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IRS Thunderbird half shaft geometry?
Setting up rear end question, by raising and lowering the IRS Diff head aligns better with the prop shaft, but also alters the half shaft angle from diff head to the wheels, is it better to have the half shafts slightly up at the diff, then horizontal or under level with full power applied, any recommendations please?
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The driveshaft will function nicely from about 3 degrees to 10 degrees. The CVs work up to about 15 degrees. Since the CVs plunge more if their angle is higher, I would tend to keep them horizontal at the expense of the driveshaft angle. Power loss through the angled driveshaft will likely be less too.
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Ant,
The driveshaft "U" joints need some offset but no angularity for the needle bearings to work correctly. The Ford half shafts use a tripod joint on the inboard end and a CV on the outer. All of the plunge is seen by the tripod joint. There are two schools of thought about the correct setup. One being that the halfshaft should be level at max acceleration or Two that they need some angle to keeping from brinelling the race due to the high loads under max acceleration. I feel that it best to just split the max angularity that the unit will see in service. I try to put in about 1>2 degrees at steady state to allow the unit to have some plunge which increases the area that the bearings see on the race. |
Richard,
That's an interesting point about the tripod inner. I'm too used to seeing Rzeppa's on both ends. There probably is some longevity advantage to a little designed-in plunge. |
Irs
Richard & strictlypersonl,
Thanks, that makes sense to move the tripod bearing area under hard use! Re: driveshaft, this one is going to be about 2' long compared to the 4" tube my friend is doing with his long tailhousing TL, so will set up head and upright heights to find angles. |
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There might be some increase in life, but nobody has put enough miles on a JBL for me to have good data points. 40k is the most so far and that is with a relatively low output motor. (400 or so foot-pounds.) So I really cannot say if my thoughts are backed up by the scientific method that we prefer. But what the hell, the halfshafts have not fallen out yet, so I am calling it a good approach. |
Richard,
In our business, we can only hope to combine (engineering and other) logic with a small amount of empirical data, throw the result against the wall and hope it sticks. :rolleyes: |
Bob,
I hope it sticks. If it does not, then I am holding it. But that is not new. Every engineer in the world understands. I just wish these folks would drive the bloody things!!! They are not fragile. They are meant to go, turn, and stop. With the shortest periods possible between the three events. But that bit is never considered. But the way it looks, I guess we should just chrome them. (Or polish the alloy.) Later my friend, |
My FFR uses the T-Bird 8.8 centersection and we have 11,000 miles on her; no problems with acceleration, cornering hard, or stopping. Not sure angles, etc. but the shafts look level on no load and the driveshaft is pretty level too.
Not much info here to help other than that setup is pretty flexible and takes a pounding and keeps on ticking! |
I've got 48,000 miles on my EM with a Lincoln IRS. I've got a stock 302 so the loads aren't that great. It has worked perfectly. In the last 1,000 miles I am starting to get a faint low pitched growling sound from what I believe is the right rear. (Sounds like a knoby snow tire on dry pavement) My local mecanic ran the car on the lift and couldn't find anything.
Unless someone has a sugestion on what to look for I will keep driving until the noise is louder and more consistant. hints: noise is not yet consistant rotated rear tires, no change in noise sometimes louder during a left hand turn not engine nooise, definiatly drive line. seems to get quiter when you aply the breaks. Any ideas? HarveyR |
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My first guess was a wheel bearing and I'm still sticking with that. It was a very faint noise when I brought it in to the mechanic. (He could barly hear it when I took him for a test drive.) When he ran the car on the lift there would be no load at all on those bearings. It is now definatly louder while making a left turn and goes quite while makeing a right. I'll take it back in.
Harvey |
Problem solved. it was FRONT wheel bearings.
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