adjustable upper rear control arms

MaSnaka · #1 (**permalink**) 06-09-2009, 12:07 AM

TCrist, Capteddie, Scotts, I know you guys had purchased a set of these to adjust pinion angle. Can you give me the part # as I'm going to need the same. Thanks.

John

capteddie · #2 (**permalink**) 06-09-2009, 10:41 AM

John,

Mine are from this Hotchkis kit. If I remember I had to call them to get the part number for just the uppers.

http://www.hotchkis.net/7998_mustang...sion_pckg.html

tcrist · #3 (**permalink**) 06-09-2009, 12:36 PM

John,
I have the part numbers at home. I will post them later. Actually I am in the process of installing them. Should have them finished up tonight.

Terry

JAC · #4 (**permalink**) 06-09-2009, 03:43 PM

So is the geometry off on all Classic Roadsters? Or did you guys modify the stock setup?
Thanks

tcrist · #5 (**permalink**) 06-09-2009, 04:40 PM

John,
The p/n for the Hotchkis adjustable trailing arm set is P/N 1204AA. This gets you everything that you need for both upper trailing arms.

JAC,
Mine is stock CR LTD from what I know. Using the upper frame holes for the upper trailing arms my trans and rearend are out of alignment almost 5 deg. This could be from wornout bushings, different motor and transmission mounts, I really am not sure. I got them because I have a vibration on acceleration that I am trying to work out.

How is your CR coming along?

Terry

tcrist · #6 (**permalink**) 06-09-2009, 07:59 PM

John,
Just a thought. You might want to take your Cobra to a place that will let you use a lift instead of laying on the garage floor. Don't ask me how I know

.

Terry

MaSnaka · #7 (**permalink**) 06-10-2009, 12:30 AM

Thanks Terry, I have a guy helping me tune my car and he mentioned right away that my pinion angle was off. If he can see that with his eye I figure it's off pretty good. Seems simple enough to correct. I thought just blocking the tires up enough to slide under the car would give good access and keep the car relative to the ground. I need to replace the differential gears, posi, and that would be a good time for the pinion adjustment. The lift is probably the way to go. Thanks for the p/n.

I seem to remember DV mentioned the lower trailing arms are shorter than stock Mustang. So using stock uppers would throw the pinion angle off. Adjustable is the way to go.

John

Double Venom · #8 (**permalink**) 06-10-2009, 05:26 AM

John, well done...What a memory!
Center to center of the bolts for mounting the rear end (Lowers is 15"s) With adjustable arms this is an excellent place to start and if you're really good you can get a true 4-wheel alignment----AND a correct pinion angle!
DV

cobraduke · #9 (**permalink**) 06-10-2009, 07:52 AM

duplicate.

Thanks,
Mike

cobraduke · #10 (**permalink**) 06-10-2009, 07:55 AM

Quote:

Originally Posted by Double Venom

John, well done...What a memory!
Center to center of the bolts for mounting the rear end (Lowers is 11-1/4") With adjustable arms this is an excellent place to start and if you're really good you can get a true 4-wheel alignment----AND a correct pinion angle!
DV

Ed,
11 1/4 is center to center on lower arms (fixed) and with adjustable uppers set that dimension on them to start? What pinion angle do you want to shoot for at normal ride height? I believe I read that it should be slightly down relative to the transmission/engine so that when you get on it and the rear twists raising the pinion, it pretty much parallels the trans/engine axis. Is that the goal? My problem with the fixed arms is not vibration, it is wheel hop when I get on it, especially out of a corner, I believe the adjustable upper control arms were developed to allow the Mustang guys to tune this out to help keep the rear planted (especially for drag racing). Is that correct?

Thanks,
Mike

MaSnaka · #11 (**permalink**) 06-10-2009, 02:50 PM

DV, 11 1/4" sounds way short for the lower arms. I just measured mine and 14 1/4" bolt center to bolt center and about 9 1/4" on the uppers. These are very approximate measurements, don't use for fabricating.

John

capteddie · #12 (**permalink**) 06-10-2009, 03:07 PM

15" center to center is what the original ones I got from Don were.

And then I had adjustable ones made based on the 15" C to C with a little over a 1.5" in/out adjustability.

Double Venom · #13 (**permalink**) 06-10-2009, 03:36 PM

Mike, you've got it, the correct measurement for the lowers is 15"s center to center! I should have known better than to trust my memory any more escpecially a bout numbers. It sounds like you pinion is going way to high under power this WILL give you a serious case of wheel hop! The pinion, with the car under load and sitting level should point down 2.5 to 3 degrees for our cars. Even with slicks (ya-boy) this will keep the pinion in a torque attitude of being still slightly negative or level. Never have it pointed UP!
DV

MaSnaka · #14 (**permalink**) 06-10-2009, 06:23 PM

15??? Now I know why I have positive pinion. I am rebuilding this car piece by piece. A great way to learn. It is getting dialed in though.

John

tcrist · #15 (**permalink**) 06-10-2009, 08:12 PM

The frame bracket for the upper trailing arm has 2 sets of holes in it. At least my CR LTD does.

Which holes are you supposed to use? Is this where you change the pinion angle if you do not use adjustable upper trailing arms?

Even using the adjustable arms which holes should I use.

The pictures in my manual are not very clear and it does not state in the manual which ones to use. Mine have been in the upper holes. Could this be where my vibration on acceleration is from?

Terry

MaSnaka · #16 (**permalink**) 06-10-2009, 11:00 PM

Terry,
I noticed mine has the two holes also and I'm bolted into the upper holes like you. Good question for someone who knows.

John

cobraduke · #17 (**permalink**) 06-11-2009, 06:54 AM

Thanks, Ed. Makes sense.

Mike

tcrist · #18 (**permalink**) 06-11-2009, 10:08 AM

DV, where did you bolt up capteddies at?

Update, I looked thru my complete manual for other pictures that might show the upper brackets and did fine one that looks like the bracket is bolted into the BOTTOM holes.

Terry

capteddie · #19 (**permalink**) 06-11-2009, 10:19 AM

I can only find one picture of my upper mounts. Its hard to tell if it has two sets of mounting holes, but the arm looks to be pretty close to the bottom of the mount.

I'm sure DV will chime in with a definitive answer.

Double Venom · #20 (**permalink**) 06-11-2009, 10:22 AM

Terry,
I was just getting ready to jump in on this but it took me a half an hour to get the picture up. Think GEOMETRY-although 'you' shouldn't have to, IF you used the top hole then the OEM upper arm is going to push/angle your pinion way to high! Impossible to line it up correctly even with adjustable lowers! IF you did the wheel would be sitting to far back in the wheel well to even work! The wheel hop must be spectacular if you used the upper hole! (Blaming this on the old manual is a righteous--Oh-CRAP!)

DV

PS Same rule applys for an 8.8 or 9" !