As always, the Workshop Manuals are a good point of reference. Since this topic has been covered in the past and you are now familiar with the Forum, it would be worth giving the search feature a try.

 

I'm taking the same approach but also moving to an aluminium rear subframe. The new control arms come with bushings installed and I'm using products from Lemforder and Febi only.

The rear anti-roll bar is the same across the range; there's many recommendations on here to move to the aftermarket Whiteline replacement.

 

I believe 2WD and AWD vehicles use different rear subframes.
Same goes for convertibles vs coupes.
Also, some older MK2's (i.e 3.2l) used different rubber mounting points. Not sure if the newer style subframe is backwards compatible?

Old style

New style

Companies that manufacture OE parts for Audi will be cheaper than the same OEM-branded parts purchased through a dealer.

Lots of aftermarket companies sell anti-sway / roll bars. Recommend you stick to companies that specialize in spring components (i.e Whiteline, H&R, Vogtland) since they will be designed for function rather than looks.

I'm taking the same approach but also moving to an aluminium rear subframe.

Got a part number for a mythical aluminum rear subframe?

 

Got a part number for a mythical aluminum rear subframe?

They're off Early model Golf Mk5 R32 and A3 8P ... Not sure if early model TT 8J also got them but they're characterised by a flat "webbed"section that brackets both sides of the subframe. A useful central jacking point if you ask me.

1K0505235N

Additionally - unsure if the headlight level sensor hardware/ magride sensor mount on this type of subframe

Above: correct way. Notice that webbed part where the AWD unit sits in.

Above: upside down. Nice jacking point.

 

Mine was manufactured week 17 in 2006 and was fitted to a 2006 V6 8J so TT's did get them.

The holes are also there for the height measurement sensor brackets to bolt to.

2wd and 4wd rear subframes are significantly different.

 

They're off Early model Golf Mk5 R32 and A3 8P ... Not sure if early model TT 8J also got them but they're characterised by a flat "webbed"section that brackets both sides of the subframe. A useful central jacking point if you ask me.

1K0505235N

Additionally - unsure if the headlight level sensor hardware/ magride sensor mount on this type of subframe

View attachment 510475
Above: correct way. Notice that webbed part where the AWD unit sits in.

View attachment 510474
Above: upside down. Nice jacking point.

View attachment 510473
View attachment 510472

Oh nice did you actually get one of these or are those pics from elsewhere? Interestingly this part is still sold by VAG--can be purchased new for $1k USD ($2k in Canada ). I wonder why if they still sell it, why they stopped using it so early on in the models that had them. Also interesting it's a 1K part, so it's a Golf part natively. I would have thought it's be designed for the TT but seems like nah they always intended the TT to have a steel rear subframe (and well rest of the rear lol).

Did you measure the difference in weight on the alum version v. the steel?

I bought one of these using this exact number off of an 8P S3
It did indeed not have BOTH sets of holes needed for the magride level sensors, just single on one side for the headlight level
Case of adding these in if wanting to use this style of frame on a mag ride equipped car - at time I didn't bother as the weight difference to steel was so marginal and could not find a polybush solution - if I am remembering rightly, as the bushes are different diameter to that of it's steel brother variant

I guess it's easy enough to measure out the one side and duplicate it on the other by drilling some holes in the correct locations to mount the other sensor. It has to be fairly precise of course, but I think it's pretty doable.

When you say the weight difference is very marginal, I suppose then you mean it's not really worth it for any weight savings. What about rigidity/stiffness? Did you end up swapping yours to the alum one and have it on the car now or did you decide against it due to the bushing situation?

 

My aluminium rear subframe weighs approximately 16kgs (35lbs) including the brace and bushes. I guess that could be getting on for half the weight of the steel one, I don't know.

The bushes are the same as the ones in the photos posted by IPG3.6 above and they look identical to the ones fitted to my steel subframe so I don't see why the same poly bush option wouldn't work.

My subframe has the holes - nutserts - on both sides for the height sensors.

As to why Audi/VW went aluminium I can only speculate but weight would seem the most likely reason. Given they appear to be only fitted to early cars the preproduction ones would be the ones tested for official emissions figures etc. so you'd want them to be as light as possible for the same reason cars don't have spare wheels any more.

The subframe is beautifully made and a work of art but would undoubtably cost more than it's steel equivalent so maybe when the costs came in for the next batch to be made Audi switched to steel to save money. Given the commonality with the Golf it was perhaps more a corporate VAG decision than just for the TT?

 

The subframe is beautifully made and a work of art but would undoubtably cost more than it's steel equivalent so maybe when the costs came in for the next batch to be made Audi switched to steel to save money. Given the commonality with the Golf it was perhaps more a corporate VAG decision than just for the TT?

Oh for sure it's almost certainly to do with cost. Also I don't believe any standard Golfs or even GTIs came with the alum one? It seems only the .:R32 did and that was a pretty darn heavy car both being a fairly heavy platform and the VR6 as well, so I guess it made sense to try to lighten it up at least some. The TT being mostly alum already, while not exactly lightweight itself (is any German car? lol), is at least a few hundred pounds less than other cars on the platform, due to its mostly-unique underpinnings and body.

The Mk6 .:R was using the lighter EA113 2.0T plus the Mk6 cars were lightened up in various other ways (some of them "cheaping stuff out") over Mk5s so there was no need for them to revisit the alum subframe there either. In fact Mk6 can kind of be summarised in being a more-efficient and cost-reduced way of producing an Mk5 car which involved various cost-cutting measures;, production efficiency improvements; and, intentional or not, weight savings.

I find it interesting though, the use [of the alum rear] on the TT which was done sparingly. It's not on all 3.2s so we can rule out that reasoning; it's a 1K part so it was never really part of the TT's master/original design (or anything unique to it as 8J parts would be); and even though we can probably all agree lighter would be better, it seems Audi had no interest in using this part across all TTs. Cost cutting was indeed the preferred route, which even the "top car on the platform" and the most performance-oriented, did not withstand!

 

Guessing Audi saw no value in lightening up the rear end of an already nose-heavy car. Plus no galvanic corrosion concerns when used with a steel rear-end....

 

They actually try to add weight in the rear as it's too light otherwise.

 

I'm sure there is an 8J aluminium subframe, which I'm guessing would be the one that doesn't have issues with bushes or sensor mounting holes. Though I'm saying this from memory about something I read a long time ago...

@Johneve what part do you have?

 

I've lost the label with the overall part number on. Individual components of the subframe have numbers stamped on them and they all start 1K0, such as 1K0 505 540C.

 

I'll have a study of etka and see what I can find

 

What I recall reading at the time the MK2 was introduced was that the rear was made of steel in an attempt to get the car near to a 50 50 front rear weight distribution.

 

This makes most sense to me too

You know, stupid me I wasn't even thinking about this--doh! I guess it's just me thinking the car is not exactly lightweight but then forgetting about how front heavy it is.

What I recall reading at the time the MK2 was introduced was that the rear was made of steel in an attempt to get the car near to a 50 50 front rear weight distribution.

Well they didn't do a very good job there given the S was 62/38 apparently lol, but I suppose it would have been worse with the alum rear subframe!

Weight distribution notwithstanding, here it is out BMWing a BMW back in 2009 😁 :

2009 Audi TTS vs. 2009 BMW 135i

These two turbocharged 2+2s both offer performance and practicality. But which one does it best?

www.roadandtrack.com

(Unfortunately I guess they took down/moved the pictures off their server or whatever and some text missing due to missing links.)

The Z4 probably would have been a better comparison...the E89 being a hard top convertible was heavy though, at like 3500lbs (but like the 135, would be a heck of a lot closer to 50/50 than the TT).