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Discussion Starter · #1 ·
As you guys may know I'm installing a Buick Grand National Rear End in my 87 Monte Carlo Super Sport. From what I've been reading I know the drive shaft will need to be 1 inch shorter.
I know how long the drive shaft is in the car right now, but I'm not sure of the dimensions that PST is asking for, because the the new rear end is not in the car yet.
They want the length from the seal on the transmission tail housing to the front of the pinion yoke.
I have this measurement from the car currently, sitting on all four wheels. Can I just subtract 1 inch from this?
I know this is a critical measurement, but I don't want to put the new rear end in and then have to push the car around for six weeks while my drive shaft is getting made!
 

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Discussion Starter · #4 ·
I have the measurement I need for a 7.5 rear end. I was kind of hoping someone could confirm that the measurement for the 8.5 is 1 inch shorter. It seems to be the most common number I can come up with from the interwebs.

I would like to have a drive shaft ready to put in when I put the new rear end in, but if I have to I can wait to measure once the new rear end is in.

Edit.
Looks like they measure their driveshafts a little bit different.
Let me get my center-to-center measurements tomorrow. And hopefully the slip yoke will be okay.
 

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Discussion Starter · #5 · (Edited)
google Dennys driveshaft, they have a form to fill out with specific measurements.
Yes. I have the measurements for my 7.5 rear.
I am trying to figure out what they will be when I install the 8.5 rear from GN.

I know its a long shot, but I can always measure once new rear end is installed.

I just cringe at the thought of pushing this car for 6 weeks while a custom shaft is built, when some simple math may get me what I need.
Also the fact that I can't sign in from laptop is kinda frustrating too!
My phone has a nice big screen, but enjoy posting better from a laptop...

2nd edit.
CST said they would use a powerglide slipyoke. So when I get to the shop tomorrow I can measure what's in the car vs. the glide yoke... Maybe get a better idea there.
Minus one inch.
 

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Discussion Starter · #7 · (Edited)
615250
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615253
Now's your best time to also switch to 1350 U-joints, since you are getting a new front yoke and the shaft, all you have left is the pinion yoke change....and it will be bulletproof.
1350 Yoke. Check
High Dollar Cover and Stud Kit. Check
New Bearings, and Seals. (except pinion bearing). Check
Urethane Bushings. Check
SSM Double Adjustable Upper Control Arms. Check
SSM Lower Control Arms. Check
Disc Brake Conversion. Check
Reinforcement Kit for where the Control Arms mount to Chassis. Check

Built me some wheel cribs this morning. I have been wanting to do that for awhile. I didnt need any to measure Driveline angles, and such under my truck. This car is a different story! LOL!!

Tomorrow I am going to bite the bullet, and mock up the new rear so I can get a proper measurement. I really dont want to, you would think somebody would have the measurement I need seeing as this is not a combo that never came from the factory on thousands of cars...

Rant over. Some good coffee, and an early start maybe I can be done by lunch!
Like my dad used to tell me, "Stop talking about it, and just do it!"

I am happy with how this thing is coming together, it aint cheap but will be a very nice build when I am done.

Also Imsport, I checked with LaneAuto and it looks like they get their stuff from PST. As far as I can tell, they are the ones I am going to use. PST seems to have a good reputation, and really fair pricing too.
Thanks guys for all your help!
Wheel Crankset Automotive tire Tire Bicycle part
Tire Wheel Car Land vehicle Vehicle
Motor vehicle Automotive tire Bicycle part Automotive exterior Rim
 

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Steel is fine, aluminum if you want to.

3.5" dia .083" wall seamless is something like 35% stronger than 3" at the same .083" wall, but the cost difference isn't all that much.
For two shafts of equal wall and diameter, critical speed will be at a higher rpm on the larger diameter.
 

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Discussion Starter · #12 ·
Steel is fine, aluminum if you want to.

3.5" dia .083" wall seamless is something like 35% stronger than 3" at the same .083" wall, but the cost difference isn't all that much.
For two shafts of equal wall and diameter, critical speed will be at a higher rpm on the larger diameter.
PST told me 7000 rpm critical speed, and something like 1200 HP for the aluminum shaft. I'm pretty sure its 3.5.
Now to get that pesky, I mean perfect measurement.
I forget the price, but it was less than Denny's.
Sounds like it will be well balanced, for something so long to spin that fast...
 

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Sounds like it will be well balanced, for something so long to spin that fast...
PST's web site gives the stats...seamless tubing, straightened to within .010" max runout in the center, and welded with less than .006" runout at each end yoke, then assembled with slip yoke and U-joints and spim balanced to less then 1/8 ounce/inch

The yoke and joints could handle more than 7000 rpm at that balance, it's the tube that can't maintain it's shape and begins to bow.
 

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.010 and TIR of .006 is craptastic workmanship.
It should be be .005 and .003.
You've got to realize how small any of those figures really are. At .010" Total Indicator Readout(TIR) you are only .005" offcenter, with .005" TIR you are .0025" offcenter......a difference between the two of just .0025"......you are talking the thickness of one sheet of regular notebook paper.
Nothing else rotating in the entire engine and driveline is any closer tolerance than that....certainly not the trans output shaft bushing.
 

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Discussion Starter · #16 ·
615286
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Car is back on the road.
Measurements were taken.
PST got my business. Driveshaft is good for 7000 RPMs. Also 1200 HP.
I am far from both of those, so the quality is good enough for me.

Love ya Johnsongrass. And always value your opinion.
Not everybody knows about grapefruit sized hail, like you and me...
 

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You've got to realize how small any of those figures really are. At .010" Total Indicator Readout(TIR) you are only .005" offcenter, with .005" TIR you are .0025" offcenter......a difference between the two of just .0025"......you are talking the thickness of one sheet of regular notebook paper.
Nothing else rotating in the entire engine and driveline is any closer tolerance than that....certainly not the trans output shaft bushing.
im quite aware what that means. It’s also why I don’t buy commercial driveshafts.
I can’t say about your house, but at mine if needs a washer welded on it, it wasn’t done right to begin with.
Fastshafts is one of the worst ones about it.
These days we use CF for safety and weight but when we didn’t, a 2”-2.5” driveshaft had to live at 9500 rpm or possibly kill someone. I’ll have to agree with ya, it’s probably overkill for street ride. Maybe it’s just the millwright in me coming out trying to hold tenths.
In any case, the GN is looking like a pantie dropper.
 
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