Just picked up an 8 1/4 out of a Jeep

Transmissions and Rear Ends

  1. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Hey guys, just got an 8.25 rear for pretty cheap (~$80) from an off-roading buddy of mine; came out of a Jeep Cherokee XJ. Pretty sure it was working fine when pulled, he just wanted something bigger for wheeling. Also it has 3.55 gears in it which would be great for my '70 Duster street machine or basically anything with Overdrive but I want 3.07s for my 5th Avenue to keep it a nice highway cruiser. So my main question is, aside from having the Jeep-style shock mounts cut off and the spring perches flipped what needs to be done regarding the Iso-Clamp setup? Do I need to keep them unless I swap the leaf springs as well? I'm trying to keep it as low-budget as possible and while it would be nice to have new rear springs (mine are too soft and of course sag a bit) I don't exactly need them. I've heard there are poly inserts to replace the rubber pads in the Iso-clamps, I think it would be easiest to go with those and maybe swap out the leaves under the main one kind of like a bastard-pack setup just to stiffen it a bit? What do you guys think?
     
  2. BudW

    BudW Moderator Staff Member

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    A great price for an 8¼”.

    I have seen some 3.07’s for sale on eBay and are not that hard to change over (or to get a differential shop to change for you). The old 3.55’s should be a good seller.

    Poly spring inserts help a lot.

    The weak link on the Iso-clamp setup is item # 21.
    Iso-Clamp B.JPG
    That part has a tendency to break on one side, close to the bolt holes. When that happens, that corner of car is dragging the ground (time for a tow truck).

    I have no facts, but personally I think the poly inserts stresses that part (item # 21) more so. That said, I hadn’t heard of anyone on this site with a breakage using poly, yet.

    I see shock plates on eBay for $80-100 all of the time. A person can find a set at a salvage for a lot less than that.
    You would need new U-bolts – but I wouldn’t reuse U-bolts anyway.

    I will support you no matter what you do. I’m only trying to advise on what I see break on these cars.

    I would get new perches and you can find new ones for about $10.00. The hard part is making sure they are welded on parallel with the pinion shaft. If not, you can purchase pie shaped shims to get pinion angle correct.

    My opinion, I think less is best. The older shock plates are thicker than what is used on your car, and I have yet to see one fail or damaged. I think costs are about the same, either way.

    More details on this on thread XHD springs on Fifth Avenue
    Post # 15.

    BudW
     
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  3. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Just an update here, I found a 3.07:1 ring & pinion at a specialty Jeep salvage yard in Co. Springs (FN Jeep) for a good price, $50 + shipping to my home as I live about 2 1/2 hours away.

    BudW I took your advice and got new perches for welding onto the Jeep 8 1/4. I will likely have a shop do most of the housing mods, maybe even the R&P swap as I don't have a whole lot of patience for adjusting gear mesh, particularly pinion depth... done it before, PITB and to make it all worse I did it wrong and had to take it to a shop anyway.

    As far as the shock plates go, there are very few salvage yards out here anymore that get much old RWD stuff let alone Mopars. I really want to keep this on a budget but I get sick looking under the back of my 5th Avenue and seeing the horribly S-shaped and sagging leaves. Might have to go with new springs, iso-delete, the works...
     
    Last edited: Apr 9, 2017
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  4. BudW

    BudW Moderator Staff Member

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    New/repop shock plates are getting more commonplace now.
    Leaf springs, on the other hand . . .
    BudW
     
  5. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Hey so I want to go drop off the housing today, is there a specific angle I should tell the shop to weld the perches on in relation to the pinion or is straight parallel OK?
     
  6. BudW

    BudW Moderator Staff Member

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    I would say perpendicular to the pinion gear.

    Be sure to check your driveline angles afterwards (may need to take to a spring shop to get this performed) for if perches are not on correctly, one can have angled spacers in to fix the driveline angles.

    If driveline angles are not set up correctly, you will go through U-Joints as if they are made out of butter - if not also have a horrible vibration.

    From my '77 FSM (but should be the same).
    77 DS Angle 1.JPG

    77 DS Angle 2.JPG

    77 DS Angle 3.JPG

    77 DS Angle 4.JPG

    77 DS Angle 5.JPG

    77 DS Angle 6.JPG
    77 DS Angle 7.JPG

    From my '86 FSM
    1494890310528700324810.jpg
    BudW
     
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  7. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Alright guys, got the housing back a couple weeks ago and the build-up is going smooth so far. I have run into a hang-up though regarding what to do with the pinion depth... The 3.07 ring and pinion I'm swapping in place of the 3.55s are factory pieces as are the 3.55s. The 3.55 ring and pinion were both marked "+111" with the white paint (three ones) but the 3.07 ring and pinion have no markings besides "243" also in white paint. Can someone with experience explain what these mean? My understanding was each set would be marked "+0, +1, -2" etc. from the factory and the pinion depth shims would be changed accordingly, but in this case I don't know what these weird numbers mean, especially the "243" on the 3.07 set. FWIW the 3.55 pinion I removed had a .030" shim under the large bearing, some other how-to articles say to just go with the same shim thickness as long as both the gear sets are factory pieces...? Of course I don't have the tools to properly measure proper pinion depth or I'd just do it that way. I'd also rather not have to pull the pinion back out again and press off the bearing to change shims, I know you can reuse an old bearing with the press-fit surface ground down but I cut up the old bearing to get it off the pinion. o_O
     
  8. BudW

    BudW Moderator Staff Member

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    Sense the bearing is already off, I don’t have any recommendations.

    The shims are to allow for machining differences for both the pinion gear as well as differential housing.

    On the assembly line, a different person does each thing. In this case one person measures and marks, the next person selects shims and installs, and so forth. The good news is with this process is things get marked (in this case with white numbers).
    In the repair shop, nothing gets written down – for its all in memory.

    If the bearings were still intact, a person could make tools to get the job done. It won’t be like using factory tools – but at least will get the job done.

    Even when I worked in a Chrysler dealership, some special tools would walk off (Yes, Fred, I know that special-tool Miller Y-409, is locked in your bottom drawer of your toolbox . . .) so a lot of our tools were “created”, but got the job done.

    What we do when we had a missing arbor is to use the next size smaller arbor (note finding a piece or section of steel (or thick plastic) pipe will work as well. Finding one the exact diameter might be difficult to do, but with one a bit smaller is not hard.

    Cut the section of pipe to fit in the carrier bearings location. Then find some rubber or thin (but wide) fender washers. Place pipe in as shown in picture, then place fender washers (or rubber or whatever) between the pipe and bearing caps and tighten down caps.
    77 8.25 Diff Setup A.JPG
    That will place the pipe at bottom of channel and should keep it from moving.
    Diff Setup.png
    Note: distance between pinion gear (or gauge block tool) to green line is what is being measured.

    Next, take your two pinion gears – before bearing removal (well, actually, this goes before the pipe/arbor install) and measure the distance from gear to arbor/pipe. If distances are the same, then you can reuse the old shims. If not, then add (or subtract) to get correct shim(s) needed.

    The nice part about using the factory set-up tools, is it is pre-setup, so the distance from tool and arbor is the exact thickness shim needed – which makes setup a breeze.

    A person can still make a mockup of factory set up and use it to get an approximation of correct shims via measuring – but it is still - not exact.

    These next pictures are all from my '77 Chrysler FSM, except for the color picture (above) which I drew up.
    77 8.25 Diff Tools.JPG

    77 8.25 Diff Setup B.JPG

    77 8.25 Diff Setup C.JPG

    77 8.25 Diff Setup D.JPG

    77 8.25 Diff Setup E.JPG

    77 8.25 Diff Setup F.JPG

    77 8.25 Diff Setup G.JPG

    77 8.25 Diff Setup H.JPG
    Continued >
     
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  9. BudW

    BudW Moderator Staff Member

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    77 8.25 Diff Setup I.JPG

    77 8.25 Diff Setup J.JPG

    77 8.25 Diff Setup K.JPG

    77 8.25 Diff Setup L.JPG

    77 8.25 Diff Setup N.JPG

    77 8.25 Diff Setup P.JPG

    I'm sure the tools and procedures are different on a 20-30 year newer Jeep differential.

    Hopefully this helps.
    BudW
     
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  10. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Thanks so much Bud that was super helpful I will probably download and save that for future reference. It looks like I got really lucky with this setup though, I measured the pinion head thickness with calipers and found the 'new' one to be about 0.013" shorter. Not wanting to go too far I dropped a .035" shim on, crossed my fingers and pressed on the new pinion bearing... Here's the contact pattern I got, bear in mind this is without having set the backlash with a dial indicator I just did it by feel a few times and tightened it up each time until the pattern looked decent...

    20170626_140730.jpg
     
  11. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    I still need to set the pinion preload (I just tightened the pinion nut until there was no more play to do an initial tooth pattern check) and once that is done I will reinstall the carrier and set the backlash properly with a dial indicator then do a final tooth pattern check.
     
  12. BudW

    BudW Moderator Staff Member

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    I’m a bit concerned with your contact pattern.
    I had to blow up your picture to look at it better, but the pattern looks all over the place – which is odd.
    20170626_140730A.jpg
    I added the pair of black lines to clarify.

    I would like to see the contact pattern more in the middle of the tooth, but at least it is not at the very edge of the tooth.

    If I was doing the job, I would double check my work, and try a different shim to get gear pattern closer. Yes more work, but end product is much better off.
    Having the contact that close to edge of gear will feather edge the gear causing noise and excessive “wear” metal. Metal floating in the fluid causes bearings to fail much faster than expected.

    NOTE: you only have a contact pattern on one side of gear – so check other tooth pattern before doing anything else!

    These are PDF copies from my '77 FSM.
     

    Attached Files:

  13. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Ok well my shim options are limited, I can go down to a .030" but the next step up in thickness is a .028 and .018 stacked for .046", I'm thinking that would be too far? Which direction do you think the pinion needs to move? It has a .035" shim in it now...

    I also just checked the pinion again, turns out the bearings still had some play I think that's why the pattern wasn't consistent :confused:
     
  14. BudW

    BudW Moderator Staff Member

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    You need to use the ole big screwdriver/pry bar to hold resistance to carrier as you rotate - in both directions.
    It is the pattern on both sides of the gears that dictate what to do next.

    For a non-high performance vehicle - the current tooth pattern is usable, as long as other sides’ pattern are within specs (ie: stock /6, 318 or 360 2-bbl). If any more power is being made than say a stock 360 2-bbl, then I would highly recommend getting the tooth contact pattern in the middle.

    Under high stress, the gears flatten temporarily at the contact area which allows for more gear to gear contact (less stress to components as power is dispersed over wider area – yet a tiny area for less friction for “cruise”).

    With contact area being so close to edge of gear, it will start to wear metal away at the edges (what I call feather edge – but there may be another, more correct term to use). Also sense contact area is less overall, the likelihood of breakage goes up.

    A stock engine on an 8¼” – the current tooth contact pattern shouldn’t be an issue.

    On a 7¼” my opinion changes. Sense there is not a lot of gear width to begin with – it needs to be right in center.

    If you can get a contact pattern on other side of gear – then we can start to get somewhere.


    Also, shims can be obtained from any transmission or differential parts house – or online as well (if needed)
    BudW
     
  15. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Alright got the pinion tightened up and checked the pattern again... this is what I got with exactly .007" of backlash. Looks damn near perfect to me...?

    20170629_160347.jpg
     
  16. BudW

    BudW Moderator Staff Member

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    It does look at lot better!
    Got any (more) pre-install pictures?
    What did you use for spring perches?


    Note: I believe the Jeep differential cover also uses a rubber plug. If so, get a NEW rubber plug, for old ones get rock hard and leak.

    Also, don’t use the drain plug hole distance for lube level – for it will not be correct.

    You will want to have 4.4 pints of fluid added (2.08 Liter). For a fresh rebuild – it is easy to know how much to put in. Matter of fact, it will be easier to install before you put the inspection cover back on.
    Once it is installed, and on level ground, you might want to remove the inspection plug and measure how far fluid level is to plug – for future reference,


    I know as a fact, car 8¼” covers are different than trucks (which also have a 2*4, a 4*4 and front differential cover versions – which I also believe is different from Jeep (which also has a 2*4, 4*4 and front versions) because of the inspection plug location.

    4*4 differentials have perches welded on at a (I’m guessing at angle) 10’ incline because 4*4’s typically ride higher than the 2*4 – which is at an 5’ angle.

    Pretty much all cars (A, B, C, F, J, M and R-bodies) 8¼” differential cover will be the same and will interchange with each other.

    No need to locate a cover - but you will not be able to check fluid level from distance of fluid to hole - so just keep that in mind.
    BudW

    Edit: Also use a touch of RTV on bolt heads and tips – to prevent leaks.
    Not the threads, per se.
     
  17. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Here are a couple pics, just about ready to put it in the car... I'm letting the RTV cure and then I'll fill it up.

    20170630_203839.jpg

    20170630_203846.jpg
     
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  18. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    Regarding the fill level/pinion angle, as far as I've seen working on my Jeep ('93 Cherokee you can see part of in the first pic) there is no upward pinion angle. But I'll watch how much fluid I put in anyway, thanks for the tip.

    One point to note, I had to drill and tap the bosses on the 8 1/4" for the factory pinion snubber as they obviously aren't used in Jeeps. I also ended up pulling the parking brake cables out of the backing plates on the new and old assemblies and leaving the old ones in the car, when I put the new one in I can just pop the originals back in and it should be good to go. I also left the brake line assembly hooked up in the car, it may need a bit of tweaking but it'll be a lot easier than trying to adapt the lines that came with the 'new' rear end. Not to mention the flex hose was cut, pretty annoying and I don't think replacements are very cheap.
     
  19. BudW

    BudW Moderator Staff Member

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    The rear brake hose is part number 4126502 and appears to still be available from Dodge (MSRP as of today is $39.10 (US)).

    RockAuto.com has them ranging from $9.82 to $20.79 (US) (plus freight).
    Centric 15063307
    Dorman H98911
    Wagner BH98911
    Raybestos BH36962

    For having a 30+ year old rubber hose, I would reccomend replacing it sense it is mostly disconnected, now.
    BudW
     
  20. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    OK guys, it's been a few weeks now since I completed the swap and I am very pleased with the results! Acceleration was MASSIVELY improved as well as in-town gas mileage; average fuel economy went up since the swap. The only real downside is the higher RPM freeway cruising it's right around 3000 RPM at 75-80 MPH, it's noticeably more noisy (engine) and there are some very minor vibrations from the driveline no doubt due to being spun much faster than before. However passing is much easier and there's no reason to downshift to 2nd if I'm going over 55. Also the Iso-Clamp delete made it feel more like a real Mopar not a steel block floating on jello.

    Now I'm definitely going to do the 4-bbl swap, not just for more power but for the weight savings and better driveability (stock carb is REALLY worn out and stumbles off-idle). IMO a gear swap is absolutely crucial if you want to get any more performance from your later M-body, power upgrades will do nothing with 2.2 gears in the back. I'd also like to shave some weight from the car, the 4-bbl swap should save 35-40 lbs. with the aluminum intake manifold and it would be nice to get another 40-60 lbs. I weighed the car on the scale at my work (metal recycling center) and it was exactly 4000 lbs. with me in it (I'm 150 lbs.) and a ~25 lb. toolbox in the trunk. I know the 8 1/4" was quite a bit heavier than the 7 1/4" I took out and my big-a$$ tires and steel Rallyes don't help... each rear wheel and tire feels like it weighs at least 60 lbs.