Surge brake spring tension

[pops2]

so I have a tow dolly that seems to lock up when I get my speed down to approx. 5 mph. it keeps bending the hitch as if it is trying to dive under the m/h. Is there an adjustment to the surge hitch as to spring tension so that the dolly with not jack rabbit and push the hitch into the bent position?

[BFlinn181]

You didn't say what make or type of dolly or surge brake, so it's hard to really help. If they are hydraulic disk brakes, no adjustment is needed, drum brakes must be adjusted. You might contact the manufacturer and ask if there is an adjustment, I would imagine you'll have to replace the spring as it may be weak or bent so not supplying proper resistance.

[mpierce]

Originally Posted by pops2

so I have a tow dolly that seems to lock up when I get my speed down to approx. 5 mph. it keeps bending the hitch as if it is trying to dive under the m/h. Is there an adjustment to the surge hitch as to spring tension so that the dolly with not jack rabbit and push the hitch into the bent position?

Not understanding problem. You state that the dolly brakes "seem to lock up" under 5 mph, then state that it is bending the hitch, "as if its trying to dive under MH".

How can it be trying to dive under the MH, while the brakes are locked up?

What angle is the hitch? It should be almost level. Is your ball quite a bit higher than the car attachment? If so, that may be the problem.

the hitch needs to be close to level, or the tow will try to either go under, or over, the hitch.

[pops2]

firstly the model is a 1993 automatic and it has been refitted with hyd. shoe brakes. (which have been adj. properly) the problem seem to be in the hitch actuator.
what I wanted to know is how to adjust the spring in the hitch that works the plunger in the hitch's compression cylinder? (as a master cylinder in a standard vehicle)

[JohnRR]

If I'm not mistaken those springs are factory calibrated and are used to make sure the master cylinder does not allow pressure to be applied to the system when not needed.

[wa8yxm]

Originally Posted by JohnRR

If I'm not mistaken those springs are factory calibrated and are used to make sure the master cylinder does not allow pressure to be applied to the system when not needed.

Nope, can't be done.. you see the factory has no way of knowing what is going on the dolly, it could be a little 2 seater that does not weigh 2,000 pounds soaking wet and full of groceries, or it might be a 1992 Lumina APV (chosen as an example because it happens to be 4000 pounds title weight) or it might be 5 thousand or more of truck.. No way to factory calibrate the spring tension. HAS to be field adjustable.

Now to do it.... I do not know, i tow 4 down.

[JohnRR]

Well having serviced them for a few decades as a Ryder, Budget, Penske Rental maintenance facility let's just say I disagree.

Check the link for the only spring included in a tow dolly or auto carrier (trailer). Demco is one of the largest produces of these products. Same spring for disc or drum brakes, 1 axle dolly or trailer, tandem or tri axle carrier.

Spring Return/ dampener assy, 07623-30, Demco - Ryder Fleet Products

[BFlinn181]

Originally Posted by JohnRR

Well having serviced them for a few decades as a Ryder, Budget, Penske Rental maintenance facility let's just say I disagree.

Check the link for the only spring included in a tow dolly or auto carrier (trailer). Demco is one of the largest produces of these products. Same spring for disc or drum brakes, 1 axle dolly or trailer, tandem or tri axle carrier.

I agree, if they were adjustable, it would be in the instructions. If the spring is broken or bent, it might malfunction, but I'm still not clear how the OP's description, "tow dolly that seems to lock up when I get my speed down to approx. 5 mph. it keeps bending the hitch as if it is trying to dive under the m/h" If it was locking up, wouldn't it PULL on the hitch rather than dive under the m/h? If the dolly were empty, perhaps brake lock up would try to cause nose down twitch, but not bending of the hitch.

[JohnRR]

The only tow dolly neck I've seen bent except actual accidents has been from reversing actions usually the brakes don't apply at the 5 MPH range.

Perhaps some pictures would help.

Just a tid bit of information the use of the spring started with the advent of disc brakes being installed then somehow got retrofitted to a lot of the older drum brake equipment. I'm referencing that to Ryder rental equipment only.

[IdahoSRT10]

Originally Posted by mpierce

Not understanding problem. You state that the dolly brakes "seem to lock up" under 5 mph, then state that it is bending the hitch, "as if its trying to dive under MH".

How can it be trying to dive under the MH, while the brakes are locked up?

What angle is the hitch? It should be almost level. Is your ball quite a bit higher than the car attachment? If so, that may be the problem.

the hitch needs to be close to level, or the tow will try to either go under, or over, the hitch.

The tow dolly will dive down when it's brakes are applied, just like you car dives down when the brakes are applied.
I suspect his dolly return spring surge brake is malfunctioning.

[pops2]

just to let everyone know I had to replace the backing plates (both sides)
also changed the surge hitch. so now the experiment begins again with all new parts. thanx to all.

[RJsfishin]

How much you take for all those used parts,......my dolly needs brakes !