21 replies to this topic

[Sask_Mini]

Hey Guys, 

 

So I finally finished getting my master cylinder replaced, getting the lines reconnected and bled the system.  Everything seemed to be working alright when I had the car up on stands, the wheels all spun relatively easily but had a slight amount of drag.   Tried out the brakes quite a few times and the wheels never seemed to get stuck, I could always turn them by hand.  I used a power bleeder to bleed the brakes and I ended up with a nice firm pedal so I thought it was all good.  

 

Took the car out for a trip around the block a couple times and by the time I got back the brakes were sticking pretty badly.  Took quite a bit of effort by the engine to get the car back up the driveway and into the garage.  The brake pedal was really really hard as well, it would barely move when I pressed on it.

 

I jacked up the front of the car and tried turning the wheels and both front wheels take a fair amount of force to rotate, way more than just a slight drag like they used to be.  Then I did the same to the back and the back brakes weren't locked on as bad but still harder to turn by hand than they used to be.  

 

I tried pulling up on the brake pedal to see if something was preventing it coming all the way back, but it sure felt like it was at the top of its travel and I couldn't pull it up any further.

 

I did a forum search and read that its possible that the master cylinder might not be returning enough and that I might need to shim it up off the body a little bit?  I am going to head out the garage soon, unbolt the cylinder and see if the brakes release if I pull up on the master cylinder a bit.  Edit:  Did some testing and after loosening off the bolts that hold the master cylinder to the body, the brakes released and the wheels spun more freely as they had before.  I thought maybe the split pin that keeps the clevis pin from falling out was contacting the firewall and preventing the brake pedal from returning all the way, but after some more testing that doesn't seem to be the problem.  Any ideas on how to fix this?  I can't seem to find any supplier that lists any shims for the master cylinder.  

 

I'm just wondering what else it could be...here is a little more info:

 

- Brand new yellow tag master cylinder, replacing an old type 2 master cylinder.

- There used to be a PDAW pressure differential switch on the bulkhead that I removed and placed unions in its place since it wasn't working anyways.   I am not talking about the FAM type proportional valve that is present on newer mini's.  This was just the brake failure switch and I was given some advice on this forum that it wasn't needed and that the inertia type proportional valve on the rear subframe would be sufficient.  

-  Drum brakes on all 4 wheels

 

Did I need to readjust all the brakes after fitting the new master cylinder?   I didn't adjust any of them.  

Edited by Sask_Mini, 24 July 2017 - 03:29 AM.

[Sask_Mini]

Well.....after reading some more old posts, I think I figured it out.  I didn't fit a gasket between the master cylinder body and its mounting plate.  I bet if I fit that gasket that it would shim up the master cylinder the extra mm or so that I need.  I guess I just assumed that I didn't need one since the old master cylinder that was on there didn't have one.  

[Ethel]

Wouldn't have thought that'd be your problem, but you never know. If you swapped an earlier dual circuit master for a yellow band are you sure the lower pipe union is connected to the rear circuit? If that checks out and your old master was faulty it could just be the caliper pistons are seizing and it never showed up before because they weren't being pushed as hard.

 

Edited to add......

 

Disregard the last bit now I've realised you have drums all round  . 

 

Nick's also right about the gasket, I was on about your split pin comment - still unlikely. The pedal isn't actually attached to the master's piston so the pedal can return even if the piston doesn't. It is front/rear split and not diagonal?

[nicklouse]

the gasket is a Gnats hair thickness and will make Zero difference.

[blacktulip]

Are the brake hoses new? If not it could be a collapsed hose.

[Wim Fournier]

It's obvious, you found the problem. Raising the mastercilinder a bit will do. It's a 'known' problem. The pistons do not come down enough te free the in / outlet to the reservoir.

[nicklouse]

It's obvious, you found the problem. Raising the mastercilinder a bit will do. It's a 'known' problem. The pistons do not come down enough te free the in / outlet to the reservoir.

 a "Known" problem? where is it written? have you see how thin the gaskets are? if the pistons are not coming down far enough then it will be the pedals that are causing it or something internal not the lack of a piece of paper.

 

if raising the MC by 1mm fixes it then I would be looking for the real issue.

[Sask_Mini]

I did know that the brake circuits were reversed with the new yellow tag master cylinder.  I double and triple checked that when I fitted the lines, the lower union with the larger port is connected to the rear brakes and the the upper union is connected to the front.  It is a front/rear split system.  

 

The brake hoses aren't new, but having all 4 hoses collapse simultaneously is a bit of a stretch since the brakes stick at all 4 corners.  

 

I read some old posts (mainly by tiger99) and he stated several times that there are actual shims that you can purchase that were made specifically to raise the master cylinder.  So I figured missing that gasket just may make the difference.  

 

I really dont' see what else could be the problem, sure seems to me like the pedal is hitting its stop and not allowing the master cylinder rod to drop far enough to return to its "home" position.  It also seems like the brakes get incrementally more stuck the more I pump the pedal.  Raising the master cylinder up and allowing that rod to drop further down always releases that built up pressure.  

 

I haven't checked to see if the brake switch/stop can be adjusted.  Is this stop adjustable?  

 

Edit:  Went out to the garage to check a few more things.  Tried adjusting the brake switch/stop to see if that would let the pedal travel back a little further and it seemed to help.  But....while I was under there I noticed that the part of the pedal that holds the clevis pin actually hits the sheet metal and that is what limits how far back the pedal can travel.  I imagine this isn't normal?  The clutch pedal seems to do the same thing, rests on the sheet metal.  

 

Edited by Sask_Mini, 25 July 2017 - 01:32 AM.

[Spider]

There's the problem ^ ^ (nice photo by the way).

 

The shim quantity were listed as 'A/R' which means 'As Required'.

 

P/N for the single circuit type was AYA5117, then became MYH404. The ones for the Tandem Masters were P/N NAM1718.

[nicklouse]

There's the problem ^ ^ (nice photo by the way).

 

The shim quantity were listed as 'A/R' which means 'As Required'.

 

P/N for the single circuit type was AYA5117, then became MYH404. The ones for the Tandem Masters were P/N NAM1718.

interested in what the material for NAM1718 as the current gaskets are such that thy are thinner than a sheet of paper a search brings up the exact same issue.

http://www.theminifo...m-brakes-again/

so what were the originals made from? to give any lift without need 10s of them.

[nicklouse]

ohhh just thinking about it I may actually have some in a box somewhere. Will have to look at lunch time.

[Spider]

 

There's the problem ^ ^ (nice photo by the way).

 

The shim quantity were listed as 'A/R' which means 'As Required'.

 

P/N for the single circuit type was AYA5117, then became MYH404. The ones for the Tandem Masters were P/N NAM1718.

interested in what the material for NAM1718 as the current gaskets are such that thy are thinner than a sheet of paper a search brings up the exact same issue.

http://www.theminifo...m-brakes-again/

so what were the originals made from? to give any lift without need 10s of them.

 

 

I have a few in the parts bin. They are just plated steel, probably about 0.8 to 1.0 mm thick, nothing special and no reason why they can't be made in the workshop for that matter. I'd post up a photo but haven't had time as yet to reorganise myself following the Phootbucket debarkle.

[nicklouse]

ahhh just re read your earlier reply. Shim not gasket. never knowingly seen one of them.

[Sask_Mini]

Thanks so much for all the replies guys, really appreciate the help.  

 

I talked to a guy I work with who does a fair amount of metal work in his spare time and he said it would be no problem making me some shims.  I used some wood shims to approximate how much shim I would need to keep it from contacting that bulkhead crossmember and I figure 2mm would just about do it.  So some 16 guage sheet metal should be just about right.  I figure I will get him to slot the shim so I can just slide it in from the side instead of removing the entire master cylinder (I really don't want to mess with that clevis pin again!).  

 

I am guessing this problem came about because of the pedal type that is in the car?  Digging around the forum I see that there are several different pedal styles and they seem to have different bend angles between where the clevis pin attaches and the arm of the pedal.  Maybe the older pedal style I have isn't fully compatible with the new style of master cylinder without shimming it up a bit.  Could also be because its a LHD mini and the master cylinder doesn't sit on the plate which has the motor stabilizer arm.  The plate that the stabilizer arm bolts to is quite a bit thicker than the thin little plate the master cylinder sits on, on the left hand side of the car.  

[Wim Fournier]

Yes Nicklouse, I understad that you don't like my answers. But I experienced it myself  that this problem was over whn I used two iron rings under the foot of the bmc. Maybe it's because I have a lhd Mini.