UCA Upper Control Arm Length

RC Cola XJ · Jan 10, 2011

98 XJ 4.0 D30, 35

I recently changed out one my upper control arms with another stock arm. I only changed the passenger time because of time. The driver side arm is going on soon.

However, the aftermarket "stock" arms I bought are slightly shorter than the original uca's. They're about 1/4" shorter from bolt hole center to bolt hole center. I thought the difference was nothing to worry about but I wanted to get a second opinion. Thanks.

CharlesS · Jan 12, 2011

Since there is a 1/4" difference in length; are both UCAs of the same manufacturer?
The difference in length will alter your alignment; so once you install the other UCA you should have the alignment checked paying attention to the caster...

RC Cola XJ · Jan 13, 2011

CharlesS said:
Since there is a 1/4" difference in length; are both UCAs of the same manufacturer?
The difference in length will alter your alignment; so once you install the other UCA you should have the alignment checked paying attention to the caster...

Yes, both UCA's are form the same manufacturer. The new arms are the same length, they are just a little shorter than the originals. Do you think that the caster should still be within the limits of alignment in regards to the 1/4" difference? Thanks!

CharlesS · Jan 14, 2011

RC Cola XJ said:
Do you think that the caster should still be within the limits of alignment in regards to the 1/4" difference? Thanks!

IIRC shortening the UCA length will decrease the amount of caster and although .250" isn't that much of a decrease; there will be a change in caster.

Depending on what your caster was set at before replacing the UCAs; a decrease in Caster can cause the front end to drift on the crown of the road (lighter feel of resistance in the steering) if the caster is below 5*.

I would recommend you have your alignment checked.

49erRider · Jan 14, 2011

If you want I can ship you stock arms for just the cost of shipping.

wheeling365 · Jan 14, 2011

CharlesS said:
IIRC shortening the UCA length will decrease the amount of caster and although .250" isn't that much of a decrease; there will be a change in caster. QUOTE]

Actually you have that backwards. Shortening the uppers will increase caster angle as it tilts the axle further back at the top. If it was the lower arms that he was shortening your 100% right.

With the arms mismatched right now I wouldn't be suprised if you notice a pull to one side. In many vehicles if caster is over a 1/2 degree different from side to side it will pull.

RC Cola XJ · Jan 17, 2011

CharlesS said:
IIRC shortening the UCA length will decrease the amount of caster and although .250" isn't that much of a decrease; there will be a change in caster.

Depending on what your caster was set at before replacing the UCAs; a decrease in Caster can cause the front end to drift on the crown of the road (lighter feel of resistance in the steering) if the caster is below 5*.

I would recommend you have your alignment checked.

Yea, I'm going to get the alignment checked, I replaced the other arm today. It didn't drift much before I installed the first new UCA. After I installed the second UCA it still felt fine, maybe wandered slightly more.

I'm going to replace the axle side UCA bushings next weekend. Working on making my own tool to remove/install. Then I will check alignment.

49erRider -> thanks for the offer, I'm not really concerned that the new arms are shorter anymore, the new second UCA lined up just like the original one.

moneypit_k5 · Jan 25, 2011

on an XJ, 1/4" of caster change can be HUGE depending on your front axle tolerances. have your alignment checked, and/or remove a shim from behind the LCA.

UCA Upper Control Arm Length

RC Cola XJ

NAXJA Forum User

CharlesS

NAXJA Forum User

RC Cola XJ

NAXJA Forum User

CharlesS

NAXJA Forum User

49erRider

NAXJA Forum User

wheeling365

NAXJA Forum User

RC Cola XJ

NAXJA Forum User

moneypit_k5

NAXJA Forum User

Similar threads