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76 MGB Brake Overhaul

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BumbleB74 Avatar
BumbleB74 William Milholen
Tidewater, Tidewater VA, USA   USA
Make sure you read the manual a few times about the bleeding order.....it does matter in my experience, in particular the presences of the pressure warning/failure switch in the bottom of the MC. If done wrong, you can turn off either the front or the rear brake circuit.....by tripping the safety switch. Been there....done that.

After you drive a few miles, plan on re-adjusting the rear brakes as they will center them self. Also pay attention after a few short drives (10 miles?) and check for heat level on the rear drums. If you have minilite style wheels, you can get a finger tip or two through the spokes and see if the drums have any heat in them. Hopefully you won't find too much heat. If you do, back off one click on that wheel and repeat the test drive.



1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!

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flipton Avatar
flipton Fred Lipton
Philadelphia Area, PA, USA   USA
1976 MG MGB "Godfrey"
This post ends with a question regarding bleed sequencing. Please help me.

Good advice William, thnx. I need to be extra careful testing the work based on the inverse relationship between my experience level as a mechanic [minuscule] and the importance of this oh so critical safety system.

The book I have is The Complete Official MGB 1975-1980 comprising the Drivers Handbook and Workshop Manual. I lost the original owners manual in a coffee shop somewhere along I-95 in South Carolina back in December 1977.

Bleeding:
Since I'm replacing all the hydraulic components the system will start out dry. I've read pros and cons regarding bench bleeding which to me makes sense if one is replacing just the MC on an otherwise wet system. The Workshop Manual, section M page 208, says for initial priming checking all screws are tight, keep the reservoir at least half full and start with the near side rear brake; "near side" suggests the left rear wheel. However, the editor's notes at the end of the chapter, page 218, say to start with the right hand rear wheel, the farthest in terms of brake line length for left hand drive cars, which mine is.

That jives with the reading I've done on this and other sites but I have an opposing observation.

The rear cylinders are fed by a single line from the MC which terminates to a 3-way junction mounted off the rear axle. Separate lines go from there to each rear cylinder. The 3-way is located on the right/passenger side of the differential. The replacement lines for the left rear cylinder is about 46 inches, 18 inches for the right rear. Based on those measurements the left rear cylinder has to longest brake line distance from the MC, not the right rear cylinder.

So I'm confused - which cylinder to bleed first?




The real reason that we can’t have the Ten Commandments in a courthouse: You cannot post “Thou shalt not steal,” “Thou shalt not commit adultery,” and “Thou shalt not lie” in a building full of lawyers, judges, and politicians. It creates a hostile work environment...George Carlin

MGB 1976 Avatar
MGB 1976 Silver Member Mark Turechek
North of Boston, MA, USA   USA
1976 MG MGB "The Never Ending Project"
Brake lines run from the master cylinder across to the right side, then to the rear axle on the right side, then splits to the rear wheels. The longest run is the left rear wheel. Left and right are determined always from sitting in the driver's seat. Left = driver's side.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/1975-80-mgb-dual-line-servo-assist


I've been told (by a good source) I have to remove the wiring from the pressure failure switch #41 on Moss catalog page below and remove the switch from the master cylinder (found underneath, screwed into body) while bleeding to allow a shuttle inside the MC to travel fore and aft to to allow it to self-center. Otherwise it is possible that you could have only front or rear brakes if it is not centered. I'm going to be bleeding my 1976 this weekend (hopefully), and have my shop manual open.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/dual-line-servo-assist-brake-master-cylinder-1974-5-80



Edited 2 time(s). Last edit at 2019-02-06 11:20 AM by MGB 1976.

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
Fred,

Nice job on the front brakes.. thumbs up

Hard to tell from your photo, but do note that the LF and RF calipers are different. They are physically interchangeable, but it is critical that they be installed such that the bleeders are uppermost, adjacent to the port where the brake hose attaches. From your photo it appears possible that the caliper you show is upside down and should be installed on the other side of the car. Suggest you double-check...

Your near neighbor,

Dick





In reply to # 3882287 by flipton progress, but in a different area as I ran into a problem with the rear cylinder retaining clip. I tried the Chicagoland method and failed, or rather, gave up after some *expletive deleted* attempts. There's a tool I saw on youtube that makes it look easier [search youtube for "brake cylinder clip tool" you'll find it] waiting for it to arrive, should be here in a few days. then we'll pick back up working on this wheel.

in the meantime and since the right side is up on stands I went after the front brake. probably should have started there as a confidence boost, as a physical effort it will prove to be the easier of the two. forced me to learn how to repack wheel bearings along the way. also as an excuse to buy another tool [torque wrench] for the castle nut. more tools, life is good.

thanks to John Twist's video's for proper handling of the hub components and repacking the bearings a few other youtube entries helped too. also thanks to every post on this site always relevant even after a dozen years or more.

once the cylinder tool arrives I'll complete the right rear drum and post notes on that.

nice, clean, shiny. oooh.





If you're going to be crazy, you have to get paid for it or else you're going to be locked up. Hunter S. Thompson



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

flipton Avatar
flipton Fred Lipton
Philadelphia Area, PA, USA   USA
1976 MG MGB "Godfrey"
Howdy near neighbor!

You are right in that there are R and L versions and it is possible to mount on either side. I double-checked and it's the correct caliper for that side, hose port & bleed screw uppermost. Whew!









Crazy' is a term of art; 'Insane' is a term of law. Remember that, and you will save yourself a lot of trouble. Hunter S. Thompson


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BumbleB74 Avatar
BumbleB74 William Milholen
Tidewater, Tidewater VA, USA   USA
Fred - It gets discussed and argued from time to time, but the Haynes manual is specific about the late cars with the power boosted brakes. I haven't read it in a while, as I did the brakes on my '76 about 2 1/2 years ago, but I had to follow that procedure to NOT trip the pressure failure switch in the MC. If memory serves you unscrew the switch far enough to not have contact with the sliding shuttle in the MC. Pretty sure you started at the drivers side front and worked around clockwise looking down from the top of the car, and finished at the left rear. Left and right is always referenced from sitting in the driver's seat.

I didn't bench bleed mine, but used a simple power bleeder that has been discussed on here quiet a bit....basically made from a clean/new pump up sprayer you use for spraying weeds in your yard. You don't need much in terms of PSI to push fluid through.

Once you are done, if you have the car up on jack stands, it is easy to have a helper push the brakes (even with the car off) and try to turn a front and a rear wheel by hand to judge if both circuits are active.

One last note, always clean up any drop of spilled brake fluid right away. I just keep a bucket of soapy water handy with a rag or paper towel in it. This is VERY true if you are using DOT 3, it will strip paint.



1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!

twentyover Avatar
twentyover Greg Fast
Lives in SoCal, Resides in the Burbs of Detroit MI, USA   USA
In reply to # 3886547 by flipton ...I lost the original owners manual in a coffee shop somewhere along I-95 in South Carolina back in December 1977.
...

Call. You never know, they may still have it

flipton Avatar
flipton Fred Lipton
Philadelphia Area, PA, USA   USA
1976 MG MGB "Godfrey"
William - I've seen other posts say What you say about unscrewing the pressure failure switch for the bleeding procedure and why that makes sense. I shall do that.

Regarding testing the dual line brake circuits: I wondered how to easily test that. Now I know.

Regarding what you wrote about the Haynes manual bleed sequence, now I'm really confused. "Pretty sure you started at the drivers side front and worked around clockwise looking down from the top of the car, and finished at the left rear. Left and right is always referenced from sitting in the driver's seat.". This is totally against what so many other posts and the workshop manual says. Start bleeding from closest to the MC? Now I wonder if the stated sequences make sense at all: there are 3 direct lines from the MC, 1 to the rear and 1 each to the front wheels. From the MC perspective does it matter which order each line is bled?

Greg - Why not? Couldn't hurt ;-)





Just give me a comfortable couch, a dog, a good book, and a woman. Then if you can get the dog to go somewhere and read the book, I might have a little fun...Groucho Marx



Edited 1 time(s). Last edit at 2019-02-07 09:38 PM by flipton.

BumbleB74 Avatar
BumbleB74 William Milholen
Tidewater, Tidewater VA, USA   USA
The later cars are different due to the presence of the pressure failure switch. I believe the physics is that when you bleed in "reverse" direction you first trip the pressure cut off switch, and by moving around the car to the rear last, you re-center the switch.

This gets argued about a fair amount. Others have done it the more common way of farthest to closets and said it worked. I can't judge their success.

No matter what path you do, verify that both circuits work by simply having the car up on jacks, and have somebody depress the pedal. Even with the car off, the brakes will work, just require a little more effort.

After you drive the car some, the rear brake shoes will self center, and you may have to readjust them to get the right amount of drag. On odd occasions after you drive a little, a rear shoe may drag some if you have it too tight. Generally this will be obvious, and you might hear the shoes chatter a little at higher speeds. If so, then back that side off one click and see how it behaves.



1974-1/2 Roadster, "Bumble Bee", Corvette Yellow - in shambles, wire wheels
1976 Roadster, "Virus", Sandglow - "driver" condition (stock + 32/36 Weber DGEV, cast iron header, 25D distributor), bolt on wheels, ON the road!

flipton Avatar
flipton Fred Lipton
Philadelphia Area, PA, USA   USA
1976 MG MGB "Godfrey"
This is all good, planning ahead. I have to finish the left front and rear wheels before tackling the MC's and fluid lines. At the pace I'm going it'll be a couple or three weeks to finish those wheels so there'll be a hiatus before my next update.

Btw: the calipers I acquired via Basil Adams are marked L & R so there's no mistaking which caliper fit which wheel.

I can't say enough how much I appreciate this forum's support. Without all you folks [and John Twist youtube vids] I'd never be able to do this.






Suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself...Mark Twain


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jseabolt Avatar
jseabolt James Seabolt
Mount Carmel, TN, USA   USA
1977 MG MGB
In reply to # 3886901 by MGB 1976 Brake lines run from the master cylinder across to the right side, then to the rear axle on the right side, then splits to the rear wheels. The longest run is the left rear wheel. Left and right are determined always from sitting in the driver's seat. Left = driver's side.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/1975-80-mgb-dual-line-servo-assist


I've been told (by a good source) I have to remove the wiring from the pressure failure switch #41 on Moss catalog page below and remove the switch from the master cylinder (found underneath, screwed into body) while bleeding to allow a shuttle inside the MC to travel fore and aft to to allow it to self-center. Otherwise it is possible that you could have only front or rear brakes if it is not centered. I'm going to be bleeding my 1976 this weekend (hopefully), and have my shop manual open.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/dual-line-servo-assist-brake-master-cylinder-1974-5-80

I'm glad I read this thread. I just got through doing a major brake overhaul on my MGB and put the driver's side rear brake back on the other day but ran out of time to bleed the brakes.

This is the first time I've even heard of this switch. I've never even paid any attention to it. So I looked up it's purpose.



Before I start digging through all the threads regarding this switch, does this switch serve any other purpose other than to kick the warning light on the dash?

So lets say you hit the brakes hard and the rear brake hose busted. Because of the differential pressure in the lines, the pin moves in that direction and shuts off fluid to the rear brakes so you don't loose any fluid?

After I bought my Citroen 2CV, I noticed a button below the windshield wiper switch. When I'd press it, it would kick the low brake fluid light on. I asked what the deal was. Apparently in France, there is a law that cars must have a button to test the light for the low brake fluid indicator! Just to make sure the bulb is not blown. That's all it does.

I check the brake fluid in my cars every time I check the oil.



http://s222.photobucket.com/user/turbofiat/library/?sort=2&page=0

1977 MGB
1980 Fiat 124 Spider (turbo)
1987 Yugo (1500 turbo)
1981 Trabant 601
1987 Citroen 2CV
1968 Ford Fairlane 500



Edited 1 time(s). Last edit at 2019-02-09 11:23 AM by jseabolt.

jseabolt Avatar
jseabolt James Seabolt
Mount Carmel, TN, USA   USA
1977 MG MGB
In reply to # 3887436 by BumbleB74 Fred - It gets discussed and argued from time to time, but the Haynes manual is specific about the late cars with the power boosted brakes. I haven't read it in a while, as I did the brakes on my '76 about 2 1/2 years ago, but I had to follow that procedure to NOT trip the pressure failure switch in the MC. If memory serves you unscrew the switch far enough to not have contact with the sliding shuttle in the MC. Pretty sure you started at the drivers side front and worked around clockwise looking down from the top of the car, and finished at the left rear. Left and right is always referenced from sitting in the driver's seat.

I didn't bench bleed mine, but used a simple power bleeder that has been discussed on here quiet a bit....basically made from a clean/new pump up sprayer you use for spraying weeds in your yard. You don't need much in terms of PSI to push fluid through.

Once you are done, if you have the car up on jack stands, it is easy to have a helper push the brakes (even with the car off) and try to turn a front and a rear wheel by hand to judge if both circuits are active.

One last note, always clean up any drop of spilled brake fluid right away. I just keep a bucket of soapy water handy with a rag or paper towel in it. This is VERY true if you are using DOT 3, it will strip paint.

I'm planning on building the same contraption out of a $9.00 1 gallon pump sprayer. I have all the bits and pieces, I just have to put it together. You can buy these already made up for around $60 but why?

I've been using my Gunson Easy-Bleeder for years on various cars and it works well but leaks like hell.

I end up having to wrap Teflon tape around threads on both the bottle and the master cylinder cap despite both having gaskets and it still leaks! I usually wrap some rags around the master cylinder and bottle to soak up any brake fluid that might leak past the caps.

Anymore than 5 lbs, otherwise fluid will start spraying out.

I bought this Gunson system while in the U.K. back in the late 90s and one of the caps just so happens to fits the MG reservoir perfectly. Maybe it fits other British cars. So no need to buy a spare cap and drill out the center.

A friend of mine warned me against pressure bleeding brakes on an MGB but if I did not to go more than 3 lbs. He said he did this on his 71 model and the reservoir exploded! I don't know how much pressure he was using. Maybe his tank had a crack in it. I'm going to lay several bath towels over mine and around it just in case.

He recommends using a vaccum bleeder. I bought one of those Mitey-Vacs ages ago to bleed the brakes and never had much luck with it. But the Gunson system works better than having a second person pump the brakes. It's just the bottle they supply is doesn't seem to hold enough fluid to generally do all four brakes and it leaks.



http://s222.photobucket.com/user/turbofiat/library/?sort=2&page=0

1977 MGB
1980 Fiat 124 Spider (turbo)
1987 Yugo (1500 turbo)
1981 Trabant 601
1987 Citroen 2CV
1968 Ford Fairlane 500

dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
So lets say you hit the brakes hard and the rear brake hose busted. Because of the differential pressure in the lines, the pin moves in that direction and shuts off fluid to the rear brakes so you don't loose any fluid?

No. All that happens is that the shuttle moves off-center, activating the plunger in the warning light switch and turning on the brake warning light on the dash. It is moved by pressure differential, but performs no hydraulic function...

Dick





In reply to # 3888509 by jseabolt
In reply to # 3886901 by MGB 1976 Brake lines run from the master cylinder across to the right side, then to the rear axle on the right side, then splits to the rear wheels. The longest run is the left rear wheel. Left and right are determined always from sitting in the driver's seat. Left = driver's side.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/1975-80-mgb-dual-line-servo-assist


I've been told (by a good source) I have to remove the wiring from the pressure failure switch #41 on Moss catalog page below and remove the switch from the master cylinder (found underneath, screwed into body) while bleeding to allow a shuttle inside the MC to travel fore and aft to to allow it to self-center. Otherwise it is possible that you could have only front or rear brakes if it is not centered. I'm going to be bleeding my 1976 this weekend (hopefully), and have my shop manual open.

https://mossmotors.com/mgb/brakes/brake-master-cylinder-hydraulics/dual-line-servo-assist-brake-master-cylinder-1974-5-80

I'm glad I read this thread. I just got through doing a major brake overhaul on my MGB and put the driver's side rear brake back on the other day but ran out of time to bleed the brakes.

This is the first time I've even heard of this switch. I've never even paid any attention to it. So I looked up it's purpose.



Before I start digging through all the threads regarding this switch, does this switch serve any other purpose other than to kick the warning light on the dash?

So lets say you hit the brakes hard and the rear brake hose busted. Because of the differential pressure in the lines, the pin moves in that direction and shuts off fluid to the rear brakes so you don't loose any fluid?

After I bought my Citroen 2CV, I noticed a button below the windshield wiper switch. When I'd press it, it would kick the low brake fluid light on. I asked what the deal was. Apparently in France, there is a law that cars must have a button to test the light for the low brake fluid indicator! Just to make sure the bulb is not blown. That's all it does.

I check the brake fluid in my cars every time I check the oil.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
In reply to # 3888509 by jseabolt 1) does this switch serve any other purpose other than to kick the warning light on the dash?

2) So lets say you hit the brakes hard and the rear brake hose busted. Because of the differential pressure in the lines, the pin moves in that direction and shuts off fluid to the rear brakes so you don't loose any fluid?

1) Yes this switch is completely electrical.

2) No! Simply take a look at the master cylinder reservoir, you will see that there is a divider in this reservoir for either the front & rear brake system.

B



Check your ego Amigo!

jseabolt Avatar
jseabolt James Seabolt
Mount Carmel, TN, USA   USA
1977 MG MGB
In reply to # 3888631 by dickmoritz So lets say you hit the brakes hard and the rear brake hose busted. Because of the differential pressure in the lines, the pin moves in that direction and shuts off fluid to the rear brakes so you don't loose any fluid?

No. All that happens is that the shuttle moves off-center, activating the plunger in the warning light switch and turning on the brake warning light on the dash. It is moved by pressure differential, but performs no hydraulic function...

Dick

OK. When I got to reading on this subject, it lead me to believe this valve also functioned as some sort of safety valve.

I don't know if this makes any sense or not.

From what I thought, if you bleed the brakes in the typical order : PR,DR,PF,DF, pressure can force the shuttle past it's normal travel and stay there (say if the front lines were void of any fluid) and then not allow you to bleed the front brakes. I'm just trying to get an understanding why it matters which end to bleed first. Is there a stop/limiter inside this brake union which makes it OK to bleed the brakes at the front first but not the rear?

I don't want anybody to think I'm hard headed and I'll do it my way. I'll do whatever way it's supposed to be done.

I have replaced all the brake hoses, rebuilt the front calipers and replaced the rear wheel cylinders,and shoes (among other things) so all the lines on my car are basically void of any brake fluid. So I'd rather not be scratching my head as to why I can't get any fluid out of the brakes when I go to bleed them. A similar scenario would be if you don't support some RWD cars equipped with proportioning valves with jack stands under the axle instead of the chassis, when the rear suspension hangs the proportioning valve will shut off flow to the rear brakes and prevent proper bleeding. If you were not aware the car was equipped with such a device.

Concerning this switch:

It was mentioned to remove the switch or back it out three times before bleeding so as not to trip the switch. Is this a "one time switch"? Meaning it's not spring loaded and once it trips, you have to replace it?

Looks to me if the switch was backed out, when you start charging the system, fluid would leak past the threads of the switch. This is providing the O-rings on the shuttle are OK. From one thread that I found doing this search, someone mentioned brake fluid was leaking from the switch because the O-rings on the shuttle had failed. So as long as the O-rings are good, this shouldn't happen?

I haven't seen this mentioned but is there any harm in just removing the shuttle from the brake union? My fear would be it could possibly stick in one position. I guess as long as the braking system is OK this may not ever happen.

My next assumption would be the plastic body switch would now be exposed to excessive pressure when the brakes are applied and could blow. Some people mentioned using a bolt in place of the switch but so far I have not read anything about also removing the shuttle.

This car being the mechanical basket case it is, it wouldn't surprise me if I found something else wrong with the brakes. Like the O-rings on the shuttle being worn out. I have never seen the brake light come on the dashboard.

I actually bought this car based on the overall condition of the body and interior. It didn't have any brakes when I got it. Well sort of. Before I started working on it, the pedal would go to the floor. I could pump the brakes up a bit but then the rear brakes would lock up (in my driveway). But bleed off after awhile. The rear hose was swollen and must have been acting as a check valve. Once I got into inspecting the other braking components, I found allot more than I bargained for. The master cylinder could be bad as well. I first want to give it a shot before replacing it just for the heck of it. A friend told me if I had a good working master cylinder to keep it because some of the replacements are not worth squat.



http://s222.photobucket.com/user/turbofiat/library/?sort=2&page=0

1977 MGB
1980 Fiat 124 Spider (turbo)
1987 Yugo (1500 turbo)
1981 Trabant 601
1987 Citroen 2CV
1968 Ford Fairlane 500

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