Brakes jerking/reverberating when towing trailer without boat

[Josh7711]

Hi and thank you in advance for any help.

Yesterday I was towing the trailer home after I launched the boat for the weekend and my truck or trailer brakes were jerking/reverberating somewhat violently when I was stopping at red lights. Is this normal when towing without the boat on trailer? Is there something I should do to fix this? Thank you!

It's the trailer that came with the boat 2018 Malibu mlx. Truck is GMC Sierra.

[CaptainMorgan]

could be your surge brakes engaging.  if i tow my trailer without boat and stop suddenly, the tongue will compress as the trailer tries to keep going and the surge brakes engage - but only with sudden stops or on downhills, light braking won't do it.  Once engaged, doesn't take much for surge brakes to slow down the trailer without boat though, so it may engage/disengage 2-3 times quickly almost like slow-motion anti-lock brakes.    

[oldjeep]

Lock them out when boat is not on trailer.  Mine bucks like a bronco

[CaptainMorgan]

https://www.amazon.com/dp/B0969LF3SK?ref_=cm_sw_r_cp_ud_dp_YQYEQEHTYAHZDPYQCBAW

i use something like this when repositioning in a driveway with a vehicle that doesn't have a 7pin hitch

[oldjeep]

I have one of these on my trailer

https://pacifictrailers.com/products/ufp-top-lockout-upgrade-brake-lockout-cap-34359?variant=36463647242&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&utm_source=google&utm_medium=cpc&utm_term=&utm_content=&utm_campaign=18134776771&campaignid=18134776771&adgroupid=&adid=&tmid=&gad=1&gclid=Cj0KCQjwqNqkBhDlARIsAFaxvwwrcUi2qo0SJxOgEha7NwSbHa0Uj_OXJ03GEM47CogpOolRtXATNWUaAtnpEALw_wcB

Edited June 24, 2023 by oldjeep

[Josh7711]

1 hour ago, oldjeep said:

I have one of these on my trailer

https://pacifictrailers.com/products/ufp-top-lockout-upgrade-brake-lockout-cap-34359?variant=36463647242&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&utm_source=google&utm_medium=cpc&utm_term=&utm_content=&utm_campaign=18134776771&campaignid=18134776771&adgroupid=&adid=&tmid=&gad=1&gclid=Cj0KCQjwqNqkBhDlARIsAFaxvwwrcUi2qo0SJxOgEha7NwSbHa0Uj_OXJ03GEM47CogpOolRtXATNWUaAtnpEALw_wcB

thank you! this is my first time reading about brake lock out. why would the trailer do this when boat is off but not when it's on? 

[CaptainMorgan]

when you brake with the boat back there, you've got thousands of pounds that is trying to run into/push the tow vehicle.  thus the tongue compresses and engages the surge brakes to help stop the boat/trailer so the truck can focus on stopping itself.  thus, the brakes are engaging with the boat on the trailer, but you don't feel it as they are engaging a single time as you begin to brake and only stop helping when you come to a complete stop. (no bucking bronco)

Your surge brakes are probably designed to stop say 7-8k lbs of boat+trailer...but when there's no boat, its only a ~1500 lbs trailer.  So hard truck braking means surge brakes may engage but the brakes are WAY stronger than necessary for an empty trailer.  So if the surge brakes engage at all, the trailer slows down faster than the truck is slowing - tow vehicle starts "pulling" the trailer briefly which stretches the tongue and disengages the brakes.  BUT your vehicle is still slowing, so then the tongue compresses again...surge brakes rapidly slow the trailer faster than the truck...repeat.  

if i brake gently, i don't get any bucking.  if i brake hard, maybe 3-5 hard bucks before the difference in speeds/accelerations aren't that big anymore.

note these same surge brakes should get locked-out electrically when you go into reverse so that the tongue compression that says "brake" does not engage when you are backing the trailer up a small hill for example.  the orange lock-out pin i posted is useful for when you need to reposition/push on a trailer but don't have the full 7-pin hitch (you'll see boatyards do this when moving boats with a fork-truck, or if i use my 4-pin SUV to reposition an empty trailer around in the driveway).

[SurfNAZ]

2 hours ago, oldjeep said:

I have one of these on my trailer

https://pacifictrailers.com/products/ufp-top-lockout-upgrade-brake-lockout-cap-34359?variant=36463647242&currency=USD&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&utm_source=google&utm_medium=cpc&utm_term=&utm_content=&utm_campaign=18134776771&campaignid=18134776771&adgroupid=&adid=&tmid=&gad=1&gclid=Cj0KCQjwqNqkBhDlARIsAFaxvwwrcUi2qo0SJxOgEha7NwSbHa0Uj_OXJ03GEM47CogpOolRtXATNWUaAtnpEALw_wcB

X2 these are great.  I don’t drive much with my trailer empty, but if the trailer starts bouncing on the road, especially downhill, I have noticed that surge brakes can try to engage.

[oldjeep]

3 hours ago, Josh7711 said:

thank you for the reply! does that mean to press truck brakes all the way? wouldn't that be pretty violent of a stop? i think i'm missing something sorry for needing clarification.

What it means is that the surge brakes are sized for the boat on a boat trailer.  A proper tow vehicle doesn't need the trailer brakes when it is empty.  Lock the trailer brakes out when boat not on it.

[Josh7711]

18 hours ago, CaptainMorgan said:

when you brake with the boat back there, you've got thousands of pounds that is trying to run into/push the tow vehicle.  thus the tongue compresses and engages the surge brakes to help stop the boat/trailer so the truck can focus on stopping itself.  thus, the brakes are engaging with the boat on the trailer, but you don't feel it as they are engaging a single time as you begin to brake and only stop helping when you come to a complete stop. (no bucking bronco)

Your surge brakes are probably designed to stop say 7-8k lbs of boat+trailer...but when there's no boat, its only a ~1500 lbs trailer.  So hard truck braking means surge brakes may engage but the brakes are WAY stronger than necessary for an empty trailer.  So if the surge brakes engage at all, the trailer slows down faster than the truck is slowing - tow vehicle starts "pulling" the trailer briefly which stretches the tongue and disengages the brakes.  BUT your vehicle is still slowing, so then the tongue compresses again...surge brakes rapidly slow the trailer faster than the truck...repeat.  

if i brake gently, i don't get any bucking.  if i brake hard, maybe 3-5 hard bucks before the difference in speeds/accelerations aren't that big anymore.

note these same surge brakes should get locked-out electrically when you go into reverse so that the tongue compression that says "brake" does not engage when you are backing the trailer up a small hill for example.  the orange lock-out pin i posted is useful for when you need to reposition/push on a trailer but don't have the full 7-pin hitch (you'll see boatyards do this when moving boats with a fork-truck, or if i use my 4-pin SUV to reposition an empty trailer around in the driveway).

I understand completely now, thank you so much for taking the time to thoroughly educate me on this. Definitely makes sense now. I'll get that lock-out pin for sure. Thanks again for taking the time!

[Josh7711]

Thank you in advance for any.

This lock out key came with the trailer. Should I use this with electrical tape or purchase a separate lock out key? I don’t tow trailer without boat too often. 
Any downside to just taping this key to trailer? Thank you!

[LakePTDoc]

4 minutes ago, Josh7711 said:

Thank you in advance for any.

This lock out key came with the trailer. Should I use this with electrical tape or purchase a separate lock out key? I don’t tow trailer without boat too often. 
Any downside to just taping this key to trailer? Thank you!

you could probably zip tie or connect it to the trailer.  I bought the magnetic one from bakes that allow me to put the lock out into the spot and not have to keep it in.  You do not want to leave it in permanently since that will cause the surge brakes to not work.   

[LakePTDoc]

does the trailer use the 4 pin, 5 pin, or 7 pin hook up to the truck?  if it has a 5 or 7 keeping the trailer hooked up to the tuck will use the back up brake lock out to allow you to back up without the breaks locking up on you.  we tend to use the lock out when moving the boat when the trailer is not connected to a truck, ie tractor, but have used it a few times when backing up a steep incline.  

[CaptainMorgan]

1 hour ago, Josh7711 said:

Thank you in advance for any.

This lock out key came with the trailer. Should I use this with electrical tape or purchase a separate lock out key? I don’t tow trailer without boat too often. 
Any downside to just taping this key to trailer? Thank you!

for your limited use case to avoid bucking while trailer is empty, that lock out will work fine if you tape it good -- else it'll jiggle out almost immediately as they need pressure to hold them in place vs the magnetic ones which are often so strong its a 2-hand job to remove them (and you don't need to remember to have tape on-hand).  If using the one above, zip-tie or string is a smart idea to keep it on/with trailer as well or if it comes out. 

[Josh7711]

12 minutes ago, CaptainMorgan said:

for your limited use case to avoid bucking while trailer is empty, that lock out will work fine if you tape it good -- else it'll jiggle out almost immediately as they need pressure to hold them in place vs the magnetic ones which are often so strong its a 2-hand job to remove them (and you don't need to remember to have tape on-hand).  If using the one above, zip-tie or string is a smart idea to keep it on/with trailer as well or if it comes out. 

Perfect, thank you!

[Josh7711]

1 hour ago, LakePTDoc said:

does the trailer use the 4 pin, 5 pin, or 7 pin hook up to the truck?  if it has a 5 or 7 keeping the trailer hooked up to the tuck will use the back up brake lock out to allow you to back up without the breaks locking up on you.  we tend to use the lock out when moving the boat when the trailer is not connected to a truck, ie tractor, but have used it a few times when backing up a steep incline.  

Thank you! I’ll check. I appreciate the help.