Brake master cylinder leak

Hi everyone,
we have just had our first bush outing in our Oka. All went well except for a leak from the brake master cylinder. Fluid was found dripping onto the brake pedal, and after very careful tracing the source, it appears to be coming from between the lid and the body of the master cylinder. The rubber seal is intact, but apparently not sealing very well. We were on quite a few corrugated roads which is probably moving the fluid around in the reservoir and and the lack of an adequate seal allowed fluid to leak out. The resevoirs are now about half full. The master cylinder was replaced a couple of years ago by the previous owner.

Has anyone else had this problem? Any suggestions for a fix?

Thanks for any ideas.

cheers

Tony

Different MC problems, but my eyes on your problem for ideas.

A very common problem with replacement master cylinders. The lids are made out of thinner gauge steel than the original and warp with the heavy tension of the lid retaining springs. Paul Nott recommends that people use the old lid when replacing the master cylinder.

If this isn't an option it may be possible to decrease the retaining clip(s) spring tension and still retain a good seal.

Deano

Had the same problem on OKA 124 after replacing the master cylinder. After talking to Paul Nott and ordering a replacement unit, I removed the tin lid and found it to twisted. On a flat surface with three corners sitting the fourth was about 4 to 5 mm off the surface. As I was away from home and did not have access to the old lid I carefully flexed the twisted lid until it sat with all four corners on a flat surface. Refitted the seal and the lid to the master cylinder and have had no further leaks in the following 2000km. I now have a new spare master cylinder (still in its sealed plastic bag) if anyone needs one.

Tim
0409547440

From A PM I had the following comment "I suspect it is a mongrel job to change one out,...?"

So have posted my reply here in case it is helpful to others having to replace an XT master cylinder.

I completed the job in two days, but much of this time was spent working out how to get access and going to Repco for the extra spanner etc. I estimate with the benefit of hind-site that I could now do it in 4 to 5 hours including bleeding.

The steps were:

Unplugged the wiring harnesses as necessary so as to allow the Instrument pod to be swung towards the passenger side after undoing the hinge retaining screws.

I sucked up all possible brake fluid from the reservoirs using a plastic sauce bottle to minimize fluid release when the pipes are undone. This results in some fluid loss when the pipes are undone but leaves most of thee pipes charged with fluid.

I drilled a hole about 17 mm in diameter (just big enough to fit my thinnest 1/2 drive socket extension through) in the face of the dash surrounds facing the drivers door, aligned with the bottom securing bolt of the master cylinder. This hole gave me access to the bottom securing bolt of the master cylinder, all other bolts and fitting could be accessed as necessary either from above or below the dash panel work.

All necessary pipe nuts and securing bots were undone. To be able to remove the master cylinder it is necessary to loosen the nuts securing the pipes form the master cylinder into the differential-pressure switch so that these pipes can be moved to the side. I did not remove these pipes from the differentiation-pressure switch.

The old master cylinder was carefully maneuvered out of the dash.

Refitting was a simple reverse of the removal.

After completion of the master cylinder replacement all wheels were bleed until new fluid came through and no air was evident.

One thing o be aware of:
You will need flare-nut spanners (pipe spanners) with a length short enough to enable the necessary swing in the limited space within the confines of the dash metalwork. In my set the smaller (7/16) required flare-nut spanner was OK but my original larger (9/16) spanner was too long to allow me to work the fittings. I went to Repco to purchase another (9/16) flare-nut spanner intending to cut it, to make a shorter spanner. The Repco flare-nut spanner was about 13mm shorter that my 20 year old Sidchrome flare-nut spanner and so did the job without cutting it. The other thing that helped was that the Repco flare nut spanner had the nut-flat rotated about 85 degrees to the spanner axis while my old Sidchrome spanner had the nut-flat at 90 degrees to the spanner axis, hence no angular advantage by turning the spanner over.

The flare-nut spanners I used to do the job were:
Sidchrome 7/16 - 3/8, tip to tip length 157 mm with nut-flat 90 degrees to the spanner axis.
Repco 9/16 - 1/2, tip to tip length 175 mm with the nut-flat 85 degrees to the spanner axis.

Any questions please feel free to call.

Regards

Tim
Mobile 0409547440

Thanks everyone for your replies. Fortunately I have the old master cylinder and have swapped the lids over. On checking out the "new" lid I found it was slightly bowed along one of the long edges, probably causing the leak. The''old' lid was perfectly flat with no distortion.
Thanks Tim for the instructions on replacing the master cylinder. I will file it and hope to never need it!
cheers
Tony

TR wrote: From A PM I had the following comment "I suspect it is a mongrel job to change one out,...?"

So have posted my reply here in case it is helpful to others having to replace an XT master cylinder.
...

Regards

Tim

Well most of the people I ask tend to say most of the jobs are mongrel ones...
Why should this one be perceived any differently?

Hi,
I am having master cylinder leak issues with 430.. Have been there with my 187.. and was able to procure new 'O' ring seals.. The teflon backup washers and bore were fine. and fit.. Problem solved.. That was a few years and a lot of miles ago.. As you say a mongrel job to remove...
Unfortunatley I was not smart enough to measure and record the bore diameter.. and I dont need to have the vehicle off the road while waiting for parts..
Would you be able or interested in either selling your spare master cylinder or measuring the bore size for me please..Being it American... it would be imperial??
Cheers,
Nobby.

I was ready to tell you I binned it a couple of months ago, but after waddling outside I found it was sitting right where I left it.

You want it AusPosted, or how does one get the (roughly 1-1/4" plunger out to measure the bore?
(I held my thumb near it and it is bigger than an inch, so somewhere is in the 1.25 to 1.375 range I think)

Nobby wrote: ...Being it American... it would be imperial??
Cheers,
Nobby.

I am running a combo Queen's birthday/4th of July sale on it, so the timing is great.

Hi,
That is good news... Are you willing to part with the old master cylinder?? assuming that it has not been out in the rain?? if it has been and gone rusty.. than it may not be reuseable..If you can still move the piston / plunger in the bore, it will be quite reconditionable.. It is usually less than half the price to have brake cylinders resleeved with stainless steel than replace..and they then will outlast new ones.. [which are mostly Chinese these days]. Highly unlikely the Oka replacement is Asian though..
I look forward to hearing from you,
Nobby.

Nobby wrote: Hi,
That is good news... Are you willing to part with the old master cylinder?? assuming that it has not been out in the rain?? if it has been and gone rusty.. than it may not be reuseable..If you can still move the piston / plunger in the bore, it will be quite reconditionable.. It is usually less than half the price to have brake cylinders resleeved with stainless steel than replace..and they then will outlast new ones.. [which are mostly Chinese these days]. Highly unlikely the Oka replacement is Asian though..
I look forward to hearing from you,
Nobby.

It doesn't rain here, and was under the cover.
But it was removed as it was pissing out fluid onto the jandels.

You would need to cover the AusPost...
(And a joke or latte is also appreciated.)

Hi.[again],
Thanks for the update... I am more than happy to pay the postage,, as well as a contribution to cover you for your trouble... The reservoir is still attached?? I will have an older style lid...from reading the feedback, the older ones are the way to go...Modern trend you know.. Please excuse my facetiousness... comes with the aging process...
I will go along with whatever ..
Cheers,
Nobby.

PM an address, or an email and I can send a photo.
The reservoir is attached... not sure how to get it off, and there is no cover.

(For a pun... "give me a brake")

Hi,
I am pretty sure they are all the same.. Reservoir being detachable... and aluminium..and the actual cylinder is cast iron.. Will use the old cover.. I have a very good long term relationship with 'Brakeland' in Toowoomba.. They have amazing skills at procuring difficult and obsolete parts...
Email is <This email address is being protected from spambots. You need JavaScript enabled to view it.>.. and address is P.O.Box 2412, Katherine NT, 0851.. Dont live there,, is a tad small.. but Aus Post dont deliver.. so we are blackmailed into having to pay for a P.O.box..
For a pun.. we hope they dont brake it....
Cheers,
Denis.