W900 flat cab big hole conversion

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Felixw9, Jun 21, 2020.

  1. Felixw9

    Felixw9 Bobtail Member

    Oct 26, 2019
    Hey I’ve been trying to research what all it takes to convert my standard cab w9 into a big hole. I really need the extra leg room but nobody around me does it(tri cities, wa). I’m wondering what all it takes to complete this sort of project. Thank you guys in advance
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  3. AModelCat

    AModelCat Road Train Member

    Jul 7, 2015
    @W900AOwner might pop over and view this since I tagged him. He may have some insight into this project.
    Tug Toy and W900AOwner Thank this.
  4. W900AOwner

    W900AOwner Heavy Load Member

    Jul 2, 2014
    Sorry for the delay in replying...busy man these days.
    So here's what I did with my "big hole" project Felixw9...

    I ordered the Peterbilt Unibilt aluminum "rings" (boot frames,) and the rubber boot from Peterbilt, cost was approximately $1,500.00 for the 3 pieces.

    You can see in the first set of pics when I had the truck all apart, it had a "sit in" hole already.

    I clamped the first boot ring to the rear panel of the cab and sat there and hallucinated for a while. Notice how the top of the ring is higher than the fiberglass roof cap rivet line? I wasn't crazy about compromising the structural integrity of the roof cap by cutting into the rivet line and weakening that area, so I decided to cut 7.5" in height out of both aluminum rings, and welded them back together. That way, the rings were now below the rivet line and not compromising the strength of the cab.

    I figured it doesn't matter how tall or short you are, you're still going to have to duck to get in the bunk anyways...so that extra original height wasn't going to do anything except weaken the cab, and then in addition I would have had to cut the brand new headliner to match that cut, and I wasn't interested in that either. I was able to install a factory headliner right in place.

    I clamped the frame to the back of the cab after doing that modification, and then began to trace out the hole with a Sharpie. That's the critical part...you don't wanna make that hole too big, or there's gonna be heartache, lol. Once I traced it out and was satisfied, I mocked it up on the sleeper too. I sat the sleeper on the mounts and traced the hole the same way. (Note that I removed a stock 36" bunk, and replaced it with an Aerodyne II which was a little more of a challenge to mount because they are designed for a B model cab, which is 4" taller than an A model cab.)

    So I had to drop the sleeper mounts down on the frame and re-drill them to get the proper height for that as well. Once established...I proceeded to get the correct elevations for both cab floor and sleeper and marked the holes with the aluminum frames. (I'm sure you're not going to have to do this...I had no choice because I needed more bunk than a 36", and there weren't any period-correct Aerodyne 1 bunks available at the time of my restoration.)

    Once I cut the holes out using a normal Black & Decker jigsaw, and the frames were in place, I just went and used 1/4" stainless bolts, washers and nylock nuts. The "purists" will start convulsing over this, citing indecency in not using huck rivets...but call me a hack. The nuts and bolts work fine, and you don't see them behind the exhaust anyways. Me and a 7/16" wrench and an 18V electric impact did quite nicely in fastening everything together. No special tools to rent or buy, and I'm completely satisfied with the results.

    Once the bunk was mounted and tight, I married the bunk and cab together with the rubber boot. Note I had to cut 15" out of the length of the rubber boot to compensate for the 7.5" I took out of the aluminum frames, and I don't get that because I never got that fancy higher education book learnin' like a lotta folks did; but all's I know is I had to cut the rubber boot so it went into the channel properly and at the bottom where the two ends meet...I used vulcanizing cement to weld them together with a short piece I cut to overlap the seam, and glued that to the top for extra strength.

    And there you have it. A complete Unibilt opening that I am very, very glad that I went through the trouble of doing, because I can recline the drivers seat all the way to the mattress and nap in it, or make it easier to get in and out of the sleeper, etc. There's no better feeling than to be able to stretch your legs out and not be slamming the back wall with the seat.

    Of course you're going to sacrifice the shelving and storage behind the seats if you do this...I added a new storage shelf straight across the bunk over the bed to have my storage back. Just a simple steel wire shelf and some wood framing and I am satisfied with the extra storage there. I put an RV sink with a 6 gallon water tank and a 12v pump behind the passenger seat so I can wash up and stuff, so I do not miss those storage closets or shelves one bit myself. unibiltHole#2.jpg unibiltHole#3.jpg unibiltHole#1.jpg unibiltHole#4.jpg unibiltHole#5.jpg unibiltHole#6.jpg unibiltHole#7.jpg

    If you need more insight, let me know...I'll be glad to help. Good luck!!!
    Last edited: Jun 28, 2020
  5. Vampire

    Vampire Medium Load Member

    May 14, 2011
    Awesome job. Is that your own garage in the above photo? Looking to build a garage to accommodate at least 1, possibly 2 trucks with one bay having a lift and a bridge crane spanning the length and width of the garage.
  6. Brettj3876

    Brettj3876 Road Train Member

    Nov 18, 2014
    Stuck in Limbo
  7. 99FTClassic

    99FTClassic Bobtail Member

    Apr 22, 2021
    I know I’m late to this but would you know all the parts a part numbers for the peterbuilt rings and boots and what else I need this is a great job I have a flat top classic and would love the leg room

    Attached Files:

  8. Rubber duck kw

    Rubber duck kw Road Train Member

    Dec 9, 2017
    What did you do for bracing in the corners or didn't you worry about that too much?
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