Vacuum pump for Unified Tow Brake

Question

I have been using the US Gear Unified Tow Brake in my last two tow vehicles, and now want to install it in a third. Unfortunately, it seems as if the vacuum pump has failed: testing the system before removing it resulted in only a small movement of the brake pedal (suggesting low vacuum), and testing the pump after removal showed virtually no air movement and no appreciable vacuum (although the motor still runs). My motorhome brakes are also showing evidence of overheating, again suggesting that the dingy brakes are not all that effective.

I have emailed US Gear to see about a replacement pump, but have had no reply. I have also researched availability on the internet, and find that it will set me back over $500 even assuming that the advertisers have stock.

So I am considering using a generic vacuum pump as a replacement, as I can get one for a quarter of the price. But before I do, I want to be sure there are likely to be no technical issues. The way the pump and the electric solenoid are wired to the same terminal on the power module leads me to question whether there is something I need to be aware of, as the pump continues running well after the solenoid has become idle.

Has anyone tried using a non-US-Gear vacuum pump with this system? Does anyone have any technical insight as to how the pump and solenoid work together? I am electrically savvy enough to be able to work around whatever issues there might be, as long as I know what they are. For example, I may use a relay for such a generic pump to be sure I don't overload the Power Module, etc.

Any thoughts on this would be most welcome. Thanks.

c_oneil · Answer

Hello,Your post is a little old but nobody has posted any replies and maybe you still are looking for input on this so here goes.  I just installed a used UTB-1000 brake on my toad and did a little testing.  I think you could find a stock automotive brake booster pump.  I checked the vacuum on my pump and got about 15" of vacuum.  It took about 3-4 seconds to pull it to the max (would vary on the size of your toad brake booster and capacity of the pump you found)and it held it after the pump shut off with no leakage.  The pump inside the black plastic case acording to the label is a Geman made electric motor and a small plastic piston pump on the end.  The label was hard to read but it looks like 12vdc and 2.1amps.  There is no electrical control in the pump itself.  If it gets 12v it runs.  The power module supplies 12v to the pump and the solenoid at the same time on a single circuit.  The reason the solenoid turns off before the pump is that it is controlled by the power module through the ground wire fron the solenoid back to the power module.  The pump ground just goes direct to the frame of the toad. Over load of the power module shouldn't be a problem if the new pump draws somewhere in the neighborhood of 2amps.  Judging by the size of the wires the solenoid draws way more current than the pump.  There was some troubleshooting information on the Unified Gear web site that would help you tell if there may be a problem with your solenoid or power module. If you find a suitable replacement I would me interested to hear in case mine goes bad.

off_pavement · Answer

Amazing this thread showed up today as my UTB vacuum pump just failed and we're about ready to head out on vacation... figures!

A replacement UTB vacuum pump is over $400 and is a special order taking a couple weeks at best according to the service rep I spoke to at PPL. It was the only retailer I found online offering the pump new.

Fortunately I found a guy on ebay selling all the towed vehicle parts without the towing vehicle control selling "buy it now" for less than a new pump so now it's on it's way to it's new owner. However...

My toad service manual specifies a minimum 12" of vacuum. Jegs, Summit Racing, and a host of other retailers offer various electric brake vacuum pumps. Looking at the description of many of these pumps, they state not for vacuum brake use as they may not be adequate.

Personally, if I have another vacuum pump failure, I'll be trying one of these aftermarket pumps. They all provide way more than the minimum vacuum my Jeep specifies, and after disassembling my old pump, I can't imagine I'll be giving up anything in quality or reliability.

canadianembassy · Answer

i finally installed a generic vacuum pump (ACDelco 20804130 GM Original Equipment Power Brake Booster Auxiliary Pump Assembly, from Amazon), and it seems to operate the brakes OK. I installed it in place of the original US Gear pump, but because it draws quite a lot more current than the original I used an inexpensive automotive relay (with snubbing diode!) to drive it.

The pump runs when it should, and the brakes come full-on when I pull out the breakaway switch, suggesting that it works.

But I have another issue, one that may or may not be related to the pump. The "proportional" feature of the system no longer operates: the brakes are either off or fully on - on when braking in the motorhome, off when driving normally. The motorhome unit and the car controller seem to be communicating OK judging by the indicator lights in the MH, and the manual lever in the MH brings on the car brakes fully. But when I operate the MH brakes, there is a second's delay then the car brakes come on fiercely, resulting in quite a severe jerk (and probably stress on the towing system).

While I have still one or two things to try, I wondered whether anyone has seen this, and I would welcome suggestions to help me decide whether it is a fault in the MH unit or the car control unit. Or whether it's just a matter of adjustment.

Thanks.

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Vacuum pump for Unified Tow Brake

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