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By STX - 10 Years Ago
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I need to weld new perches on a nine inch rear end.
Which is the perch angle for 1954 Ford/Mercury rear ends?
I have heard that all Fords have 5 degrees pinion upwards relative the perches, correct?
Which perch angle is desired for a high power car?
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By The Master Cylinder - 10 Years Ago
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You should be more concerned with the pinion angle inrelation to the output shaft of your transmission. The pinion centerline should be relatively close to parallel to the centerline of the transmission centerline to avoid excessive vibration and wear on the u joints. Set it with the car sitting on the all fours. This is a difficult question to answer on a forum because alot of factors come into play, i.e. ride height, engine installation, etc. I don't think anyone would just say "Yeah, set it at 5°".
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By marvh - 10 Years Ago
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Here is a link to very useful information on drive lines and driveline angles.
http://www.iedls.com/
then click on the top right education zone.
I have never heard of the 5 deg perch to pinion angles.
I always set up rear ends to meet the transmission angle.
As The Master Cylinder said make sure the weight is on the four wheels when setting the pinion angle because if you don't have the weight on the wheels by just having the springs hanging and you set the pinion angle to the transmission angle then when you lower the car the pinion angle will drop downwards. You will then have to shim the perches afterwards to raise the front of the differential.
marv
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By Canadian Hot Rodder - 10 Years Ago
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Proper pinion angle should be approximately 3 deg. positive from the center line of the axle and 3 deg. negative, down from the center line of the transmission.
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By Canadian Hot Rodder - 10 Years Ago
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To clarify a bit more, the perches are basically parallel to the center line of the yoke on the rear end or are slightly pointing the yoke downward (approx. 1 deg.) The drive shaft needs to have this 3 deg. +/- offset or you will get a skipping rope effect if the rear yoke is pointing up to the transmission. Remember when you accelerate, the yoke is going to try and rotate upward towards the floor boards of the car, unless you are running ladder bars or a 4 link.
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By CK and his 55Tbird - 10 Years Ago
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We always set the pinion a degree or two down from the parallel drive/tail shaft as the pinion will drive its way up the crown, and lift the pinion. Hence the way a car squats under power.When the car is on its wheels the shaft, gearbox and pinion should all be as inline as possible.
So the pinion down a bit and the gearbox up a little. Then during squat etc.
However most of the diff/9" I fabricated was done in a jig. But i would place the perches and diff sitting on the springs, bolt them with the u-bolts and place some ramps under the wheels and let it settle adjust the pinion 4" offset and angle, tack it up then remove to weld completely.
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By 57FordPU - 10 Years Ago
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I agree with Rob (Canadian Hot Rodder). I set my spring perches with the drive shaft installed and a 3* angle to the shaft. I tack weld them in place and of course I remove the axle to finish welding. There are perhaps some other reasons for the angle difference, but my thoughts are that it encourages the roller bearings to turn in the universal cup. With a straight angle at the transmission tail shaft or pinion, the bearings will not turn and create flat spots.
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By The Master Cylinder - 10 Years Ago
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CK and his 55Tbird (3/20/2014)
When the car is on its wheels the shaft, gearbox and pinion should all be as inline as possible.
You want them parallel (+/- 1-3°) but should not be inline. If they're inline the u-joints will not rotate properly, causing flat spots on the needles bearings.
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By lyonroad - 10 Years Ago
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STX (3/17/2014)
I need to weld new perches on a nine inch rear end.
I have heard that all Fords have 5 degrees pinion upwards relative the perches, correct?
Which perch angle is desired for a high power car?
I'm no expert but maybe the 5 degree notion comes from here.
http://www.fordmuscleforums.com/rear-end-articles/489830-leaf-spring-perch-installation.html
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By lyonroad - 10 Years Ago
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Further to this discussion regarding perch angles and driveline angles I recall setting this all up on my '56 Merc pickup. It has a 351C, T5transmission and the stock Dana 44 rear end, an aftermarket front x member and a owner fabricated trans x member. The engine/transmission was set up with a 3 degree incline with the intake manifold level. The rear end was mounted as stock and ended up with the pinion angled at 3 degrees to match the engine trans. Unbelievably, when I hooked up the driveshaft it too was at 3 degrees, meaning everything was in a straight line. Like the second image in Mastercylinder's post. Not good. But I soon realized that the pinion on the Dana 44 is not in the centre of the axle housing (I don't know if all rear ends are like this). The edge of the ring gear is centred and the pinion is 1.5” -2” towards the passenger side, meaning if the engine/trans is centred then the drive shaft angles to the passenger side at approximately 3 degrees. I concluded that the u joints didn't care whether the alignment was vertical or horizontal and left it that way. I have been driving it for 10 years now and have had zero driveshaft u-joint issues. You can't see me but I am knocking on wood.
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By pegleg - 10 Years Ago
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I also use a couple degree down angle on the rear end, with leaf springs. The torque required to drive the car down the road will rotate the housing some amount. How much depends on torque required to do that.
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