Recently purchased a 1999 S2000 and first thing I did was put coilovers on it.

Prior to lowering, the s2k would have vibrations when accelerating around 50mph/80kmh however it was only slightly noticeable.
After lowering with the coilovers, the vibrations are now significant from 25mph/60kmh onwards.

Strangely this does not occur in 1st-3rd gear but 4th gear onwards.
Checked the diff and it has quite some play and has been leaking for a while by the looks of it.

What to do?

• My mechanic told me the diff needs replacement and will fix the issue - have managed to source a 4.77 with detroit locker however unsure whether to save my money
• From my googling I've found that driveshaft spacers are a necessity when lowering the s2k and may fix the vibration issue?
• Anything else?

Any help would be much appreciated!!

 

Driveshaft spacers, especially with coilovers.

 

Almost definitely your CV shafts. Look up on how to swap the buckets. I run fairly low for Autox (not slammed) and no driveshaft spacers are needed. But, you move the contact point in the CV shafts out of their initial wear area and it can cause vibration.

The vibration symptom for this or a pitted CV bucket is a vibration, mostly under load, when accelerating from 40-50mph up to 60-80 mph. The good news is that unless they have already been swapped, you can fix this for free yourself by swapping the CV buckets side to side. Not that hard of a job at all. There are threads on it.Well worth trying that before looking at the diff or something else. Not saying you have an issue with the diff, but the symptoms match CV issues. And, if you dont want to deal with a 4" breaker bar and huge tq on the axle nut, you can do the job without removing that. Pop lower ball joint loose, detach shaft from diff, pull out, swap buckets and put back together. It is a lot messier that way under the car, but in case you have issues with the axle nuts, it is an option.

I would put my money on that being the issue, especially since it popped up after changing ride height.

 

^^^ Yep Exactly what the issue is. Swap the CV buckets and the vibration will be gone. Had to do it to mine some years back.

 

If its worn cups, you can either swap them side to side as suggested (big messy job) or buy the common driveshaft spacers. Either one will work. If your going to do the spacers, get the ones that come in two pieces so you only have to back out the bolts to slip them in, so much easier/quicker.

 

Since the OP mentioned there was some vibration before, I assumed the cups were likely pitted, and lowering just added the misalignment of the worn area to the already pitted spots. So if he just ran spacers, he would likely still have the same vibration he had before lowering. So in that case, swapping the buckets will be the correct fix. If the vibration started only after lowering, then yes, spacers would be a good option. However, when I first swapped my buckets, I did it in 30 min with the axle nuts still on ... it is messy, but it is a simple job. I later had to work on it again, but that was due to the tripod in the CV breaking at nats last year ... so on that one ... had to replace with my spare axle. Actually looking at it I could have swapped just the tripod with the axle on the car in a pinch, but to ensure I had any metal fragments cleaned out, I just swapped in a spare :P

To the OP, if you swap the buckets, DON't cut the CV boot bands off. Re-use them. You can open them with a pair of pliers. The ones that came on the car are way nicer than what you get from the parts store and Honda dealerships do not have the same style that came on the car. They are re-usable.