Roll Control, How well should it hold?

Question on a Hurst Roll Control unit I have installed on my Dakota.

The unit is installed in the front brake line just after the combination valve. Per the instructions this seems like the correct location. (see picture)

When I set the brake, then press the button, and release the brake pedal, the truck will only hold position for about 3 seconds before starting to creep forward at idle.

It absolutely won't hold position if I add any throttle to the equation.

Do I have a bad plunger in the roll control unit, or is something else going on?

A little extra information, the unit was originally installed incorrectly just off the master cylinder, before the combination valve, in the front brake line and did the same thing, with the only difference being it would trigger the BRAKE warning light. So this was corrected, and the combination valve was reset.

The front brakes work just fine and will hold the truck under power if I two foot the pedals. But I really would like to be able to set the roll control, do a burnout, then be able to line up and stage under throttle without rolling away.

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I installed a Hurst line loc ( that was the name in '79). This is on a 1969 340 Dart 4spd. I installed it right after the master cylinder and before the low pressure switch. It would hold the front brakes on until you took your fingers off the button. It would hold the front brakes on equal to the pressure you originally applied. Those were simpler times...no abs or anything. Still works today.

Just to add a bit more info, the truck is a 92 Dakota. No front ABS, and the rear ABS was deleted years ago.

How many times do you pump the brake after you activate the button? I'd always push the brake, hit the button, then pump the brakes 2 or 3 times then let it eat.

I had one on the roadrunner prior to taking it all apart, 4 wheel drum. I don't recall where it it was plumbed in but I also had pumped the brakes a few times before hitting the button. It held when doing this. I am sure you checked you fittings but do you see any seepage of brake fluid anywhere? Try pumping a few times as A39 mentioned. Also, does the peddle move to the floor after holding it down? Are the wheels locked and it is just sliding on the tires?

I have tried pumping up the brakes before hitting the button. It doesn't make any difference.

Pedal stays where it is, it doesn't sink to the floor. Two years ago I replaced the master and booster when the booster failed.

I have no leaks, and reservoir is staying full.

The fronts tires are not sliding, they just roll.

It's been a problem I've been chasing since last year. But next week I am getting the front suspension replaced and it will be ready to drive in a spirited and aggressive manner again. Due to the current condition of the upper A arm bushings and ball joints, its only been out for the occasional Sunday drive.

I'm tempted to get a new roll control solenoid and have it swapped in while the front is torn apart. But wanted to see if anyone here might have had a similar problem and have some insight into the problem.

The only thing I can come up with is a fluid must be getting past the plunger while the solenoid is activated.

Did it ever work or is this something new? If it's new and the truck has sat it could have crud on the plunger. If it never worked do you by chance have the IN and OUT ports crossed?

If the brakes initially hold and then are apparently releasing, without any fluid leakage to the atmosphere, what else can it be other than the roll control solenoid leaking? I'd put the vehicle on a lift and with a helper setting the roll control, see how much resistance to turning the front wheels have over a period of time. If they initially can't be turned, and then they can be turned with force, and then turned easily, I'd say you are losing your hydraulic pressure and the only way that can happen, if fluid isn't running on the ground, is through a solenoid leak.

I've never looked at the inside of a booster. Is there a direct link between the rod on the back of the booster(that's connected to the brake pedal) and the rod on the front that pushes on the master cylinder? If not, could the booster be the issue? Could you disconnect the vacuum to the booster and try it?

To find out whether the roll control is leaking or the master cylinder, first the brake pedal needs to be depressed at about half pressure with the roll control button not engaged to see if the pedal creeps to the floor. When pedal is fully depressed, that can cause the rubber piston in the master cylinder to expand gripping the bore more tightly. With about half pressure applied that doesn't happen, making it easier to determine whether the cylinder needs to be rebuilt or replaced. If the master cylinder checks out to be ok, the roll control becomes suspect. Quite likely, it didn't get flushed thoroughly before instillation, or if it did, the internal parts may need replacing. I have seen repair kits listed, so it must be a common problem.

This is what is happening. At first activation the wheels cannot be turned, then a couple seconds later, you can turn them with some drag, then they turn free at about 4-5 seconds,

Thank you for the help guys, I will try to remember to report back next week after getting the truck back on the road.

I was about 99% sure it was a solenoid leak, but just wanted to be sure I wasn't missing something else in the equation.

I will try the brake test at 1/2 pedal, just to eliminate that possibility.

if the vehicle has a brake warning light, i like to plumb in the line lock so the light activates when pressure is applied to just the front brakes. if the solenoid bleeds off, the light will flicker, giving you an indication the solenoid needs attention.
that's just me. your mileage will vary.