Sub-frame & Diff mount reinforcement kits

[zielritter]

I intend on keeping my Z until I can pass it down to my son (I got it from my grandfather). I've already reinforced the front and rear strut/shock towers. One issue I plan on tackling in the next year is reinforcing the differential mount and cross member connection points. I also plan on swapping in some poly bushings for the frame to subframe mounting point.

Are there any kits out there still? There are old posts referring to the RF and Dinan kits, but I can't actually find online where those are sold. This is more of a preservation effort to prolong the life of my car.

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[BladeRunner919]

The only kit worth mentioning is the Randy Forbes kit, and he is active on this forum - I'm sure he'll be along shortly.

[Randy Forbes]

I'm still here, maybe not posting as frequently as I did eighteen (>18) years ago, but I still contribute when I can (I am pleased to see newer and fresher blood taking up my slack).

shoot me an email at sports cars plus @ aol dot com (no spaces) for more information.

I haven't done any installations myself since last November (some health maintenance required) but I am still producing the reinforcement kits for DIY and (your local) local shops to install.

Jon Maddux' S52 Coupe*, the subject of his Coupenut blog, was my 100th installation. http://coupenut.blogspot.com/2017/09/



* Jon is also the original owner of an Imola Red '01 M Coupe; a Day Two One-Off with a Walnut extended leather interior (swapped with brother Andy's '01 Z3 3.0 Dakar Yellow/Walnut Coupe and the 3.0 received the full black M interior; Jon was in Seattle, Washington at the time, while Andy was still based in Cincinnati, Ohio. Even the shipping crate__used for shipping in both directions__was impressive). But I digress...

[zielritter]

Thanks all. I'm still a few months out from saving up enough to do this. Just fact finding and looking at options. I'm going to definitely do some poly bushings on the subframe to minimize the movement and stress on the welds, but I'm still up in the air about the reinforcement kit. I'm not racing, but I am lowered and realize that if I'm paying for the labor on the bushings it might be silly to not go ahead and do the reinforcement.

I snapped some quick pictures this afternoon. The underside looked fine. No damage to the ear or crossmember that I could see from a quick glance. However, I do appear to have two welds on the top side that have "popped". My build is Jan 99.



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[Mr Bingley]

You're there. It's time to start planning on doing it.

[SteveG66]

Zielritter, I'm just wrapping up the reinforcement installation for my Jan 99 M Roadster, I implore you to get it reinforced soon, sooner the better. My rear subframe and hanger had failed badly with a previous owner, it was a "hack" repair from what I've seen. If you've got two popped welds, now it's just a matter of time. I can tell you the installation is not that hard to do yourself, especially if it hasnt failed yet, mine was especially difficult because of the failure and repairs from before.

BTW-I purchased the Randy Forbes kit, it's the only way to go!! Good luck.

[therarestbundls]

i am just wondering for future reference as i have yet to inspect the subframe bushings, what is the price range that i will be looking at to purchase a Randy Forbes kit for my 96 z3. i figure that i might as well go ahead and do it since i will not be having to invest any major money into motor work ( that makes me super happy ). mostly just having to replace interior pieces, but i want to put great quality into the suspension and what not.

[Mr Bingley]

You should never need one for a '96--you're safe.

[Vintage42]

... 96 z3. i figure that ... i will not be having to invest any major money into motor work... i want to put great quality into the suspension and what not.

The 1.9 cooling system needs complete replacement to avoid sudden breaking of plastic parts.
https://www.bimmerforums.com/forum/s...1#post29790421
https://www.bimmerfest.com/forums/sh...9&postcount=12

[zielritter]

Zielritter, I'm just wrapping up the reinforcement installation for my Jan 99 M Roadster, I implore you to get it reinforced soon, sooner the better. My rear subframe and hanger had failed badly with a previous owner, it was a "hack" repair from what I've seen. If you've got two popped welds, now it's just a matter of time. I can tell you the installation is not that hard to do yourself, especially if it hasnt failed yet, mine was especially difficult because of the failure and repairs from before.

BTW-I purchased the Randy Forbes kit, it's the only way to go!! Good luck.

I'm going to pay this to have it done at my local shop. I have a place that I trust in Cincinnati and is specialized for German cars. I know it's not a cheap kit or install which is why I'm stashing away cash for it. I'm probably going to do subframe and RTAB bushings at the same time.

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[JeffPortland]

You're there. It's time to start planning on doing it.

I hear this a lot on these forums and there is no doubt RF has the ultimate solution and I would love to put it on my car... It's $3000-$4000 with labor and parts... on a functioning 20 year old car. Some Z's are selling for less than that.

Here's my understanding:
There is a lot of play when the sub-frame bushings go bad (I can feel it in my Z now)--Differential tugs, pulls, and pushes on the diff hanger due to the loose bushings and causes movement near the hanger. People don't realize the issue or ignore it and movement will cold work the dif. hanger and surrounding welds until it falls apart.

After switching to polyurethane bushings ($1300... still not cheap) to keep everything tight, has anyone actually seen a clear progression from a couple pulled spot welds to full failure? The welds pulled because the dif hanger is still rigid (a good sign) and the weakest point is the connection to the trunk. Is the differential hanger really structural beyond holding the differential up? The bushing looks like it allows for a lot of play between the under-body and the differential. Isn't most of the road-car/engine energy transfer taking place at the sub-frame bushing?

Please correct me where I am wrong! I am not saying this as an expert but trying to know why there is so much certainty that a pulled spot weld = guaranteed RF kit needed.

Thanks!

[zielritter]

I hear this a lot on these forums and there is no doubt RF has the ultimate solution and I would love to put it on my car... It's $3000-$4000 with labor and parts... on a functioning 20 year old car. Some Z's are selling for less than that.

Here's my understanding:
There is a lot of play when the sub-frame bushings go bad (I can feel it in my Z now)--Differential tugs, pulls, and pushes on the diff hanger due to the loose bushings and causes movement near the hanger. People don't realize the issue or ignore it and movement will cold work the dif. hanger and surrounding welds until it falls apart.

After switching to polyurethane bushings ($1300... still not cheap) to keep everything tight, has anyone actually seen a clear progression from a couple pulled spot welds to full failure? The welds pulled because the dif hanger is still rigid (a good sign) and the weakest point is the connection to the trunk. Is the differential hanger really structural beyond holding the differential up? The bushing looks like it allows for a lot of play between the under-body and the differential. Isn't most of the road-car/engine energy transfer taking place at the sub-frame bushing?

Please correct me where I am wrong! I am not saying this as an expert but trying to know why there is so much certainty that a pulled spot weld = guaranteed RF kit needed.

Thanks!

This summarizes exactly where I'm at too. I'll bite the bullet and do it, but would be interesting to see if anyone has witnessed a stop in the progression of damage to the welds after doing to poly subframe bushings. My understanding too is that you want to leave the more pliable rubber differential mount bushing to allow the movement in the mount itself.

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[Mr Bingley]

It's not merely the couple of popped welds you can see, there are always more that you you can't. As each weld breaks it places a larger load on those remaining, which in turn fail more rapidly. The reason you "see this a lot on these forums" is from hard experience.

[timreldridge]

I can tell you from personal experience once the welds start going switching to poly bushings will not stop the progression. I had one weld popped when I installed IE bushings and less than a year later I had two more popped welds. The only solution is a Randy Forbes or similar kit. I am pretty handy so after looking at a lot of pictures on line and Randy's CAD drawings I made my own kit and installed it this spring when I had the trans out for a clutch replacement.

[JeffPortland]

It's not merely the couple of popped welds you can see, there are always more that you you can't. As each weld breaks it places a larger load on those remaining, which in turn fail more rapidly. The reason you "see this a lot on these forums" is from hard experience.

I got my car up on a lift at the local BMW racecar/tuner shop (owner had an supercharged M coup he tracked and modded for >100k miles, no reinforcement) and we scanned every weld you can see together and MY car is spotless... Just a single pulled weld in the trunk. We've decided to repair the the one weld and redo ALL of the bushings. I will make sure to document my experience on the forums--maybe you'll hear me say I am buying a RF kit in 2 years.

Randy, Please share your CAD drawings or sell your designs to someone not greedy so that we can still buy it before you go into full retirement! I have connections in the machinist world. I would happily set up an indefinite RF kit E-store.

[zielritter]

I'm still here, maybe not posting as frequently as I did eighteen (>18) years ago, but I still contribute when I can (I am pleased to see newer and fresher blood taking up my slack).

shoot me an email at sports cars plus @ aol dot com (no spaces) for more information.

I haven't done any installations myself since last November (some health maintenance required) but I am still producing the reinforcement kits for DIY and (your local) local shops to install.

Jon Maddux' S52 Coupe*, the subject of his Coupenut blog, was my 100th installation. http://coupenut.blogspot.com/2017/09/



* Jon is also the original owner of an Imola Red '01 M Coupe; a Day Two One-Off with a Walnut extended leather interior (swapped with brother Andy's '01 Z3 3.0 Dakar Yellow/Walnut Coupe and the 3.0 received the full black M interior; Jon was in Seattle, Washington at the time, while Andy was still based in Cincinnati, Ohio. Even the shipping crate__used for shipping in both directions__was impressive). But I digress...

Randy, I sent you an email. Just making sure it came through.

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[CLOWN5HOE]

Anyone recommend a shop that has experience installing the reinforcement kit in Socal (close to Orange County)???

I've sent Randy emails inquiring about the kit but no responses.

[khammack]

I've sent Randy emails inquiring about the kit but no responses.

As stated above, Randy is having "some health maintenance required" issues. I expect that he may be out of circulation for a few days, but I'm sure he will get back to you as soon as he can.

[Pat Gautier]

I have 4 popped welds and pulled the trigger on an RF kit, new exhaust and all the trimmings. To me it wasn’t a question of value. After 6 years I am in no way ready to sell the car plus I couldn’t in good conscience given the condition ( Popped welds). This will be a DIY job but in the end I will have sunk a bit more than I few grand into it. It will leave me with a car that I can continue to enjoy and potentially further mod over the years. I realize that’s not an easy choice for everyone but if your car is a keeper to you, I would try to close the chapter on this part of it’s repair history. One further note, I have been studying this issue for six years and I have not seen anyone successfully propose a reasonable alternative to the RF kit. Once I knew I had an issue it was a no-brainer. I also reached out to some local repair shops and they all knew the kit and offered no alternatives.


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[Mr Bingley]

It's not such a big deal. You won't have to address a 1.9 at all or likely a 2.3 at all. The most likely to need it are the ///M's, and for them, an RF kit is an investment. The car should be worth at least dollar for dollar more after a clean install than before, and stop depreciation cold in its tracks. The only issue is if you overpaid for the car in the first place (or bought new), not knowing about the problem before you bought--which is why there has been a sticky devoted to the topic on the forum header since the original members first discovered it back during the warranty period (not that that helped ). If the car is a rat, or a high miler, it may not be worth doing, but it is the rare ///M that's worth less than 10k, and even a rare 2.8 or 3.0 that worth under 8k when done. There is a peace of mind that comes from having the kit installed properly--you can let lose, down shift, goose through a banked curve, or make a 90 deg turn way too fast without concern (depending on your tires). It is also a great excuse to go ahead and supercharge it...

[zielritter]

It's not such a big deal. You won't have to address a 1.9 at all or likely a 2.3 at all. The most likely to need it are the ///M's, and for them, an RF kit is an investment. The car should be worth at least dollar for dollar more after a clean install than before, and stop depreciation cold in its tracks. The only issue is if you overpaid for the car in the first place (or bought new), not knowing about the problem before you bought--which is why there has been a sticky devoted to the topic on the forum header since the original members first discovered it back during the warranty period (not that that helped ). If the car is a rat, or a high miler, it may not be worth doing, but it is the rare ///M that's worth less than 10k, and even a rare 2.8 or 3.0 that worth under 8k when done. There is a peace of mind that comes from having the kit installed properly--you can let lose, down shift, goose through a banked curve, or make a 90 deg turn way too fast without concern (depending on your tires). It is also a great excuse to go ahead and supercharge it...

I actually have the 2.3 (with a 2.5l engine mind you ) with the two popped welds. So apparently the 2.3 isn't immune.

Granted within the past couple of years I have lowered and added catback, headers, tune, pulleys, intake, mech fan delete etc... But I've also only put about 100 miles on it total in that same period. 70k total mileage.

Prior to me, my grandfather drove it very gingerly for over a decade. Before him a new elderly doctor did the same and was the original owner. It was not modded prior to me save for the addition of a spoiler.

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[Meeners]

I'm going to pay this to have it done at my local shop. I have a place that I trust in Cincinnati and is specialized for German cars. I know it's not a cheap kit or install which is why I'm stashing away cash for it. I'm probably going to do subframe and RTAB bushings at the same time.

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Will you let me know where this place is? I have a 99 Z3M and even thought things are good now, I know this is coming. Will you give me a ring via PM?

[khammack]

If you can't find a recommendation for a local shop, just look for a local race shop. They do lots of fabrication and should be able to help you out.

[JustinHalverson]

I hear this a lot on these forums and there is no doubt RF has the ultimate solution and I would love to put it on my car... It's $3000-$4000 with labor and parts... on a functioning 20 year old car. Some Z's are selling for less than that.

Here's my understanding:
There is a lot of play when the sub-frame bushings go bad (I can feel it in my Z now)--Differential tugs, pulls, and pushes on the diff hanger due to the loose bushings and causes movement near the hanger. People don't realize the issue or ignore it and movement will cold work the dif. hanger and surrounding welds until it falls apart.

After switching to polyurethane bushings ($1300... still not cheap) to keep everything tight, has anyone actually seen a clear progression from a couple pulled spot welds to full failure? The welds pulled because the dif hanger is still rigid (a good sign) and the weakest point is the connection to the trunk. Is the differential hanger really structural beyond holding the differential up? The bushing looks like it allows for a lot of play between the under-body and the differential. Isn't most of the road-car/engine energy transfer taking place at the sub-frame bushing?

Please correct me where I am wrong! I am not saying this as an expert but trying to know why there is so much certainty that a pulled spot weld = guaranteed RF kit needed.

Thanks!

There was a similar discussion at this thread: https://www.bimmerforums.com/forum/s...r-Subframe-Fix

I described my logic and experience for a repair similar to what you propose in that thread. I quote what I said in that thread below to save you the trouble of finding it:


"I took an approach similar to that proposed by OP. My spot weld failures were not as severe as he has described. Two key parts of my repair, which has proven successful for almost 5 years and 15,000 miles of semi-spirited driving (no track driving or autocross for example), was the addition of IE rear subframe bushings (RSFB), and the help of a nuclear qualified welder. My logic was that the stress on the trunk has to be the result of torquing motion allowed by the relatively soft RSFB, and the poly RSFB's would transfer more of that torque to their mounting points thereby reducing the forces on the trunk welds. I thoroughly cleaned up the area around the failed spot welds, drilled holes between the failed spot welds to allow for additional plug welds, and then I had my highly qualified welder friend plug weld both the failed areas and the newly drilled holes."

"Since the repair, I check the welds religiously, and have not seen a hint of failure. Honestly however, I wish I had bitten the bullet and bought the kit and had my welder friend weld it in instead of going with what is possibly a temporary fix. Once I decided to go with replacement RSFB's, the labor involved to add Randy's kit would not have been that much more."

Two things that are not clear in my previous post are 1) that the additional holes I drilled were drilled only through the top most piece of the trunk, leaving the cross member in tact and allowing the welder to make plug weld at that point, and 2) the failed spot welds had not displaced at all, and were only showing rust around part of their circumference.

Here is a photo showing the plug welds soon after the repair was completed. They have remained unchanged for 5 years. Roughness of welds is greatly accentuated by the grazing light used to take picture. The welder stated that he had to "chase" some cracks in the upper layer of metal that developed when he started welding. This is a sign that the metal was stressed and weakened, which makes me worry that additional failure is only a matter of time.

Z3 Welds.jpg

[CLOWN5HOE]

I have 4 popped welds and pulled the trigger on an RF kit

Where did you buy the kit? I'm unable to find one for sale.