Balancing caravan brakes - driving me slightly insane.

[FullEnglish]

Hi all,

Van is a Sprite Alpine 1964.

I took the brakes apart, derusted, checked the springs, shoes etc, and reassembled them as all the parts were good. Balancing them took ages, as they were fine until I activated the brakes a few times, whereupon they were out of balance again and I had to start over. I finally got them right, took the caravan for a test run of a few miles, and found out that one brake drum was really hot and was dragging. Balanced them *again* (last night), took the caravan to be inspected (like an MOT) only to have it fail on brakes - out of balance. One side now has twice the effect of the other side.

Does anyone have any idea how to go about adjusting the brakes so that they STAY correctly adjusted?

All ideas greatly appreciated!

Cheers.

[FullEnglish]

The rain stopped. Finally. Briefly.

Jacked the van up, and the brakes are indeed still balanced.

The inspection showed that one side has half of the braking effect of the other side. The brake shoes were whole, undamaged and had plenty of meat left when I inspected them, but I'm supposing one side must be glazed/contaminated.

Is it possible to get away with sanding down the pads and cleaning the inside of the drum? Although they are at least 20 years old, and possibly original to the van (1964) so could well be asbestos.

I'd change all four of them for the sake of it, but finding new ones can't be the easiest thing in the world.

As you might have guessed, I know naff all about drum brakes...

[outnumbered]

is this off any help.
http://uk-trailer-parts.co.uk/adjusting-knott-brakes
mike

[rogerthechorister]

Back when I was a Morris Minor man we regularly used to sandpaper off glazed shoes, and clean them off with petrol too if they had been contaminated with grease. We were bold in those days!

[FullEnglish]

Mike; my system is older than the ones described in your link, but thanks for posting, I appreciate it.

The rain stopped again (it's actually a beautiful summers evening now) so I took the "bad" side apart. As I suspected, it was beautifully glazed. I decided I was probably immune asbestos dust due to the protective properties of caffeine and nicotine and filed the surfaces until they were nicely, er, deglazed.

I then took the "good" side apart, to do the same thing so I had shoes that were in the same condition on both sides. The "good" side was also quite glazed. So I don't know if my braking imbalance will remain, albeit with more braking effect over all. Trouble is, I don't have a brake testing machine (although I do have a cunning idea to make one).

Of course, if I'd known anything about drum brakes I'd have spotted the glazing first time round. One learns. Sigh.

I've reassembled everything and now even with the adjuster slackened right off, the brakes are dragging a lot. I suspect I need to drive over some potholes to allow everything so settle into its proper place and then adjust again.

rogerthechorister, I actually used your petrol trick as I couldn't be bothered to drive into the village and buy brake cleaner.


Of course, if all else fails, I'll just add a smear of grease to the "good" side. What could possibly go wrong?

[BugEyed]

Originally Posted by FullEnglish

Of course, if all else fails, I'll just add a smear of grease to the "good" side. What could possibly go wrong?

Nothing!

Coming from the other era of technology (20's and 30's drum brakes) I'd also check whether the drums are dished. Most drums are pressed from flat sheet and when heated (dragging brake for example) they start reverting to flat. Then the inside of the brake shoe is all that is engaged and hence efficiency drops off dramatically. The only solution is to skim the drums or replace them.

Most van shoes are from car parts so can be replaced cheaply.

Good luck.

Duncan

[FullEnglish]

Originally Posted by BugEyed

Most drums are pressed from flat sheet and when heated (dragging brake for example) they start reverting to flat. Then the inside of the brake shoe is all that is engaged and hence efficiency drops off dramatically.

My drums are cast, no doubt about it. I cleaned the glazed surface off the shoes with a large flat file, which revealed that the middle of the friction surfaces were in fact lower than both outer edges. They're completely flat now (which clearly won't help them to make full contact, but I had no choice).

Cue cunning plan to make a brake testing aparatus.

Basically, without a brake testing machine, I can only verify the point at which the brakes start to engage. After the point at which I can no longer turn the wheels by hand, I have no way of verifying if the brakes continue to engage progressively by equal amounts. I got the van jacked right off the ground, and bolted on the spare wheel, which has slots around the rim. I pulled the handbrake on as hard as I could (thereby simulating around 60% braking effect) and attached one end of a large ratchet strap into a hole exactely at the bottom of the rim and the other end of said strap to the end of the under-floor frame. I took up the slack in the strap, then counted the clicks until the ratchet strap had enough tension to start to rotate the wheel against the force of the brakes. I then swapped the wheel and ratchet strap over to the other side and repeated the procedure. One side has around twice the braking effect of the other.

This is both good and bad, bad becasue my brakes are still hopeless, but good because I've confirmed that my homemade ratchet strap test produces roughly the same results as a 200,000 kronor brake testing machine.

Plan for tomorrow is to work backwards from the hitch to the shoe actuator and verify that the actuator is getting the same amount of input on both sides (the cable mechanisim is primitive and wobbly, to say the least). Then tow the van around for a bit to bed the shoes in, and retest.

Out of interest, do drum brakes produce the same braking force forwards and backwards?

It's a bugger trying to get 100 old French technology that was manufactured in the 60s to work to 2014 standards...

Thanks, as ever, for all the input and suggestions.

[Orca2]

It is interesting that you have an MOT for caravans, I don't think we have any real testing of caravan or trailer brake systems in the Uk. At least not that I have ever heard of. Which presumably means anyone towing a British caravan on holiday to Sweden might have problems in the event of an accident.

[FullEnglish]

Originally Posted by Orca2

It is interesting that you have an MOT for caravans, I don't think we have any real testing of caravan or trailer brake systems in the Uk. At least not that I have ever heard of. Which presumably means anyone towing a British caravan on holiday to Sweden might have problems in the event of an accident.

If the outfit is legal in the UK, it'll be legal here, even without the inspection, becasue it's not necessary in the UK. I'm not one for eccesive regulation really, but I always wondered why you could attach wheels to a bedframe and tow it on public roads in the UK. I understand that's starting to change now though, and certainly in the future an MOT and insurance will be mandatory. I pay £40 per year insurance on the caravan, sadly in the UK it's likely to be a far, far higher amount.

I've been looking around the internet today in my (fruitless) search for brake components, and I've stumbled upon such gems as "the axle on my caravan was rusted through, I didn't know about it, but it was ok as the brake cable held the wheel on..." Stuff like that scares me.

[60041]

Have you checked all the cables?
Normally the brakes have a compensator in the linkage that allows an equal pull to either cable and, as you have explored all the other obvious possibilities, I would start to suspect that you have a dry or rusted cable on the bad side.
Regarding your other question about whether the brakes are as effective in either direction of rotation: it depends on the design of the brake.
If the shoes are identical then, in theory, the braking force should be the same; but often the shoes are different and one will have the friction material cut short, or the material will be placed closer to the fulcrum end on one shoe than on the other. You can also get Twin Leading Shoe brakes which are much more efficient in the forward direction than in reverse; these are identified by having two actuators in each drum. They are quite common on drum braked cars and motor cycles, but I have not seen them on trailers.
As your 'van is 1960's it will not have an automatic reverse device in the drum; later ones cannot be braked in reverse because the mechanism allows the actuator to release the brakes when the wheel turns backwards.