Trailer brakes

[JonC]

16 minutes ago, Andy135 said:

Yes to slack, yes to brake lever being off, yes to centralised shoes. I'm scratching my head as to what else to try other than removing some of the linings.

They are definitely the correct parts? I know it’s a silly question but suppliers do fuck things up. 

[Andy135]

16 minutes ago, JonC said:

They are definitely the correct parts? I know it’s a silly question but suppliers do fuck things up. 

It's a fair question but everything looks the same as the old stuff that came off.

[GPSguru]

37 minutes ago, Andy135 said:

It's a fair question but everything looks the same as the old stuff that came off.

I was going to suggest that it is the wrong shoes.

What axle have you got  ? .......Alko, Knott, BPW ? . if it is indespension it is probably a mix of all of them !

Edited April 19, 2021 by GPSguru

[Andy135]

1 hour ago, GPSguru said:

I was going to suggest that it is the wrong shoes.

What axle have you got  ? .......Alko, Knott, BPW ? . if it is indespension it is probably a mix of all of them !

Alko 2051

[GPSguru]

7 minutes ago, Andy135 said:

Alko 2051

200 x 50 shoes.

Used by indespension,  Ifor williams, and a whole host of others.

2050 & 2051 shoes are the same, so I doubt they are wrong.

But, something is not right ............ is the adjuster backed hard off ? Are the shoes centralising ?

And most of all, have you fitted the auto reverse cam correctly ? ......... if you haven't, the shoes will be in the reverse braked position and the drum will not fit.

 

[Andy135]

2 minutes ago, GPSguru said:

And most of all, have you fitted the auto reverse cam correctly ? ......... if you haven't, the shoes will be in the reverse braked position and the drum will not fit.

I didn't remove the auto reverse cams when I removed the brakes, so they're still in the same positions they were before the brakes were removed a few seasons ago. They still move ok but are fairly corroded.

However, I believe the brake coupling is currently in the compressed (reverse?) position. I suspect it's stuck in that position. Not sure if this is relevant?

[JDP]

14 hours ago, Gordmac said:

What operates the disc brakes on the trailer? When they started fitting disc brakes to cars they had to fit servos to get the pedal force down.

Galvanised break callipers, with cables to a piston that moves and pulls the breaks when you break, much like drums . Like suzook mentioned though, the disk that comes in contact with the pads will get a light coat of rust. However spraying the breaks with saltaway or any other saltwater remover stops this and gives a coating to stop rust. Also if you dont use any of these cleaning products, simply using the breaks removes that coating of rust very quickly. Ive only ever needed to replace disk pads and cables in the last 20+ years of towing boats this side of the pond. My boats in the UK didn't have braked trailers but in saying that most were on moorings.

We also need to have Ellectric break away breaks that will break the trailer if it comes unattched from the tow vehicle but only in rigs over 2 tons.

[GPSguru]

1 hour ago, Andy135 said:

 

However, I believe the brake coupling is currently in the compressed (reverse?) position. I suspect it's stuck in that position. Not sure if this is relevant?

Yes, that is why the shoes don't fit.

In the compressed position the trailer brakes are applied, via the rod and cables. You need to pull the coupling completely forward and make sure the cables are not seized. The cable equaliser should sit square. If it is pointing to one side when the coupling is forward then that side cable / brake is not moving freely.

When the coupling is uncompressed there should be a 3 - 5mm gap at the coupling end that operates the rod.

Effectively, right now, even with the adjusters backed off, it still thinks the brakes are on, therefore the drums wont fit ..............

Edited April 20, 2021 by GPSguru

[JonC]

So basically the problem isn’t the brakes or the new parts, it’s the guy who is trying to fit them doing it wrong?

I think we all suspected that from the start. 

[Andy135]

Just now, JonC said:

So basically the problem isn’t the brakes or the new parts, it’s the guy who is trying to fit them doing it wrong?

I think we all suspected that from the start. 

Lol, not quite, but nice try.

[Andy135]

4 hours ago, GPSguru said:

Yes, that is why the shoes don't fit.

In the compressed position the trailer brakes are applied, via the rod and cables. You need to pull the coupling completely forward and make sure the cables are not seized. The cable equaliser should sit square. If it is pointing to one side when the coupling is forward then that side cable / brake is not moving freely.

When the coupling is uncompressed there should be a 3 - 5mm gap at the coupling end that operates the rod.

Effectively, right now, even with the adjusters backed off, it still thinks the brakes are on, therefore the drums wont fit ..............

Thanks. Will see if I can free off the coupling. Might have to take it apart rather than use brute force given that the trailer is up on blocks.

[Gordmac]

9 hours ago, JDP said:

Galvanised break callipers, with cables to a piston that moves and pulls the breaks when you break, much like drums . Like suzook mentioned though, the disk that comes in contact with the pads will get a light coat of rust. However spraying the breaks with saltaway or any other saltwater remover stops this and gives a coating to stop rust. Also if you dont use any of these cleaning products, simply using the breaks removes that coating of rust very quickly. Ive only ever needed to replace disk pads and cables in the last 20+ years of towing boats this side of the pond. My boats in the UK didn't have braked trailers but in saying that most were on moorings.

We also need to have Ellectric break away breaks that will break the trailer if it comes unattched from the tow vehicle but only in rigs over 2 tons.

They are mechanically operated then. I wouldn't think you would get much braking with mechanically operated disc brakes without some sort of assistance. Is there a solenoid helping?

You see motorhomes towing cars, they must have some sort of legal way of operating the car brakes.

[JonC]

57 minutes ago, Gordmac said:

They are mechanically operated then. I wouldn't think you would get much braking with mechanically operated disc brakes without some sort of assistance. Is there a solenoid helping?

You see motorhomes towing cars, they must have some sort of legal way of operating the car brakes.

They are usually on an A frame,  I’ve never noticed any cables or hoses. 

[suzook12]

1 hour ago, Gordmac said:

They are mechanically operated then. I wouldn't think you would get much braking with mechanically operated disc brakes

There were a few bikes around in the 80's and on that had cable operated disc brakes, and can definitely say they were an improvement over drums. Obvious disadvantage would have been how difficult the arrangement would be for twin discs compared to hydraulic.

Back to trailers, an overrun brake uses the energy from the trailer to apply force to the brakes, so should be more than possible to apply adequate braking to each wheel as long as its matched to the right damper.

[Gordmac]

Legally the car being towed is a trailer and will need brakes to be legal if over 750kg. They generally run on their own wheels.

There is next to no weight in a bike, won't need a lot of force at the disco work compared to a trailer.

[suzook12]

11 minutes ago, Gordmac said:

There is next to no weight in a bike, won't need a lot of force at the disco work compared to a trailer.

You seem to have missed the point. The point is you don't need a servo, it's all about leverage and ratios.

A trailer wouldn't need servo assisted brakes becayse the trailer is the energy source. No overrun =No brakes required, if the trailer is pushng the tow hitch with 1 tonne of force, that's 1 tonne of braking force available as it is transferred via mechanical coupling to the brakes. As long as the damper is suited to the loads required it will work just as drum brakes do. Servos were around long before disc brakes were the norm....

[Gordmac]

What makes you say there is a one ton braking force? Not often you would be looking for 1g deceleration. Thing about levers is to get a lot of leverage you need a lot of movement. Drum brake normally have a self servo action on at least one shoe which increases the braking considerably. Servos did exist before discs but that made them necessary.

 

[Andy135]

11 minutes ago, Gordmac said:

What makes you say there is a one ton braking force?

As the vehicle pulling the trailer slows down, the weight of the trailer (and boat) moves forward and compresses the coupling damper to provide the energy required to activate the brakes. This is the force that Zook is referring to I think, which is why servos aren't necessary on trailer brakes. In effect the weight of the rig provides all the energy needed for braking and probably more. So not quite 1 ton of force at the brakes (drums couldn't do that) but 1 ton of force to activate the brakes.

[JonC]

1 minute ago, Andy135 said:

As the vehicle pulling the trailer slows down, the weight of the trailer (and boat) moves forward and compresses the coupling damper to provide the energy required to activate the brakes. This is the force that Zook is referring to I think, which is why servos aren't necessary on trailer brakes. In effect the weight of the rig provides all the energy needed for braking and probably more. So not quite 1 ton of force at the brakes (drums couldn't do that) but 1 ton of force to activate the brakes.

Tons being a measure of mass? Can we work in Newton’s of we’re talking about force please as it’s a different thing. 

[Andy135]

2 minutes ago, JonC said:

Tons being a measure of mass? Can we work in Newton’s of we’re talking about force please as it’s a different thing. 

Quite right. 9800-ish Newtons of force available for braking from 1 ton of mass being towed.

[JonC]

18 minutes ago, Andy135 said:

Quite right. 9800-ish Newtons of force available for braking from 1 ton of mass being towed.

Thanks, now I understand. 

[Andy135]

8 minutes ago, JonC said:

Thanks, now I understand. 

Happy to help 😉

[GPSguru]

1 hour ago, Andy135 said:

Quite right. 9800-ish Newtons of force available for braking from 1 ton of mass being towed.

Not quite that simple. The force applied is dependent on the inertia, i.e the faster the rate of speed decline of the towing then the inertia of the trailer is increased.

you need to draw up a vector diagram to see the full effect, as it is not linear.

[Andy135]

1 minute ago, GPSguru said:

Not quite that simple. The force applied is dependent on the inertia, i.e the faster the rate of speed decline of the towing then the inertia of the trailer is increased.

you need to draw up a vector diagram to see the full effect, as it is not linear.

Agreed but I have to keep it simple for Jon, remember. Frankly I'm surprised he's managed to read this far down the thread...

[GPSguru]

7 hours ago, Andy135 said:

Agreed but I have to keep it simple for Jon, remember. Frankly I'm surprised he's managed to read this far down the thread...

In its most basic form it is really just Newtons second law, which is F= m a.

However with a declining acceleration (retardation / deceleration) then the formula is more complex. I will post it up later.

Edited April 22, 2021 by GPSguru