Frequently Asked Questions
I will get to this at some point. If you have any questions, please go to the contact page and send them to me. I'll try to highlight them here. Thanks!
Bolt on ball joint swap - 620 to 521
I just posted this to a FB question, so I thought I'd put it here, too, for future reference. The question was basically, why can't you take the arms off the front of a ball joint 620 and bolt them on to a 521(or older).
If you look at the shock towers, from the top down, you'll see why. The ball joint versions are at an angle while the kingpin ones are in line with the frame. Tiny history lesson I haven't shared much over the years since it's not an option for 99.99% of those looking for ball joints.
The swap was done way back when....before the internet for sure. I talked to Steve Epperly(owner of ZTherapy). They used to do it, but it's not a bolt on swap. At the time, they could buy the shock towers...new...from the dealer....for the ball joint trucks. They would cut off the kingpin shock towers and weld on the new ones. I'm guessing they also did the lower pieces too since the width of the LCA pivot is different...we didn't talk about that, so I don't know the answer. The frame width changed too, but I'm not sure if the LCA pivot point moved with wider frame.
Without the tower swap, there's no UCA's that work....at least not perfectly. You can flip the ball joint UCA's from side to side to help counter act the angle difference, but then the length is wrong.
I did a swap with a couple of friends many years ago. We used 720 LCA's and built custom UCA's. That's when we found that the wheel mounting surface(face of the hub) was moved out about 1.250" PER SIDE. It wasn't an issue at the time since Bre620(Dave) was running Z71 rims, which have a FWD offset and he needed the extra length on the arms. Heck....I still have most of the pieces that were supposed to become my UCA's....but they never got built. lol
Years ago, I started working on a "stock track width" ball joint conversion. I spent a lot of time on it....it was a royal nightmare trying to do it. I stopped before I was done. After a few years, I got back on it and finished it. The lowers are modified(shortened 1.125") HB arms with press in ball joints. The older LCA's(620/720) use bolt in, but they take up too much real estate....can't get the sway bar mount in anywhere.....at least, I couldn't. You can run any of the ball joint spindles this way, but the only ones actually worth running, IMO, are the HB units. There's a good bit of overlap on the brake setups....like early 720's running 620 spindles and the late 720's running HB spindles. The 620 disc brakes are pretty close to crap, but are better than drums. The 720's won't fit behind stock 521 rims without an 1/8" spacer. The HB ones will fit behind any of the drum brake rims. The top hat on the rotor changed between the 720 and HB. The HB caliper is pushed inboard more, so there's more clearance.
For those that don't know, I'm bluehandsvideo on Facebook, Instagram and Youtube if you go looking for that info. I'm mklotz70 on the ratsun.net forum and I'm pretty sure I have a build thread on there about the conversion.
If you look at the shock towers, from the top down, you'll see why. The ball joint versions are at an angle while the kingpin ones are in line with the frame. Tiny history lesson I haven't shared much over the years since it's not an option for 99.99% of those looking for ball joints.
The swap was done way back when....before the internet for sure. I talked to Steve Epperly(owner of ZTherapy). They used to do it, but it's not a bolt on swap. At the time, they could buy the shock towers...new...from the dealer....for the ball joint trucks. They would cut off the kingpin shock towers and weld on the new ones. I'm guessing they also did the lower pieces too since the width of the LCA pivot is different...we didn't talk about that, so I don't know the answer. The frame width changed too, but I'm not sure if the LCA pivot point moved with wider frame.
Without the tower swap, there's no UCA's that work....at least not perfectly. You can flip the ball joint UCA's from side to side to help counter act the angle difference, but then the length is wrong.
I did a swap with a couple of friends many years ago. We used 720 LCA's and built custom UCA's. That's when we found that the wheel mounting surface(face of the hub) was moved out about 1.250" PER SIDE. It wasn't an issue at the time since Bre620(Dave) was running Z71 rims, which have a FWD offset and he needed the extra length on the arms. Heck....I still have most of the pieces that were supposed to become my UCA's....but they never got built. lol
Years ago, I started working on a "stock track width" ball joint conversion. I spent a lot of time on it....it was a royal nightmare trying to do it. I stopped before I was done. After a few years, I got back on it and finished it. The lowers are modified(shortened 1.125") HB arms with press in ball joints. The older LCA's(620/720) use bolt in, but they take up too much real estate....can't get the sway bar mount in anywhere.....at least, I couldn't. You can run any of the ball joint spindles this way, but the only ones actually worth running, IMO, are the HB units. There's a good bit of overlap on the brake setups....like early 720's running 620 spindles and the late 720's running HB spindles. The 620 disc brakes are pretty close to crap, but are better than drums. The 720's won't fit behind stock 521 rims without an 1/8" spacer. The HB ones will fit behind any of the drum brake rims. The top hat on the rotor changed between the 720 and HB. The HB caliper is pushed inboard more, so there's more clearance.
For those that don't know, I'm bluehandsvideo on Facebook, Instagram and Youtube if you go looking for that info. I'm mklotz70 on the ratsun.net forum and I'm pretty sure I have a build thread on there about the conversion.