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Old 18-03-2018, 07:18 PM
shaunv8 shaunv8 is offline
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Possible Booster Issue

Hi All,

Long winded post following.

I own a 64 Aussie Delivered RHD Belair. It has power DRUM brakes all round. Since I have had the car, a touch on the brake pedal of 3-5mm will put me through the windscreen. I did a bit of googling the other day and read that the booster was possibly at fault. I tested the booster according to Mr Google, (hold foot on brake, start car and it should go down a bit as booster builds up vacuum, and then turn car off and pump pedal and it should become firm as vacuum is exhausted), and NONE of the above happened. The pedal stays exactly the same. I then proceeded to pull out the vacuum check valve from the booster after I turned off the car and it was as if I pulled an air hose off a compressor (pssssssscccccchhhhh) sound. Would anyone have any input, do you think the Booster is bad. I believe its a MORAINE model, single cyl master. Thanks in advance.
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  #2  
Old 19-03-2018, 08:11 AM
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cluxford cluxford is offline
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Shaun, I recently went through brake hell after my Buick had awesome brakes but then didn't (basically my booster shat itself and the brand new booster was poorly manufactured with 1mm of movement, which I fixed by pulling it apart and rectifying their poor design, after they would not return and replace. But I did that after literally trying everything else, including add new lines, proportioning valves etc). It's been a long journey in which I have learned a LOT. So sorry for the long winded reply, but will try to cover what I learned (note mine is disc front, drum rear).

When it is that touchy it is Not the booster. if the booster has failed your pedal will go to the floor it will be really hard to brake. You essentially have no power assist. It will require both feet on the pedal to stop it. Easiest way to check this, is remove that vacuum check valve and take it for a short drive. That will show you how it stops when you have no power assist. You will notice a massive difference.

When the pedal is so touchy, that means you have a great booster that's working awesome.

But it may mean other things, and it will be trial and error to figure out what might be causing the issue. Some of these are easy some are not.

1. The brake shoes might be dragging, adjusted too tight, hence grabbing hard on immediate application of brake. Try adjusting them 1-2 mm looser
2. You can also adjust the brake pedal to give it more transition. Under the dash it screws to the booster (yes you have to remove booster to do this), screw is further out, it will give the pedal more movement
3. On some masters they run a one way valve to keep fluid to the wheel cylinders, sometimes called a non-return valve or residual pressure valve. This is a good read on the subject http://mgaguru.com/mgtech/hydraulics/ht116.htm
4. It could also be the master. Is it a standard master or an after market one. It may have to do with push rod length and pressure. being produced as a result

so more questions than answers above, but as a start I'd be looking at those.

What you are describing is not a booster issue. It's a pressure / brake shoe issue. Lots of pressure really quick being applied to the shoes
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Old 19-03-2018, 08:55 AM
shaunv8 shaunv8 is offline
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Thanks for the feedback. The booster and master are original AFAIK. I was thinking to myself that over the years, I wouldnt be suprised if the wheel cylinders have been replaced for ones with a smaller bore (HQ or similar), hence more pressure.
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Old 19-03-2018, 11:04 AM
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yep could be, pull the drums and get a part number stamping. These are cheap and easy to get ABs can get them. They got the right wheel cylinders for mine in less than 24 hours
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Old 19-03-2018, 07:25 PM
Geoff 4 Geoff 4 is offline
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Shaun,
The first thing to check are the brake linings. Make sure there are no leaking wheel cyls & /or grease on the linings.

If these check out, then it is most likely the booster. The Moraine boosters use a plastic reaction lever as part of the 'feel' mechanism. When it breaks, you get the very sensitive brakes that lock up easily.
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Old 19-03-2018, 07:58 PM
shaunv8 shaunv8 is offline
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Quote:
Originally Posted by Geoff 4 View Post
Shaun,
The first thing to check are the brake linings. Make sure there are no leaking wheel cyls & /or grease on the linings.

If these check out, then it is most likely the booster. The Moraine boosters use a plastic reaction lever as part of the 'feel' mechanism. When it breaks, you get the very sensitive brakes that lock up easily.
Thanks, yep I have checked all brake linings. they are good and clean, and fitted right way around. No wheel cyl leaks either.
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Old 20-03-2018, 07:06 PM
Geoff 4 Geoff 4 is offline
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There is a place in SA that can repair boosters, ph: 08 7070 1065
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Old 21-03-2018, 12:30 PM
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Quote:
Originally Posted by Geoff 4 View Post
There is a place in SA that can repair boosters, ph: 08 7070 1065
https://www.powerbrakes.com.au
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Old 21-03-2018, 04:05 PM
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Are there two holes on the brake pedal assembly where the rod connects to?



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Old 21-03-2018, 10:27 PM
shaunv8 shaunv8 is offline
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IIRC mines in the top hole, but the brake light switch is in the bottom one?
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Old 24-03-2018, 02:12 PM
shaunv8 shaunv8 is offline
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Hi All,

Had a bit of time today to look and try out your recommendations above. Unplugged vac from booster, and near on couldnt stop, needed 3 feet to push the pedal down!! I have attached some pics of the setup. The rod is in the top hole, and the brake switch is in the bottom but it doesnt look like I can swap them. I did notice the end of the rod to booster has thread on it as can be seen in the pics, Can this be adjusted? Thanks




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Old 24-03-2018, 07:41 PM
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Nev68 Nev68 is offline
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Stating the obvious, brakes are a critical safety item.
If you are guessing at what the problem is or guessing on how to fix the unknown it might be time to seek an expert.
Just sayin'......
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Old 25-03-2018, 12:09 PM
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That means the boosts is doing its job. It assisting. Problem is elsewhere
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Old 25-03-2018, 02:07 PM
shaunv8 shaunv8 is offline
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OK, I think I have found the issue. I think the pushrod to M/C is too long. I saw on another forum that someone suggested spacing the M/C away from the booster using a washer or 2 and if it fixes it, then thats the issue. I did so this morn, spaced by about 2-3mm and brakes are very nice now, progressive and have more travel prior to lock up. Now to figure out how to shorten the pushrod in booster......

---------- Post added at 12:07 PM ---------- Previous post was at 11:49 AM ----------

Oh, and I just pulled off the MC and there is no adjustment on the pushrod coming out of booster...I may just leave the spacers between thm.....
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Old 25-03-2018, 04:06 PM
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That could mean you have a shallow m/c where before you had a deep piston one. Run into the problem many times.
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