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Thread: A few IRS center section questions

  1. #1
    JohnK's Avatar
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    A few IRS center section questions

    OK, this is officially my first question since "joining the family"! I just ordered a Mk4 complete kit yesterday, and it's set up for a Dec. 22 completion which will (hopefully) put it in my garage in early January. That should work out perfectly for me, as we'll be travelling over the holidays and I didn't want to try to coordinate a delivery around our travel schedule. I chose to order the IRS center section and knuckles from a different source other than FFR, partly for cost and partly because I could get them sooner than the rest of the kit which gives me something to play with and not go crazy waiting for the kit to arrive. The plan is to clean everything up, get the knuckles trimmed and drilled out and clearcoat/POR15 everything so it's ready to go when the kit arrives. To that end, I have a few questions:

    (1) I know the kit includes the mounting bolts for the center section, but I've seen where folks have hung the case by the bolts as lift points and that looks like a good idea. Does anyone know what size bolts I'd need to do this? I'll still use the bolts that come in the kit to install the center section when those arrive, but I can also use these temporary bolts to make some tapered guide pins for installation eventually, as edwardb has shown.

    (2) Perhaps a dumb question (won't be the last) but I'm assuming that folks don't remove the aluminum cover from the diff to paint them? I assume that things get masked off, spray the clear, let it dry, re-mask for the POR15 and brush that on? If so, did you spray the bolt heads on the cover, or mask those off? Sorry for the oddly specific questions, but this is what happens when OCD-types like myself have too much excitement and time on their hands waiting for something to arrive.

    (3) I also know that the kit comes with the correct wheel studs for the rear hubs, but if I wanted to get the stud replacement out of the way and get everything painted before the kit comes, can someone advise the correct size studs? I know they're 1/2"-20 but I'm not sure of the knurl size or correct length. They're not terribly expensive so I'm OK buying these even though they'll come in the kit. It gives me another thing to do before the kit arrives.

    (4) Regarding installation of the center section, I've seen where folks have devised some pretty clever ways of lifting the thing into place by themselves. What I'm wondering is, if I had lots of pizza and beer on hand and that happened to unwittingly lure several of my friends over, could I put them to use lifting the thing into place by hand or is it just too heavy and unwieldy to attempt this without some sort of lifting fixture? I have a 4 post lift in a garage with an 8' ceiling so I'm able to get the chassis ~4ft or so off the ground

    Thanks,
    John

  2. #2
    Senior Member q4stix's Avatar
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    (2) I did the POR15 first on the differential cast iron and then cleared over it and the aluminum all at once. Makes for an easier job and the clear coat also helps UV protect the POR15. I know it's under the car so UV exposure is not great (and I live in Seattle which means never), but it's protected anyway. I also just cleared right over the cover bolts. Unless you plan to remove the cover for some reason and like having oxidized bolt heads while the rest is clean, I'd suggest painting those too.
    Gen 3 Type 65 Coupe builder

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  4. #3
    JohnK's Avatar
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    Thanks, that sounds like a good way to go. I don't foresee having to remove the cover so I guess there's no need to worry too much about messing up the clearcoat if I ever had to remove the bolts.

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    Senior Member edwardb's Avatar
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    1. The front bolts are 5/8-inch, and that's the size bolts I used to make the tapered pins for installation. I don't know what size the rear bolts are. I'm not home for a couple weeks and don't have that info with me. I do know they're metric because they're threaded into the diff. Unlike the fronts that use nuts on the other side of the frame mounts. Based on some of the recent build threads, seems maybe FF loosened up or adjusted the frame to make the diff easier to install. Seems some are getting them in and aligned more easily. But the tapered pins do work really well.

    2. As already stated, brush or spray over the mounting bolts. No problem.

    3. https://www.dormanproducts.com/p-22276-610-290.aspx work perfectly for the replacement 1/2-20 studs.

    4. By all means, a couple helpers and you can get it installed without any lifting devices. You'll want to use lots of towels or rags so you don't scratch up your shiny paint or the chassis.

    Congrats on your kit order and good luck!
    Last edited by edwardb; 10-25-2018 at 11:51 PM.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
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    JohnK's Avatar
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    Thank you very much!

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    On my 33 Hotrod I put the IRS in using a floor jack (chassis on jackstands), an extra pair of hands would have made it much easier. The IRS is about 100Lbs, get a few buddies over to give you a hand.
    '33 Hotrod, #1047 Gen 1, delivered on 2/27/18, go cart on 9/24/18.
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    Senior Member Fixit's Avatar
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    It's not much more than a bribe with beer & 'za and a few drift punches from on the floor to in the car in 10 minutes... especially with a lift.
    (do the beer after it's bolted in! )

    I installed mine by myself, on an "extended height" dolly. Linkage
    John D. - Minneapolis 'Burbs

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    Quote Originally Posted by JimLev View Post
    On my 33 Hotrod I put the IRS in using a floor jack (chassis on jackstands), an extra pair of hands would have made it much easier. The IRS is about 100Lbs, get a few buddies over to give you a hand.
    I used a transmission jack with my son helping.

  10. #9
    JohnK's Avatar
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    My IRS center section and hubs/knuckles arrived today. I'm looking forward to having something to work on in advance of the kit showing up. First order of business was removing the studs from the hubs. I decided I'd try to pound them out and see how that went. I set each hub in my vise with padded inserts so that the sides of the flange were resting on the vise jaws. This way, I wouldn't be transmitting forces into the bearings as I drove out the studs. 5-6 blows with a mini sledge on each stud and they popped right out. It took a total of 10 minutes to get all the studs out of both hubs.

    Next up is enlarging the holes in the knuckles and the center section to 5/8", installing the new studs, and then prepping and painting everything.

    Here comes the question:
    What do you use to degrease aluminum prior to clear coating? I bought the POR15 'kit' with the cleaner/degreaser and metal prep and that sounds perfect for the cast iron portion of the IRS, but the metal prep says that it leaves an alkaline finish behind so you need to follow it up with the metal prep, and the metal prep says that it leaves a zinc phosphate coating behind. This doesn't sound to me like it's what I want for the aluminum portion of the IRS that I plan to clear coat, but what do I know? So, I do know that there are a few of you that have done the POR15 on the cast iron portion of the IRS and clearcoat on the aluminum - what did you do for prep? I suspect that, since nobody has specifically called out some elaborate clean/prep process in their discussion of painting/clearcoating the IRS, you all just used the cleaner/degreaser followed by the metal prep and then paint, and everything worked out fine. I'm very likely overthinking this, but I'd rather not assume that this is the case and impart some ugly finish on the aluminum cover. So what are everyone's metal prep secrets for nice shiny clearcoated cast aluminum parts?

    cfpaD%N%T%Wq9BbFxMuwNQ.jpg

  11. #10
    Senior Member edwardb's Avatar
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    Quote Originally Posted by JohnK View Post
    What do you use to degrease aluminum prior to clear coating? I bought the POR15 'kit' with the cleaner/degreaser and metal prep and that sounds perfect for the cast iron portion of the IRS, but the metal prep says that it leaves an alkaline finish behind so you need to follow it up with the metal prep, and the metal prep says that it leaves a zinc phosphate coating behind. This doesn't sound to me like it's what I want for the aluminum portion of the IRS that I plan to clear coat, but what do I know? So, I do know that there are a few of you that have done the POR15 on the cast iron portion of the IRS and clearcoat on the aluminum - what did you do for prep? I suspect that, since nobody has specifically called out some elaborate clean/prep process in their discussion of painting/clearcoating the IRS, you all just used the cleaner/degreaser followed by the metal prep and then paint, and everything worked out fine. I'm very likely overthinking this, but I'd rather not assume that this is the case and impart some ugly finish on the aluminum cover. So what are everyone's metal prep secrets for nice shiny clearcoated cast aluminum parts?
    Yea, don't overthink it. I used the POR15 process before painting the diff, knuckles, hubs (front and back), and sprayed clear on the rear diff cover. Followed their directions wiping it on with a rag then back off again with only water. For both products. I don't go crazy with the amount of product or water. Just so the rag is wet. You don't want or need it running everywhere. Once dry, painted and was done. If the surface is cleaned and prepped with these products, most anything including especially the POR15 will stick like glue. Also on your hands, brushes, and anything else you choose to put it on. Purposely or not. Strongly recommend wearing Nitrile gloves or something similar throughout the process.
    Last edited by edwardb; 11-02-2018 at 10:51 AM.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  12. #11
    JohnK's Avatar
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    Quote Originally Posted by edwardb View Post
    Yea, don't overthink it.
    I resemble that remark!

    Thank you very much. Just what I wanted to hear (and suspected).

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