Pulls Left When Braking While Towing...

[bigbluesuburban]

My 89 Sub pulls hard to the left when hard braking when I am towing and it does not seem to matter the size or weight of what I am towing. It did it the first time when I was towing 55Willys Jeep back from Mary's peak. The trailer was really heavy and I had a lot of tongue weight. But we both about crapped ourselves when I had to brake hard and we did an automatic lane change in the process.

Then today I am towing a Honda Foreman Quad on my lightweight ATV trailer and out of the mountains it starts pulling hard left everytime I touch the brakes.

WTF is going on?

I have done emergency braking proceedures while not towing to test the brakes and it stops straight as an arrow.

 

[Jason4x4]

check to make sure the rear brakes are adjusted properly, and it may have a valve in the rear that attached to the axle that allows more rear line pressure when the rear is sagging, which might be why it only does it when towing.

 

[bigbluesuburban]

Proportioning Valve... Hmmm, good idea. I disconnected the one on my Toyota when I first got it cause it was a PIA. THX!!!