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Mustang Technical Discussion > Pre 1973 > Dems the brakes > Community Forums > Mustang Forum Australia - Mustang Tech

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smh00n
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My 70 has factory discs and a power booster.

When I go to brake there is nothing, nothing, nothing then WHAMMO the brakes are on and my forehead is on the screen. Once you are used to it it brakes OK but it all happens pretty quickly once you have gingerly squeezed the pedal some.

Bought this rebuilt so who knows whats happened. It does not have a distribution block, the booster appears to be about 7-8" diameter and is 4" deep.

Photo is about the best one I could take.

Anyone offer miracle advice based on my short description?? I'm thinking it may be the booster, but it seems to hold vacuum and def getting vacuum from the lump.
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Last edited by smh00n on Mon Dec 28, 2015 5:00 pm; edited 2 times in total

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nassi
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It sounds like pedal ratio or pushrod length.
Can you take a pic from under the dash?
This is more a test of dexterity than anything else. Very Happy


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scedd
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Get the 19 year old girl next door to lay upside down on the drivers seat with her head under the dash to take a photo of the brake pushrod.


The word "swims" upside-down is still "swims".
- If you rip a hole in a net, there are actually fewer holes in it than there were before

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moe
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Could be a incorrect brake pedal. Was the 70 factory optioned with boosted disc brakes?


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Nuts
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Check whether the pedal is hinged from the very top of the pedal box, if so it's the correct pedal.
Check out Mustang Steve for more info.
www.mustangsteve.com/f...edals.html


My Motto - Don't get Caught! If you do, Blame Someone Else!

MUSTANG - Fantastic Not Plastic

Last edited by Nuts on Tue Dec 29, 2015 10:16 am; edited 1 time in total

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smh00n
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Get the 19 year old girl next door to lay upside down on the drivers seat with her head under the dash to take a photo of the brake pushrod.

I did ask her but she was washing her hair or something. Is Google Girl free??


Being in denial does not always mean you are in a river in Egypt.

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scedd
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smh00n wrote
Get the 19 year old girl next door to lay upside down on the drivers seat with her head under the dash to take a photo of the brake pushrod.

I did ask her but she was washing her hair or something. Is Google Girl free??


She wont fit under your dash!!!


The word "swims" upside-down is still "swims".
- If you rip a hole in a net, there are actually fewer holes in it than there were before

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smh00n
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OK, I have done all suggestions. Be nice if you all posted at once so I wasn't under there 3 times Head Bash

Picture of pedal attached. Is hinged at the top and appears original. It also looks like a manual box as it has worn/used clutch pin bushes.

As far as I know it's a factory boosted disc car. But the Marti report does not list any brakes. How do you know if they are factory?

Just checked the push rod again and it is a curved end to where it fits to the pedal. So, worst case is it has been converted and have used the 69 brake booster with a 70 pedal. The pedal is a boosted one, the pin is in the right position according to Mustang Steve.

So, do I just buy a 70 booster/cylinder/distribution block assembly?
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Last edited by smh00n on Tue Dec 29, 2015 10:48 am; edited 3 times in total

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Nuts
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Everything is working so I wouldn't buy anything yet. Best advice is to take it to a good brake joint and get their advice. Are the rear brakes adjusted correctly? are they working? FDo you have a long pedal ie do you have to push the pedal down a long way before the brakes take up? No answers yet but lots of questions..


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mert
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The Bendix unit looks like a era-correct one.

As power disc brakes were an option one would expect it to show on the Marti, but not if part of any other package on the car (not familiar with '70 options)

The causes could be related to the pedal, the booster (not too likely), the calipers, sticking pistons, worn/misadjusted parts, etc...

A pressure test at each corner and looking at the fluid (is it clear or cloudy/brown?) can give a quick indication of any issues.

Oil or grease on the brakes can cause grabbing, as can wear/scoring on pads/rotors. Have you looked at them?

If its been a while since a brake job may be best to pull it down, inspect the drums/calipers and pads and see what they tell you. If all that looks good the proportioning valve could be faulty....

...not a simple thing to diagnose on the web.


8R01S
8R03S-GT
8F01X -EXP500 Repli-bute
8R01C-Cal Special

Last edited by mert on Tue Dec 29, 2015 11:58 am; edited 4 times in total

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smh00n
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Supposedly this was rebuilt prior to me buying it so I am assuming that the cylinders etc are fine.

I've not yet pulled it apart to see what it is like. Rotors are fine visually.

The brakes do work well, once you have got them working. It's just the massive grab when you first apply them that's the issue.

It does not have a proportioning valve so I may just go a new brake package from the US, at least then I know it's all good.

Mustang Steve does state that you cannot use the 69 booster with a 70 pedal so I may post a Q on there to see what the result would be if that were done.


Being in denial does not always mean you are in a river in Egypt.

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Nuts
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smh00n wrote
Supposedly this was rebuilt prior to me buying it so I am assuming that the cylinders etc are fine.

I've not yet pulled it apart to see what it is like. Rotors are fine visually.

The brakes do work well, once you have got them working. It's just the massive grab when you first apply them that's the issue.

It does not have a proportioning valve so I may just go a new brake package from the US, at least then I know it's all good.

Mustang Steve does state that you cannot use the 69 booster with a 70 pedal so I may post a Q on there to see what the result would be if that were done.


The only difference between the 67-9 and 70 bendix boosters is the pushrod shape.


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ozbilt
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Single piston KH brakes. The shafts they run on jamb so make sure they are greased & sliding correctly. The rubber boots should be in good shape, if not pull apart & fit new ones.


Reading what is going on, I would look straight at those shafts.

Edit; another issue is the pistons getting stuck on the first push, but again I would be looking at the free movement of the caliper on the shafts.


Kerry

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Last edited by ozbilt on Tue Dec 29, 2015 3:01 pm; edited 1 time in total

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smh00n
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OK, we have made progress.

The pedal and booster is a 69 setup, which I understand is not an issue as they are matched.

However, it has had a PBR master cylinder fitted and no proportioning valve.

I have a new master cylinder here so that is good. However the proportioning valve is causing grief; Mustang Steve does not have the original style in stock and only has adjustable. I like his product as he has stated it is a later model so he includes adaptors for the brake pipes, all others don't mention this.

Question is; Do I go with the adjustable and risk NSW laws? I don't know, but I would not be surprised if you need an engineers report for such a beast. Or do I buy a original style valve from the likes of Summit/CJ/CPC/etc and expect hassles with fittings?

Anyone bought a proportioning valve for a 69/70 and how was fitment?


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ozbilt
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PBR master does not need a proportioning valve.

Your symptoms tell me it is in the calipers, not up top ....

You stated in the OP ...... "When I go to brake there is nothing, nothing, nothing then WHAMMO the brakes are on and my forehead is on the screen. Once you are used to it it brakes OK but it all happens pretty quickly once you have gingerly squeezed the pedal some."


Kerry

It is easier to get older than it it is to get wiser

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