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56 brake bleeding issues


56 Buick
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Anyone ever had difficulty with their brake bleed. Rebuilt master cylinder and all new ss brake lines / rubber hoses. I also replaced all wheel cylinders a while back. I also took apart the check valve that distributes fluid between the front and rear wheel lines. Have fluid coming out all 4 wheel bleed screws but brake pedal will not firm up. Any ideas?

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20201011_111235.thumb.jpg.46add7494a7f4881ad425a6cdecf1553.jpg20201011_111226.thumb.jpg.64eeca1ab940c3105f99b3e7790ce917.jpgCouple of photos of the shop manual showing the check valve location and configuration. My understanding is the check valve itself is supposed to stop fluid being drawn back to MC.

 

In regard to process of bleeding, I fitted the MC and all new lines and filled MC with fluid. Bled the MC at the MC outlet port. Reconnected the MC to check valve line and then bled each wheel cylinder at the bleeder screw - starting from closest to furthest from MC as per the shop instructions. 

 

Brake pedal will not firm up. If I isolate the MC by plugging the outlet port then pedal is rock solid. So the issue appears to be after that part of the system.

 

I did just read in shop manual that a leaking check valve can cause loss of static pressure in the system and allow air to be drawn in past the wheel cylinder cups and if valve leaking badly theb it is impossible to 'pump up' the pedal. Perhaps that is an issue. I just opened it up and cleaned it as I have never seen that anyone sells replacement parts.

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Thanks for the reply.  I learned something:  earlier cars had that valve in master cylinder.  If you think the valve is bad, you may not find parts unless it is universal, but then you would have to buy a MC kit for something like a 55.  Check Summit Racing for a "residual pressure valve" that you may be able to adapt.

Actual bleeding technique?  vacuum bleeder?  Assistant?

Will it pump up at all?

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I couldn't get my pedal to firm up no matter what I did, until I adjusted the anchor pins on each wheel.  If the shows are not centered with the drums, it will take quite a bit of pedal travel to make full contact with the drums.  The adjustment procedure is described in the manual, and it's pretty easy to do.

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7 hours ago, old-tank said:

Thanks for the reply.  I learned something:  earlier cars had that valve in master cylinder.  If you think the valve is bad, you may not find parts unless it is universal, but then you would have to buy a MC kit for something like a 55.  Check Summit Racing for a "residual pressure valve" that you may be able to adapt.

Actual bleeding technique?  vacuum bleeder?  Assistant?

Will it pump up at all?

Thanks Willie. I will see if I can find something. I have been using an assistant but it will not pump up at all. I am going to try a vacuum bleeder I bought and see if that helps. It has me stumped!

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6 hours ago, Smartin said:

I couldn't get my pedal to firm up no matter what I did, until I adjusted the anchor pins on each wheel.  If the shows are not centered with the drums, it will take quite a bit of pedal travel to make full contact with the drums.  The adjustment procedure is described in the manual, and it's pretty easy to do.

Thanks, agree the anchor pins properly centreing the shoes is crucial but I have done these. I am going to clamp the 3 rubber hoses and see if the pedal firms up. Should tell me whether the problem is after or before the hoses, that is it is not the wheel cylinders.

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  • 3 weeks later...

Still having no luck with this. I cannot see any leaks and the system is bled and anchor pin set but the front drums won't bind on depressing the pedal. The drums have been turned to 12" 40 thou but I have new standard shoes. Is it possible it requires 30 thou oversize shoes at this drum diameter? Any experience would be appreciated. Thanks

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On 11/2/2020 at 3:05 AM, 56 Buick said:

The drums have been turned to 12" 40 thou but I have new standard shoes. Is it possible it requires 30 thou oversize shoes at this drum diameter?

 

If you can adjust the adjusters to lock the drum, when the pedal in NOT depressed, then this is not the current problem.

On 10/11/2020 at 7:23 PM, 56 Buick said:

I am going to clamp the 3 rubber hoses and see if the pedal firms up.

 

Results?

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I did notice that the wheel cylinders do expand with operation of the pedal but they appear to have no holding force as you can spin the drum with effort. That is what made me think I required oversize shoes.

 

You are correct about the oversize shoes not being required because I then clamped the shoes from expanding and it made no difference.

 

If I clamp the hoses then the pedal firms up but no obvious leaks on the wheel cylinders.

 

I think all I can do is replace all the wheel cylinders and see what happens. I am at a loss.

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5 hours ago, 56 Buick said:

I then clamped the shoes from expanding and it made no difference.

 

You clamped with an outside force? Or you simply adjusted the shoes tight against the drum?

 

If you simply adjust the shoes tight (so the drum cannot be turned by hand) does the pedal get hard, or stay the same?

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17 hours ago, 56 Buick said:

I did notice that the wheel cylinders do expand with operation of the pedal but they appear to have no holding force as you can spin the drum with effort. That is what made me think I required oversize shoes.

 

You are correct about the oversize shoes not being required because I then clamped the shoes from expanding and it made no difference.

 

If I clamp the hoses then the pedal firms up but no obvious leaks on the wheel cylinders.

 

I think all I can do is replace all the wheel cylinders and see what happens. I am at a loss.

 

I understand the M/C was rebuilt and related items replaced.  When you apply the brakes do the wheels stop at all?     

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On 11/4/2020 at 3:16 PM, Frank DuVal said:

 

You clamped with an outside force? Or you simply adjusted the shoes tight against the drum?

 

If you simply adjust the shoes tight (so the drum cannot be turned by hand) does the pedal get hard, or stay the same?

My reference to clamping the shoes was me using a large woodworking G-clamp to stop the shoes expanding. In other words, give the shoes resistance to replicate having a less worn brake drum or oversize shoes. I did this on one of the wheels only, that being a wheel where I suspected an oversize shoe may help. The pedal firmed up some but only while I had clamped off the rear line brake hose. When I released the clamp on the rear brake hose then the pedal went bad again. I think that possibly confirms there is an issue in the rear line/rear wheel cylinders.

 

If I simply adjust the shoes tight (by use of the star wheels) then the pedal firms up but again only if the rear line hose is clamped off.  Again this appears to mean there is an issue in the rear line/wheel cylinders.

 

I will purchase new wheel cylinders and see what happens.

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20 hours ago, avgwarhawk said:

 

I understand the M/C was rebuilt and related items replaced.  When you apply the brakes do the wheels stop at all?     

No, not at this stage. Pedal going to floor but I will see what happens on changing out the wheel cylinders. Can't see obvious leaks but hey, maybe that is the problem.

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2 hours ago, 56 Buick said:

No, not at this stage. Pedal going to floor but I will see what happens on changing out the wheel cylinders. Can't see obvious leaks but hey, maybe that is the problem.

 

I don't believe the replacement of wheel cylinders will solve the problem.  These cylinders are simple metal pistons with o-ring.  No bleed back hole or port to loose pressure.  If fluid was getting around the o-rings it would be visible.  For me, the master cylinder is suspect. 

   

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3 hours ago, 56 Buick said:

If I simply adjust the shoes tight (by use of the star wheels) then the pedal firms up but again only if the rear line hose is clamped off. 

This is telling me that the problem is in the shoe adjustment.  Before new parts you should tighten all 4 star adjusters till you have resistance at each wheel and then see if you have some brake pedal. 

 

I would note that the "major "brake adjustment procedure calls for adjusting all four star adjusters to the point it is difficult to turn all the wheels (drums)  by hand.  All four at the same time. Then adjusting the anchor pins and then backing off each star adjuster 15 clicks as a starting point to fine adjustment. 

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5 hours ago, 56 Buick said:

The pedal firmed up some but only while I had clamped off the rear line brake hose. When I released the clamp on the rear brake hose then the pedal went bad again. I think that possibly confirms there is an issue in the rear line/rear wheel cylinders.

 

If the shoes were held steady, and the only thing you did was release the clamp on the rear brake hose to make the pedal bad, then you have air in the rear system. Somewhere between the clamp and the bleeder screws.

 

Are the wheel cylinders upside down? The bleeder HAS to be at the top of a cylinder to release the air.

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Why he thinks it is impossible? I've seen stuff done the impossible way!😁

 

You can not put on offset pin lamp (1157) into the socket wrong. That's why it has offset pins.    Ha!🤣

 

Could be the hole into the cylinder is closer to middle than the top of the bore. That would make it hard to bleed.

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6 minutes ago, old-tank said:

Cylinders with metric bleeders leak fluid and air around  the threads during bleeding.

This is a problem if you are using a Mighty-Vac or similar sucking tool on the bleeder. Since I am a Mighty-Vac type mechanic, I have wrapped Teflon tape on many a loose fitting bleeder screw!😉 This is not an antique vehicle repop part issue, I've had it on many newer vehicle cylinders and calipers.

 

 

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I can confirm the wheel cylinders are fitted the correct way :)

 

As Willie says, there is only one way backing plates will allow. Anyway, after a bit of Googling it appears that these cheap aftermarket wheel cylinders can have an issue where the bleeder screw never locks off correctly and can allow air in. I will find out soon, after I fit new wheel cylinders and bleed.

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5 hours ago, 56 Buick said:

I can confirm the wheel cylinders are fitted the correct way :)

 

As Willie says, there is only one way backing plates will allow. Anyway, after a bit of Googling it appears that these cheap aftermarket wheel cylinders can have an issue where the bleeder screw never locks off correctly and can allow air in. I will find out soon, after I fit new wheel cylinders and bleed.

 

Issue here is if air is permitted in the bleeder screws fluid will certainly drip when pressing the brakes.  

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Before changing the wheel cylinders, go over it one more time:  adjust all shoes until you cannot turn the wheel; bleed one more time using an assistant that can follow directions (never a wife :) ).  You should have a tall hard pedal.  If the pedal is low adjust the master cylinder apply rod.  When satisfied with the pedal back off 6 clicks and drive around the block a few times.  Adjust again by adjusting tight again and backing off 6 clicks....repeat until no change.  But the service manual says 12-15 clicks?...my experience will get only 1/2 pedal and it seems that modern shoes do not expand as much when heated, but always monitor the heat and any pulling.  If all good then adjust every 100 miles until minimal change.

Even when working correctly check that the residual pressure valve is working by cracking a bleeder --- you should get a spurt of fluid.

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5 hours ago, old-tank said:

Adjust again by adjusting tight again and backing off 6 clicks....repeat until no change.  But the service manual says 12-15 clicks?...

 

Old Tank, I had the same experience trying to follow the manual's 12-15 clicks after installing new shoes. That left the pedal down uncomfortably far so I left the adjustments at 6. I have a nice hard pedal now. The pedal is much higher but no issues after several hundred miles. Is that why they used to say 15-16 clicks, because the older asbestos shoes expanded a lot ??

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4 minutes ago, Kestrel said:

Is that why they used to say 15-16 clicks, because the older asbestos shoes expanded a lot ??

That is the reasoning I read in an old Motors Manual circa ~1950.  Realistically in the past, without any 'reading' we just clicked it tight and backed off until free. 

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5 hours ago, old-tank said:

Realistically in the past, without any 'reading' we just clicked it tight and backed off until free. 

 

And just free, drum still scraping the shoes. Not a heavy drag, but a scrape scrape sound. Drag= Heat, very bad!😲

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I have finally got some pedal after replacing one of the rear wheel cylinders. Appears to have had a slow leak I didn't notice. After continuous bleeding and the inevitable dripping it seems I didn't notice the leak. I will change the other side as well but for now there is progress which is good. Much appreciate all the input everyone had as it was all useful. Thanks, Drew. 

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