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MG Midget and Sprite Technical - Rear brake adjustment

Has anyone out there got a good method for adjusting the rear brakes?
Recently it was pointed out to me there was too much pedal travel before my brakes started & as I had the system blead professionaly recently was advised the rears needed adjusting.
Have done this a few times before so did it again. After about 5 miles the drums were fairly hot so pulled over to level ground and eased off. Another 5 miles & had to repeat. After about 20 miles the offside shoes started to cook - wisps of smoke/smell of burning/& too hot to touch drum. Backed off further and nursed home.
Today I have romoved both drums checked all the springs & cleaned all components on both sides. Both drums look good and round. However, I find if I back off enough to prevent overheating of the drums then I get back to where I was with the pedal travel.
3 points: to mention:-
1.The adjuster screw on the offside goes further in to the adjuster on the nearside and loses it's click stop.
2.The cylinder on the nearside is very slightly loose.
3.I find it difficult to judge when adjusting what is resistance/noise from the transmission & what is the drums binding slightly on the shoes. Would disconnecting the prop help?
Thanks.
GN Rowles

do the shoes return properly?(hydraulics)
are they fitted the right way around?

you should not have to disconect the propshaft to adjust your brakes.

could you take us through your way of adjusting the brakes?
Onno Könemann

Maybe the shoes aren't centered to the drum.
Lock the shoes / drum by over adjusting and hit the drum on the circumference with a plastic hammer, they will come loose again. Repeat, also with handbrake on until satisfied.

First check if the handbrake leavers aren't to far adjusted, otherwise loosen them.

If the adjusters goes too far in something is worn. Measure inner dia of the drum and check shoes and the two adjuster thingies.
Alex G Matla

Secure the cylinders with a screw instead of the roll pin & check your drums for roundness. If the adjusters are worn, then change them, they are cheap enough.
Disconnect you hand brake, adjust the drums first then refit the hand brake.
I've always had problems getting the hand brake right & in the end made the longer rod adjustable.
Brad (Sprite IV 1380)

Have you checked the inside diameter of your drums? If they have been skimmed you will never get a good pedal, it usually shows up by the shoes wearing rapidly at one end.

Carl
C Bintcliffe

I find that the position of the adjuster needs to be set very precisely. Using a proper square ended brake adjusting spanner just a few degrees one way or the other from the centre positon on the flat of the adjuster will cause the shoes to bind. I usually deliberately overtighten, then back of the adjusters 2 or 3 flats. It also helps to stamp on the brake pedal at intervals to centre the shoes properly. Even so I still find that when adjusted I still have to compromise betwee dragging shoes and too much pedal movement.

However I wonder if in your case the dragging / overheating shoes may be due to deterioration of the flexible rear brake hose. That would prevent the shoes releasing again after being applied.

Guy
Guy Weller

Growing up working with my dad on cars during the 50's and 60's we did a lot of brake jobs and adjusting brakes was routine. One of the basic things was to make sure the arc of the shoes matched the arc of the drum. In those days shoes could be purchased in usually three different arc sizes as needed (thicker linings made larger arcs). And if the shoes were taken to be relined the drums were usually also taken with them so the drums could be turned and/or the shoes could be arced so they would match.

Was not quite as much of a problem if the shoes had a slightly larger arc. They still would need to be adjusted more often as they would wear in faster due to there being less contact on just the heal and toe of the shoes in the beginning.

Having shoes with a smaller arc than the drums was a little more problematic. When adjusted so they would not rub they would require more pedal and the pedal would be somewhat spongy. The reason is that the high part of the shoes would make contact first and the pedal pressure would force the shoes to flex until the shoes made full or close to full contact.

I am not saying this is the problem here but it is a basic thing to check before installing new shoes.
tomshobby

One thing you might want to think about is the rear brake hose. Sometimes they break down inside and they will let fluid in but slow to let it return the the master cylinder. Are the wheel cylinders sticking perhaps?

Maybe not the solutions but something to consider.
Clive Reddin

motorcycles with drum brakes use this trick to match the shoes to the drum: spray tack adhesive some sand paper to the inside of the drum and use it to sand the new shoes to match the shape.

Norm
Norm Kerr

Make sure your slave cylinder is able to float, so that t can align properly when you press the pedal.

A
Anthony Cutler

Anthony - that's an interesting point.

I like many others chose to fasten the cylinders with a set screw in place of the roll pin. Mainly because they were "floating" to the extent that the rubber dust seal cover was wearing away on the drum. But I do find that when adjusted to their optimum setting, there is still a little uneven dragging on new shoes. It usually wears itself away pretty well as the shoes adjust to their new home.

But now you have said that, I can see that the sloppy fit of the cylinder is perhaps not a design flaw but an important and intended attribute!

Guy
Guy Weller

For 2 seasons in my race car I had real issues similar to you. Tried everything; new drums, shoes, cylinders etc. and eventually fixed the problem with new adjusters. The old ones looked fine but obviously were not. Nice and cheap/quick fix as well.
John Collinson

Guy

I got hold of an engineering book that described the design of the drum-brake system in detail, incl analysis of forces etc that was much more complex that I was expecting.

The position of the elements of the system is much more finely designed that I previously thought, and the servo effect depends on minute/correct positioning of the various elements.

After seeing this, I assume the s/cyl was designed to float; after all, Lockheed (or whoever) could have specified a bolt-on s/cyl had they thought it desirable.

And I know I can fit a circlip faster than anyone can engage/tighten a bolt!

A
Anthony Cutler


Lots to ponder here thank you.

I have centre the shoes by breaking hard 4/5 times on the pedal. I will obtain some new adjusters.

If the shoes are making irregular contact (my guess) with the drums it could be the drums are not true despite use of No1 eyeball. Will try swapping the drums to see if this helps proove the case. If so, I'll get new drums & hope this works.

Will disconnect the handbrake when doing the work.

All the flexible brake hoses are braided & replaced less than 5K miles ago.
Gavin Rowles

My drums where round but made an irregular contact with the shoes because I could not centre the drums. The inner circle witch normally just fits the hub was too large. I could feel the irregular braking if I turned the wheel by hand (car on axle stands) while somebody was braking very gentle.
Changing drums helped a lot

Flip
Flip Brühl 948 frog 59

hey guys (and gals),

for those who hate the E clip that comes with rear cylinders (and who doesn't), I did a bit of research and found retaining rings and spring washers that are very close to the original factory ones, and as a bonus, are available in stainless:

Grainger #5DA81 = 11/16" external retaining ring, stainless steel. $12.94 (10)
Grainger #6ZA12 = 11/16" wave washer (3 wave), stainless steel. $16.42 (10)

Because they are only available in packs of 10, I now have enough of them to last me for 100 years (at the rate that I replace my rear cylinders).

To prevent galvanic corrosion (stainless vs. cast iron and steel back plates) coat everything well with copper grease / anti-seize compound. Or, buy the plain steel ones and do the same, and probably get the same result, if you use enough of that goop coating it!

Here is a link to Grainger (there is surely an equivalent kind of commercial supply company in the UK):

http://www.grainger.com

Brown and Gammons USED to sell these parts, but even they are now listing them "NLA", so I found them commercially.

cheers!
Norm
Norm Kerr

Whats the problem with the clip you push it on or prise it off. I've never had a problem with them, but then i may have engineers solid no feel fingers.
Brad (Sprite IV 1380)

Strange to some as it may seem, I use both the E -clip (which I find quick and easy to fit) and a locating set screw. The latter was to just keep the cylinder in place and prevent the rubber dust seal from wearing away on the rotating drum. Reading Andrew's explanation about floating cylinders and the self-centering effect I am not so sure that mine were too loose in the first place.

It may be that the problem is simply that the dust seal on the "pattern" copy cylinders is just badly produced and is too bulky.

Guy
Guy Weller

Everyone seems to be focusing on the rear brakes. The original problem was too much pedal travel. If the rears are binding the problem is probably with the fronts.

As for adjusting the rears, if the adjusters are good and the shoes centred (one hard stab on the pedal) I have always found doing them up until they lock then backing off one flat always works fine.

Trev
T Mason

One thing that hasn't been mentioned and regularly tricks me if I'm not absolutely thinking 100% is that the nearside handbrake rod can catch on the exhaust pipe with the car is jacked up and sat on axle stands under the sill. I have to take the tension off the nearside bu jacking the axle up a little bit so it releases the rod.

I've done more rear brakes and then wondered why they weren't right too many time, but as I said, even now it still catches me out occasionally.

Andrew
Andrew McGee


More intersting ideas & comments here thanks folks.

For the moment I'll concentrate on the drums - new ones ordered together with adjusters, springs, & shoes.

Will watch out for the cable snagging thing.

If I need new calipers that will be the next step - bleeding is such a bleeding pain in my experience.

Gavin.
Gavin Rowles

This thread was discussed between 31/05/2010 and 02/06/2010

MG Midget and Sprite Technical index

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