New Brake Drums - Poor Friction!

[chrisrichards]

Hi All,

Firstly, let me introduce myself as a "newcomer" to the message board. For the record, I've driven my current 1968 Traveller for 20 years, and I do all the necessary DIY work on it - except for the steering and welding, which I leave to the experts!

For various reasons, I need to improve my braking performance. My local MOT inspector thought it didn't come up to scratch at my annual test recently. I thought it was OK, and could do an emergency stop. True the shoes were aged, but they mated well with the old well-polished drums. OK there were some score marks on their insides, and the rear drums kept exfoliating layers of rust every year!

I decided to fit new drums and shoes all round a week ago. The front drums arrived by mail order conveniently greasy! A good swab with petrol soaked paper towel, and a follow up in a bowl of hot water, with washup liquid, got them scrupulously clean again.

The problem is there was so little friction. I had to stamp on the brakes just to bring the car to a halt on the white line at the end of my residential road! I know brakes need to bed in, but this seemed odd. I notice the MMOC Technical Manual boasts that "you will be amazed how good a set of new Moggy brakes are". I'm waiting to be amazed!

Has anyone fitted new drums recently, or experienced similar problems? Do the drum surfaces need roughening up, or polishing, before use? I note the insides are certainly not a mirror finish. If anything, you can make out the machine milling marks if you look closely!

I've since driven 200 miles just to bed them in and they do feel better, but I don't fancy having to do an emergency stop just yet! The MOT awaits my return in the next fortnight too!

Helpful suggestions would be welcome! (I'm not replacing the old drums and shoes!!!)

Regards,

Chris Richards

[Alec]

Hello Chris,
I would look more to the new linings rather than the drums, (I'm assuming that you don't have a low pedal) can you see the contact patch on the linings, after your 200 miles, to see whether there is some sort of misalignment problem? Could they be a high performance lining that may need a special bedding in process, such as getting them very hot by hard braking.

regards,
Alec

[Willie]

Got to agree with Alec, it will be the linings not the drums. The
drum friction surfaces SHOULD look shiney, do not' roughen them
up'!! 200 miles is enough for you to inspect the linings and see
where the contact with the drums has occurred and if it appears that
only a small part of the linings have been touching then you could
remove those 'high spots' to speed up the bedding-in process,or,if you
can find a quite stretch then you could try what I have done in the
past by driving with one foot on the brake and one foot on the throttle.
I dont know if your final wipe of the linings was with a petrol soaked
rag? I did this recently after renewing a front hub and the brakes
were awful ( I use unleaded). since I had done nothing to the brakes
I deduced that unleaded may be more 'oily' than our old petrol was??
When I wiped them again but with cellulose thinners they reverted
to their original efficiency. Any comments RAYof leamington since
you know about these things??

[Willie]

Having re-read your post it would seem that your brakes were not
good enough for the MOT man before you fitted all the new parts so
did it fail on foot AND handbrake readings? Is the pedal nice and
hard when you apply the brakes, is it better if you pump the pedal,
does the pedal go slowly to the floor if you keep pressing? How long
ago did you change the fluid? Did you have the handbrake cables
slackened right off before you adjusted the brakes?

[rayofleamington]

I've always had problems with new brake shoes and MOT's
In the past I've resorted to over adjusting the brakes (so they are permanently on) and using them for a week to get them bedded in.
Technically this is a BAD thing to do as they will be permanently hot (brake fade = unsafe car) and also it is a pain if you forget to readjust them as the MOT man then fails it on 'brakes dragging'
However there are times when I've been desperate - On one occasion I only had half an evening to bed in the brakes before the re-test and drove 50 miles with dragging brakes. I had to de-adjust them to stop the dragging and this left a very long pedal travel so I breathed a huge sigh of releif when I did get an MOT. After a few hundred miles everything was fine.
I guess the moral of the story is not to leave the sevicing until just before the MOT, but if the car comes with no MOT, then you need an 'understanding' MOT man who knows what a pain new shoes can be

[forbesg]

The front drums arrived by mail order conveniently greasy! A good swab with petrol soaked paper towel, and a follow up in a bowl of hot water, with washup liquid, got them scrupulously clean again.

I always burn off any oil on shoes with a burner. The linings spark slightly when all the oil is removed, and you can see the colour change.
I'm not sure that soaking them in petrol is such a good thing.

Regards

Grant.

[rayofleamington]

I always burn off any oil on shoes with a burner.

He was on a bout the new drums not shoes.
A lot of people degrease using solvents or fuel etc.. but if you need to remove all oil from metal parts then detergent is the right way, so I'm glad to see that was done (solvents only thin down the oil and spread it around so you remove most of it but not all)
For degreasing brake shoes... Many of us have probably done it at some time - I even got very good at freeing up (and re-using) stuck wheel cylinders on cars that have stood for decades - but now I'm old and dull I wouldn't recommend it.

[newagetraveller]

I always roughen up the drums and the shoes with coarse emery paper.

At least they work immediately and they also bed in quickly.

You don't then have to drive around for miles trying to bed them in while hoping that you don't have to stop quickly during the process.

The principle is the same as roughening up the inside of a cylinder bore when you fit new piston rings so that they bed in more easily.

(Glazebusting is the term I was trying to think of here.)

[rayofleamington]

newagetraveller,
Cheers for the tip - I'd never considered roughening the drums to help speed up bedding in new shoes but I may try that in future. (not very often in the near future though, as it takes a long time to wear out shoes when the car does barely a few thousand miles a year )

[chrisrichards]

Thanks all for your suggestions,

Several points have been made. Yes, Willie, I'll check the "hot-spots" on the linings when I get my car back from my local welder in a couple of days' time. I did a check on them after my initial test drive, and it was obvious a large area of the linings were not making contact with the drums. The handbrake cables were slack when I tightened the adjusters.

Ray, I'll tighten the adjusters more. They probably need doing now in any case.

The previous brakes did fail the MOT. The inspector felt that resistance ought to be happening as soon as the free pedal distance had been taken up. Now, following advice in an earlier discussion this year on brakes, I tightened up all adjusters till the drums could not rotate, then measured the pedal travel. The pedal only moves an extra 1.5 to 2cm, when I push the pedal down by hand, then it remains firm. There is clearly a little residual air in the system so I re-bled it at the time. A little air appeared in the "Easybleed" plastic tube I use.

However, what is more worrying are the "pulses" of tiny air bubbles that suddenly appeared from the rear O/S nipple - in phase with the pedal strokes down to the floor. I need to check on the other nipples first before suspecting a faulty Master Cylinder. I only replaced it a year ago. I'll keep you posted!

Regards,
Chris

PS My location details did not appear on my original posting. It is West Kirby, Wirral.

[Alec]

Hello Chris,
the lack of full contact explains the poor braking. It used to be the practice years ago to put the relined shoes on a jig to grind them to the correct radius and remove high spots, so it seems that bedding in is the answer. The air issue is seperate and really unconnected to the lack of retardation.

Alec

[Willie]

erased

[Willie]

OH, bring back Carbon Tetrachloride! that would remove all traces
of grease or oil from ANYTHING. Its banned now unfortunately but
I thought RAY would know of a modern equivalent! I also used to boil
contaminated linings in TIDE washing powder that always worked too!

[ColinP]

Erm,

Hammerite thinners?

Colin

[Willie]

Never used it, you think it is a good sustitute?

[Pyoor_Kate]

OH, bring back Carbon Tetrachloride!

I bought an old can of brake cleaner a while back from a bike-factor... I was so pleased to get carbon tetrachloride that I went back the very next day to see if I could get more... it appears that was the last can, which is disappointing (if anyone was going to get to release the hideously environmentally damaging stuff into the atmosphere I could think of no-one better than me ).

The new stuff's just not as good.

[forbesg]

He was on a bout the new drums not shoes.

Opps, must have missed that bit.

-Grant

[ColinP]

Willie,

Some time ago I used the Hamerite thinners, and I reckoned that they smelt of di-chloromethane. i.e. Cl2H2C; Carbon tetrachloride is Cl4C,
so it's similar.

However, the Montreal protocol has removed a lot of these compounds from the market, so we may have to end up using things like paraffin, detergent.

Most greases are long chain hydrocarbons (with additives!), so they will dissolve in shorter chain hydrocarbons (like toluene, benzene, petrol). However, some of the commercial solvents (petrol) do have other bits in which have to be removed by another one....

Colin

[galaxie390]

Hi Colin,

You reminded me of days studying Chemistry (a while back!!)

the Di-chloro:

Could you remind me: Carbon12 Hydrogen 2, what was the last C???


Sorry to get off topic folks, but curiosity got the better of me.

Rich

[ColinP]

Rich,

The perils of plain typing!

Read the formula as "Cl" x 2 ; "H x 2"; C
That's two chlorine atoms, two hydrogen attached to one Carbon atom (four hydrogens & one carbon is methane - take off 2 H's, add two Cl and you have di choloro methane).

For the other, "Cl" x 4 and 1 carbon = tetra chloro methane (or carbon tetra chloride)

This type face doesn't show the difference between "l" - lower case L, and "1".
Oh yes it does . £$&%^(%!

Colin