Whoa Maggie!
Ain't No Stopping Us Now!
When I went into Maggie a few months ago, I discovered that somewhere in her life, a previous owner had swapped in an entire 109 rear axle. Apparently Maggie had broken a halfshaft or worse, and someone could get a 109 axle cheap. Problem is, the previous owner kept the 11 inch brakes. I made a mental note and continued to rebuild Maggie, including the 11 inch rear brakes. Now that I can drive her, however, I would like to stop her as well. It was taking three pedal pumps to get any pressure at all. The wife felt that brakes should not be optional. There were so many possible causes for lack of braking, it was difficult to choose which possibility to attack first. I decided to isolate, troubleshoot, and convert as little as possible, stopping when I had a good pedal. I couldn't help but wonder if the non-Rover master cylinder that was grafted to Maggie by the previous owner was necessary for the rear brakes to function.
After weighing the symptoms, I concluded that the larger 109 wheel cylinders in the rear just were to large a bore for the 88" CV master cylinder I had installed. The rear wheel cylinder bore of the 109 are a whopping 57mm compared to 38mm on the 88 inch wheelbase. According to the Green Bible, the 109 only came with the CB master cylinder or a variant of it. The CB master cylinder is 6mm larger in bore.
By isolating the rear brakes (clamping the rear flex hose) I was able to achieve a good pedal. Release the clamp, and Maggie becomes a three pump death trap. I believed that I could swap in the 88 inch wheel cylinders and have them work with the 11 inch brakes.
To clamp the brake line, I use needle nosed Vise-Grips with half inch fuel line slipped over the jaws. By clamping, I also eliminated the possibility of the large loop I had placed in the common rear hard line being an air trap. I had already replaced or rebuilt every hydraulic cylinder, and line. I had bled and rebled. This seemed to boil down to one or two issues. Either the rear cylinders were to large in volume for the CV master cylinder, or the rear drums had been turned out of spec. The stroke of the 109 and 88 inch wheel cylinders was the same, so that did not seem to be an issue.
When I began to discuss various options on a couple of Land Rover Bulletin Boards, I was told everything from "mixing 11 inch and 10 inch brakes is a recipe for death" to "This might work". I normally do not monkey around with brakes. I figure the engineers that designed them know more than me. But the prospect of having 11 inch brakes work with a 10 inch wheel cylinder intrigued me. I researched back into my Navy Hydraulics manuals to refresh my mind on the physics at play, and it appeared my calculations were correct. I removed the 11 inch (57mm bore) wheel cylinders and installed the 10 inch (38mm bore) wheel cylinders. Perfect fit. I rebled the system and viola! No difference! It seems at times practical application will whip theory's ass when it wants to. I checked the entire system for leaks and found none. I checked the 11 inch shoe installation and adjustment. No joy.
With resignation, I began to shop around for 10 inch backing plates and drums. I figured that the best route would be to quit playing around, and convert back to 10 inch brakes on the rear. I already had the 10 inch wheel cylinders, and a spare set of 10 inch shoes. At this point, swapping back to the original set-up seemed to be the quickest and surest option to get brakes that worked.
I ordered the parts from Wise Owl, and true to form, Ray and Chris gave lagniappe along with the necessary parts. When the parts arrived, I saw they had left the shoes and wheel cylinders on the backing plates. The drums had a good surface, so I double checked the location of the cam adjuster to make sure I had them on the appropriate sides.
I pulled the wheels, the hubs and then the backing plates. While I was in disassembly, I removed the half shafts for inspection.
There was no visible twisting. I inspected the wheel bearings and the races. It was a nasty job, as packing wheel bearings always is. I used my rebuilt 10 inch wheel cylinders, but opted to use the old brake shoes Ray had sent, just in case the hub seal leaks. If the hubs do not leak, I can swap in the new shoes later if needed.
Once everything was together, I put on the drums, adjusted out the shoes, removed the line clamp, and bled the system. I had a firm brake pedal, no pumping. Sweet. I took Maggie out for a test drive, and the brakes held up beautifully.
I am not sure why the 11 inch brakes with the smaller wheel cylinders did not work. It seems they should have. I suspect the 11 inch drums were out of spec. I will mic them at some point, and if they are in spec, I will sell all the 11 inch brake equipment on ebay to recoup some of my losses.
You could kill yourself and other innocent people. Never mix and match brake components. Just because I screwed around with my brakes, is no reason for you to do the same. You are responsible for the stupid decisions you make, and your own safety. Please remember that these pages are for entertainment. They are not a how to guide on vehicle maintenance or restoration. I will not be held responsible for any dead doofuses. For more of this legal CYA stuff, click here. |
[ Rover Assessment ] [ Steering Straight ]
[ Minimal Wiring ] [ Worth $500? ] [ Fuel Supply ]
[ Idle Thoughts ] [ Tough Decisions ] [ Spinning Wheels ]
[ Stripping Down ] [ The Bulkhead ] [ The Bulkhead 2 ]
[ Maggie's Motor ] [ Chassis Prep ] [ POR15 & Parabolics ]
[ Synergy ] [ The Breakfast ] [ Waking the Neighbors ]
[ A New Look ] [ Test Drive! ] [ Designing Woman ]
[ Mystery Solved ] [ More Juju ] [ Whoa Maggie! ]
[ Finish Line! ] [ Epilogue ]
[ Due Thank Yous ]
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