RB26 S13 – Rear Tub Rework Part 1

Sorry I didn’t get this up last week, I had a few things on and didn’t get around to posting it.

One of the reasons my gearbox blew up in December was because of the rear tubs. It might seem a bit odd but I am 99% sure this is what caused it.

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After ruling out a bunch of things that could have led to gearbox failure, I started looking over the rear end.

If you didn’t know,I tubbed the rear end of the car last year. The original idea was to do something similar to what most pro drag cars do, but I wanted them to be a little more subtle. There needed to be a way to protect the widebody from destruction, keep the rubber out of the cabin while also making the interior side of the tub look neat.

While there was a lot of time spent on making that happen, they didn’t come out 100% perfect. It was pretty obvious that my tyres were scrubbing and I knew the tub had taken away some of the room available for the tyre to move, but I couldn’t let myself think it was the problem.

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Things definitely looked pretty bad underneath the widebody. Both tyres had been catching halfway down the back side of the tub. There has been some serious heat in there so I can imagine it wasn’t just a little rub and go, more like a constant rub while on load.

As you can imagine, going from zero load to 100% load the car will go through a solid squat session, which would mean things are going to foul on each other if they don’t have enough room. Basically, every time I put my foot down, the car would squat and tyres would catch on the rear half of each tub.

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The stress that puts on everything mechanical is huge. Imagine an engine at 5,000rpm trying to push those revs through a gearbox and instead of transferring the power, the gears inside the box don’t rotate because the wheels are stuck. With that in mind, there is realistically only two things that will fail. Either the diff, or the gearbox.

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The gearbox is just a standard RB25 option. Yes they are renowned for their strength, this failure had nothing to do with gearbox strength. My diff is from a 32 GTR and again, loved for its strength. Unfortunately, one of the two had to fail and in this case the gearbox was first to give up.

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There was a bunch of things I could possibly try to fix the problem like stiffer springs, smaller tyres or even raise the car. Not only would all of this be something that ‘might’ fix it, it would mean I would be wasting money if I had another gearbox fail.

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So instead I made the choice to go ahead and cut the tubs out.

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Quick side note, I got to try a Blue Point air powered angle grinder. This has to be one of the most useless tools I’ve ever seen. I’ll definitely be sticking with an electric grinder.

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I’m disappointed with the outcome of this whole situation because of how many hours went into the tubs, but if something is done wrong on the car and is going to cause things to fail, then there’s no point in keeping it. Pretty much the same choice I made with the wiring, but obviously this problem was nowhere near as bad or as costly.

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20+ hours of work, all gone in the space of 5 minutes.

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Now that I’ve cut them out, I’d love to redesign the setup so it works better. Aside from the negatives, they did a good job of protecting the widebody and keeping rubber out of the cabin. While I’d love to redo them straight away, I think I’ll have to leave it as is until I have a bit of free time. I did a quick drawing of a 13mm rail setup to hold the wide body out temporarily but I’m unsure if I’ll go ahead with it.

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I want to incorporate the widebody protection again but this time i’ll make sure the whole tub is much higher.

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I’ll also be patching all the holes in the chassis skin so I can prevent smoke from filling the cabin. Like this…

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See my face? I was completely blind at this point. You know how some trucks have that sticker saying if you can’t see me I can’t see you? I need a sticker saying ‘If you see me, cool, I can’t see shit, sorry’. Hopefully with those holes in the skin patched up, it will keep the smoke on the outside of the car and I won’t be blind.

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I’ll be cleaning up both rear tubs to make them as neat as possible, but I don’t think I’ll have new tubs for a little while.

I’ve also been working on my dash a fair bit and doing more hours on my exhaust setup over the past couple weeks. I’ll try and get another post together this week with more updates.

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