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Pressure Differential Valve

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74 Eski
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2010/06/04 22:18:50 (permalink)
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Pressure Differential Valve

Hi Guys,

I have a Mk1 Eski fitted with 2lt brakes all round and 2lt motor. I have discovered the person who did the brake upgrade/mod before we bought the car has left the original Mk1 valve in and not changed it to the Mk2 valve. The only difference I can see between the two are; that the Mk1 only has the front brakes lines from MC go into the valve and then out to each front wheel and the rear line from the MC goes straight to the rear wheels, the Mk2 has both brake lines from the MC go into it and then to front Left and Right and one to the rear. Can anyone advise me if there is any great difference between the two valves and if going to the Mk2 valve will improve braking and pedal feel.

Also, can anyone advise what is an economical brake upgrade when using Mk2 struts and running 15'superlites and who on the north side of brissy know what there doing with Eski's.

Regards,

Marty
#1


5 Replies Related Threads
    na.charrett
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    RE: Pressure Differential Valve 2010/07/04 08:16:27 (permalink)
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    Not sure about Mk1's, but Mk2's came with 2 braking systems...
    Early Mk2 did not have a pressure differential switch and the master cyl had a stepped bore to get the bias and had only 2 pipes coming from the master cyl which had a relatively rounded bottle. The front line then went to a T piece and then split to the front wheels. The later Mk2's (all 2Lts and later 1.6's) had a pressure differential switch which was supposed to light up the brake fail light under the dash. These cars had master cyl that has 3 pipes coming out from it (2 front lines and a rear line) and a squared off shaped fluid bottle. In these systems the bore is the same for both the cycls within the master, and the LHF brake line and the rear brake line both run through the pressure differential switch..... Swapping maters between these systems will result in rear brakes locking or not working enough (depending which way you swap).
    I have pulled 3 pressure differential switches apart, and noe have been operational as the piston seizes in the middle (unfailed) position and I doubt that a fluid loss in one or the other part of the system would have allowed it to move across to light up the fail light - as I could only budge them after using Ford Special Tool #1 (hammer) repeatedly...

    I run an early system on my highly modified 2Lt with no problems using Volvo calipers and 19.05mm rear cyls (2Lt) in the 9" drums. But it did originally run with M16 calipers and 20.64mm rear cyls (early 1.3) in the 9" drums (2Lt drums), but on the race track was locking up the rears too early causing the rear to skip 2-3 times under brakes. My Autocross Escort uses the 20.64 rear cyls in 9" drums in the rear for a nice rear bias (without the rear being able to overtake the front) on dirt....

    I would guess that a Mk1 would be the same as an Early Mk2, but hving owned only 1 Mk1 and given it away before playing with it, I am not sure... (Maybe my memory is playing tricks with me too, but it could be the other way round with the stepped master cyl with the late square tank one being stepped and the early one a single bore ...??? Has been a while)
    #2
    JamesR
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    RE: Pressure Differential Valve 2010/07/04 10:23:55 (permalink)
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    Nicholas, i dont think that is completely right?
    my '77 MK2 had the old 2 pipe M/C that then went to the differential valve, from there, one comes out the front to the RHF brake, and one out the side the LHF brake, then one at the rear of the valve goes to the rear brakes.
    my brake fail does work. the original M/C failed.
    but i have since changed masters clys over to a reconditioned 3 pipe master, but have blocked the front bottom hole off, and using it as a 2 pipe master.
    brakes work fine, with front locking first if i jump on them heavy enough.
    im also running un boosted, with grooved and vented front rotors [rebuilt p16 calipers] and standard rear drums.
    #3

    74 Eski
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    RE: Pressure Differential Valve 2010/07/04 19:24:12 (permalink)
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    Thanks for the feed back, I understand there was two braking systems fitted to the mk2, i was just curious if swapping the valves over would make any improvement to braking. I don't get any rear wheels locking up under heavy braking; therefore, all is well. Thanks again Marty.
    quote:
    Originally posted by na.charrett

    Not sure about Mk1's, but Mk2's came with 2 braking systems...
    Early Mk2 did not have a pressure differential switch and the master cyl had a stepped bore to get the bias and had only 2 pipes coming from the master cyl which had a relatively rounded bottle. The front line then went to a T piece and then split to the front wheels. The later Mk2's (all 2Lts and later 1.6's) had a pressure differential switch which was supposed to light up the brake fail light under the dash. These cars had master cyl that has 3 pipes coming out from it (2 front lines and a rear line) and a squared off shaped fluid bottle. In these systems the bore is the same for both the cycls within the master, and the LHF brake line and the rear brake line both run through the pressure differential switch..... Swapping maters between these systems will result in rear brakes locking or not working enough (depending which way you swap).
    I have pulled 3 pressure differential switches apart, and noe have been operational as the piston seizes in the middle (unfailed) position and I doubt that a fluid loss in one or the other part of the system would have allowed it to move across to light up the fail light - as I could only budge them after using Ford Special Tool #1 (hammer) repeatedly...

    I run an early system on my highly modified 2Lt with no problems using Volvo calipers and 19.05mm rear cyls (2Lt) in the 9" drums. But it did originally run with M16 calipers and 20.64mm rear cyls (early 1.3) in the 9" drums (2Lt drums), but on the race track was locking up the rears too early causing the rear to skip 2-3 times under brakes. My Autocross Escort uses the 20.64 rear cyls in 9" drums in the rear for a nice rear bias (without the rear being able to overtake the front) on dirt....

    I would guess that a Mk1 would be the same as an Early Mk2, but hving owned only 1 Mk1 and given it away before playing with it, I am not sure... (Maybe my memory is playing tricks with me too, but it could be the other way round with the stepped master cyl with the late square tank one being stepped and the early one a single bore ...??? Has been a while)
    #4
    na.charrett
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    RE: Pressure Differential Valve 2010/07/04 19:34:06 (permalink)
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    James...
    Something does not sound right about your description of your brake lines... Quote " had the old 2 pipe M/C that then went to the differential valve, from there, one comes out the front to the RHF brake, and one out the side the LHF brake, then one at the rear of the valve goes to the rear brakes."

    Only telling you what I have found from experience and been advised by brake specialists... Not sure when they changed from early (2 pipe round bottle master) to late (3 pipe square bottle master)master cyls, but I have always presumed that it was around 77 when they went to the larger strut tops... All early systems I have seen have 2 pipe masters with round bottles, with the T piece under the brake pedestal extension to fee the 2 front brakes with the rears fef by their own line not going through anything. The late ones have a squarer bottle with a 3 pipe master. The line from underneath goes direct to the front RH brake while the side front line goes to the pressure differential swithch and then onto the front LH brake. The side rear line on the master goes to the rear brakes through the pressure differential switch. At the pressure diffferential switch the lines for the front LH and rear lines have different sized thread with 11mm and 13mm spanner sizes so they cannot be mixed up....

    I do have an early Mk2 paddock bomb with a late 3 pipe master cyl that has 1 line blocked off.... It does seem to work OK though, but I cannot tell you what the bias is like... The only car I have driven with the wrong master on it locked rear brakes way too easy so that is why I said do not mix systems...
    #5
    JamesR
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    RE: Pressure Differential Valve 2010/07/04 22:16:28 (permalink)
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    well that's interesting.
    i have a late '77 2Ltr GHIA, small strut hole, and 2 hole, round bottle M/C.

    im only using a late, 3 hole, square bottle M/C now because im running the M/C on the firewall, and the filler sits to the back.

    i'll get a photo tomorrow.
    #6

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