Setting up for towing - request advice - Page 2 - Club Touareg Forums
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post #11 of 33 Old 05-16-2016
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Only factory bolts. Get the right ones, they have a specific strength rating (that is very high). Early 2003-2004 Treg's had bad factory bolts (for example) that had issues bending and nearly failing. Better safe than sorry and get the right stuff.

I would still do this even if you don't plan to tow big, because later you might and forget the bolts are not up to the job.
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post #12 of 33 Old 05-18-2016 Thread Starter
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The factory non-hitch bolts are an M12-1.5 flange bolt with a 18mm head. Standard thread for an M12 is 1.75, and neither of my socket sets don't included the 18mm.

For the hitch, I need an additional 37mm of bolt length past the 45mm on the stock bolts. 90mm should work, but maybe 100mm.

McMaster has M12-1.5mm 90mm Class 8.8 McMaster-Carr ($11.79/5)
Fastenal has M12-1.5mm 90mm Class 10.9 https://www.fastenal.com/products/de...M12-1.5+x+90mm ($4.74/1)

From my calculations, the Class 8.8 will work just fine. They are rated at 115,000 PSI so each can hold 20,000 lbs in tension, and were the Treg suspended from the bumper that would only be about 625 lbs per bolt. So it seems like even at the soft Class 8.8 there is plenty of overkill. Tension forces should be limited to acceleration and slope; accelerating a 7700 lb boat up a 30 degree boat ramp should max out the tension on the bumper at about 4000 lbs. Divide that by 8 for 500 lbs tension on each bolt, giving a 40x safety margin. There's less than 100 lbs in sheer on each, so sheer is well under the limit too. If you really don't like the idea of a Class 8.8 (US class 5 equivalent), then the Fastenal bolt is an option giving Class 10.9 (US class 8 ).

8 bolts on the hitch is crazy overkill. I like that.

Torque the 8.8 to 69 ft lbs for maximum strength.
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post #13 of 33 Old 05-18-2016
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Excellent post I don't fully understand except that the bolts will do the job required of them!

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post #14 of 33 Old 05-18-2016
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Quote:
Originally Posted by CurtCharlesPDX View Post
The factory non-hitch bolts are an M12-1.5 flange bolt with a 18mm head. Standard thread for an M12 is 1.75, and neither of my socket sets don't included the 18mm.

For the hitch, I need an additional 37mm of bolt length past the 45mm on the stock bolts. 90mm should work, but maybe 100mm.

McMaster has M12-1.5mm 90mm Class 8.8 McMaster-Carr ($11.79/5)
Fastenal has M12-1.5mm 90mm Class 10.9 https://www.fastenal.com/products/de...M12-1.5+x+90mm ($4.74/1)

From my calculations, the Class 8.8 will work just fine. They are rated at 115,000 PSI so each can hold 20,000 lbs in tension, and were the Treg suspended from the bumper that would only be about 625 lbs per bolt. So it seems like even at the soft Class 8.8 there is plenty of overkill. Tension forces should be limited to acceleration and slope; accelerating a 7700 lb boat up a 30 degree boat ramp should max out the tension on the bumper at about 4000 lbs. Divide that by 8 for 500 lbs tension on each bolt, giving a 40x safety margin. There's less than 100 lbs in sheer on each, so sheer is well under the limit too. If you really don't like the idea of a Class 8.8 (US class 5 equivalent), then the Fastenal bolt is an option giving Class 10.9 (US class 8 ).

8 bolts on the hitch is crazy overkill. I like that.

Torque the 8.8 to 69 ft lbs for maximum strength.
What is the shear strength on the bolts? or are they actually loaded in tension? I've not had a look at how the bolts work on the towbar for the touareg, hence my question about the loading direction.
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post #15 of 33 Old 05-19-2016
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All you need is 3 things to get that brake controller plug out of your dash.
A flashlight
A coat hanger
And a shot of Vodka
That's it.
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post #16 of 33 Old 05-22-2016 Thread Starter
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Outstanding. I was considering having a u-joint installed between my elbow and my wrist...

In installed the hitch this weekend. Very easy, but way too many fragile plastic clips on the wheel-well trim pieces. Also, a little tricky to get the bottom of the bumper cover over the safety chain rings, but not impossible. Looks great fully installed.

I checked the 7-pin too. Right turn, left turn and running lights work fine. Didn't check brake lights or battery charge. So far, it's looking good!

Without stopping the engine I disconnected and pulled away. Much to my delight I saw messages "Trailer brake lights not working" and "trailer right right out". I didn't expect that!
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post #17 of 33 Old 05-22-2016 Thread Starter
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12,814 lbs force in sheer.
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post #18 of 33 Old 05-28-2016 Thread Starter
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SUCCESS! I finally located the ellusive connector, and I found it on my 2012 exactly where folks said it would be. However, even with really long arms I was unable to extract it. Desperate times call for desparate measures. In my case, I first removed the fuse block. The I located 4 bolts (10mm hex heads with a T30 inside) that restrain the black plastic electronics interconnect boxes. This allowed immediate and easy access to the brake controller connector, visible above a black connector with a purple lock.

The only surprise is that the Tekonsha P3 appears to be powered even with the engine off, which seems like a bad idea.

Here's my schematic for the wire harness I built. I won't know if it really works until I connect the trailer.
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post #19 of 33 Old 05-28-2016
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Curt....
The schematic is exactly the same as the harness I made for my P3, except I included a switch on the earth wire to the relay (have never used the switch so would probably leave it out if repeating the exercise). A big thanks to those early posts that pioneered this solution.


This set up has worked perfectly for me and I can see no reason that you should not see the same results.

Ewhen

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When's the last time you did something for the First time?
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post #20 of 33 Old 05-30-2016 Thread Starter
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I did a short test run, and the P3 controller works great! Stopping is well controlled and I feel very confident.

However, one serious problem. No trailer brake lights. Right turn, left turn work fine. Running lights are fine. 4-way flashers are fine. But no trailer brake lights.

I get a "left trailer light out" warning on about 50% of the engine starts when connected.

Yes, I used the factory harness and 7-way connector.
No, I don't have the car coded for towing yet.

Suggestions?
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