.

Removing the internals of the master cylinder revealed a bunch of sludge around a plastic filter ring, I’ll attach a picture I forgot I took. This thing only has like 3 seals in the whole internals of the master cylinder so I can assure everyone the seals went back exactly as they were removed. All I did was clean the insides and reinstalled in the car.
After reinstalling I bled the LP side correctly, and then bled the rear brakes by opening the bleeder first then pressing the pedal for about 10 seconds. This is when my father yells down that the pedal is stuck to the floor. Do I tighten the bleeder after the pedal is released? That just seems strange to me.. That’s when I found the rear brakes weren’t returning fluid.
THIS BEGINS THE STUCK BRAKE PEDAL BS^

Day 5. New rear rubber brake line, and temporarily bypass proportioning valve. Didn’t solve pedal issue.

Day 6. Remove entire unit and take it completely apart inspecting every inch. It literally looks like brand new inside the unit. Nothing out of the ordinary inside the master or the high pressure actuator, and I’ll tell you all I’m very picky about inspecting parts.
I re installed the unit and the pedal is still stuck.

Day 7. I removed the rear brake line at the ABS block and installed a plug in its place to eliminate the possibility of a rear caliper causing the pedal to not return. That also did nothing. Pedal still sticks to the floor, but I should add that even if you press the pedal 1 inch it’s stuck there too.