Mopar 8.75 posi. wont work. Why are there 2 rows of spline?

-
7

73 Plymouth Duster

Well-Known Member
Joined
Aug 21, 2012
Messages
67
Reaction score
1
Location
vancouver, WA
MAIN QUESTION. why are there two rows of splines in my 8.75 3.55 posi? and what happens if I don't grab the second row?

So I am a bit new on rear ends and have fought a long hard battle with my new one. So here is the condensed version of my story then i'll get to the current problem. you'll understand why I have to narrate this first two paragraphs once you read the problem.

I have a 1973 Plymouth Duster, it had a 7.25 with 2.76 open gears. For obvious reasons I too wanted the 8.75. One day looking on Craigslist a guy was selling an A-body 8.75 housing for $50. I went to go buy it but before I bought it I found the measurements online and measured the housing I was about to buy. It matched up so I bought it. The very next day a guy listed a 3.55 posi 8.75 center section with new A-body axles and green bearings (basically everything except housing and brakes). Thinking this was a match made in heaven I went to go buy the posi unit/axles. I gave it a good once over and bought it for $400.

Here is where is gets interesting. when I went to go put the two together I found out I had the wrong housing. I used the measurements off that "wrong chart" floating around the internet that everyone curses. So my "right" measurements were actually wrong. The correct length is 52 5/8in (if i remember correct) and I had bought an early 60's B-body that was 53 1/4in. We spend a few days of measuring and calling around and determined that no one could really shorten each side by 1/4 of an inch and still maintain the structural quality of the housing. The Axle's I bought were correct length and had 1in long splines. So everyone came to the conclusion that with a 318 (not stock but still a 318 ) I was okay with only grabbing 5/8 to 3/4 of of the 1 in I needed. SO I had him re-weld the perches, bought new U-bolts and brakes (the works) and tonight I set it down and went to go drive it/

PROBLEM AS IT STANDS:
I jacked it up before I drove it an ensured it did turn with no terrible noise. It seemed good so off I went. It backed out fine and forward (with no gas). But when I went to give it some gas it felt like the tranny was slipping. I checked and indeed it was low I added a quart and tried again. This time I gave it a bit more gas, around 2500 rpm it develops the loud (like LOUD) whining and the car doesn't go any faster. when i pulled it in I put it in park and there was a loud ratcheting sound, like you would get if you tried to throw it into park while still moving...but I wasn't moving. I held the brake and revved it up. My dad confirmed that the DRIVESHAFT WAS TURNING AND THE CAR WAS NOT MOVING. and the whining sound persisted.

DIAGNOSTIC:
I pulled it all apart and the axle slrines were perfect, the yoke and splines were great, and all the pinion and ring gears were excellent. WHAT'S GOING ON!?!? So I found that there are 2 rows of splines in the center section. the first spline is only..what do ya know, 5/8in wide and the second set starts after 3/4in and goes to 1.25In.

MY CONCLUSION:
I am only grabbing the first row of splines on both sides but why does that cause the whining problem and the ratcheting noise? why wont the car drive just fine without the second row engaged. I cannot find any other problem but I figured before I buy a new housing or axles to accommodate the 2 row engagement I would ask you guys.

Sorry for the really long post but I feel it all is relevance to the problem and I couldn't leave one part out without the others. Thanks for your guys time for helping me.
 
Read this:


http://www.moparmusclemagazine.com/...8_mopar_8_3_4_rear_gear_buildup/photo_08.html

From your description, you don't have the Spicer style clutch type SureGrip but rather the "coil spring" unit. Unfortunately the shop manual handily leaves sevice for these right out of the books!!!

I'd say your axles are TOO SHORT, are not engaging the inner spline which are the side gears, and were attempting to drive the car through the SureGrip clutches, which are now ruined.

Coupl'a photos from the above article:

mopp_0308_06_z+rear_gear_setup+limited_slip_differentials.jpg


mopp_0308_08_z+rear_gear_setup+reassemble_sure_grip.jpg


mopp_0308_07_z+rear_gear_setup+cone_style_sure_grips.jpg
 
See and that is EXACTLY what I thought was happening. When I first backed out I was like "oh crap this thing has a bad clutch" and I thought that is why it was slipping. BUT I am 100% sure I have the cone style posi without the clutch pack here are some pictures of my rear end center section that I took last night. Like I said I'm not expert but there aren't any springs or clutch discs. it's cone gears.
 

Attachments

  • Image11072012214059.jpg
    57.4 KB · Views: 915
  • Image11072012214144.jpg
    85.8 KB · Views: 893
  • Image11072012214206.jpg
    75.1 KB · Views: 852
  • Image11072012214217.jpg
    56.5 KB · Views: 883
Sounds to me like your axles are to short and like you said not engageing with the inner side gears.
 
So because I the axles are too short, when I get longer axles/ shorten my housing to make it work can I put it all back together or have I hurt the until internally now? what have I hurt and how can I fix it?
 
Keep in mind I only backed it in and out of the driveway twice and revved it a couple times to confirm the driveshaft was spinning and hear the noise etc. I never drove it like this, just revving and slight movement forward and back. Do you really think my clutch is burned up? and how much is a new one?
 
Yup, that's not the type I originally posted. From your description, it sounded right. Here again, the shop manual is not a hell of a lot of help. They don't even SHOW an exploded view of an 8 3/4 clutch pack. Here's one of a 9 3/4 which is similar

This thread:

http://www.forabodiesonly.com/mopar/showthread.php?t=57471

and here

http://www.moparts.org/Tech/Archive/axle/13.html

"Sure Grip - clutch type

If it's a clutch type sure grip (741/2 casting), there will be "pins" in the hole where the axles go in. I've seen sure grips at swap meets that are missing the pins. They might give you a little hassle finding some but they are avail."


suregrippin.jpg




clutch.gif


clutch2.gif


clutch3.gif


"I just asked DocDiff about the 8 3/4 clutch sequence and yes it is different then the larger rear. Here is his PM he sent me:
OEM clutch pack orientation starting at clutch hub:
1. Flat plate with ears
2. Flat disc
3. Dished plate with ears**
3. Dished disc**
4. Thin flat plate with ears
** Install with ID contacting outer plates (away from clutch hub).
Pre lube clutch plates with straight friction modifier additive.
Torque case-half bolts to 50 lbs with red loc-tite."



discs.jpg
 
Had the same thing happen in my b body. Went from a Eaton posi that had the full spline to the factory sure grip old style 2 sets of splines( lack of what the actual wording of this type is.) Same as you backed it out of the garage, put it in park and watched the car roll down the drive.Hopped in and got it stopped,put it in drive and no movement just a whining sound. Pushed it back in the garage and back apart it came.Called Dr. Diff and he explained to me the cause,and the cure.Like you I assembled this rear from many different parts and the axles were too short for the 2 spline setup. He has the rebuild parts to up grade what you have.Just to let you know the Eaton set up with green bearings was raced alot before the change over so the axles did fine with the single spline set up.
 
Pic 2 he posted looks like broken spider gears.
Hard to tell with the crap pictures posted.
 
Sooo I should have the rear dif. rebuilt. Did someone mention that I can fix my problems in the center section? Darter 6 you said "He has the rebuild parts to up grade what you have.Just to let you know the Eaton set up with green bearings was raced alot before the change over so the axles did fine with the single spline set up." Do you mean I can just have single splines put into my posi and put it in and go without having to deal with getting new axles or shortening the housing?
 
If you have the rebuild-able Spicer clutch pack you can use Dana 44 spider gears. They have a solid spline (not split). No need to rebuild the rear if everything else looks good. You can reuse your axles then. Although if you plan on drag racing or hot rodding your car, you may have problems with axle strength in future.
 
How do I know if I have the rebuildable spicer? and who do I contact to rebuild it besides someone in my area? Darter6 you said you called Dr. Diff, is that just a generalization to someone who works on these or is there actually someone I can contact?

thanks again guys, this is really helping me out!
 
73 Plymouth Duster said:
How do I know if I have the rebuildable spicer? and who do I contact to rebuild it besides someone in my area? Darter6 you said you called Dr. Diff, is that just a generalization to someone who works on these or is there actually someone I can contact?

thanks again guys, this is really helping me out!
Click to expand...


Contact Dr. Diff by e-mail. Or by phone number.
http://www.doctordiff.com/?page_id=50

He will help you get squared away. The pictures show you have the rebuildable clutch pack.
 
fired an email off to him and I can't wait for a response, I sure hope I have the rebuildable type. i really dont want to get a new housing or axles.
 
Demon416 got to you first. Dr Diff advertises on Moparts. His Name is Cass. Well known over there. Very helpful. I think he is in the mountain time zone. Call him.
 
73 Plymouth Duster said:
fired an email off to him and I can't wait for a response, I sure hope I have the rebuildable type. i really dont want to get a new housing or axles.
Click to expand...

I have rebuilt several clutch type sure grips and absolutely guarantee the pics you posted are of a clutch type sure grip. Like the others said the cone type has springs visible through it's 2 openings. Unlike a clutch type which has several openings and no springs.

BTW: Notice I called it a SURE GRIP, not a posi... That's cause it's not a Chevy rearend.:D
 
You must log in or register to reply here.
-

Back
Top