Jump to content


Photo
- - - - -

Brake Master Cylinder Rebuild/disassembly 1987 Gmc227

brakes

  • Please log in to reply
23 replies to this topic

#16 Harwoods

Harwoods

    Learner Driver

  • TMF+ Member
  • PipPip
  • 16 posts
  • Location: Kent

Posted 30 August 2020 - 10:26 PM

Just to update everyone, especially anyone who also comes across this in future since I found nothing on this specific master cylinder.
 

 

Then I usually bang them down on a block of timber and they come out pretty easy.

 

That will get the lower piston set out. There's usually a Pin behind the Upper Reservoir Seal that retains the Upper Piston.

 

 

Yep, bashing the flange part on a hard edge caused the first piston to come out. Though again due to documentation we weren't sure why the other one was staying put, There's definitely an upper pin I bet holding the top piston in place as that's not coming out.

Referring back to my original post of course the pin that holds the reservoir in is sticking well in the cast metal body. Awaiting more elbow grease for that one, had enough for today.

Regarding replacement, it may be most important part of the car but so is any safety conscious part, if we're going to go with that then we'd need an entire new car as no classic Mini survives any collision well.

As I mentioned before the front most important circuit on the discs works fine, we are starting to think it was just build up of grime blocking the lowest part of the reservoir and clogging our rear circuit, all of our seals look fine, we had no leaks and the bore looks perfectly clean past the surface grime from being in the engine bay.

Thanks for the advice and useful links, as always very much appreciated.



#17 Spider

Spider

    Moved Into The Garage

  • Admin
  • PipPipPipPipPipPipPipPipPipPipPip
  • 11,151 posts
  • Location: NSW
  • Local Club: South Australian Moke Club

Posted 30 August 2020 - 11:06 PM

 

Though again due to documentation we weren't sure why the other one was staying put, There's definitely an upper pin I bet holding the top piston in place as that's not coming out.

Referring back to my original post of course the pin that holds the reservoir in is sticking well in the cast metal body. Awaiting more elbow grease for that one, had enough for today.

 

 

Just to be clear here, the Roll Pin you don't have to remove.

 

Just swing the Reservoir up, swinging around that Roll Pin. It is only the Seals that hold it in.

 

Once you've swung it up, you can slide it off.

 

Then remove the Top Seal for the Reservoir. Under that is a small Pin - that's the one that retains the Upper Piston. You'll need to poke something up the Cylinder Bore and compress the upper Spring a little, it take the pressure off the Pin, then you can remove it.

 

You don't remove the Roll Pin at all.



#18 Revd

Revd

    Stage One Kit Fitted

  • TMF+ Member
  • PipPipPip
  • 64 posts
  • Location: Warwickshire

Posted 31 August 2020 - 07:11 AM

As mentioned above, for £70 just replace. Not only is it safety critical it is also a pain to remove/re-install. I replaced my ‘87 master cylinder last month, bleeding brakes is my least favourite job, and a refurbished m/c is just another grey area if you struggle to get a firm pedal

#19 Harwoods

Harwoods

    Learner Driver

  • TMF+ Member
  • PipPip
  • 16 posts
  • Location: Kent

Posted 31 August 2020 - 10:37 AM

We are fully aware we can buy new for £70.

Replacing or Repairing both involves remove/re-install. Buying new doesn't necessarily mean any better result or quality. Especially with reproduced models and alternatives. We appreciate the sentiment about our safety, but again as mentioned previously we're not choosing to drive around in a Mini for it's 5 star safety record.

Our Mini only has 40,000 miles and the only reason it seems to have failed is build up of brake fluid grime after sitting off the road for 20 years. Bore is completely clean, even the old seals are in perfect condition still as flexible as ever, no cracks, no leaks, we just needed to give it a once-over.​

 

 

Just to be clear here, the Roll Pin you don't have to remove.

 

Just swing the Reservoir up, swinging around that Roll Pin. It is only the Seals that hold it in.

 

Once you've swung it up, you can slide it off.

 

Then remove the Top Seal for the Reservoir. Under that is a small Pin - that's the one that retains the Upper Piston. You'll need to poke something up the Cylinder Bore and compress the upper Spring a little, it take the pressure off the Pin, then you can remove it.

 

You don't remove the Roll Pin at all.

 

This will be a life saver if it works out, thanks Moke Spider. Appreciate you helping me with my original post. The previous diagram is what we were looking for.



#20 Revd

Revd

    Stage One Kit Fitted

  • TMF+ Member
  • PipPipPip
  • 64 posts
  • Location: Warwickshire

Posted 01 September 2020 - 08:55 PM

Well, I quite agree there is much satisfaction to be had from refurbing old components and a Mini provides more than its fair share of opportunities. I'm intrigued by the original problem- the rear circuit was completely dry -  down stream from the pressure regulator? or at the rear circuit port on the master cylinder? 



#21 Harwoods

Harwoods

    Learner Driver

  • TMF+ Member
  • PipPip
  • 16 posts
  • Location: Kent

Posted 23 October 2020 - 04:50 PM

Just to update as circumstance has led to the project slowing down.

Got everything apart thanks to the advice about swivelling the reservoir around the pin to get it out, replaced only the circlip and the 2 rubbers that go between reservoir and cylinder.

Seals on both pistons were great condition.

All I will ask is advice for refitting? I found trying to test it by filling it with brake fluid it has a weird suck/blow effect that means it needs to suck fluid from the output to get any suction to bring new fluid in. I assume there is a priming process but any advice before we refit would be great.

Our current lines will still have old fluid in them and we plan to to a full cycle through with new stuff from the refitted cylinder, is priming just a case of fitting it and filling the reservoir, or will air be permanently stuck in the piston?

Thanks again.



#22 Harwoods

Harwoods

    Learner Driver

  • TMF+ Member
  • PipPip
  • 16 posts
  • Location: Kent

Posted 23 October 2020 - 04:53 PM

Well, I quite agree there is much satisfaction to be had from refurbing old components and a Mini provides more than its fair share of opportunities. I'm intrigued by the original problem- the rear circuit was completely dry -  down stream from the pressure regulator? or at the rear circuit port on the master cylinder? 

So originally I had to unseize the rear drums as the handbrake was left on for 10+ years and cable was stuck in all the runners and needed cutting off completely. Shoes were then stuck on the drum. After bashing that and getting both drums off I then saw the cylinders were pretty seized open and wanted to also bleed them to see state of fluid left in them as pedal was not operating the cylinders at all.

After attempting to bleed, bubbles and only a couple of drops came out after many cycles of pedal pushing. We then followed it back straight to the master cylinder and found nothing was coming out of the rear circuit straight from the piston. So then that led to taking the cylinder apart. 



#23 Revd

Revd

    Stage One Kit Fitted

  • TMF+ Member
  • PipPipPip
  • 64 posts
  • Location: Warwickshire

Posted 24 October 2020 - 09:49 PM

My approach would be:
-Replace rear wheel cylinders, replace seals on front callipers or replace callipers if required, and replace front /rear flexible hoses
-Replace pressure regulator-it is a non-service item and if original fitment should be considered a consumable part and due for replacement.
-Refit master cylinder, (overhauled or new replacement)
Adjust rear brake shoe clearance as per Steveston’s you tube video, ie barely able to rotate drum by hand.
-Eezibleed system, first pass with all bleed nipples open, give the brake pedal a couple of prods too. All open should prevent shuffling air between front and rear circuits
-Re-bleed and close front o/s rear o/s, rear n/s, front n/s - again to push air out of long pipe runs.
-Final bleed in conventional pattern, rear o/s, rear n/s, front n/s, front o/s. Close nipples whilst eezibleed is still pushing fluid.
Buy plenty of fluid, I bought 4L for £30 and used about half of it. All a bit of a faff but pedal is now rock hard.

#24 sonscar

sonscar

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 818 posts
  • Location: crowle
  • Local Club: none

Posted 25 October 2020 - 10:23 AM

MY bodgers way of bleeding is to remove wheels and open all bleed nipples.Fill master cylinder and brew up.Sit watching car,top up as required.As fluid comes out of a nipple shut it off.Repeat for all four.Brew up again and call for assistant to push pedal,open nipple close nipple release pedal starting furthest away and working in.Enjoyable morning for all.Make sure that the hole in the reservoir that supplies the cylinder is uncovered when the piston is fully back or the push /pull effect occurs.Hope I am not teaching you to suck eggs.Steve..







Also tagged with one or more of these keywords: brakes

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

Mini Spares