Gary L

Something I don't understand, and maybe someone can explain it to me, is why and how does the tank get pressurized. For example, as the fuel pump pumps fuel from the tank to the engine to get burned, I would think the tank would develop vacuum and hence the need for a fuel filler cap with the vacuum relief valve. But I have trouble understanding why pressure develops in the tank. (just trying to educate myself) Gary

I did find it. When I blow in the line with my mouth at the carbon canister, air will flow through it fairly easily and pressurize the gas tank. However, when I try to suck air through it I can draw air but it seems more difficult to do. But the again it is easier to blow air though a small tube than suck air. If I disconnected it (which I'm not going to bother doing at this point) and then tried blowing through it from the tank side as outlined in the test procedure it may be easier to do. But anyway, it does allow air to pass in either direction which sounds to be correct Thanks Gary

Hi Captain Obvious Thanks for the info. My 76 FSM doesn't have the test procedure. And I haven't been under the car in awhile, but it looks like it should be accessible from under the car, not behind the side panel in the trunk. This weekend I'll have to put it up on the jack stands and look around under there. I remember where the fuel pump is and the fuel damper, but I don't recall seeing a check valve anywhere under there. Gary

Thanks guys. It's reassuring others get the same "whooosh" and that its normal. I guess I'll leave well enough alone. It's getting near peak color here in the UP of Michigan and so I'm hoping to take it on a couple of Fall Color road tours in my area. Gary

So when I try sucking through the vent line at the carbon canister, it is difficult to suck hard enough to tell if I am drawing any fuel fumes through it. However, if I hook the vacuum cleaner to the vent line for a couple of seconds with the gas cap on, when I then take the gas cap off, there is a considerable vacuum present, hearing the air rush in to the tank. So I don't know if that is good and indicating proper operation or not. I hope that makes sense.

This is on my 76 280Z. After running the car for awhile, my fuel tank gets pressurized ---- When I take off the gas cap I get a huge rush of air coming out of the tank, a big whoooosh. Looking at my service manual, I can't tell if if the check valve is under the car or behind the passenger side rear panel near the vapor separator in the hatch. I saw in an old post where a guy had a similar problem which was corrected by replacing the check valve. Of course, I'm never going to find another check valve for sale, but I first just want to know where it is located. Thanks Gary

Thanks Zed, I found the diagram in my SM also. Could it also be the purge control valve on my canister?

This is on my 76 with stock EFI. When I remove the gas cap I get a rush of gas fumes coming out. How can I test my vapor canister? I did put a new filter on the bottom. Do vapor canisters go bad (eg, the charcoal inside)? I do have a new fuel pressure regulator on it and a new fuel pump. My newer vehicles don't build pressure or vacuum in the gas tank. Can someone explain how the vapor system works on these cars? Thanks Gary

I was actually thinking of picking up a sheet or bar of lead weighing 10 or so pounds and bolting it on top to those 2 unused holes Zed mentioned. It'd be nice tho to see how NIssan fashioned/configured such a weight. Bars of lead are fairly inexpensive but the sheets are a little more costly for example http://rotometals.com/lead-sheet/sheet-lead-1-4-16-lbs-sq-ft/ And I'm sure the companion flange must be a precision, well balanced piece as Zed mentioned.

No, thats the language used in Wick's book - atop; probably due to the original Japanese bulletin interpretation ! Below is taken from an old post on another Z web site at the following link http://www.zcar.com/forum/10-70-83-tech-discussion-forum/40849-differential-damper-plate.html "9-5-1975A remedy for excessive noise from the early-style or R180 differential was isssued by Datsun in 1975. This is not to be confused with the kit used in 1971 to correct high vibration levels of the differential. It is not applicable to the alter R200 differential, which has no side-bearing retainers whith their five distinctive bolts. Nor is it recommeneded for 2+2 models due to interference with the rear seatbelt-attachment bolts. The noise was identified as coming from the meshing of the ring and pinion gears, then amplified by virbratiions in the body. Datsun's solution was to add mass - a 10 pound wight bolted to the differential housing. Also included was a replacement companion flange that included a torsional damper that helped absorb torsional vibration inthe drive line. The parts were cataloged under the part number 99991-20000, which included mounting hardware. The companion flange includes a disc section, much like a crankshaft vibration damper. It is easy to distinguish from the previous part. Installation was the same as that descrbied in the service manual. The mass damper is a solid lead weight that bolts atop the differential pinion-gear housing with two 7/16 inch bolts." But Zed is correct, I'm not talking about the one pictured in 4 above.

In Wick Humble's book HOW TO RESTORE YOUR DATSUN Z-car, In the chapter on technical bulletins he mentions that in 9-5-1975, in order to dampen rear differential noise, Nissan made available a 10 lb lead weight that bolts ATOP the differential to quiet noise from the ring-and-pinion gears. Has anyone ever seen one of these and has a pic of one that they could post ? And I'm not referring to the one that attaches to the differential's rear mounting support studs to cut down on vibrations or the stack of metal plates that hangs (bolts) beneath the differential's front cross member. This is supposed to be a lead weight ATOP the differential? I just put a rebuilt diff in my 77 Z and although it is quieter that the original one, there is still some whining which must be from the ring and pinion since the bearings are all new. I've read that even when these cars where new the diffs were a little noisey and I'm never going to get it completely silent, but I'm wondering if one of the lead weights Wick mentions would help. So if anyone has a pic of one of these I'd like to see what they look like. Thanks Gary

That being the case, with my stopper backed all the way off, mine is only at 8". I can't see how I could get it to another 7/8th inch.

No, I got rid of the old MC after measuring the rod to clevis setting which I copied for the new MC. I've got lots of thick insulation besides carpeting in my car so maybe thats the problem, but in the SM they makes it sound like the 8 7/8th is the distance from the toe*board metal pedal stop. May be I'm reading it wrong and it should be from the thin OEM carpeting.

Any thoughts on the pedal height adjustment issue I mentioned above. Am I just measuring from the wrong points? The reason I thought I'd check that is because there is a warning in the SM that talks about an incorrect MC rod length could block port .....

Thanks again Zed H. So if I get another MC, would you recommend a new OEM, new aftermarket, or re-manufactured? I see NAPA for example has some that aren't to costly. If I remember correctly tho, it was a real pain getting that pin back in the clevis due to the tight spaces.