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Discussion Starter #1
I've just ordered the roller perches from Opentracker and plan on doing my own UCA LCA mods using his reinforcment plates and dimensions. I'm planting a 428 in the 68 Fastback. I'm also planning on using the 620 springs and good standard (non-strut)gas shocks. My questions are two fold;

What are the pro's and con's of doing the longer (1.75") drop over doing just the 1" drop. I'll be mostly using the car for street duty with a couple of stints and the drag strip. But street duty will include winding mountain roads banging through the gears.

When does it become necessary to cut down the outer bolt in shock tower brace that holds the rubber UCA snubbr?
Will I need to do this with either drop or does it depend on tire size?

Thanks in Advance!! ::
 

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I've always understood 1" was the max drop for a stock upper arm because the ball joint will bind if you drop any farther. All the new tubular arms (and Opentracker's mods) have changed the ball angle because more than 1" drop gives better geometry. I didn't think the drop was more than 1.5" though. My Global West arms came with a template so I didn't do any measuring.
 

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A good bet would be to pm Opentracker if he doesn't respond to your post. A couple years ago I was considering modifying my UCAs like his. At the time I asked him about how far to drop and he suggested about 1-3/8", iirc (which I believe is the drop made when using Global West). I've read elsewhere (and perhaps this is why) that there may be some issues with "roll center" when lowering the UCA "too far".

Note: when doing opentrackers slice and bend mod you not only change the angle of the ball joint, the process also results in a shortenced distance between the UCA chassis pivot and the the ball joint. My guess is that the net result is practically a dimensional clone of the GW UCAs.

- Gord
 

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Discussion Starter #4
The 1 3/8ths is 1.375. I must have just forgot the "3". I am going to modify the UCA's to correct the balljoint bind, so technically I can go more than the 1" drop. My question centers on whether there is a benifit in going the extra .375 with any trade off. And of course when is the outer shock tower brace mod an issue.
 

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Outer shock tower clearance is related to spring height more than UCA drop. With the GW drop (guess it is 1 3/8") and a full coil cut off the springs I still have had no problem with the outer tower. You probably have to be dropping pretty low or using a low rate spring to have problems.

Here is a recent pic that shows the stance on my '67.
 

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Discussion Starter #6
Outer shock tower clearance is related to spring height more than UCA drop. With the GW drop (guess it is 1 3/8") and a full coil cut off the springs I still have had no problem with the outer tower. You probably have to be dropping pretty low or using a low rate spring to have problems.

Here is a recent pic that shows the stance on my '67.
With the lower drop, does this not allow the tire to bounce higher up into the wheel opening? Would tire width have anything to do with it? The shock tower mods I've seen do niot raise the bump stop, it only moves it inboard several inches. So at what point is the shock tower mod required for clearance??
 

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I lowered mine 1 3/4. The only thing I could tell you about it at the moment is to watch the clearance between the back of the arm and the shock tower. When test fitting mine I noticed an interferance problem there. It could be the repop arms? I ended up grinding a little off the arm and peaning the tower a little. Then when I remembered to put the shims back :eek: I had plenty of clearance :winkgrin:
 

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So at what point is the shock tower mod required for clearance??
With the springs out, it would be easy to check. I'm guessing, though, that it's the shocks that run out of travel first, and that this damages them. So maybe you should test fit with shocks in place and use a jack on the LCA to see how far you can compress the suspension before the shock bottoms out.
 

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When you drop the UCA, you're really changing the camber curve, so I suppose that's what the discussion should really be about.

Here's what I found when I compared the stock geometry with the PM drop on a '65. Since you're working on a '68 please only use this as reference because your results will be slightly different. I don't know how much, so please report back what you find!

http://forums.vintage-mustang.com/forums/photopost486/data/500/37250UCA_Change_Camber_Curves.jpg
 

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I lowered mine 1 3/4. The only thing I could tell you about it at the moment is to watch the clearance between the back of the arm and the shock tower. When test fitting mine I noticed an interferance problem there. It could be the repop arms? I ended up grinding a little off the arm and peaning the tower a little. Then when I remembered to put the shims back :eek: I had plenty of clearance :winkgrin:
There have been a few posts recently about the back of the upper arm rubbing the shock tower. All have been the overseas repro pieces. The quality USA units have not had any clearance issues. There were with cars that didn't have the drop.
 

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Now that graph is a keeper. Thanks for posting it!

Question: What was the orientation (relative to level) of the UCA at "0 in." rebound/travel?

- Gord
 

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http://home.earthlink.net/~myradpc/sitebuildercontent/sitebuilderpictures/dscf0339.jpg
http://home.earthlink.net/~myradpc/sitebuildercontent/sitebuilderpictures/shocktwer.jpg
http://home.earthlink.net/~myradpc/sitebuildercontent/sitebuilderpictures/bs65.jpg
http://home.earthlink.net/~myradpc/sitebuildercontent/sitebuilderpictures/outershock1.jpg

Our car uses a 16X8 wheel with 4.5" of backspacing. The tire was hitting the outer shock tower before the mod. If the car isn't real low and you don't have a lot of camber, you should be fine without it.

The upper arm mod I do is for a 1" to 1 3/4" drop. Some of the guys on CC.com think a 1 1/2" drop is best. We did a 1 3/4" drop on our orange car.

John
 

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Question: What was the orientation (relative to level) of the UCA at "0 in." rebound/travel?
Gord, the lower control arm was a zero degrees. This was measured with with an magnetic protractor on the main flat (the arm 'kicks' a little by the ball joint.

At three inches of compression the suspension started to bind, so that is beyond what you would see on the street (my outer shock tower/bump stops were removed.

Here's a picture of the car with the tire on (15x8) at the zero height.

http://forums.vintage-mustang.com/forums/photopost486/data/500/37250Zero_Height1.JPG

http://forums.vintage-mustang.com/forums/photopost486/data/500/37250DSCF0011-zero.JPG
 
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