Trans build
 

I just got the following installed:
DSS Axels
DSS driveshaft
Cusco LSD
Cusco Ring and pinion
Cusco collar
PAR gears 1st-5th (assembled by jacks transmission)
Verus Synchro kit
Whiteline rear bushings kit
Megan Racing adjustable trailing arms

ISSUE: The problem is that I have a vibration once I hit 67-70mph on the highway. It is so strong that I figured something was broken. I have taken it afterwards to get an alignment and balancing of the two rear tires. I have also checked the tire pressure to eliminate all the things that I would know.

Has anyone experienced this after installing any of these parts?

DSS Al or carbon driveshaft?

May want to try unbolting the driveshaft, rotate the driveshaft 1/4 turn and bolt it back on to see if it gets better or worse.

We finished installing the 3" al driveshaft

Thanks for the input, we have looked at that and also run a stethoscope type instrument on the LSD, thinking maybe it was something in rotation...at this point..i am a little lost..thanks for checking in bro

DSS has admitted design fault in the AL driveshaft. The issue is the CS of the shaft is not high enough, though this only appears over 105mph. You likely have a balance issue. Mine vibrated at bit at around 65mph too but at track speeds you couldn’t see out of the rear view mirror. If it’s a street car have someone balance it again, if it is a track car call and talk with Kevin at DSS, if you have room in the trans tunnel they can do a 3.5” shaft reusing your joints that will fix it. Here’s a forum member who had failure on the dyno with one.

https://www.ft86club.com/forums/showthread.php?t=148537

+1 to what NoHaveMSG said, seems to be the most common issue with the 1 piece driveshafts to have vibrations that start around that speed and get worse the faster you go. This thread had some good ideas regarding it, perhaps some of it could apply to you - https://www.ft86club.com/forums/showthread.php?t=147489

@Fa20Toybaru: If you haven't already done so, reinstall your original DS and test drive.

Trans build
 

Also keep in mind if you are running a lower gearing in the diff it will lower the mph that it happens since it is the driveshaft speed that is causing it. DSS told me the CS was 110-115mph as in blsfrs’s thread. I was running a 4.3 and seeing it at 105.

I was testing, the install on all parts. I just got around 65-67 when I felt the initial vibrations. At the time, we had not done alignment and balancing. We were planning on doing it, just had not gotten to that step. After the initial testing, we did the alignment, and we checked tire pressure and balanced rear tires. The vibration was less, the car was able to get to about 90mph before the vibration started. We attempted to research, found that there had been issues with driveshafts causing vibrations, so I wanted to ask if anyone had similar issues, and what was the solution. I believe it might be because it no longer uses the center bearing that the stock driveshaft uses, but not sure, id rather ask and compare notes.

Still testing today, took everything apart yesterday, that is why I was unable to respond until today. I checked all bolts, marked to see if after driving if bolts loosen. We checked the rear DSS axels to see if that was causing issues. Everything, seems correct, we double checked everything still a strong vibration in the rear of the car at high speed. Trans shifts smoothly, I can feel the rear diff doing it job, the axels do not seem to be loose or pop out of the diff. It comes down to the tires or driveshaft

I was testing, the install on all parts. I just got around 65-67 when I felt the initial vibrations. At the time, we had not done alignment and balancing. We were planning on doing it, just had not gotten to that step. After the initial testing, we did the alignment, and we checked tire pressure and balanced rear tires. The vibration was less, the car was able to get to about 90mph before the vibration started. We attempted to research, found that there had been issues with driveshafts causing vibrations, so I wanted to ask if anyone had similar issues, and what was the solution. I believe it might be because it no longer uses the center bearing that the stock driveshaft uses, but not sure, id rather ask and compare notes.

Still testing today, took everything apart yesterday, that is why I was unable to respond until today. I checked all bolts, marked to see if after driving if bolts loosen. We checked the rear DSS axels to see if that was causing issues. Everything, seems correct, we double checked everything still a strong vibration in the rear of the car at high speed. Trans shifts smoothly, I can feel the rear diff doing it job, the axels do not seem to be loose or pop out of the diff. It comes down to the tires or driveshaft

Sorry cant answer your question, but how do you like your transmission? Any issues? How much power putting down for it?

Thanks for sharing the information regarding the gearing. I had information regarding the MPH. I am just concerned about the vibrations, it is crazy...I am unable to even look out the rear mirror. The car will be on the track eventually, I am however testing it on the street. I am thinking about doing the home balancing of the driveshaft and seeing if that helps.
I am just stuck on where to start, I think it is just test and move, test and move...until it is right. Thanks for all the information and help

The trans alone is good, I am able to feel the grab. I wish I could be more specific, I have done alot to the drivetrain, so I am unable to tell you if alone it was the greatest things since sliced bread...however the transmission has not given me any issues. I am able to go through every gear, no grinding, it is loud, but it does make the car move a little quicker and reduce speed as well.

What ring and pinion gears are you running? If it is the cusco 4.56 it will vibrate even lower speeds then I was getting. When the driveshaft hits around 6200rpm is when it exceeds its CS. So if you are running 4.56's it is going to happen around 95mph. There is nothing that can be done balance wise to fix it, or trying to shim the diff/engine to get it in better alignment and it is at risk of failing. The issue is for the length of the shaft, it is not big enough in diameter to be made out of aluminum.

Thanks for reaching out, yes it is the CUSCO ring and pinion at 4.556. So if I understood you correctly, we cant balance the shaft to fix the vibrations at acceleration? Also the shim part, will that cause it to fail, or I need to shim it further to prevent early failure for the diff? I appreciate your time, I cant find anyone in TX that has any knowledge on this.

The only way the issue can be fixed is to have DSS make you a new AL shaft out of 3.5, or go to a carbon shaft, or go back to stock. I would recommend calling DSS about it. You can also email Kevin at Kevin@driveshaftshop.com.

They won't flatout replace it for you, but will work with you on a replacement.

Edit: The 3.5" shaft won't clear the stock shifter extension. Need to measure under the car to see if it will fit.

Sorry to threadjack, but I have never been really clear on the reasons for replacing the driveshaft. Can someone help me here? Reading numerous posts over the years has persuaded me that doing so is just borrowing trouble.

For me, the car drives smoother with sudden inputs and after harsh shifts with boost as a part of the recipe. The Verus carbon fiber driveshaft was a nice upgrade and I think it'll help reduce shock through the diff and transmission.

The aluminum DSS shaft is cheaper then stock and 1/3 the weight. Price alone convinced me to buy this 5ft long paperweight.

Thanks. I guess I’m in the IIABDFI (if it ain’t broke don’t fix it) camp on this part. That’s unusual for me. I’m usually in the “if it ain’t broke let’s fix it til it is” crowd.

I had a rear u joint that was feeling bad in my car so I swapped it. I think the stock driveshaft is a couple hundred more. Now I have a new stock driveshaft and a used spare.

Even the 3.5" have a critical speed. With the 4.55 gearing you might reach it sooner than you think. Like 8100 rpm.https://www.ft86club.com/forums/atta...1&d=1645019697

Did you have a trans with mileage updated, or a new one modified. Curious about the noise and if it'll degrade over time or you learn to live with it.

My CJ7's T-18 took a year for the shifting detents to wear in and get smooth. My arm hurt after driving it quite a few times shifting all day in it on the trails.