Unified Tow Brake help wanted

[CanadianEmbassy]

I have a US Gear UTB, which I have just transferred from one car to another, and it doesn't seem to be working quite right.

But first some history. The system was working fully when initially installed in the first car. Bit in this car, it hasn't been working properly of late, because the vacuum pump had quit, so there were no really obvious symptoms (and probably very little braking effect either). In the new car, I have installed a new vacuum pump. Wiring in the new car has been triple-checked and is OK.

Here is what is now happening. The "proportional braking" aspect of the system isn't working: the car brakes are either off (when no braking is being called for) or fully on when any amount of MH braking is called for. When I apply the motorhome brakes, there is a 1-2 second delay where the car brakes don't seem to be doing anything, then a big jerk as the car brakes come on fully - and this is irrespective of the setting of the braking effort knob inside the motorhome. When I use the manual lever in the MH to operate the dingy brakes, one or two steps (LEDs on the MH unit) has no effect in the dingy, whereas 3 or 4 steps brings the dingy brakes on fully; there is no in-between.

The MH unit and the UTB power module in the car seem to be communicating, according to the indicator lights. The system works as it should when I pull out the breakaway switch (full dingy braking). The mounting angle for the MH unit is within US Gear's specs.

I am unhappy with this operation because of the stresses imposed on the towing system caused by the severe dingy braking, and also because of the possible premature wear on the car brakes, tires, and suspension system. So I would like to fix it. I like this system, and have gone to a lot of trouble to re-install it, so would prefer not to switch to something different.

I assume that the problem is either with the control unit in the motorhome or with the power module in the dingy, and I would like some help or suggestions as to how I can determine which item is faulty. Both are difficult to obtain as spares and are expensive, so I don't want to guess wrong.

Is there anybody out there sufficiently savvy about this system who can help me through this, and help me determine where the fault is?

Thanks.

Paul.


PS. I posted an briefer description of this problem as an appendix to an earlier post (Vacuum pump for Unified Tow Brake), but thought it better for it to have its own topic.

[CanadianEmbassy]

Thanks for the reply. No solution yet, but here is where I am at.

I have changed the coach unit, car solenoid and cable (I found a complete new system at a reasonable price), but the problem is still there. So by elimination, it must be the power unit PM6001 that goes into the car. Unfortunately, the new unit has a fault (brake light disabling relay doesn't open), so I haven't been able to swap this out. AP Products are sending another PM6001, so when it arrives I will try it.

Watch this space.

Thanks, Paul.

JCM wrote:
I have been having a problem where the solenoid wouldn't retract any more but with a tech supports help we isolated (I hope) to a defective computer box - by measuring voltages to the solenoid. He said that that the solenoid almost never fails and that sounds so in your system. The only 2 other parts would be the controller on your dash and the computer box under the dash.
If your brake away switch activates what you say I would think it is the darn computer.
If you are in the US Amazon has them for about $319.00.
I would spend the time and phone the company. Keep calling until you get a human.
He was really helpful and I hope when my new computer arrives it will fix my problem.
Good luck - it is a great system when working. Again reviewing your problem I am inclined to also question your dash unit since I believe that is the component that sets the proportional braking.
Let us know the results.

[JCM]

I have been having a problem where the solenoid wouldn't retract any more but with a tech supports help we isolated (I hope) to a defective computer box - by measuring voltages to the solenoid. He said that that the solenoid almost never fails and that sounds so in your system. The only 2 other parts would be the controller on your dash and the computer box under the dash.
If your brake away switch activates what you say I would think it is the darn computer.
If you are in the US Amazon has them for about $319.00.
I would spend the time and phone the company. Keep calling until you get a human.
He was really helpful and I hope when my new computer arrives it will fix my problem.
Good luck - it is a great system when working. Again reviewing your problem I am inclined to also question your dash unit since I believe that is the component that sets the proportional braking.
Let us know the results.

[CanadianEmbassy]

Thanks OP for that reply.

I hadn't seen the troubleshooting guide - I don't know how I missed it. But there is quite a good bit of useful information in there, so I will get the MH from its storage yard and go through the relevant bits. Hopefully I can deduce enough to decide which item is at fault.

I know it's not the cable from the solenoid, since it's not kinked and it operates smoothly and brings the brake pedal fully on and off freely, so it's either an electrical funny or one of the electronic boxes.

And like you, my vacuum pump failed and I had to replace it with an aftermarket one. I don't know if it might be an issue or not (I'm inclining to think not), but will keep it in mind as I proceed.

[Off_Pavement]

I'm not a UTB expert by any means, so here is my 2cents worth...

For starters, I'd go through the UTB troubleshooting guide being sure to check voltages carefully... US Gear UTB Troubleshooting Guide

Is it possible your pedal cable needs adjustment or the cable kinked?

I recently had to replace my UTB compressor with an aftermarket vacuum pump. The new pump provides considerably more vacuum than the standard UTB compressor which may an issue for a different vehicles brake system.