J-bar - Torque arm clearance

[rubbinsracin]

ok. so in an efford to loose some weight weight we switched to an aluminum Jbar this year from the steel one that we had been using. obviously the steel jbar was alot smaller and there were no worries about clearance issues with the top of the jbar hitting the bottom of the top bar of the torque arm under cornering conditions(hope this makes sense) now with the aluminum one in place, even though it has the same amount of rise in the jbar, it is about a 1/3" or so from hitting the torque arm at static ride height due to the bar itself being thicker.

should we worry about the Jbar hitting the torque arm during cornering when the car is way up on the bars?

[Matt49]

Simulate it the best you can.
With the car on the ground, jack the left side up (under the seat) until the LR just wants to come off the ground. That's about as extreme as it's gonna get but you could have someone compress the right side a little bit.
If that makes it too hard to see clearances, put the car on jack stands with the springs OFF but with the shocks ON. Put a jackstand under the right side axle tube about half way between the bell and the birdcage and put a jack under the LR hub. Play with both sides until you've got ride heights pretty close. Then just drop the jack under the LR until the LR drops as far as it can. It's easier to get under the car and see clearances doing the second way but a bit more tedious.
If your liftbar is braced back to the axle tube, it will point out to the right as the LR drops and open up more clearance so you shouldn't have a problem.
But if your liftbar is braced to the frame up by the 6th coil, it won't move much at all and you could run into clearance problems.

[rubbinsracin]

we will try that this weekend. i just have a nasty feeling i bought a fairly expensive piece that is going to do me no good.

anyone else that runs an aluminum J bar care to thow out there what you guys are seeing as far a clearance between jbar and torque arm at both static and/or at full roll?

[Graff Spee]

I hate to say this but the aluminum J bar will do nothing for you. Yes it will look pretty (yes I have one) thats about it! You won't be able to repair it easly, if the need ever came up. What about the clearance issues you are having? I would put the old J bar back on. I am sure you could spend some more money for a different lift arm. You may want to get a arched billet dual mount for the pinion and then one for the frame also. Yes I also am guilty of shiney object syndrome! Unless it lowers your lap times by a consistent measurable amount, I would forget about it. Not trying to be a jerk, by the way.

[sj valley dave]

We run an AFCO aluminum J Bar and it gets close, but we have no marks on it from hitting the torque arm and have ran it for the last 2 seasons...I think it is cheap easy weight to lose..Why not run it??

[zeke23z]

Learned this at school in Jan.Build your racecar as lite as possible without sacrificing durabilaty.If your worried about it before hitting the track put the old trusty one back on look for somewhere else to lose weight.No reason to sit in the car and woory if something is going wrong,just worry about gettin around dude thats in front of you.

[billetbirdcage]

First thing is both of those will move in relation to each other, meaning if it has 1/2" of clearance is will always have a 1/2" clearance unless the bar on the torque arm bows under stress/power. As long as the j-bar has enough clearance to allow it to move and allow it to be able to full rotate the mono-ball to allow for misalignment when it pinions up, you are fine. (this is describing the j-bar being above the torque arm bar - if it is beside it and you have a sideways link on the far end of the torque arm then you need to make sure that it doesn't get into the j-bar when the LR pulls forward.)

Second, If a steel j-bar bends it generally bends the J part more and moves the rear end left. This can be very hard to see with out checking the side to side on the rear end, I've seen guys miss this and struggle for several weeks due to just missing this as it really hard to notice by eye balling. However an Aluminum j-bar will pretty much never bend in the J part, it will bend the long part forward or backwards and will be very easy to see even at a quick glance. This alone can save you a lot of grief as many of the steel j-bars bend really easy in the J area with the slightest bump, so you really need to measure the side to side after any contact with the rear wheels.

The basic premise is that the rear end, j-bar and torque arm move together so generally the clearance doesn't change, so unless your really close 1/4" or less you are usually good to go. It is also possible that you have an older torque arm (older Rayburn or Rocket) as their older ones where much closer then the newer stuff. Most have added clearance in this area over the last 3 or 4 years.

Hope that helps