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1999 Z3 Build

3K views 7 replies 4 participants last post by  ricratcat 
#1 ·
Here is my 99 Z3 project. The car was given to me so I don't have a whole lot in the car up front. Here is how the car looked when I got it. In the pictures I have already repaired the bent driver side lower control arm.





Fortunately I have a friend who pulls cars for a living and has a professional quality machine in his home shop. So I ordered all new quarter sheet metal and had him spend some time working on my car. Some of the parts had to be ordered from Germany and were held up in customs for several months. But they were finally released and here is where we are now:





 
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#2 ·
Now that the body damaged has been fixed I pulled the rear out to repair some bent brackets, upgrade the rear diff cover and install some stainless brake hoses.



One thing I notice is a slight tear in the diff bracket. I inspected the unibody under the trunk and inside the trunk but did not see any signs of the issues Randy Forbes has documented. I think this was caused by the accident and have spot welded the cracks.



I have looked for re-enforce brackets for this area but have only found pieces for the front control arm and sway bar areas. Anyone know of an update. I know Randy makes an upgrade for it but that may be a tad overkill for this car. This will be my wife's nice weather play toy. No track days or anything like that.

I will say that I replaced the rear original diff with the one from my project car. This car is a 5 speed and the parts car was an auto. I went from a 3:15 gear to a 4:10 gear so it should be quite fun to drive.

I will be keeping the car at stock ride height and will be installing Bilstein HD shocks and struts, upgraded lower control arms. I am pretty much going through all the suspension and replacing with new. The front tires are wearing on the inside tread where the back tires look great.





I will keep updating with pictures as I move forward. When done we will be painting this a pearl white.
 
#3 ·
While you have the entire subframe out, I would replace the diff clutches (if so equipped) with ones from Bimmerdiffs.com, weld-in camber and toe eccentrics from Ireland Engineering, and weld-in sway bar reinforcements from various suppliers, and of course replace the subframe bushings with polyurethane ones.
 
#4 ·
I don't know if I would go with polyurethane bushings. It's not a track toy, just a weekend cruiser.While polyurethane will offer longer wear, I think the noise will get old. Stock rubber will last for years, especially if she only occasionally drives it.

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#6 ·
The poly subframe bushings don't make any noise. They just limit movement in hopes of preventing the subframe failure. I have the Ireland Engineering in both my cars, both used as daily drivers. On the 2.5 (completely stock except for the subframe bushings), there is NO noticeable difference in sound or ride quality. Many state that they feel the car is more stable after they made the switch. I can't say that as I never pushed that car at all before or after the switch. That's what the ///M is for.

Poly in other areas of the suspension do make for changes in ride quality and may squeak as they move quite a bit more but that is not an issue at all with the subframe.

I would replace the stock subframe bushings while you are there. When I did my subframe reinforcement, I found my mount to be cracked as well. I thought it was going to be purely preventative maintenance on my car as it only had 55,000 miles on it, but the crack was there. I'm glad I didn't track the car until I had the Forbes fix done.
 
#5 ·
Thanks for the feedback! I had the rear assembly checked out by Korman Auto, which specializes in BMW restorations and services. They gave it a thumbs up for installation. I will probably keep the stock bushings for now. The car will be just a toy and certainly won't be driven over aggressively. The occasional spirited run yea but nothing like track days.

Anyone know of a reinforcement kit for the diff mount?
 
#7 · (Edited)
Absolutely! The reason to install polyurethane subframe bushings is to stiffen the subframe-to-frame joint which prevents the motion that tears the unibody differential mount apart. And it's not just for track cars; they all can break. Every Z3 needs this fix.
I have never heard a complaint about Noise, Vibrations, Harshness (NVH) from installing polyurethane RSBs, only positive reports of more stable handling. That's not true of polyurethane Rear Trailing Arm Bushings (RTABs) or Sway Bar Bushings. Polyurethane there can be miserable.
With the subframe laying on the floor, it is so easy to replace the RSBs. You can press them out, cut them out with an electric saw, burn them out with a torch, etc. Polyurethane bushings just slip right in after that.
By the way, don't put polyurethane, Delrin, Solid Aluminum, or any stiffer bushing in the diff mount. That part needs to be free to move some to reduce the stress on the unibody parts. You can upgrade to the solid M-style mount, but no stiffer.
 
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