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Discussion Starter · #1 ·
I am recommissioning a heavily modified 1957 Jaguar Mark v111and cannot get the brakes to release in less than 5 seconds. I have renovated all 4 calipers, replaced metal brake lines with braided hose, renewed the brake reservoir, master cylinder, servo, adjusted the push rod to ensure travel\return, and adjusted brake pedal in all directions and stops.

Bled manually. Bled using a Clarke pressure bleeder. 'Racing bled' by compressing/holding closed the brake pistons. Bled overnight. Bled one man on each caliper. Yet still the brakes will not release in under 5seconds.
Photos included

The system comprises
Girling Master Cylinder 3/4" CV-NP; feeds to...
AP Lockheed Servo 4.25:1, out port into a T piece which splits front and rear calipers (each split via 2 T pieces)
Jaguar Mark 1X rear disc brake assembly, single pot caliper
Jaguar XJ6/Limousine 4 pot front calipers (AAU2102 and AAU2103)

Help needed as reaching end point!

632094
632095
632096
632097
 

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Is it a genuine Lockheed servo ? Have you a picture of how it's mounted .

Don't know if it's part of the problem but you m/c is mounted so it will be vectoring ie pushrod is straight to start with but as it moves it changes angle and will reduce pressure applied due to angle it's passing through. It MAY also be causing it to hook up on side of cylinder internally.

I'd also be increaing the thickness of the bracket the m/c is mounted to. Lack of thickness could be allowing twist.

Other favourite is making sure you have a return spring on brake pedal as with a servo if you don't just the weight will apply the brakes due to servo effect multiplying its unsprung weight.
 

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Also pushrod into m/c should have 1mm free play and be roratatble between your fingers . If set up correctly you should see the 1mm free play multiplied by pedal ratio ( can you tell me what the ratio is as well please ) at the pedal..
 

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Discussion Starter · #4 ·
Hi Kapri, Thank you for responding to my plight.

I do have a spring connected to the brake pedal, it was off when this photo was taken. There is a gap and play with the push rod. I'm afraid I don't know about pedal ratios - how do measure and calculate the ratio, please?

The servo is genuine lockheed and is mounted with the air control valve at 5 o'clock and at roughly a 30 degree incline.

Thank you for your response.
 

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to work out pedal ratio measure (a) from the pedal pivot to the pedal pad, then (b) from the pivot to the pushrod attachment point. divide one by the other to get the ratio. ie if (a) is 6" and (b) is 1" then 6 divided by 1 is 6 so you have a 6:1 ratio.
neil.
 

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Had a similar problem with a 64 Mercury when it had been stood for a while, the main pushrod lubrication had hardened and just needed cleaning and coating in copperslip or similar. Hope this is the problem as it's quite easy to remedy.
 

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Have you tried braking and then manually returning the pedal to see if the wheels free up immediately? It would give a pointer as to where the issues lies ie mechanical or hydraulic .

I've seen brakes get stuck on with too thick carpet before now , slowing down pedal return.
 

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Might be my interpretation of the photo, but I think the MC could move back a bit (or shortern the rod). The angle between the actuating rod in to the MC and the mechanism above (pedal?) seems quite acute to me.
 

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Discussion Starter · #11 ·
Is it a genuine Lockheed servo ? Have you a picture of how it's mounted .

Don't know if it's part of the problem but you m/c is mounted so it will be vectoring ie pushrod is straight to start with but as it moves it changes angle and will reduce pressure applied due to angle it's passing through. It MAY also be causing it to hook up on side of cylinder internally.

I'd also be increaing the thickness of the bracket the m/c is mounted to. Lack of thickness could be allowing twist.

Other favourite is making sure you have a return spring on brake pedal as with a servo if you don't just the weight will apply the brakes due to servo effect multiplying its unsprung weight.
Thank you I have beefed up the bracket for the MC with a 3mm shim and will certainly look into the vectoring as a potential jam point.
 

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Discussion Starter · #12 ·
Might be my interpretation of the photo, but I think the MC could move back a bit (or shortern the rod). The angle between the actuating rod in to the MC and the mechanism above (pedal?) seems quite acute to me.
Thank you for your suggestion. I have moved the MC backwards by using a 3mm shim as part of beefing up the mounting.
 

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Discussion Starter · #13 ·
Have you tried braking and then manually returning the pedal to see if the wheels free up immediately? It would give a pointer as to where the issues lies ie mechanical or hydraulic .

I've seen brakes get stuck on with too thick carpet before now , slowing down pedal return.
Thank you for you response. I have had my mechanic mate pull the rod back immediately the brake pedal is released, another mate on the tyre turn, still it took a few seconds to release.
 

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Discussion Starter · #14 ·
Might be my interpretation of the photo, but I think the MC could move back a bit (or shortern the rod). The angle between the actuating rod in to the MC and the mechanism above (pedal?) seems quite acute to me.
Thank you. I have tried a shorter rod and the problem is still the same.
 

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Discussion Starter · #15 ·
As an update, I advent managed to get to the car during the past week nor this weekend. Because the pressure releases with a hiss when I undo the banjo on the MC immediately post brake pedal depress, and that the MC is brand new, I'm wondering whether the banjo bolts could be grounding out in the bottom of the MC. I'm going to shorten them by a few mm and see if it makes any difference. has anyone ever experienced this?
 

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i've heard of it with banjo bolts bottoming in wilwood calipers so it's possible.
also have you tried cracking open a bleed nipple just a second or 2 after pedal release. then each joint going back to the master cylinder. it'll tell you what's holding pressure and where.
 
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