CAN MAC 26M BE BOUGHT WITHOUT THE SINGLE AXLE MAC TRAILER

Richard O'Brien · Post by **Richard O'Brien** » Tue Dec 14, 2004 5:42 pm

[quote="Moe"]

How does the coupler know the truck is pushing the boat back versus the boat pushing the truck.

The new trailer uses a 5 pin trailer connector, using the reverse light to disengage the surge break. If that fails there is a little metal "gizmo" to stick in the surge "gap"? to prevent it from collapsing.

Moe · Post by **Moe** » Tue Dec 14, 2004 5:48 pm

Thanks, guys. That's all I needed to know. There are some pretty steep roads going down to some of the ramps here. I'd like to have the option to back up if I had to. With my luck, I'd try to Tim Taylor it, put the diesel truck in 4WD low in reverse, and rather than slide the trailer tires back, bend the tongue.

Richard, the M coupler sounds like the ones I'm familiar with.
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Moe

Chip Hindes · Post by **Chip Hindes** » Tue Dec 14, 2004 6:40 pm

It's not the cylinder which "knows" that you're backing, it's the shoes. It has to do with where the shoe anchor pins are on the backing plates. When the wheels are rolling forward, the shoes are self energizing. When rolling backward, they're sort of self cancelling. They don't shut down completely, so they do "grab" a little, but not much. Normally, unless you have a really weak tow vehicle or are backing up a fairly steep grade, you can overpower them.

With discs, they lock up tight. Even without the boat, just the weight of the trailer locks them up so tight I can only back by sliding all four trailer wheels. With the boat on the trailer, I can't slide the wheels so can't back at all.

The idea of getting out of the truck and pinning the coupler every time I want to back, then getting out again to pull the pin so I have brakes when I go forward, is unacceptable.

Blocking solenoid, $34.95
Seven pin harness connector, $15.00
Backup light relay $18.50
Ability to back whenever I get the whim to do so, priceless.

PeteC · Post by **PeteC** » Tue Dec 14, 2004 6:50 pm

Chip,

Please post the setup for your "backup-brake-disabler" along with the details of your second axle mod when you get around to it.

Thanks,

Pete

Robert · Post by **Robert** » Tue Dec 14, 2004 7:29 pm

I used to do a multipoint turn to turn around on my driveway (including some of the lawn), which is steep, that involved backing the trailer. Also backing up a gravel road that was kind of steep. The trailer seemed to offer extra resistance backing up hill, but the trailer wheels always turned even on the gravel and lawn.
..
I did install the backing valve with the disc brake conversion.
..
Pulling to the side will easily bend the stock coupler as I found out turning around in my driveway in the first season, but it towed OK while bent for 3 more seasons until I ground it off and replaced it.

Don T · Post by **Don T** » Tue Dec 14, 2004 8:04 pm

Hello:
Typical drum brakes on a trailer use shoes that dis-engage the cylinder when the force is in reverse. If the primary shoe is rotated backwards to the upper support pin, it disengages the cylinder. However, my trailer is a 95 model and it does not have the overcenter device on the shoes. Me tinks Macgregor just counts on the rotation / friction of the drums to counter the pressure of the wheel cylinder pushing the opposite direction (Read - cheaper). This can be controlled some by adjusting the actuating spring on the master cylinder. If the spring is too tight the brakes will drag excessively in reverse. When adjusted properly the spring can not overpower the reverse drag of the primary. Of course this also affects the forward braking although not a lot because the drag force from the primary shoe is multiple times higher than the force exerted by the cylinder.

FYI, the reason drum brakes work better going forward than in reverse is because the drag force of the primary shoe is added to the pressure from the cylinder. IE, the secondary shoe has cyl force plus primary drag exerted on it. In reverse it is cyl force minus primary drag. So essentially, the hydraulic pressure is multiplied by the primary shoe. Primary shoes are smaller to balance wear and are always installed facing front.

Don T · Post by **Don T** » Tue Dec 14, 2004 8:08 pm

Wow, I've been promoted!

P.S. I don't think drilling and pinning (as in Jeff Stagg) is necessary. If you temporarily put a bolt or similar through the loop of the actuator, the brakes can not actuate. However, I have never felt the need to do even that.

Moe · Post by **Moe** » Tue Dec 14, 2004 8:28 pm

Thanks, Don. It's been about 34 years since I worked on hydraulic (or electric) trailer brakes, so I can't remember how they worked. I'll have to pull the drums next year and take a look.

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Moe

Newell · Post by **Newell** » Tue Dec 14, 2004 9:06 pm

I back my trailer up a steep driveway each round trip. I drilled and use a pin to disengage the surge brake, yes it may be a pain in the butt.

When I lost a wheel and wasn't able to get the right parts on a 2300 mile trip, I used the pin to disengage the unit and completed the trip without brakes and dumping all my brake fluid. Don't know if the solonoid would do this or not.

I also made a lever to use when rolling the boat and trailer by hand on incline, I use the lever to control speed and to brake the momentum.

Newell

Catigale · Post by **Catigale** » Wed Dec 15, 2004 5:05 am

I also made a lever to use when rolling the boat and trailer by hand on incline

Yikes Newell.....this would have "insurance claim" written all over it if I tried this...

Jeff Ritsema · Post by **Jeff Ritsema** » Wed Dec 15, 2004 10:59 am

Moe,
FWIW: I had a repeated experience where as I backed up, the brakes would lock, and I mean firmly. I was told that the selenoid was supposed to inactivate the brakes on backing, and was not operating (apparently not uncommon). Danny, at Powersailing, suggested simply to put the pin in the coupler "behind" the piston that activates the hydraulics.
In the case of my trailer, there was a dedicated hole already in the coupler intended for that purpose. Worked perfectly fine when I did this and have done it that way ever since. Interestingly, the brakes only locked when I would back up an incline or on a flat surface (enough of a pressure for the boat to push the piston forward), never when I was backing downward (i.e. down the launch) because the weight of the boat would then pull the piston back, thus not activating the hydraulic.
Not sure if that's clear enough, but it works for me.
Jeff

Moe · Post by **Moe** » Wed Dec 15, 2004 11:09 am

Thanks, Jeff. I'll look at mine more closely.

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Moe

Chip Hindes · Post by **Chip Hindes** » Wed Dec 15, 2004 11:10 am

My solenoid system came with a warning that says if you stop on a hill, then attempt to back up, the solenoid can lock the brakes in the "on" position. The suggested solution was to stop, pull forward slightly until the tongue is extended, then engage reverse and back up.

I'm thinking this probably wouldn't work on a really steep hill, but so far I've never had the need to do so.

Jack O'Brien · Post by **Jack O'Brien** » Wed Dec 15, 2004 11:21 am

Champion Trailer Technical Articles advise to always pull forward to extend your coupler/master cylinder and take pressure off the brake system when parking your trailer so the shoes or pads do not stay in contact and freeze to the drums or discs.

Moe · Post by **Moe** » Wed Dec 15, 2004 11:29 am

You'd have the same problem pinning it on a steep hill. I'd chock the trailer wheels and let the tow vehicle roll forward a little to relieve the pressure.

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Moe

MacGregorSailors.com

CAN MAC 26M BE BOUGHT WITHOUT THE SINGLE AXLE MAC TRAILER

Never had trouble backing with stock brakes

Backing Trailer

Brakes Locking