Thomas, does a smaller M/C reduce pedal effort as a result of a given pedal effort being concentrated on a smaller cross-section, this resulting in increased hydraulic pressure in the system?
Are you doing away with the booster?

 

Greg,
The simple answer is yes. For the same amount of pressure on the pedal, a master cylinder with a smaller bore will generate higher system pressure than one with a larger bore. Check out this chart and let's look at my situation. I have a 1" bore master cylinder now and my pedal ratio is 7:1. If I press on the brake pedal with 100 pounds of pressure, that will generate 886 psi in the brake line. Changing to a 7/8" bore master cylinder will result in 1,167 psi in the brake line.

The complexity lies in that you must balance the brake line pressure with the volume of brake fluid. If I went to a 1/2" bore master cylinder I would have 3,500 psi but there would not be enough fluid volume displaced to activate the brakes. There are many online calculators that help you determine what size.

I think I am going to remove the brake booster this weekend. It's not currently hooked up to engine vacuum so it isn't doing anything. If there was a way to go with a traditional two-circuit boosted brake system I would go that route.

Thomas

 

Today was a busy day but not many pictures.
First up was finishing the driver's seat and reinstalling back into the car. When I catch up I will definitely be pulling the passenger seat and redoing it the same way I did the driver seat.



After that was replacing the master cylinder and bleeding the brakes. I didn't take pictures of this because the new master cylinder looks the exact same as the old one; it just has a sticker that says 7/8" bore instead of 1" bore.
I pressure-bled the system then had my wife step on the brake pedal while I cracked the bleeders.

After that it was time to align the front wheels. I picked up and while I do not think it is going to as accurate as a 4 wheel laser alignment, it will be better than they eyeball method I used last summer.
First up was loading the front suspension; I did this by putting jack stands under the lower control arms as far outwards as I could.


The I bolted the plates to both front wheels and ran the tape measures.


This is the tape measure towards the rear of the car measuring 58 and 5/8".


The tape measure towards the front of the car was reading right about 58", meaning I had about 5/8" of toe-in.


I decided it was best to have a very slight amount of toe-in so I adjusted the steering tube until I got to about 1/16" of toe-in.

The plan for tomorrow is to put the white walls on the 3 remaining tires. I had to pull all the wheels off to bleed the brakes so this is a great time to do it. After that it's time to check out the new master cylinder and see how it behaves. I have a few more items on the punch list such as finishing bolting in the passenger seat, installing the passenger side seat belt, and cleaning out the trunk.

 

This morning I put the whitewalls on the three other tires, mounted them up, then rolled her outside.

Isn't she beautiful?


My trip around the block showed that the 7/8" bore brake master cylinder was perfect. The pedal feel was precisely where it should be and the brake feel was spot on. You did not have to stand on the brakes to get it to stop - it had almost the exact same feel as my MGB (which was what I wanted to duplicate). I thought as was well.

I put the passenger side seat belt in, I finished bolting in the passenger seat, I cleaned out the trunk. I called my wife and told her I was going to meet her for lunch. I get in the car and think about how it smells like a new car. I start driving and after about a mile I can tell the brakes are dragging when they weren't before. I decide to loop around and go back home but by the time I pull in the driveway the brake pedal is hard as rock and the brakes are hot. All 4 corners are putting off an incredible amount of heat.

I pulled the wheels off and let it cool for several hours and all the wheels turn freely. The brake pedal is back to normal.

I'm thinking the master cylinder is bad. That's the only scenario I can think of where all 4 brakes are "on". The only other thing I can think of is that the front brake lines run about 3" away from the exhaust downpipes. I could see the fluid getting hot and expanding but that does not account for the rear brakes. I am going to put heat shielding around the sections of brake lines near the downpipes and test it tomorrow. But I suspect I will be calling Summit Racing on Monday morning.

Does anyone else have any thoughts would could be causing this?

 

Relief passage in the master cylinder plugged?

 

Is the push-rod on the booster adjustable? Is it possible you don't have enough clearance between the tip of the rod and the piston in the master cylinder? If I recall correctly, a typical clearance specification is in the range of 0.020".

 

Don my friend, you have won the internet today. I read your post, went out and looked at the car, and sure enough you were right. The pushrod between the brake pedal and the master cylinder is threaded into the pedal assembly and your thought was correct - the pushrod was not threaded deeply enough into the pedal assembly which mimicked a small-but-constant brake pedal application.

I threaded the push rod farther into the pedal assembly until there was visible clearance between the mushroom end of the pushrod and the brake master cylinder, then tightened it until I could slide in a thickness of card stock.. Then I tightened up the locknut to prevent the pushrod from adjusting itself. Before adjusting the pushrod the wheels were hard to turn; after adjusting the pushrod the brakes hold the wheel when the brake pedal is pushed and the wheels turn freely when the brake pedal is released.

I am looking forward to testing it out tomorrow but I feel fairly confident this was the problem.

 

Great find! What a good forum this is!
That Mark VII looks magnificent, Thomas. What a fantastic achievment.

 

Glad to hear you got it working and that is important.
There is a tool to set it up properly. Just went thru this on my old 1959 Thunderbird. See the attached from Baer. Tools are cheap and all over.





Mine was $10.
.
.
.

 

So are the brakes in the Mark VII un-assisted, or is there a remote booster as in my S-Type? The standard two-ended gauge for adjusting a booster rod like clubairth1 mentioned probably won't work on your car if the push rod is threaded directly into the brake pedal lever.

I meant to mention earlier after you posted the photo outdoors, the car looks fabulous! The lines of the Mark VII are classic perfection! It's obvious why Jaguar was slow to change as vehicles from other automakers became less and less curvaceous and more like boxes.

Cheers,

Don

 

Today was a busy day but I was able to put about 60 miles on the Jaguar today.
We had some light rain showers this morning, so I took some time to make a new gear shift lever. I bought two pieces of half-round steel and used that as a starting point. Here I am drilling the two holes in one of the pieces of half-round so I can bolt it to the transmission.



After that I welded the two half-rounds together to make a rod.
I could have started with a rod but the part that bolted to the transmission needed to be flat and this was the easiest way to get there.
Then I chucked it in the lathe and turned it to down to a smaller diameter.

Here is the original Camaro shift lever on the left and my new one one on the right. The new one is about 3" longer.


After painting it black I installed it and put the shift boot back on.


By this point the rain was done, the sun was shining, and there was a nice breeze blowing. It was a good day to take my wife for a ride.

Shortly after my wife took the video the engine stopped running and I coasted to a side street.


One of the fuses for the ignition circuit would blow as soon as the key was turned on, so it was time for the haul of shame.


It took me about 3 minutes to find the problem. Tracing that circuit showed that the fuse was shared with the heated o2 sensors and the 1-4 shift skip solenoid.
To help meet economy requirements the computer forced the Camaro to skip gears 2 and 3 at part-throttle loads. I decided to omit that feature but failed to secure the connector. It met the exhaust pipe and melted, and when the computer tried to send power to the shift skip solenoid it went straight to ground and popped the fuse. That was my mistake. I clipped the melted connector off, insulated the wire ends, and made sure the rest of the wiring harness was out of the way.


After fixing that it was more driving around, including an evening drive where I got to enjoy the dash lights.


I am really happy with how the car drives. The engine has plenty of power and you don't really have to downshift unless you want to. The cruise works great and is going to be nice on long drives.

I did decide to replace the brake pads after yesterday's fiasco but the benefit to converting to disc brakes is that you can pick up a set of brake pads for $7.

 

Don,
In stock configuration the Mark VII has the brake pedal pivot mounted to the frame rail with the master cylinder under the floor. There is a remote booster under the car, roughly where the passenger sits. It is a single circuit system.

In my modified configuration, I have Wilwood pedals mounted to the firewall with the brake and clutch master on the engine side of the firewall. They are not boosted and the measuring device clubairth1 showed would not work. They do work with vacuum boosters and are a required tool to set up the vacuum booster and brake master cylinder.


Here's a picture of the original-ish Mark VII brake master cylinder setup. This is not the Jaguar brake master cylinder; someone before me put the master cylinder from a 1960's Ford truck in.



These are the Wilwood brake and clutch pedals I installed.
You can see the yoke hanging down from near the pivot of the brake pedal; ;this is what the push rod from the brake master cylinder screws into.


Here are the Wilwood brake and clutch master cylinders mounted on the engine side of the firewall.

 

It's a good sign when you spend more time driving your project car than working on it. Today I took the Jaguar to a business lunch and I really enjoyed driving her. It was a bit cool so I got to test out the heater and it works very well.

This evening I pulled all 4 wheels and the brake pads. They definitely showed signs of being heated and were probably fine but I picked up new pads for all 4 corners for about $30 - cheap insurance.
I thought it was interesting to compare how the $30 would compare to new brake shoes if I had kept the stock drum brakes. Moss does not sell them but SNG sells the friction material you can rivet onto the your existing shoes (once you remove the existing lining). $200 per axle or $400 for all 4 corners.