It’s necessary to do MGB brake hose replacement from time to time. The MGB from 1962-1980 have the same brake hoses on all models. There are variations to the overall brake system. Single line masters (early cars pre 1968), dual line masters (1968 to 1974 production cars), and dual line masters with a brake booster (servo) on the later cars (1975 to 1980). However, the hoses from the hard lines to the front brake calipers and across the rear axle, are the same for all years.
If your braking system is functional there is a tendency to leave it alone. The fear, certainly from my perspective, is always the challenge of bleeding the system. No one wants to screw up a working brake system. However, the rubber hoses don’t last forever, and should be changed periodically. Brakes (like tires) are critical safety elements and so don’t ignore their maintenance.
Single Line vs. Dual Line Systems #
A quick word about dual line brake systems. Cars with dual lines from the master cylinder (1968-1980) these have a pressure failure switch. This is an “H” shaped fitting with a shuttle valve inside. If there’s a leak in fluid from either the front or the rear part of the system, the shuttle valve moves to close off the half of the system that has the leak. This is obviously to prevent the loss of all brakes. However, be aware that the front brakes probably provide 80% of your braking capabilities. So losing the front brakes is likely to be much more problematic than a failure in the rear.
There are 2 approaches to managing the shuttle valve on dual line systems. You can get it back and centered as part of the bleeding process. Or you can remove the sensor and potentially use a custom tool (bolt with a prong on it) to screw in place and prevent the valve from moving.
Step By Step Process – Rear Hose #
What follows is how I approached MGB brake hose replacement on a 1977 MGB.
Step 1 – Preparation for the Rear Brake Hose #
To give yourself more room to work its best to place the jack stands under the front leaf spring mounts. This allows the rear axle to hang lower. As such it provides easier access to the rear hose and its hard line connections. You should also in advance prepare to plug or cap the hard line from the front of the car. I used some vacuum hose caps but note that the nut may not move up the hard line much. So getting something to create a pretty good seal may not be as easy as you might hope. I suggest having several options on hand. In my case, I connected an old spare hose I had to the hard line. I then capped the end that would connect to the metal 3-way junction on the axle.
Step 2 – Break Loose The Hard Line Nut #
Start by breaking loose the nut that is on the hard line from the front of the car. Ideally you have a flare nut wrench, if not be very careful not to round off this nut. Just break it loose. Use another wrench on the hose fitting to counter your force as you try to break it loose. If not you risk breaking off the hose mount.
Once you have the connection broken free, tighten again the nut just snugly. You can work on the hose retaining nut that is on the top side of the hose mount. There will be a nut and a star washer there – 9/16ths. Again, countering your undoing force by using a wrench on the lower hose connection to get the retaining nut to break free. Continue to loosen this nut up the threaded hose fitting – at least halfway. This will allow the hose to move a little. Now go back to the hard line nut and remove it. Plug the line as quickly as you can to prevent excessive brake fluid loss. You will get brake fluid on you – plan accordingly!
In the image I have connected an old spare hose I had to the hard line. Then I capped the end that would connect to the metal 3-way junction on the axle. I couldn’t cap the hard line itself.
Step 3 – Rear Hose Removal #
Now complete the removal of the retaining nut from the threaded part of the hose. Expect some more brake fluid to come out as you let the hose hang. You can now remove the hose from the 3-way junction. This will likely require some force to disconnect. You should again use something to brace the mount for the 3-way junction. If not you will risk shearing this off the axle. This may be a punch or larger screwdriver but just ensure you are countering the undo force you apply. Once you break the connection you can undo the hose. Watch out for the copper washer that helps seal the hose to 3-way junction connection. Ideally you should plan to replace the copper washer with a new one. You can re-use this with success usually. You might anneal the washer if reusing.
Step 4 – Install New Rear Hose to 3-Way Junction #
To install the new hose, make sure you have the copper washer on. Connect the hose to the 3-way junction. This will be the end of the hose with the shorter threaded piece. Tighten the hose initially by hand. You should not need a wrench to tighten the hose to get the two to mate. If you feel the need for a wrench something is wrong/cross threaded so back off and start over. Once the hose is mated properly fully tighten the connection. Again brace the mounting bracket to counter your applied force.
Step 5 – Fit New Hose Into Retaining Mount #
Now put the other end of the hose into/through the mount. Put the star washer on and get the retaining nut started on the threads. It should be possible to get the nut halfway down the threads by hand. Do not fully tighten the retaining nut yet. Leave it so the hose cannot come out of the mount but not so the hose cannot move a bit.
Step 6 – Connect Hard Line and New Hose #
Unplug the hard line from the front of the car. Mate it to the top of the hose and get the hard line nut started onto the threaded part of the top of the hose. You should be able to do this with your fingers only. If not adjust/reposition as necessary until you can. This is why you want the hose to still move to assist with the alignment.
If the nut will not go on with using your fingers only again something is wrong/not aligned. Do not cross thread this connection or you’ll be replacing the entire hard line! Snug the hard line up enough to have no or very little fluid leaking. Now you can get the hose nicely oriented before completing the tightening of the retaining nut. Once the hose is firmly secured in the mount, check and make sure the hard line nut is secure. Check for obvious leaks. Hopefully you have none.
Step By Step – Front Hoses #
This details the process for the front wheel brake hoses for an MGB brake hose replacement. The setup is basically the same as you just have gone through except one end of the hose is in the brake caliper. The hard line connection will be the same as the rear with a mount, hard line connection and 9/16ths retaining nut and star washer.
Step 1 – Brake Hard Line Nut Loose #
As with the rear start with the hard line nut and get it broken loose. Once you have the connection broken free, tighten again the nut just snugly.
Step 2 – Loosen Retaining Nut #
Next is the retaining nut that is on the top side of the hose mount. There will be a nut and a star washer there – 9/16ths. Again, countering your undoing force by using a wrench on the lower hose connection to get the retaining nut to break free. Continue to loosen this nut up the threaded hose fitting – at least halfway. This will allow the hose to move a little. Now go back to the hard line nut and remove it. Plug the line as quickly as you can to prevent excessive brake fluid loss.
Fully remove the retaining nut and star washer and remove the hose from the mount.
Step 3 – Remove Hose From Caliper #
Remove the hose from the connection to the brake caliper. Note there will be a copper washer between the hose and the caliper.
Step 4 – Install New Hose to Caliper #
Put the copper washer onto the new hose and then connect the new hose to the caliper. This should be done by hand, there should be no need for a wrench to fully thread the hose into the caliper. Once done tighten the hose to the caliper with a wrench.
Step 5 – Secure In Mount, Connect Hard Line #
Get the hose loosely into the mount and put the star washer and nut onto the threaded end of the hose. Do not fully tighten the retaining nut. Now the hard line is reattached. By hand tighten the hard line nut onto the hose and snug up at the end with a wrench.
It is more important to get the hose to orient nicely on the front. It is worth moving the wheels from full lock to full lock to check for kinks, rubbing or stretching of the hose. When you are happy with the orientation secure the hose in the mount and then recheck a full lock to full lock of the wheels. Adjust, if necessary, by loosening the hose retaining nut and get the orientation right. Repeat for the other front hose to complete your MGB brake hose replacement.
Brake Bleeding Overview #
The manuals tell you start with the wheel furthest away from the master cylinder. For a LHD US specification car, this is the driver’s side rear. Bleed until there are no air bubbles coming out and always make sure the master cylinder never gets too low. Check and top up with fresh new fluid regularly during the process. Then move on to the other rear wheel, the passenger front wheel and lastly the driver’s side front wheel. Then return briefly to the driver’s side rear and bleed a little fluid off which should reset the shuttle valve in the dual line H piece valve.
You can check to see if the shuttle valve had engaged by seeing if your brake warning light comes on (assuming this is functional). The other test is to have an assistant press on the brakes with the car in the air on stands and see if you can move either the front or rear wheels. This is a good test to make sure both parts of a dual system are working. If you can move either, obviously something is wrong and may require additional bleeding to get air out and/or reset the shuttle valve. It’s a good time to adjust the rear brakes also. You screw in the adjusters until the rear wheel locks completely and then back off the adjust one “click” or position. I sometimes find I back off 2 positions. Now you should be complete with MGB brake hose replacement.
Other Materials #
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