LCA cup diameter

[daved]

I have a 68 c10 and this is my first time installing bags. I was wondering if anyone knows what the correct diameter is for the lower control arm cups. The first set I got are 5.5" and did not sit all the way down in the lower control arm as seen in the pic

the second set sent to me are only 4.5" in diameter (smaller than the bag mounting pad) and they have ample room in the control arm....but seem pretty small to me. will these small cups work or does anyone know the diameter of the cups needed for these trucks?

[jimmydean]

The ones I used were from Suicide Doors and were 5.5" OD tube on my '69.

[tubbedII]

Originally Posted by jimmydean

The ones I used were from Suicide Doors and were 5.5" OD tube on my '69.

Ditto...I cut mine down a little to make them shorter. It was a little bit of a pain to get them to sit flat when installing the springs though.

[jimmydean]

I didn't cut mine because it was pretty flush with the arm when I got them. But I didn't have any issues with them sitting in the pocket.

[daved]

This is frustrating to say the least....I have lost ten days (counting last weekend) and I am still in the same spot. I measured the first set of cups and they are actually 5 and 9/16 but I dont think that is keeping them from seating. the 4.5 cups are too small and it looks like it would let the bag move around...someone told me to modify the hole in the lca (by cutting and rewelding) to get the cup to fit.. or weld them in place.....if I have to do that why not just do a 9" shallow cup to the control arm itself and eliminate the "drop in" cup......I hope someone else has ran into this and has a simple solution...otherwise I guess I will break out the plasma and go to cutting...but really not my first choice.......ideas? help? anyone?

[lotik]

Make a template out of cardboard that fits how you want it in the control arm. Take it out and measure it.

[tubbedII]

daved, I don't think you need to put too much thought into it. Mine sit exactly like you have it pictured. I did trim mine, but just to make the cup a little shorter for the top to sit just a little bit above the control arm. The cup bottom didn't match the contour of the spring cup on the lca, but I've cycled the bags at least 20 times now and have driven it around the block with no issues.

The problem I mentioned about getting them flat is probably due to my bags being hard DOMs that aren't that flexible. I mouned the bag to the top plate, then the plate to the crossmember, then the cup the bag and shoved it in place. Since the lca was all the way down and the bag was verticle, the cup wasn't sitting flat when I first pushed it in. It just took me some trials to compress the back of the bag by hand to have the cup sit flat.

[daved]

this is a pic off of tcb-1's build thread...


the tube part of the cup appears to be smaller than the plate unlike the first photo in this thread (my cup) which the tube is larger than the plate....I talked to nick over at AVS (maker of the cup) and he said to weld in place so it does not "rock" or move.. and then bolt in place through the bottom.....has anyone done this???? would seem to me that you better be right on the height or it would be a pain to cut out in order to cut it down...any thoughts?
the bottom of the taper at the smallest part (not perfect round)in the stamped arm is like 5.25......

[daved]

Thanks tubbed, again this is my first install and want to make sure it is right (would hate to have a bag fail do to improper install).....AVS said they would send me pics of where to tack it which is what he recommends...

[fenton_cj]

I made my own cup and sunk it into the lca so i can get my truck to sit lower

[Shane]

they aren't ever going to sit flat because the bottom of the "well" in the lower control isn't flat ...

[tech@scottshotrods]

Daved U can allow the lower cup to float no need to weld the weight of the vehicle will hold the lower cup in place.

[daved]

they "wobble" on the taper (the side of the control arm).... not even bottoming out...i realize the bottom is not flat...but these are a 1/2 from the bottom....at this point I will install and see what happens....i have test fitted and can get them somewhat flat but can tap back and forth still....did not one side to seat different than the other....we will see....

[72gmcshorty]

i have the same problem dave. i know exactly what you are talking about. The LCA tapers inward slightly towards the bottom and the cup doesn't get all the way down. I was thinking maybe grinding a bit of the cup (taper it to fit) and the lca to straighten it out where it rubs.

[smashingchuck]

I don't have any experience with cups, but if 4.5" is too small and 5.5" is too big... sounds like you need a 5" cup. and don't weld those things in place you'll be kicking yourself if you did.

[daved]

so I trimmed the cups down as most people do



after grinding the cuts smooth I did a test fit and after one cycle up and down the cup tilted (moved) toward the inside of the lca and allowed thw bag to touch at full collapse...so I did what Nick at avs said to do and put some good tack welds in the stamped depressions (there are 3) like this



I just set the cup in where if fit best (the least amount of wobble) I dont know if the angle is right as it kinda looks more parallel to the lca and maybe it should be more parallel to the crossmember above it...to attach the bottom of the bag i went thru the hole in the lca and used the center bolt (slam bags)..this is what I ended up with....will see if it works..but a couple of weeks away from trying it out..

[daved]

.....AVS said to do this....why would I be kicking myself for tacking in place??? the only thing I dont like about tacking in place is I can only use the center bolt on the bottom of the bag (tried to eyeball lining up the two but was of by half a hole)....

[clemsonteg]

Having a similar issue with my truck. I have a set of 5.5" diameter 2" tall cups that don't seat correctly. I also have a set of 5" diameter 2" tall cups that fit much better, but they seem to rub slightly on the rear of the lower a-arm when aired out

[dec010974]

Interesting. The smaller bag cup will move and float in the spring pocket. The drive was very unpredictable. I'm in the same predicament. I'll go back to my larger cup an do what daved did. a wobbling front end and torquey gas pedal = accident. Please post your results once completed. Clark.

[crakarjax]

Originally Posted by clemsonteg

Having a similar issue with my truck. I have a set of 5.5" diameter 2" tall cups that don't seat correctly. I also have a set of 5" diameter 2" tall cups that fit much better, but they seem to rub slightly on the rear of the lower a-arm when aired out

Same exact issue with some cups from BC Fab. They are 5.5" OD and clearly too big, 5-5.25" would be perfect. Where did you get your 5" cups?

[jondancer]

So are 5.5" diameter cups to big for 67-72 trucks?

[crakarjax]

Originally Posted by jondancer

So are 5.5" diameter cups to big for 67-72 trucks?

Yes

[jondancer]

Anyone have a source for 5" diameter cups or should I have them made locally ?

[crakarjax]

Originally Posted by jondancer

Anyone have a source for 5" diameter cups or should I have them made locally ?

I couldn't find any but BC Fab will make you some if you ask them specifically for a 5" diameter cup.

[6DoF]

i cut up an old air tank

you can see parts of it in the upper right corner of the pic. i had to slice like an inch out of it and pull it together, but was really nicely formed to a circle. these are also 9" ID cups.