sub frame - slightly different take

[Hirsch990]

I purchased a 2000 M from an auction last year. The sub frame started exhibiting the tell tale signs. The RF kit looks great, but the cost estimates including installation would push my “good deal” car into the “not good deal” car range. I opted for a local shop to tackle the issue. I am happy with their work. It’s winter and I haven’t driven it other than home from the shop. Felt stiffer but that may all be in my mind, lol. Here are a few pics....

inside the trunk still looks stock
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Under the carpet
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A couple from under the car in the next post.

[BimmerBreaker]

Its not strengthened to the frame rails though so what will keep the trunkfloor secure?

[Hirsch990]

And the pics from below...

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I can’t remember the term the used, but the new piece, trunk floor and sub frame are attached (combined?)

[ProductUser]

It's hard to comment on their solution by looking at a handful of pictures. I'd like to know how their solution holds up long term and under what driving conditions.

[Z3 freak]

Did you purchase the kit, or did the shop, and how long did they keep it? Were you experiencing any symptoms that made you check the trunk and underneath the car, or just dumb luck?

[Mr Bingley]

Ok, I think what I'm seeing in the pics is a cross brace welded to the floor above the existing cross member and some Styrofoam blocks--is that it or am I missing something there? For underneath it looks like a bracket has been bolted to the differential cover on the driver's side and this is attached to the cross member and perhaps the muffler hanger, by welding? Hey, it looks better than nothing, albeit unconventional. Why didn't your shop want to install the RF kit? It certainly looks like they had do a lot of the same work. What did they charge you?

[nevan]

How does that additional diff ear mount? Does it have any bushing (or some sort) because it should have a matching bushing otherwise it may actually cause more issues in vibration.

[Hirsch990]

Due to the known issues with the subframe, I checked periodically and caught it before it was too far gone. The shop did the fabrication in house, no kit. They do a lot of fabrication work and said they would prefer to do it in house. This was the first Z3 sub frame issue they have worked on so I don’t want to quote a price in case they underestimated! It was quite a bit less expensive them most of the prices I have seen on the forum. They had my car about 2 and a half weeks.

I am excited to see how it works. I have confidence in the shop. They do frame up builds on Porsche race cars, some pretty intensive restoration projects and seemingly a bunch of other cool stuff based on what is sitting around. Redstone Performance Engineering. Their Facebook and Instagram pages have more images if you feel like some eye candy.

[Randy Forbes]

Either you or they need to go back underneath and clean/seal/paint the burned through areas, or you're inviting a corrosion problem.



I'd also recommend that you continue to monitor the areas immediately to the left and right of the tophat they added; the LH side in particular, as THAT is where all the separation starts.

[Hirsch990]

How does that additional diff ear mount? Does it have any bushing (or some sort) because it should have a matching bushing otherwise it may actually cause more issues in vibration.

Why do you think it will cause a vibration? I didn't notice anything on my drive home. Albeitthat is not a very big data set!

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Either you or they need to go back underneath and clean/seal/paint the burned through areas, or you're inviting a corrosion problem.



I'd also recommend that you continue to monitor the areas immediately to the left and right of the tophat they added; the LH side in particular, as THAT is where all the separation starts.

Thanks Randy. It is up on stands in the garage now and I plan on addressing that. I will be checking this work frequently to see how it performs. Not sure if it is a "money back guarantee", but they said if I had any issues to bring it back.

[nevan]

Why do you think it will cause a vibration?...

I meant to say "during the vibration". It appears the right side ear would lock in which may cause similar issue as having the harder polyurethane bushing. If I were you, I would minitor them closely for any false symptoms. - Sorry that I had to be that guy to rain on parade...

[Hirsch990]

I meant to say "during the vibration". It appears the right side ear would lock in which may cause similar issue as having the harder polyurethane bushing. If I were you, I would minitor them closely. - Sorry that I had to be that guy to rain on parade...

No rain! It's a slightly different solution. It will either work or not I suppose. Like I said these guys do a lot of interesting work so I wanted to see what they came up with for a solution. Now if will just warm up I can drive it and see!

[Z-Thrizzle]

How does that additional diff ear mount? Does it have any bushing (or some sort) because it should have a matching bushing otherwise it may actually cause more issues in vibration.

Right, the mount should have a busing. something like this could've been used

[Hirsch990]

They used a Delrin washer at the pivot. Their opinion was it did not need a bushing here. If that is an incorrect assumption on their part, what should I look for to indicate it is not working? What symptoms will I experience?

[nevan]

They used a Delrin washer at the pivot. Their opinion was it did not need a bushing here. If that is an incorrect assumption on their part, what should I look for to indicate it is not working? What symptoms will I experience?

Look at the video "bionicbelly" member included in the post:
https://www.bimmerforums.com/forum/s...4#post29549064

In worse case, I would imagine the tear would take place on the Delrin washer side... Hopefully, it won't happend to you though (nor to anyone).

[Tigershark48]

Is there any reason why spot weld tear prevention couldn’t be accomplished by drlling them out and replacing with nuts and bolts? I don’t see welds being a very good solution since the thin sheet metal is the weak link. The failing spot welds are not bad welds, since they’re not separating in the weld, but cracking around the perimeter. The thin base metal is actually what’s failing.

Obviously this doesn’t address the differential mount failure, but should provide a more solid mount.

[JRowe]

Is there any reason why spot weld tear prevention couldn’t be accomplished by drlling them out and replacing with nuts and bolts? I don’t see welds being a very good solution since the thin sheet metal is the weak link. The failing spot welds are not bad welds, since they’re not separating in the weld, but cracking around the perimeter. The thin base metal is actually what’s failing.

Obviously this doesn’t address the differential mount failure, but should provide a more solid mount.

I wouldn't drill them out if they haven't failed. If reinforcing using fasteners, then drill in between the welds and add bolts/nuts/washers etc. My Z3 doesn't show signs of welds failing, but if it ever does, I'd go the full RF treatment.

[Tigershark48]

Good point. Mine’s not failing either. My question was aimed at those that are.

What does the RF treatment look like anyway. I’ve asked for pictures, but have no clue as to details.

[Vintage42]

... What does the RF treatment look like anyway. I’ve asked for pictures, but have no clue as to details.

It goes under the trunk floor.

[khammack]

The spot welds are not the problem, they are the symptom. Somewhere is this forum Randy explains what is actually going on when you have a failure and why screws don't work.

Check out the subframe thread - https://www.bimmerforums.com/forum/s...-mount-failure

It has pictures and explains everything.

[Hirsch990]

Look at the video "bionicbelly" member included in the post:
https://www.bimmerforums.com/forum/s...4#post29549064

In worse case, I would imagine the tear would take place on the Delrin washer side... Hopefully, it won't happend to you though (nor to anyone).

I have seen that video as well as a couple other under car videos. All of the ones I have found have been single ear. I like to see one of the dual ear.

[Tigershark48]

Thank you both for your responses with picture and link. You’ve both answered my questions. I can see where nuts and bolts alone, even if they were between the spot welds could never add the strength and rigidity that Randy’s fix does. Clearly a solid design.

[Randy Forbes]

Is there any reason why spot weld tear prevention couldn’t be accomplished by drilling them out and replacing with nuts and bolts? I don’t see welds being a very good solution since the thin sheet metal is the weak link. The failing spot welds are not bad welds, since they’re not separating in the weld, but cracking around the perimeter. The thin base metal is actually what’s failing.

Obviously this doesn’t address the differential mount failure, but should provide a more solid mount.

I can think of one (1) reason...



Like Ken says, the spotwelds are merely the symptom, anything short of adding strength to the entire floor (and in my opinion, tying that into the side rails) has proven to do more harm than good. Indeed, most of the cars that I've done as the second solution usually wind up costing the owners twice as much to repair and reinforce than if I'd been chosen first. Not including the cost of the failed repair.

My own cars are coming up on fifteen (15) years now with the first two (2) prototype kits installed (some detail changes were made for production) and the same design since December 2004 when the first customer cars were being done. Nobody has come back with any structurally related issues, including cars with LS# V8 swaps and forced induction up to 650 rwhp.

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[Z-Thrizzle]

I'm using Randy's kit with a single diff ear reinforcement. Installation cost should be less going that route. To save even more you can do it yourself. I learned how to MIG weld and used the money saved to buy a lift.

[Randy Forbes]

I'm using Randy's kit with a single diff ear reinforcement. Installation cost should be less going that route. To save even more you can do it yourself. I learned how to MIG weld and used the money saved to buy a lift.

THIS, people, this is what I'm talking about!

I never foresaw a dozen shops around the country doing the installations; my kit was designed and fabricated, and the installation instructions written and illustrated for the DIY owner/enthusiasts. The money saved should more than cover the cost of a decent lift AND a MIG welder (not that you need the lift for the installation__I did the first dozen or so laying on the floor__but they're so nice to have).

My apology to the OP, [/sidetrack]