Third Member from Open to "P" Case Conversion

Iowa409

Well Known Member
Supporting Member 3
Any input would be appreciated.

64 Impala currently OPEN differential, I bought the "P" 4:11 Differential, is this a matter of pulling the two axles, then pull the OPEN differential, install the "P" 4:11, then re-install axles, or would that be to easy, and theres other things that need to be done to make it work?

What Fluid/Viscosity are you guys running in the "P" cases.
 

Iowa409

Well Known Member
Supporting Member 3
I'll be running 409/340, Muncie 4 Speed M21, 15" tires, I am guessing about 29.5"tall, my guess is the car is going to see high RPM's really quick.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
In order to put a posi unit in an open diff housing,you'll have to do a little grinding on the case.It really isn't a big hasell to do,but will need to be done.As to rhe gear oil,use straight weight, non-synthetic gear oil,likely 90 wt.The later,multi viscosity,synthetic oils do not play well with the axel seals in these old cars.Do not forget to get a good[GM] posi additive as well.If you're gonna hammer that rear,no is the time for cap straps while it's apart.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Yes,cap strap,check with either Aubrey or maybe even Show Cars has them.Check back on Rickys61 rear end posts for pictures of what happens without them under aggressive driving conditions.
 

Carmine

Well Known Member
Supporting Member 10
Don, I'm probably wrong on this, but do you still have to grind the case when installing a "P" case posi in a '57-'64 open rear?? I thought the grinding took place only in the '55 and '56 cases because a posi wasn't available until '57, therefore the internal design was different. I know it doesn't apply here, but when installing a "P" posi into the early open rears, the axles have to be cut 1/8" for proper seating in the unit itself. At least that is what I read, Carmine.
 
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Iowa409

Well Known Member
Supporting Member 3
I spoke to Bruce at Show Cars (I am in the middle of another order anyway's) he said "I think they are talking about a Girdle, we haven't carried those for years? Is there another source for these? I guess I still do not have a clear picture in my mind, what I am after? Any pics or illustrations anyone?
 

Austin Bubbletop

Well Known Member
Supporting Member 1
If you're doing the conversion, buy the girdles. It's worth the peace of mind. I believe they're only sold in pairs but you only really need the driver side if I remember correctly. You may be able to sell the other. The girdles could be fabricated as well if you've got the tools and time. I've seen guys that can run the factory girdles forever with no issues and then you have guys like me that have shelled 2 rear ends because of how thin that girdle is.
 

Iowa409

Well Known Member
Supporting Member 3
Well guys, I have an update, its nothing at all..... so I do not know if I was real clear, so I'll explain a little better, I have an original OPEN
3rd Member that was in the car when I bought it. I wanted a Posi "P" in it with my rebirth of the car., I bought a 4:11 "P" out of another car, unbolted the 10 bolts and took the whole center section out.

So today was the day it was going in for transplant, I pulled the axles back 4", drained the center carrier pulled it out, cleaned the housing, cleaned the old gasket off, put a new gasket on, put the new "P" section up there, it was direct drop in, no work of any kind, bolted it up, and it....be....DONE, I made it spookier than it actually was, easy change out, thank you all for the help and input.
 

blkblk63ss

Well Seasoned Member
Supporting Member 5
Well guys, I have an update, its nothing at all..... so I do not know if I was real clear, so I'll explain a little better, I have an original OPEN
3rd Member that was in the car when I bought it. I wanted a Posi "P" in it with my rebirth of the car., I bought a 4:11 "P" out of another car, unbolted the 10 bolts and took the whole center section out.

So today was the day it was going in for transplant, I pulled the axles back 4", drained the center carrier pulled it out, cleaned the housing, cleaned the old gasket off, put a new gasket on, put the new "P" section up there, it was direct drop in, no work of any kind, bolted it up, and it....be....DONE, I made it spookier than it actually was, easy change out, thank you all for the help and input.
i was thinking that is what you were doing ,instead of building the 3rd member.
 

heddrik

Well Known Member
Please illuminate my ignorance on this issue. What is an open carrier? Pics plz. How does a posi differ? I thot it was just another gear for the other side . Never tore into one so any help is a good thing. My 62 SS was a 10 bolt 3.08 powerglide. Thank you gentlemen.
 

Phil Reed

Well Seasoned Member
Supporting Member 10
The open case is a little smaller on the inside dimensions. The posi unit is a little larger so the P-case is modified to have the posi unit fit. In order to put a posi unit in a non-posi case...you need to ground out some clearance Clarence!!!!!!!
 

heddrik

Well Known Member
Thank you Mr Phil. Do they look the same from the outside? Is the pumpkin the gears that go inside? Guess I need to google it, but thank you again esteemed Mr. Phil. What s this I hear about you buying up all the 409 s from Texas? Nasty rumor or truth?
 

Phil Reed

Well Seasoned Member
Supporting Member 10
The posi one has a big P on it.
I don't know about the rumors???? Did buy 6 engines from the same guy late in my career. 1 had an Algon FI on it and another had a MT crossram.
Texas has been berry berry good to me!!!!!
 
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