Trailing arms vs. control arms

[andyj]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

 

[chili_pepper]

Control arms are used to "control" movement of a suspension system in a particular direction and come in many forms (single arms, A arms, etc.). Trailing arms are technically control arms, the term trailing arm is often used when referring to control in the longitudinal axis of the vehicle where the axle line and wheels "trail behind" the arms (think of your TJ's rear suspension). Personally, I tend to call them all control arms, regardless of control direction and relative location of axle line, opinions may vary on this...but it's never presented as an issue for me when buying parts and wrenching on my own vehicles (I do all of my own work).

The Quadratec arms look like factory replacements for a stock suspension. The arms your mechanic is recommending appear to be adjustable length with urethane bushings and can (likely) be used with a stock or lifted suspension. My TJ is stock so I can't speak much more to the latter, but there are plenty of members here who can offer more details on the adjustable arms and what to look out for...

 

[L J]

Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

In Off-Road and Jeep speak, when we think trailing arms we are thinking "control arms" where the shock or shocks are mounted directly to the arm instead of the axle:

 

[UKTJ]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

If it is the bushings that are the problem, why replace the whole arm?

 

[Steel City 06]

If it is the bushings that are the problem, why replace the whole arm?

OEM-style control arms are cheap, and it is probably less in labor and parts combined to replace the arms than press out the original bushings

 

[jjvw]

Your mechanic is being unhelpful and annoying.

 

[TheBoogieman]

​

What is the difference between a Trailing arm and a Control arm?​

Control arms are used to constrain the axle or wheel knuckle in a particular degree of freedom (DOF). A Trailing arm is a type of control arm. The speciality of a trailing arm is that it is mostly used to constrain the longitudinal or fore-aft DOF. In the side view and top view, the trailing arm will appear to connect the chassis to the bottom of the axle or wheel knuckle in the backward longitudinal direction. Control arms usually tend to connect the chassis to the wheel in the lateral direction or even at an acute angle to the lateral direction, when viewed from the top.

However, control arms that are longitudinal and connect the chassis to the top of the axle are generally called Upper control arms, even though they are longitudinal.

 

[chili_pepper]

That looks expensive.

 

[JMT]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

No, for God’s sake don’t put those pieces of crap on your rig. Just get some stock replacement control arms/trailing arms. And from now on just call them control arms

 

[UKTJ]

OEM-style control arms are cheap, and it is probably less in labor and parts combined to replace the arms than press out the original bushings

Then why are they not proposing to replace them with OEM arms?

 

[jjvw]

If the mechanic is stuck on being pedantic, how are his suggested front axle trailing arms trailing?

 

[chili_pepper]

Then why are they not proposing to replace them with OEM arms?

That's a very good question. I'd be interested to hear his mechanic's answer...this is assuming the OP's Jeep is stock.

 

[mrblaine]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

Don't get hung up on the pedantic nature of nomenclature. Lest we forget, the round thingy with cross joints on each end is referred to in the factory service manual as a propeller shaft. Doesn't matter that we call it a driveshaft, it still turns the pinion and makes the rig move when it gets input from the motor/engine/power plant. Those links that control side to side movement are called track bars by us, panhard bars by the rest of the world.

If you can afford them, I don't see any reason to avoid the arms that are being recommended. I'd prefer to have something that could be sourced locally and not have to wait for from the US.

 

[chili_pepper]

I'd prefer to have something that could be source locally and not have to wait for from the US.

A very fair point. We are a bit spoiled for choices and fast shipping here...this isn't the case elsewhere in the world and Nolathane would appear to be local to the OP.

 

[Blackjack]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

With the small amount of lift you have there is no reason no to stay with factory control arms. The Nolathane arms do look like they have some form of DDB in them so that would not be horrible other than the cost.

 

[Jerry Bransford]

So, I got told my lower control arm bushings are bad and I have to change them. I went to my mechanic and he tells me, that they are called trailing arms. But they look like the control arms, that quadratec sells: https://www.quadratec.com/sites/default/files/styles/product_large/public/product_images/187530.jpg

Unfortunately, I know next to nothing about these things. Could anyone shed some light on this, please? What is a control arm and what is a trailing arm and what do they do (if it is different).

He want's to put in these: https://www.nolathane.com.au/product_detail.php?part_number=46935

If your TJ is still stock height just go with factory style arms that are a much better design with more flex than many aftermarket control arms have. I'd be surprised if you can't source a factory style control arm there in Australia at a lower cost than what he's pushing. And if you have a stock height TJ there's no benefit to having an adjustable length control arm.

 

[UKTJ]

If you can afford them, I don't see any reason to avoid the arms that are being recommended. I'd prefer to have something that could be sourced locally and not have to wait for from the US.

Oops, so used to being the only non-American I missed that @andyj was in Aus.

 

[mrblaine]

Oops, so used to being the only non-American I missed that @andyj was in Aus.

We have lots of furriners on here.

 

[andyj]

Wow, what a great response! Thank you to you all. The mechanic proposed the adjustable arms because of my lift. But I can't use them anyway, they are "offroad use" as I found yesterday and I need to do it to get through the roadworthy inspection. If I can't find adjustable ones that are street legal, I'll go with the oem ones.

 

[Rickyd]

You have 1-1/4" lift roughly? I would get a set of all 8 factory style arms and call it good for another 20+ years.