66 S1 Brake Job - No Power Assist?

Hello again. Love all the feedback here as usual. I also try to share any learnings I have.

I have completed my brake job replacing the MC and servo. The good news is it is all back together and road tested. The bad news it appears I do not have the power assist. At least that is what it feels like. My brakes feel like brakes when they get wet. Requires a lot of effort at the pedal. I know all the vacuum hoses are connected. It was working before. So the adventure continues. Any thoughts on this would be appreciated. I really do not want to take everything apart again. Skene

I would start by clamping off the vacuum from the intake and testing it again. If there is no difference you can be pretty certain that the boost is not working. Of course keep in mind that if one of the hydraulic circuits is down and you disable the boost stopping distances are going to get really long, so take care.

By the by your name seems really familiar; were you once up in Colorado?

This sounds worse than no boost to me. (But I have a S2.) Maybe make sure both front & rear are working. I’d lift the tires off the ground, press the pedal, & check to see if the brakes apply at each wheel.

Thanks for the info. I don’t think the rears are not working as I believe this would be air in the line related. My supporting data is during my bleeding work after pressure bleeding all wheels I accidentally installed one of the rear bleeders without the ball bearing seal (it had popped out) and I had no brake pressure when I went to test the system (and leaked out a bunch of brake fluid). Only one of the rears was the issue. I repeated the pressure bleed with the bleeder fixed and did get good pedal pressure. It really feels like brakes with no power assist or wet brakes, but then again this is my “first rodeo” for jaguar brake systems work. I would like to think the parts are of good quallity but will be pissed it turns out to be a defective part. I will try the vacuum removal test for comparison. Next time I jack up the car will also test the rear brake theory for good measure.

David, My car used to reside in Loveland, CO where my folks live. You might have met my father (same name). Small world if so. Where in CO are you?

Thanks, Skene

I was in Boulder when I suspect I met your Dad. Bought an E-type washer pump/bottle from him. Oddly enough I’m now west of Loveland.

Skene,

Just one word of caution: there is one scenario (see the description of safety features of the braking system in the Workshop Manual) where the only thing that is providing any braking is the vacuum system. If you disconnect/block the vacuum system in this particular scenario you will have NO braking at all. This is probably not the scenario you are faced with, but it’s worth noting for those of us (myself included) who have in the past recommended disconnecting the vacuum as a diagnostic tool for brake system problems without a full understanding of the problem.

-David

I will have to mention this to my Dad. He probably will remember the transaction. I love visiting CO every summer. Loveland is a great location.

One way to test that theory is to roll the car down the driveway with the engine off I see if I have any brakes. I have a good parking brake which I could use as a back up. This would seem odd as I know I am pushing fluid to the brakes without vacuum.

I let the car coast with the engine off today (safely) to test the brakes with no vacuum assist and there is no difference in braking. So it appears my power assist is not working. Has anyone heard of defective MCs or Servos from any of the usual suppliers. I would hope there is some good QC with these parts.

Hello Skene,
Given that you have replaced the Master Cylinder and Servo, you would have had the vacuum hoses disconnected, Are you sure that the hoses to the Servo have been connected correctly? The hose from the front part of the Reaction Valve should attach to the rear section of the Servo. If connected to the front section, air at atmospheric pressure is applied to the front of the diaphragm when the brakes are applied, resulting in no Servo assistance. I had a customer come in to work today with no power assistance after he had reconditioned the Servo Unit and the problem was as described above; swapped the hoses around and power assist restored.

Regards,

Bill

Well I am pretty embarrassed. I had high confidence that I had connected all the vacuum hoses correctly, but I broke the cardinal rule of basic trouble shooting in double check and tripple check what you have replaced when something is not working properly. I even have the service manual with the diagram which I referenced. Somewhere between the grease and brakefluid I flip flopped the reaction valve connections. Now they are routed correctly and voila the brakes are perfect. The good news is I did not have to modify the hose lengths for reroute, only had to disconnect at the vacuum side and back of booster. Now I know what the feel is without power assist. Many thanks for all the input here. Skene

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