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front brakes locked

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tommylg Avatar
tommylg tom greene
murfreesboro, TN, USA   USA
With the car jacked up and on stands, I could spin the driver side wheel but the passenger side would not.
changed the ps hose and it is still stuck. Now, the ds is stuck. The pedal will not return to a normal position unless I pull it back with my toes.
Opening the bleed screw and keeping the mc topped off, the mc shoots fluid out both sides. I am guessing the seal is not allowing the fluid to go back.
So, what tests can I do before saying it is the mc?
Thank you, Tommy

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ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
If brake flex lines replaced
Release pressure and see if the stuck one tree's up
Yes good
No adjust the brake switch its preventing the brake from backing off the rotor



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tommylg Avatar
tommylg tom greene
murfreesboro, TN, USA   USA
Rob, pedal cover off, opened the bleeder and no change.
Fluid shoots.
Tommy

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Cocoa, FL, USA   USA
I had that happen to me with both front brakes locking up,it turned out to be the brake light switch being too far in. Greg.

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Steve64B Avatar
Steve64B Steve Opitz
Phoenix, AZ, USA   USA
1966 MG MGB
There are two other things to check

If, the brake MC isn't returning all the way to the out position then you will have hydraulic lock. This can because by the switch not allowing the pedal to swing freely or the flex hose might be detached inside and it's creating a one way valve to the fluid returning .

Or it could be Leprechauns?

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billymgb1000 Avatar
billymgb1000 Silver Member william gaulin
harrisville, harrisville RI, USA   USA
1973 MG MGB
1974 MG MGB V8 Conversion "Sweet Thing"
Do you have the return spring on the brake pedal.

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Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
I had an internal breakup of my original, braided rubber hose on one side once. I blocked when braking and delayed the release, so the B "zigzagged" when braking eye popping smiley
IMO a complete block is also possible if the hose is far gone. Still MC's are more often to blame, I am on the verge of renewing my early double brake MC as soon as temps go up eye rolling smiley

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tommylg Avatar
tommylg tom greene
murfreesboro, TN, USA   USA
Thanks for the replies.
Hypothetical: pull the calipers - hoses intact - and press the pistons back in with the proper tool.
Maybe that will release the pressure and all is well - maybe, ha.
I am looking at this MC: https://mossmotors.com/master-cylinder-aftermarket?assoc=20906.
Has anyone used this and how is it working?
Tommy

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Motion Avatar
Motion Gold Member Dale Spooner
Danville, VA, USA   USA
1977 MG MGB
Sounds like the compensating port in the master is covered, as in the MC piston is not fully retracting and uncovering it. That port is open to entire system when the pedal is not depressed. This allows the hot expanding brake fluid to go back into the master reservoir instead of applying the brakes. I've personally seen this several times, usually on a master cylinder change or a car that has been sitting.


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ClayJ Avatar
ClayJ Silver Member Clay Johnston
Mt. Olive, MS, USA   USA
1972 MG MGB
Sounds like you're missing the pedal return spring or have the improper spring, should not have to pull pedal back with your foot.

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Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
I always bought the more expensive, OEM version. Just received it yesterday, costing me €160 excl VAT, say $200, quite a difference! Aftermarket ones over here also come much cheaper.
Anyhow the last one mounted around 1988/90 still cost me more or less the same amount at the time (in Dutch guilders: NFL400 something); they were always very expensive in OEM!

These early double USA brake MC's are less reliable than the later type and more difficult to refurbish, see JT video on YouTube on his failure to do so. I refurbished the earlier OEM one around 1990 using some tricks of Porters and my own. But after having it lying in my humid garage for almost 30 years I did not dare to re-use it after all confused smiley

BTW I second the remarks about the pullback spring on the pedal and add the advice to look at the condition of the clevis pin and renew it if necessary. The pushrod and rear banjo joint on the rear opening have probably to be transferred from the old MC to the new one and the copper seals around this banjo annealed for re-use for assuring a dependable seal.

PS Doesn't MOSS Motors USA offer a "Lucas branded" original as well around $100 or so? This price for an OEM would be a fine offerthumbs up

PS2 I still have a set of seals for refurbishing the one now coming out of the car, but will probably not use it anymore in my remaining lifetime grinning smiley

In reply to # 3907920 by tommylg Thanks for the replies.
Hypothetical: pull the calipers - hoses intact - and press the pistons back in with the proper tool.
Maybe that will release the pressure and all is well - maybe, ha.
I am looking at this MC: https://mossmotors.com/master-cylinder-aftermarket?assoc=20906.
Has anyone used this and how is it working?
Tommy



Edited 2 time(s). Last edit at 2019-03-13 11:19 AM by Donthuis.

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frnloth Avatar
frnloth Jonathan Lane
Greenwood Village, CO, USA   USA
1949 MG TC "The Blue Car"
1960 Austin-Healey 3000
1967 MG MGB Racecar "Race Car"
1971 MG MGB GT "BRiGT"
I had a similar issue many years ago on my '71 GT. I found that inside the MC there is a little metal band that connects the 2 pistons. That band had broken and the spring was basically pushing the piston. I'd consider replacing the MC.

I doubt that the pedal returns spring has anything to do with it. I've had those break and driven for months before I remembered to replace it.

Good luck!

Jonathan

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drtyler Gold Member Dane T
Rydal, GA, USA   USA
1971 MG MGB
Don,
What is the part number of the master cylinder you purchased?
Thanks!
DT

In reply to # 3908018 by Donthuis I always bought the more expensive, OEM version. Just received it yesterday, costing me €160 excl VAT, say $200, quite a difference! Aftermarket ones over here also come much cheaper.
Anyhow the last one mounted around 1988/90 still cost me more or less the same amount at the time (in Dutch guilders: NFL400 something); they were always very expensive in OEM!

These early double USA brake MC's are less reliable than the later type and more difficult to refurbish, see JT video on YouTube on his failure to do so. I refurbished the earlier OEM one around 1990 using some tricks of Porters and my own. But after having it lying in my humid garage for almost 30 years I did not dare to re-use it after all confused smiley

BTW I second the remarks about the pullback spring on the pedal and add the advice to look at the condition of the clevis pin and renew it if necessary. The pushrod and rear banjo joint on the rear opening have probably to be transferred from the old MC to the new one and the copper seals around this banjo annealed for re-use for assuring a dependable seal.

PS Doesn't MOSS Motors USA offer a "Lucas branded" original as well around $100 or so? This price for an OEM would be a fine offerthumbs up

PS2 I still have a set of seals for refurbishing the one now coming out of the car, but will probably not use it anymore in my remaining lifetime grinning smiley

In reply to # 3907920 by tommylg Thanks for the replies.
Hypothetical: pull the calipers - hoses intact - and press the pistons back in with the proper tool.
Maybe that will release the pressure and all is well - maybe, ha.
I am looking at this MC: https://mossmotors.com/master-cylinder-aftermarket?assoc=20906.
Has anyone used this and how is it working?
Tommy

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Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
My part nr is GMC 235, MOSS Motors has it listed under 180-765 (I checked them before asking my usual Dutch parts provider: $105 for the "Lucas branded "one)

BTW MOSS Europe was out of stock these few weeks ago and charged 78 UK Pounds which more or less equals this $105, another one I found on eBay was 90 UK Pounds

All the best and be carefull for inserting the thin metal lines to the intercon\nection piece correctly or you may strip the threads on the brass couplings !
I am exchanging this MC right this morning, lets keep our fingers crossed smiling bouncing smiley

In reply to # 3908327 by drtyler Don,
What is the part number of the master cylinder you purchased?
Thanks!
DT

In reply to # 3908018 by Donthuis I always bought the more expensive, OEM version. Just received it yesterday, costing me €160 excl VAT, say $200, quite a difference! Aftermarket ones over here also come much cheaper.
Anyhow the last one mounted around 1988/90 still cost me more or less the same amount at the time (in Dutch guilders: NFL400 something); they were always very expensive in OEM!

These early double USA brake MC's are less reliable than the later type and more difficult to refurbish, see JT video on YouTube on his failure to do so. I refurbished the earlier OEM one around 1990 using some tricks of Porters and my own. But after having it lying in my humid garage for almost 30 years I did not dare to re-use it after all confused smiley

BTW I second the remarks about the pullback spring on the pedal and add the advice to look at the condition of the clevis pin and renew it if necessary. The pushrod and rear banjo joint on the rear opening have probably to be transferred from the old MC to the new one and the copper seals around this banjo annealed for re-use for assuring a dependable seal.

PS Doesn't MOSS Motors USA offer a "Lucas branded" original as well around $100 or so? This price for an OEM would be a fine offerthumbs up

PS2 I still have a set of seals for refurbishing the one now coming out of the car, but will probably not use it anymore in my remaining lifetime grinning smiley

In reply to # 3907920 by tommylg Thanks for the replies.
Hypothetical: pull the calipers - hoses intact - and press the pistons back in with the proper tool.
Maybe that will release the pressure and all is well - maybe, ha.
I am looking at this MC: https://mossmotors.com/master-cylinder-aftermarket?assoc=20906.
Has anyone used this and how is it working?
Tommy

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Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
The spring in this double brake MC is very strong so you may be right, but better be safe than sorry.
On the clutch MC this spring is vital, because the spring sitting inside the unit is very weak. The result may be a only partly freeing clutch and rapid wear on the carbon TO bearing sad smiley

In reply to # 3908311 by frnloth I had a similar issue many years ago on my '71 GT. I found that inside the MC there is a little metal band that connects the 2 pistons. That band had broken and the spring was basically pushing the piston. I'd consider replacing the MC.

I doubt that the pedal returns spring has anything to do with it. I've had those break and driven for months before I remembered to replace it.

Good luck!

Jonathan

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