Hi guys, I think I,ve messed up something with my brakes.

I did a brake pad change, changed rear and front axle pads.

Start to drive and there is no brakes, pedal goes to down and only a little braking power at the very down of the pedal. Its very soft.

I think i did a mistake by how i did the change - i simply took the pads away, pressed down the piston, and put new ones, without unscrewing the bleeder.

So all fluid went up to the main brake cylinder reservoir, even overfilled it.
I doubt if there is any air in the system , because I did not disconnect anything, just pressed pistons back.

With engine on, i took the cap of the canister and pressed the pedal many times, you can see the fluid moving( without bubbles) in the reservoir and you can hear a clunking sound inside the cylinder.

Is it possible that i damaged the master brake cylinder by force pushing the pistons to the calipers.

Is it repairable or just replacable?

Any help aprecciated.
Thanks.

 

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It should come back okay - I just did my rears and I expected the same so I just pumped lightly a few times and the pressure came back.

But be sure to check for line leaks.

As far as I have seen these brake systems are sturdy and resilient.

Sure wouldn't hurt to replace with new fluid and bleed at each caliper, too.

 

The problem it didnt came back. I drove some miles consistantly braking and still the same.
It brakes at the very end of pedal. And the power feels like 50% or less left.

Due to clunking sound and fluid bubbling while pressing pedal, in the cylinder, I suspect a seal damage in the primary piston of master cylinder.

I wonder are those cylinders rebuildable, because I found some seal repair kits for them available.

 

Your problem could be caused by vacuum leak due to air entering or a broken seal somewhere else. Look for any visible leak of fluid from the master brake cylinder, brake lines and brake pistons in the four corners. Then try redoing the brake pad replacement and doing it right this time to see if the problem persists.

 

You might have "flipped" the seals in the master cylinder. If they were well worn, the back pressure in the system as you pushed the pistons back might have flipped the edges over, thereby losing much of the effectiveness of the seal.
As has already been suggested, the pedal will be soft for a few applications until the pistons reseat after the pad change, but it sounds as if you are well past that stage.
If there are no signs of leakage, I would be inclined to try a brake bleed to see whether it helps. Thereafter, the master cylinder would be my next port of call.

 

Can you advise us on the ordering source and dimensions of the parts in the overhaul kit ( as the source may dry up and have to go generic sizing ) . Many my go through this at some time in the future and any lessons learned would help shorten the downtime until the jobs successful completion . Might ( in my opinion ) be a good idea to keep the seals on hand as the need rises . In a practical sense a dry seal kit has a limited shelf life and in the aircraft trade a legal stamped limit .

The following advise may be trivial to some including the thread starter .

The best advice I can give is that after inspection of the master cylinder unit's cylinder surface being chromed or not chromed , give the surface a good cleaning with a very strong solvent to remove any possible varnish and possibly a mechanical polish . On old O-ring removal be careful not to scratch any surface . On instillation ensure you lubricate the new O-ring so as to not roll or cut the ring

U - shape hose bleed procedure , so air does not re - enter the wheel cylinders between pulses

AUTOFREN SEINSA D1117

Below are the codes, with which the part is compatible:


ALVADI: AL12538480
AUSTIN: AAU6338
AUSTIN: RTC2387
AUSTIN: RTC3387
AUTOFREN SEINSA: D1117
BARCODE: 8430320010908
BENDIX: 132752B
BENDIX: 701266B
ERT: 200514
FRENKIT: 123004
NISSAN: 46011G9525
NISSAN: 46011G9526
PBR: K7959
PBR: K7959X
TRW: SP4139
TRW: SP7672
TRW: SP8280
NISSAN: 46011-G9525
NISSAN: 46011-G9526
MOPROD: M7672

https://britishparts.co.uk/products/...e-kit-AAU6838J


BRAKE MASTER CYLINDER SEAL KIT$63.95
Part #: SP7672

BRAKE MASTER CYLINDER SEAL KIT, FITS 1979-1987 XJ6. REPLACES AAU6838J
Editing

 

I think that's was the case, to prove my theory i bled one wheel to see if there maybe air in the system. But pumping the pedal didn't gave any efforts, pedal simply smashed down regardless bleeder unscrewed on screwed inn.
Anyway bled some fluid, convinced myself that I have master cylinder issue. Remarkable, but after bleeding the brakes where even worse, if before bleeding i had about 50% of power, so after i had about 20% power left.
And you know what happened, on the next day took a car on a short drive to see hows the braking stuff.
And brakes slowly came back, simply came back.

Till now I cant understand whats happened, but probably seals "flipped" themselves back to its primary position, because now i have a firm pedal wich goes hard on his halfway. Like it was before. And no more sound from the master cylinder.

In case i ordered a master cylinder repair kit on ebay, AUTOFREN SEINSA D1117.

So next time I will change the brake pads, to prevent the master damage, probably is worth to unscrew the bleeder while pressing the caliper piston back.

 

My advice and this is very important , and I mean this as a friendly way ,

If you suspect you have flipped or rolled the O - ring in the one and only brake master cylinder , replace it and do not drive beforehand .

I had the experience where I lost my brakes through no fault of mine and once of my own .

Thanks for the part numbers .

 

Good to know that your brakes have come back normal. If anyone wants to know the specs and parts number for rebuilding the calipers, see my thread Caliper Rebuild Kit.