kj280z Posted August 13, 2011 Share Posted August 13, 2011 (edited) Hey all Today I'll be spending time on my back under my Z. I had posted my suspicions on other posts where members have raised concerns about driveshaft bolts coming loose(mine are still tight). I have always suspected that this is due to drive shaft angles... I have now driven my Z 1,300 miles - it's ok if I stay under 65 but as you approach 70 it starts to have a sound vibration resonance, then by 80 mph it vibrates pretty bad... I think the solution will be a combination of the RT mount (which I already have) and lowering the rear tranny mount to reduce the upward angle slightly (I have the 280z mount) I would like to know if others have experienced this issue. I have also slotted the holes in my tranny mount so I have adjustment from side to side.... What are the optimal angles and what is the best way to achieve them? I guess I'm going to have to invest in a good laser angle finder. I have researched and found that the angles have to be equal front to rear and they cannot exceed 3 degrees... Edited August 13, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
zforce Posted August 13, 2011 Share Posted August 13, 2011 Hey all Today I'll be spending time on my back under my Z. I had posted my suspicions on other posts where members have raised concerns about driveshaft bolts coming loose(mine are still tight). I have always suspected that this is due to drive shaft angles... I have now driven my Z 1,300 miles - it's ok if I stay under 65 but as you approach 70 it starts to have a sound vibration resonance, then by 80 mph it vibrates pretty bad... I think the solution will be a combination of the RT mount (which I already have) and lowering the rear tranny mount to reduce the upward angle slightly (I have the 280z mount) I would like to know if others have experienced this issue. I have also slotted the holes in my tranny mount so I have adjustment from side to side.... What are the optimal angles and what is the best way to achieve them? I guess I'm going to have to invest in a good laser angle finder. I have researched and found the the angles have to be equal front to rear and they cannot exceed 3 degrees... Something is out of balance or you could have a u-joint going bad causing the vibration.Or one of your wheels is bent,try rotating the tires and see if the vibration moves up front. Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 13, 2011 Author Share Posted August 13, 2011 Something is out of balance or you could have a u-joint going bad causing the vibration.Or one of your wheels is bent,try rotating the tires and see if the vibration moves up front. Wheels were recently balanced so I've eliminated that... I've done the z31 CV conversion, so the rear u joints are eliminated (although I will check it out again). The drive shaft came from JCI brand new and balanced.... I have always suspected that the tranny mount caused the driveshaft angles not to be optimal - just eyeballing it, it never looked right... And with others having stuff coming loose in the driveline in other posts I am going to start there... I'll share my findings... Has anyone experienced vibration from the z31 CV conversion?? Quote Link to comment Share on other sites More sharing options...
EvilC Posted August 15, 2011 Share Posted August 15, 2011 Sounds like you need to get your hands on some lasers to see where the diff and tail end of the tranny are pointing in relationship to one another. From there we can see where the tranny needs to be adjusted too and/or the entire engine/trans combo from the slider mount on the pasn side of the lsx conversion bracket. Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 15, 2011 Author Share Posted August 15, 2011 Sounds like you need to get your hands on some lasers to see where the diff and tail end of the tranny are pointing in relationship to one another. From there we can see where the tranny needs to be adjusted too and/or the entire engine/trans combo from the slider mount on the pasn side of the lsx conversion bracket. Yep - I started to jack it up today and the hydraulics in my jack blew up, so I'll get all the stuff together and see what I can do tomorrow Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 19, 2011 Author Share Posted August 19, 2011 So I could use some expertise... I had the RT Mount installed today - local shop did it for me... This eliminates the stock lower mount and replaces it with a polyurethane upper mount which is mounted at the top. The shop had to notch the lower cross member so the bolts would not interfere. They also had to modify my sway bar mounts to lower it slightly because it was too close... Effectively this lowered the front of my diff around 3/4" The vibration now starts at 55 mph. I guess I now know for sure it's the driveshaft - the question is now what to do about it. In the attached picture you can kinda see how the cross member is notched - or if anything else looks suspect feel free to make suggestions... Sorry for the lousy pic from my phone... Quote Link to comment Share on other sites More sharing options...
Xnke Posted August 20, 2011 Share Posted August 20, 2011 Sounds like you went the wrong way, if the vibration starts lower. I have the same problem in my L28Z with the RT mount; but I'm fair-to-certain mine is due to a front end alignment problem...it's all in the steering wheel. Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 23, 2011 Author Share Posted August 23, 2011 (edited) I have scheduled time on Friday to get the car on a lift so I can fix this once and for all... After doing a lot of searching I haven't found any specific threads that have discussed the JCI 280z tranny mount (and JCI kit in general) as it related to drive line angles... I have suspected all along that this would be an issue, and now this problem is confirming my suspicions. I will certainly share my findings, but in general I suspect that the engine/tranny mounts are positioned about 1 inch too far to the left (these are just general observations - real measurements to follow). Additionally, the transmission mount for the 280z appears to have the output shaft 1 inch too high. I also happen to have a 240z tranny mount which mounts through the floor... I'm going to compare them as part of this trouble shooting effort. To compound the problem, if I'm right and the tranny is too high, the RT Mount lowered the snout of my about 3/4" (very rough estimate)...(which made the problem worse) The fix will be to try to re-position the motor/tranny if necessary, raise the snout of the diff and lower the rear of the tranny... There are several threads on drive line harmonics and how to get the angles right, so I won't cover that here - but I will share the final measurements. For all of you that have had the bolts that fasten your drive shaft to the diff come loose, you should pay attention to this thread! I'd bet I'm not the only one with this problem!!!! Edited August 23, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
rags Posted August 23, 2011 Share Posted August 23, 2011 Before moving the diff and trans around, why not make some cheep laser pointers mounted to magnets to see where the trans and diff are pointing? I picked up the laser pointers and magnets at Home Depot. Mounted a piece of 1/2" copper pipe to the magnet with a nut and bolt, and inserted the laser pointer into the pipe. Presto, magnetically mounted laser pointer! Put one on the diff pinion flange mount and one on the output shaft and with a piece of paper measure to distance between the laser dots on the paper. If the distance between the dots gets greater or smaller when the paper is moved closer and further from the trans, the diff to trans alignment is off. Laser traces should be as close to parallel as possible. Joe Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 23, 2011 Author Share Posted August 23, 2011 Before moving the diff and trans around, why not make some cheep laser pointers mounted to magnets to see where the trans and diff are pointing? I picked up the laser pointers and magnets at Home Depot. Mounted a piece of 1/2" copper pipe to the magnet with a nut and bolt, and inserted the laser pointer into the pipe. Presto, magnetically mounted laser pointer! Put one on the diff pinion flange mount and one on the output shaft and with a piece of paper measure to distance between the laser dots on the paper. If the distance between the dots gets greater or smaller when the paper is moved closer and further from the trans, the diff to trans alignment is off. Laser traces should be as close to parallel as possible. Joe Yeah that's the plan... measure everything first etc... OK - is it just me or are all you guys also having trouble picturing the contraption that Joe is talking about??? Joe - call me or post a pic! LOL Quote Link to comment Share on other sites More sharing options...
ritrebor Posted August 24, 2011 Share Posted August 24, 2011 Here is the laser tool. http://forums.hybridz.org/index.php/topic/43993-differential-laser-alignment-tool/ ritrebor Quote Link to comment Share on other sites More sharing options...
z-ya Posted August 24, 2011 Share Posted August 24, 2011 Ken, I had the same problem on my RB swap. It was the driveshaft balance. With the RT bracket and poly differential mount (which I also have), it is extremely important to have a very precise balance on the driveshaft. Most driveshaft shops balance good enough for a floating solid axle application, but not good enough where the differential is solid mounted to the body (especially with a poly mount). Gilbert's in Manchester NH made my driveshaft, and did their normal balance. It vibrated at 55MPH like your car. It would smooth out over 70MPH. So I brought it back and they did a more precise balance (they call it their race balance), and it fixed the problem. Pete Quote Link to comment Share on other sites More sharing options...
madkaw Posted August 24, 2011 Share Posted August 24, 2011 watching this thread in hopes of answers for my vibration at 100+mph. don,t mean to highjack here, but would a failing tranny mount cause this also? I can under the car and push up on the mount and get it to move upward a good half inch with effort. Hope this question ties in with this thread? Quote Link to comment Share on other sites More sharing options...
rags Posted August 24, 2011 Share Posted August 24, 2011 Ken, Why are you using the 240 mount? The 280 mount doesn't leave room for horizontal error as it mounts to the inside of the stock frame rails. The 240 mount gives lots of room for error. We found that out with Clive's car. Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 24, 2011 Author Share Posted August 24, 2011 Joe I assume you're talking about the JCI trans mount? If so, I'm not using the 240z version. I am using the 280z version. I have an extra 240z JCI mount that I will check out while I'm trouble shooting , but I intend to use the 280z mount unless I find some advantage to switch it. Quote Link to comment Share on other sites More sharing options...
kj280z Posted August 26, 2011 Author Share Posted August 26, 2011 (edited) OK - My problem is resolved (although I have not exceeded 70 MPH yet but) it drives like a different car!!! Here's the result... We had 2 280z's side by side that had the JCI kit installed... We'll call my Z with the vibration problem number 1 and the other 280Z number 2. Removed the drive shaft of number 2, checked all angles and it was reasonably good. The installer had modified the transmission mount (Number 2) which allowed the rear of the trans to be slightly lower. Then removed drive shaft from number 1 and did some comparison measurements - VERY different! 80% of the problem was that there was SIGNIFICANT differences between the 2 trans mounts. The mount in number one, had the output shaft 1+" inch higher than number 2! I then compared it to a 3rd JCI trans mount that I had and it was different as well!!! I will discuss this with John at JCI as there appears to be inconsistencies in whatever process they're using to make them. OK - Next I used all the laser pointers that I made as per the previous thread. The first thing I did was to get the transmission and diff lined up on a plane... To do this, the tranny had to come down 1 1/4" and the diff had to go up 3/4" (a previous installer had screwed up the installation of the RT mount) Additionally, the trans needed to move toward the drivers side 3/8" and also the diff needed to move toward the passenger side 1/4" By having the laser on the diff flange and another on the trans output shaft you can easily get things lined up - it becomes intuitively obvious what to do... Next take a piece of paper and check your drive shaft angles - they should be more than 1 degree and no more than 3 degrees and also have to be equal front to rear... In my case I have around 2 degrees - When you put the paper as close to the diff flange as possible - if you've got things lined up perfectly, you'll see that both laser dots (one will shine through the paper) as one on top of the other. In my case they were about 1/4" apart at the diff, next repeat the process and insure that you have the same distance between dots at the tranny... in my case - exactly 1/4" on that side too, you'll notice that the dot that was on top is now on the bottom and vice versa (I had 2 different color lasers so it was very apparent). If your angles are off shim and move things left/right as necessary. You can also blow some cigarette smoke (I'm not a smoker but I found someone for this purpose)... You can then see the intersection of the lines and also the plane when you're leveling - quite handy. Use an angle finder to verify that your angles are equal on both sides. OK - now I had things where I wanted them, but then I needed to get the diff and tranny mounts adjusted so that they stay where I had them... (I made my adjustments with the trans and diff mounts removed) The RT mount was fine - I slotted the holes on each side of the poly bushing which gave me left to right adjust-ability. I also contoured the top of the mount so it laid flush on the round section of the diff - it was perfect height wise and only needed a slight tweak from left to right.... Diff done... The tranny mount needed to be lowered significantly. It took several tries but we were able to use some hydraulics to bend the mount so the center was lowered enough to keep the tranny where I wanted it and accommodate the rubber trans bushing. I also slotted the holes in the trans mount so it gave me some left to right adjust-ability... Since every trans mount that we checked was different, I would highly recommend that you check your angles. This would explain why some don't experience any issues while others seem to have issues. I knew that my trans was too high just by looking at pictures of how high my shifter came up through the tunnel compared to others - Mine is now over an inch lower!!!! Edited August 26, 2011 by kj280z Quote Link to comment Share on other sites More sharing options...
Leon Posted August 26, 2011 Share Posted August 26, 2011 Good job on finding the issue. I would suggest that since you now have the angles and parts where you want them, mark the diff and trans mounts on the mount and body. Therefore, If you ever have to pull them out, you can simply align the marks when you put them back in. Quote Link to comment Share on other sites More sharing options...
johnbell Posted March 17, 2012 Share Posted March 17, 2012 My 260 has this problem, i believe. It is like a Buzz, starting at about 65 or so, pretty bad. Guess I'm heading uptown to look for laser pointers, etc..I suspected my half shafts before I read this, but now I don;t know. The half shafts, with a dial indicator at the middle will deflect about .o10 with moderate pressure, Anybody ever checked this? I took them apart and regreased and they looked pretty good to me. Quote Link to comment Share on other sites More sharing options...
kj280z Posted March 17, 2012 Author Share Posted March 17, 2012 (edited) My 260 has this problem, i believe. It is like a Buzz, starting at about 65 or so, pretty bad. Guess I'm heading uptown to look for laser pointers, etc..I suspected my half shafts before I read this, but now I don;t know. The half shafts, with a dial indicator at the middle will deflect about .o10 with moderate pressure, Anybody ever checked this? I took them apart and regreased and they looked pretty good to me. I know of 5 more (in addition to the ones mentioned previously - so yes the problem is more wide spread than initially thought) LSX Z's that have had their drive shaft bolts loosen, so as I've stated in the past, every Z that has done the conversion should verify their driveline angles. As far as your comment on the half shafts... I was running the stock half shafts initially, and experienced the vibration. I then converted to 300zxt CVs and the problem was the same. The John's Cars Tranny mounts that I've inspected are not consistent with the tranny heights (The mount bends are inconsistent) - Every one I've checked is slightly different... start there first - I'd bet your trans is up too high... Then side to side is probably off as well... I'm really surprised this thread hasn't generated more concern - I see it as a huge issue with the JCI kit Edited March 17, 2012 by kj280z Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted March 17, 2012 Share Posted March 17, 2012 Thank you so very much for the time you have taken, and for your thoroughness (is that a word?). When I get my brakes straightenened out, my diff built, and my exhaust built, I will take my car out for a cruise up to 100 and see if I have this problem. I am driving it a little on my R180 to work out the bugs that one finds after a total rebuild, but it is just too loud for me to "open 'er up" without fear of a ticket. Perhaps the mods will find your thread "sticky" worthy. I bet they will. One of the problems with the dudes who post on this site is that they like to post problems, but they rarely take the time to come back to the computer to report back on what they found to be the problem and to tell the story of the solution. I recently contacted one such person via PM, only to find out that the problem was never solved and that the half-finished car is still sitting in the shop years after the owner got burned-out. Thanks for not letting your car meet that fate, and thanks for sharing with the rest of us. I hope some day to attend an event where I can meet all the great guys who have helped me to live-out a childhood dream of owning one of the coolest and fastest cars in my area. The first day I drove my completed LS swap to work, I got a note on my windshield and an offer to buy it (which I turned down). Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.