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Old 07-07-2008, 03:14 AM   #1 (permalink)
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Swapping in an 8.8 out of a 91 fox body. Got all the old brackets off, and ordered new leaf perches.

I'm having trouble envisioning how to set the pinion angle when I weld on the new perches. For those who've already done this, how did you do it? What lessons did you learn?

Thanks,
Greg (anxiously awaiting the mail man!)
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Old 07-07-2008, 09:00 AM   #2 (permalink)
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I set the perches on my springs, wrapped the U-bolts around the rear-end and tightened them enough to hold it. I then set the car's weight down on the rear-end (on jack stands) so the springs would level out. I put a floor jack under the pinion and raised it to -4 deg. Once set, I tack welded the perches, then pulled the rear-end out and welded the perches all around.

I have Maier Racing 165# springs and the pinion angle drops (down) as more of the car's weight is placed on the rear-end. Since my car doesn't have the gas tank (or gas) in it, nor the battery in the trunk, interior, etc, I allowed an extra degree up for that weight.

This is actually the second time I did this. I tried doing it off the car using a level and inclinometer. But as I said, the springs change the angle when weighted, so I ended up cutting the perches off and re-welding them with the rear-end under the car. The pinion went down 3 deg when I put the weight of the car on it. I don't know if that is something unique to the Maier Racing springs or not, but doing it in the car with as much weight as possible is the safest way (though a little more work).[color:blue][/color]
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Old 07-07-2008, 11:04 AM   #3 (permalink)
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I put my stock 6 cyl rear end on jackstands with the leaf pads up. I used a scissor jack under the pinion to get pads level. I had trouble getting it right with a hyd jack, it was hard to make very small changes. Once all level I measured the pinion angle. Then I put the 8.8 on the stands and got the same angle on the pinion and set the pads level, tacked, rechecked width and angles, then finished welding them. Don't weld too much at a time w/o letting it cool. Too much heat on the tubes can warp them. I did about an inch at a time and then moved to the other side. Don't get in a hurry.
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Old 07-07-2008, 02:08 PM   #4 (permalink)
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Quote:
Once all level I measured the pinion angle.
How did you measure this on your old axle?
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Old 07-09-2008, 08:55 AM   #5 (permalink)
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Angle finder.
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Old 07-09-2008, 10:39 AM   #6 (permalink)
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ozarks: Well what did you measure everything against? How did you level the car? Myself, I just put an angle finder on the pinion of the 8", and then mimicked it with the 8.8.. SHOULDN'T matter that way if the angle finder says 58*, as long as they are both the same.. But we shall see I guess...

The harder part I have coming up I believe is matching it with the tranny crossmember that I have to fabricate, as I don't have much weight on the car.
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Old 07-09-2008, 10:54 AM   #7 (permalink)
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I leveled the car on jackstands, using the bottom of the rocker panel as a reference. I figured it is probably as close to a 'level' reference as there is on the car. When setting the transmission angle, I'll use the same reference.

I actually raised the rear end to put the car's weight on it. I used an inclinometer (a cheap one from Sears, the one Summit sells is supposed to be much better) and AFTER leveling the car using a level, I measured the angle of the rocker panel with the inclinometer (to correct for error). I then measured the angle of the pinion flange (allowing for 90 deg of rotation) and set is for a difference of -4 deg (again, allowing a little extra for the extra weight when the car is done).

Actually, if you just measure the difference, you probably don't need to level the car (at least not absolutely, but I figured I'd get it as close as possible to the real world - as if the car will ever be level with wheels on it!).

Measuring the difference between the pinion and spring perches on the 8" should accomplish the same thing, provided your springs don't change the angle with load, like my Maier Racing springs do.
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Old 07-09-2008, 04:04 PM   #8 (permalink)
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I did the same thing that Ozark did.
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Old 07-09-2008, 09:55 PM   #9 (permalink)
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There is a write with some pictures of this on the web page in my signature.

For a mostly street driven car the important thing is to match the transmission output shaft angle to the pinion angle. My experience has been this needs to match within 1/4 degree to keep from getting vibrations at freeway speeds. The difference between the rockers and the drivetrain should not exceed 4 degrees for the same reason.
IIRC most passenger cars will be pretty close to 3* in relation to the rockers.
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Old 07-10-2008, 08:19 PM   #10 (permalink)
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OK, I need someone to break this down real simple for me... How in the world can I measure within a 1/4 degree? I'm having trouble figuring out how to get within 2-3 degrees! I haven't made the trip into town to look for an inclinometer (?), but do these things really get down to the fraction of a degree

The car currently has way to tall front springs (see sig pic), so any measurement from the transmission output shaft is going to be suspect. I can't put it on the ground right now, because I don't have spring perches on the rearend.

I've seen 4x4s with some hellacious driveshaft angles, that I KNOW don't have matched angles between the tranny and the rearend. Do I really need to get that precise?

I really need help on this one. The one rearend shop here in town sent me to a steel fabricator to get the perches welded on. The fabricator didn't know what spring perches were! He said if I could clamp them on where I wanted them, and bring him the axle, he'd weld them for me. I can do the welding, I wanted someone with the expertise to put them in the right place! So, I guess that means I need the expertise. HELP

I was liking the idea of setting up the old 8 inch on jackstands, leveling the spring perches, then using one of these inclinometer thingies to measure the face of the u-bolt connection at the pinion. Then rig up the 8.8, get the same angle on the face, then put the perches on, level, and ZZZZZZZZ, weld them up. This seems like something my simple mind could handle, but it's probably way too easy.

When you guys say -4 degrees, does that mean tilted 4 degrees below the horizontal plane?

I appreciate all the input, keep schooling me!
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Old 07-10-2008, 11:11 PM   #11 (permalink)
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If you have the stock engine, transmission, and stock mounts, then weld the perches just like they are on your 8".

If you've changed the engine, transmission or mounts, see if this article makes more sense. Just remember they are basing the 3 degrees in relation to a level chassis, and at static ride height.
http://www.iedls.com/ptsetup.html
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Old 07-11-2008, 12:19 AM   #12 (permalink)
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My apologies--I didn't see the part in your previous post to look at your Car Domain site. That was helpful as well.

The other link you provided above explains a lot, but it seems to contradict what I'm reading others say about the negative 4 degrees? Seems like they're showing what I would call a positive 3 degrees, that is the pinion angle is above the horizontal plane?

As far as my setup goes, I'm running a different motor, on RMP adjustable motor mounts, a T5, so no, NOTHING is like it came from the factory. I did a similar deal to your car--found a 91 LX donor car with a stroker motor (no blower), good T5 and rear end (I'm sticking with the 4.11s that are in it).

Thanks for the input. I need to read this about a hundred more times, then go tackle stuff in the garage.
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Old 07-11-2008, 12:43 AM   #13 (permalink)
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When I said I set my pinion angle to -4 deg, I meant 4 deg UP (probably should have said +4 deg). I set it to 4 deg instead of 3 since my springs move it down when more weight is applied and the car is not now loaded. It should settle down to 3 deg UP when fully loaded. I will set the tranmission angle to 3 deg down. Sorry for the confusion.
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Old 07-11-2008, 02:01 AM   #14 (permalink)
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The good news is if you've got the right mount kit from Ron, you will hopefully be at 3 degrees. The T5 cross member will drop the rear about a degree, the lower engine mounts should take back that degree. So with a bit of luck you should be right back at stock, with a slightly lower center of gravity (very cool!). I'm using a modified set of '65 mounts for that same reason (but with a bit less NVH).

So step one would be to install the engine and transmission, and use an angle finder to compare the angle of the drivetrain with the angle of the rockers (which are suposed to be parallel with the longitudinal centerline of the chassis). The differnce between the angle of the rockers and the angle of the drivetrain should be as close to 3* as possible, but no greater than 4* (this is from my personal experience. Above 4 degrees and I have trouble getting the pulsing vibrations stopped). End of step one.

Step two. pull the old rear end and set blocks under the axle mounting pad of the springs so the vehicle sits on those springs with the new axle sitting on the new spring perches on top of the springs, and centered side to side. I lightly tighten the U-bolts so that I can turn the housing inside, but it won't slip by itself.
Step three.
Get a whole bunch of real cute looking girls to sit on the car, until you get it to to match the final curb weight with driver and about 1/2 tank of gas(at each corner if you can, but at minimum front and back) . Cute girls are much better than beer guzzling budies fat butts denting things. Or you can throw lots of weight in the trunk (maybe two fat buddies and a 6 pack... make sure to close the trunk lid!). with the car weighted correctly on the suspension, measure the angle of the engine-transmission, and set your pinion angle to match. Tack weld the perches, then pull it out and weld as per the above guys said. Small welds alternating side to side, allowing time to cool between welds, until you have both sides done.
Don't forget to make sure the rear end is still centered after the tack weld. For that you need to ensure you have good stiff bushings and straight springs, then you can measure from the spring to the axle flange. I don't like using the fender lips to measure, as I've seen quarter panels welded way off, and then the rear end is off set in comparison to the chassis. It may "look" right, but it won't drive right.
When you're all washed up and back from dinner you can let your buddies out of the trunk and run like hell!

That's really about all there is. I use this oportunity to check for chassis twist by measuring both rockers and comparing the angle, and I also check to make sure the rear end is perpendicular to the longitudinal line of the chassis. Then I check the distance from the center of the axle to the center of the spindle on each side and compare lengths. They should be very close to the same The only difference should be if the caster on one side is set different than the other side.
These last steps help ensure I have a good straight chassis for a great drving car.
Hope this helps,
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