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heyitsrama

Depressing Early 260z bumper struts

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Howdy,

I’m trying to flush mount a rear early 260z bumper to a early 260z. From other threads I have read that you can drill out a leak hole for the oil, the push the shock inward and weld it into place.

I drilled a hole in the strut l, drained a significant amount of oil out of the strut, but the strut does not stay depressed, it seems like it keeps popping outward. I beat on it with a dead blow hammer, I can see that it moves inward then comes right back out. Is there a trick to this that I’m missing? 

image.jpg

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Drill a hole at least 6mm while the shock is compressed , tap it, and run an M6 bolt into it. Just a suggestion. I removed those boat anchors when I swapped over to a 240Z rear bumper and used some mounts designed to affix 240Z bumpers to 280Zs.

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@SteveJ I need up fabricating my own brackets but I messed up because I copied the body side mount from the 240z, I did not realize that the holes are offset on the 260z/280z body.

I suppose I can remove the struts out of the car, but am not looking forward to dropping the tank. 
 

I can make mounts for the 260z body but the issue is that the mount position on the bumper is further out than the 240z, there might be some awkward bracket that I can make, but it seems like keeping the struts is easier to do.....

are the struts super heavy?

what’s the point of threading in the m6 bolt? Should it be in the face of the strut? Or along the shaft?

 I was able to shove a pin into the passenger side bracket and appeared to pop through something that make it able to push down, no luck on the driver side.


image.jpg
73 240z on the top,

early 260z on the bottom.

Edited by heyitsrama

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The thought for threading the bolt into the housing and the strut would be to hold it in place.

I don't remember how much the struts weighed, but it was not insubstantial. 

I bought the bumper brackets from Datsun Spirit, and those brackets allowed me to mount the 240Z bumper at the correct height.

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The bumper shocks are high pressure mono-tube struts. If you want to know what that really means, or how they work, or why it matters in this case, let me know and I'll go into the details, but the summary is...

Carefully remove the little screw in the middle of the bumper mounting flange. It's holding back significant pressure. Mostly gas, but there might be some oil in there too. Wear eye protection and don't let anything fly. I suggest covering it with a rag once you get the screw cracked loose.

After that, the shock should compress and stay wherever you put it. (Until acted upon by another outside force of course.)

monotube.png

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Actually if you already drilled a hole and significant oil came out, it really shouldn't matter. But try taking that screw out first and see what happens
P1090335.JPG

P1090344.JPG

 

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11 minutes ago, Captain Obvious said:

Actually if you already drilled a hole and significant oil came out, it really shouldn't matter. But try taking that screw out first and see what happens
P1090335.JPG

P1090344.JPG

 

On the driver side I drilled 2 holes where you are holding the tube in the second image, I also drilled out the screw hole on the face but am still not able to get the strut to collapse.... If I try to pull the strut out is it going to be a pain to get it reinstalled? Perhaps I need a deeper punch to break through whatever membrane/seal is back there. 
 

I was thinking of removing it and trying it on the shop press, seems to be more accessible. 

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There is only one significant hurdle to getting the shock out of the bracket and that's the nut on the back side. It's not hard to get to, or hard to turn, but the problem is that there is nothing (except a little friction) holding the shock shaft from spinning. But once you get that nut off, it's not difficult to take the shock our or put it back in.

So if you clean up the threads good and put some penetrating oil on it and then hit it with an impact wrench, it should come right off. If you put a ratchet on it, I give it 50/50 that the shock shaft will spin inside the body. Here's the nut:
P1090336.JPG

And if the shaft does spin, about the only thing you can do at that point is cut the nut off with a cutting disk. Big ol' PITA:
P1090337.JPG

P1090340.JPG

I did two of them, one came off easy with a ratchet and the other did not. After my (lack of) success, I helped another Z guy do the same and told him to skip the ratchet and use an impact gun. His both wizzed off with no trouble at all.

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Oh, and I mentioned above that the nuts are easy to get to... That's with the whole thing off the car. I don't remember how difficult it is when the whole assy is installed. Sorry.

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Sorry, one last thingc... I drilled up here. And you can see from the shock shaft that mine stayed compressed no problem:
P1090590.JPG

And after cutting the shock open and analyzing the guts, I left a note for myself if I ever have to do it again:
P1090608.JPG

 

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OK, really really last one this time.  LOL

My theory is that your drill hole is too close to the bumper mounting flange and because of the way the mono-tube shock works you're trying to force oil through a tiny orifice and it just takes time.  I think you have two choices:

1) Drill another hole further back.

2) Push the shock in and hold it there for enough time for the pressure to bleed off.

This is a pic with the shock cut open. If you look closely down into the tube, you'll see a very small hole in the center of the piece at the bottom. I'm thinking you've got a mix of gas and oil in the shock tube and when you push the shock in, it compresses the gas, but not the oil. If you compress it and wait long enough, that pressure should eventually equalize?

Shock cut open showing the orifice that separates the two chambers of the mono-tube design:
P1090600.JPG

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The deepest spot I got my drill bit is 3” i, I’ll drop the mount and try it tomorrow, I tried fitting my hands back there and it feels like there is a plate covering access to the nut.

thanks for the thorough explanation @Captain Obvious I appreciate it 🙂

 

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Amar, I have the same car as you and I also tried drilling the shocks.  It just didn't work and seemed like too much trouble, so I dropped the tank and removed them.  I supported the rear bumper using the factory tie-down points and some small brackets I fabricated to support the bumper ends.  The big holes in the body left by the shocks annoyed me, so I welded them up.  Let me know if you would like more info.

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9 hours ago, heyitsrama said:

The deepest spot I got my drill bit is 3” i, I’ll drop the mount and try it tomorrow

IIRC, getting the rear bumper brackets out of the car is not the easiest thing in the world. Might have to drop the tank?

Maybe try compressing and holding for a couple minutes to test my other theory first? Back the car up against something and leave it like that for a half hour?  LOL

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Yes, I did have to remove the gas tank to get the passenger side shock out.  It was worth it, though.

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I installed 240Z bumpers on my early 260Z several years ago. I didn't want to use the pistons for mounts so I removed the driver side completely. I too, at the time, didn't really want to drop my fuel tank to get the passenger side piston completely removed. My answer was my Sawzall (reciprocating saw)... I cut the end of the piston off flush with the end of that outer casing. I cut from the bottom upwards so when I got to the pressurized section it spewed oil and gas out the bottom. 

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@Captain Obvious I should have checked this thread before I started working, but I pulled the driver side strut out, had to drop the exhaust from the header back (really should get a sectional exhaust this sucks).

when I removed the nut from nut there was a significant amount of air that came out. I can now depress the strut I did not have to do anything else. 

For the next person reading this thread, put painters tape on the edges of the hole so you don’t ruin the paint on the back.

@cgsheen1
The problem is you really have to move and twist the strut mount to get it out, if I was going to do it again I would saw off the tabs/face/Falange on the strut and then hit 3 bolts under the car 3 on top (inside the trunk) and slide it out. You might be able to just lower the tank this way....

I guess I’ll be doing it again if I get those 240z bumpers..... alright back to work get this exhaust on and get the 260z bumper on to see how it fits. 

@Freez74 you have pictures of the mounts you made? I suppose it would be similar to the one Steve mentioned.

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48 minutes ago, heyitsrama said:


The problem is you really have to move and twist the strut mount to get it out, if I was going to do it again I would saw off the tabs/face/Falange on the strut and then hit 3 bolts under the car 3 on top (inside the trunk) and slide it out. You might be able to just lower the tank this way....

I guess I’ll be doing it again if I get those 240z bumpers..... alright back to work get this exhaust on and get the 260z bumper on to see how it fits. 

 

Ya, should have mentioned that I've done a few subsequently on other Z's in the shop. It is entirely possible to remove that strut without completely removing the tank AND without cutting anything. It's much easier when you have a lift. I've lowered the tank - disconnecting as few of the hoses as possible (normally right side only - but that's most of them, right?) - supported the tank variously (rope, straps, whatever) and wormed the strut out in one piece. It's kind of a PITA but completely do-able. On the floor it's a little tougher.

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@cgsheen1  that sounds like quiet the challenge, my buddy offered this lift I’ll have to take him up on it the next time I do this, working on the slanted driveway is fun till the sockets roll away.. but then again I’ve done all the work on the driveway >.>

I just mocked up the 260z bumper, a much larger gap in between the body and the sides of the bumper along the quarter than the 240z bumpers..... maybe I can adjust it.
Seems like a lot of this is wasted effort. 😪 should have just got the 240z bumpers 😐

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That's me. Mine had no bumpers, took quite a search to find early 260Z bumpers and I hated them... Later found some fairly good '73 bumpers and installed them (ya, huge front bumper mounts too)... 

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What was strange is that it looks like it is possible to do it. I think I was trying to mount it too low, on the ends of the struts.. perhaps you HAVE to use the body mounts as well. Alright back outside we go.
https://forums.hybridz.org/topic/69280-260z-flush-bumper-conversion/

image.jpeg

Does this seem too high up? @cgsheen1 do you have a picture of yours? 

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I can't tell from that photo. I used 240Z bumper mounts and the ones I have don't really fit right but mount the bumper fairly well. I should have fabbed a pair of custom brackets, but you know the old saying about the cobbler and his own shoes... I don't make the time to work on my personal Z like I should.  I'll post some phone pics.

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