Balancing caravan brakes - driving me slightly insane.

[volvorocks]

Is this any good? I am hopeless regards mechanical stuff, although why not telephone a touring caravan manufacturer and ask them?

http://www.ehow.co.uk/how_7851265_ba...ake-drums.html

Regards

[volvoid]

the EU recently rejected a German proposal to require testimg of all trailers under 3.4 tons. Seems we arent the only ones who dont need the Germans desire to control everything

[FullEnglish]

Originally Posted by volvoid

the EU recently rejected a German proposal to require testimg of all trailers under 3.4 tons. Seems we arent the only ones who dont need the Germans desire to control everything

I'm thouroughly in favour of a basic roadworthiness test. But it's beyond me why the Germans want to make other countries have one. If the Germans want a test, they can have one in Germany (as I'm sure they do).

Originally Posted by volvorocks

Is this any good? I am hopeless regards mechanical stuff, although why not telephone a touring caravan manufacturer and ask them?

Cheers Phil. I've mastered the dark art of adjusting, the problem is the adjustment system is just so primitive.

Anyway, I've removed all of the cables, cleaned and oiled them, and gone over all the linkages and added stainless steel washers where there was a ridiculous amount of play (which seemed to be in most places. UK caravan brake technology from the 60s just involves bits of metal randomly bent to sort of resemble brackets, couplings etc; holes may or may not line up from side to side).

The actuators on both sides now have exactly the same amount of travel (which they didn't before).

The thickness of the shoe friction material is the same to within 1,5 mm on all 4 shoes, so that bodes well.

Just need to find a towbar for the 740 so I can actually test the bloody thing. The previous owner removed it, but he did fit an LSD, so I guess we're even.

[FullEnglish]

Originally Posted by 60041

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.

Yup, reversing is a pain, there's a manual overrun lever that you have to get out and flip over. I do have a big 12v solenoid (an old diesel shutoff solenoid) which I'll wire in to the reversing lights to do the job for me when I get a chance.

Originally Posted by 60041

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.

Hmmm. Both shoes have have the friction material cut short towards the top of the shoe (away from the fulcrum end). But I have only one actuator. Are the shoes the wrong ones??

[gillberry]

Full English , our 1967 Cheltenham has a similar set up in that you have to put a stopper onto the main hitch to stop the brakes working when reversing which is ok when on site but a pain for a quick turn around . Glad to see another classic caravan still in use .

[FullEnglish]

Originally Posted by gillberry

Glad to see another classic caravan still in use .

I've turned mine into a mobile sauna

In my defence, the interior had suffered 10 years of water ingress and was way beyond salvagable. Better than being turned into a boat trailer, maybe.

[60041]

Originally Posted by FullEnglish

Both shoes have have the friction material cut short towards the top of the shoe (away from the fulcrum end). But I have only one actuator. Are the shoes the wrong ones??

No your shoes etc will be correct, the reason that the friction material is cut away at the fulcrum end is that this is the end that does the least work and the material would wear more quickly at the expander end of the shoe, making adjustment difficult.
Some other manufacturers brakes often have a small piece of material cut away at the expander end of the leading shoe as this helps prevent the brakes snatching on, but that is only usual on hydaulically operated brakes.

[FullEnglish]

Originally Posted by 60041

No your shoes etc will be correct, the reason that the friction material is cut away at the fulcrum end is that this is the end that does the least work and the material would wear more quickly at the expander end of the shoe, making adjustment difficult.

That makes perfect sense. Thanks!

[FullEnglish]

Went out to do battle with this again today. The brakes were binding, as they were after the last time I rebuilt the them, so I drove that van up and down a bit to free them off and let everything settle into place (which worked last time). Didn't work this time. Melted all of the bearing grease into the drums. Excellent.

I dismantled both sides again and adjusted the actuator (as opposed to the adjuster) so that I had an equal gap between the shoe and the edge of the back plate at zero adjustment. Now both sides spun freely with the brakes off. Progress, or so I thought.

Adjusted the brakes, tested at full braking effect with this setup...

[IMG]

One side still brakes twice as much as the other side.

Adjusted again, and again, and again, no change.

I swapped the drums side to side, no change.

I swapped the drums and the shoes side to side. No change, in fact worse.

All shoes are the same thickness (well, to within 1,5mm)

The cable moves the same amount (to within 2mm) both sides.

The actuator in the drum moves by the same amount both sides.

[IMG]

I'm trying to think of more components to swap side to side. All that's left is the brake wire, the actuators and the adjustors. The adjustors work, so I think I can rule them out. Somethings obviously not working as it should under load. I'm wondering if the wire is stretching on one side under load, as opposed to pulling on the actuator?

If I "twang" the wires, they resonate with the same note, which should mean they have equal tension.

I'm considering adding a tensioner to each wire to allow for individual adjustment.

4 days I've been at this now and nothing to show for it.

EDIT/UPDATERING: Brake cables swaped from side to side. No change...

[FullEnglish]

FIXED THE B*STARD THING!!!!!!!!

I was in the process of swapping over the actuators from the good side to the bad side to see if the problem followed. I decided to inspect both actuators while I had them out and compare them for differences, damage etc. I noticed that the tag (arrowed in pic bellow) was *slightly* bent. The bend was almost unnoticable, but it was causing the actuator arm to have 2mm less travel on the bad side than the good side. I bent it back, not feeling overly optimistic as the tolerances that I have observed in the braking system so far ran into meters rather than milimeters (OK, it's English, so furlongs rather than thousandths). Put it all back together and slap my **** and call me Judy, it worked.

[IMG][/IMG]

Note the expert use of Photoshop.

Sincere thanks to everyone who posted.

I still need to fine-tune the balancing and take it to clear inspection, but I have good braking effect on both sides now.

Never underestimate the determination of a man with a mobile sauna...