Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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geezer
Charles Durning
Magee, MS
(45 posts)

Registered:
11/16/2017 01:16PM

Main British Car:
1974 MGB, 1967 Morris Minor

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Little to no hydraulic pressure to the rear brakes
Posted by: geezer
Date: December 08, 2017 11:19AM

Ever since I resurrected my 74 GT I felt the brakes were not up to standard. I did overhaul the entire system including wheel cylinders, calipers, flex hoses, front pads, and rear shoes and hardware. The master appeared to be new before parked and bled quickly to a firm pedal. I did notice when bleeding the rears that the fluid did not expel with the same gusto as the fronts. I didn't think much of it at the time.

Now that I have converted the rears to disc I thought there should be a marked improvement in braking. They didn't seem to be perform as I had expected. On a whim I had the wife push on the brake pedal with the wheels in the air and I can still turn the rear wheels by hand. Drat!!! The fronts work as expected.

None of the hard lines to the back brakes are smashed.

I did not remove the trap valve from the rear circuit of the master cylinder. Is there a known issue with the master not producing pressure for the rear circuit?


DiDueColpi
Fred Key
West coast - Canada
(1259 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

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Re: Little to no hydraulic pressure to the rear brakes
Posted by: DiDueColpi
Date: December 08, 2017 02:28PM

Charles.
There is a definite possibility that the master is at fault. Especially if it has sat for a long period of time.
The cup seals on the plungers swell and cover the ports that admit fluid from the reservoir.
A more likely scenario is that the brake failure warning valve has tripped.
That is # 28 on your diagram.
When this valve trips it closes the port to the offending end of the vehicle.
It should turn on the brake warning light, but it does contain Lucas parts so.........
Try re centering the valve by opening a front bleeder and giving the brake pedal a sharp stab.

Live like you mean it.
Fred


geezer
Charles Durning
Magee, MS
(45 posts)

Registered:
11/16/2017 01:16PM

Main British Car:
1974 MGB, 1967 Morris Minor

authors avatar
Re: Little to no hydraulic pressure to the rear brakes
Posted by: geezer
Date: December 08, 2017 03:51PM

Thanks, I'll look at that before condemning the M/C. For some reason I didn't think the shuttle would close off a hydraulic circuit. In a past life after doing a brake overhaul I would pull the contact and center the shuttle manually tp shut off the light. Just didn't occur to me this time. The light must not be working.

If all else fails I do have a new M/C. It's just a PITA to change.


spridget
bill green
Maine
(39 posts)

Registered:
03/22/2008 01:29PM

Main British Car:
2 1980 TR8, 2 Bugeye Sprite TR8 3.5 and 5.0, Sprite 1098 and ?

Re: Little to no hydraulic pressure to the rear brakes
Posted by: spridget
Date: December 09, 2017 08:35AM

Consider using stainless steel flex hoses. The rubber ones can swell and restrict flow. I had that happen on a new hose.


geezer
Charles Durning
Magee, MS
(45 posts)

Registered:
11/16/2017 01:16PM

Main British Car:
1974 MGB, 1967 Morris Minor

authors avatar
Re: Little to no hydraulic pressure to the rear brakes
Posted by: geezer
Date: December 09, 2017 02:15PM

Thanks,

The hoses are all new stainless flex, front and rear. If it warms up this afternoon I'll look it over in better detail. Lots of snow yesterday and my shop has 2 open sides BURRRRR
snow.jpg


geezer
Charles Durning
Magee, MS
(45 posts)

Registered:
11/16/2017 01:16PM

Main British Car:
1974 MGB, 1967 Morris Minor

authors avatar
Re: Little to no hydraulic pressure to the rear brakes
Posted by: geezer
Date: December 09, 2017 04:46PM

Did another bleed with a pro helping instead of the wife. All is well now.


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