Classic Audi Technical Mech/Tech Suspension & Brakes » 1987 Audi Coupe Gt Rear Anti Roll Bar

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Old 20-10-17, 04:22 PM   #1
Colin Aitchison
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Default 1987 Audi Coupe Gt Rear Anti Roll Bar

Been looking at this for some time now and with the various bit of metal now here, decided to make a start. ARB can't go in front of the rear axle beam due to the panhard bar location, so needs to go to the rear and needs to fix to the boot floor, the exhaust will get in the way but that's just metal pipe that needs rerouted and an exhaust box moved back and tail pipe made shorter with two tight bends in 63mm pipe, fixing to the boot floor Hmmm!!!!! that's not going to be strong enough, will need to make frame work in boot to spread the ARB load into the chassis at each side of the boot, what RAB to use? the one I removed from my Audi S2, need to weld 5mm flat plate brackets on to the rear axel beam, two nice and short drop links would look good, how am I going to make brackets to fit the ARB bushes, these were just some of my thoughts prior to starting the project, anyway time to get down and dirty, exhausts off and on the floor and now not in the way, 30 x 60 x 3mm wall box section as an inboard ARB bush fixing point, took a little time to make this up, photos below.















5mm flat plate welded to rear axle beam and taking fixing support from rear shock bottom mount, the little link tube used as spacer is 16mm tube with 3mm wall, the dinky drop links are not from an Audi.





The flat plate on the boot floor is 5 x 100 x 390mm, yes the inboard ARB mounts are only 320mm apart and not 520mm apart as they should be but as you can see the exhaust is in the way, Yes I know the ARB will flex more than it should due to the distance between the inboard mount being further away from the drop link mount but I do have a cunning plan to be explained later.



Same flat plate in the boot with supports ( 25 x 25 x 2.5mm box section) with minimum 4 x m8 x 30mm long bolts into chassis at each side, gray panel seal used to seal plates to floor, used many 1mm thick washers to solid pack 5mm plates apart on the uneven boot floor, when I am happy with the external fixing plates the under seal will be out as a primary seal from water ingress



I did two simple Cad line drawings to see how the arc of the rear axle beam and ARB would interact and to find the correct length and location of the drop links





Test drive has happened, yes the ARB is doing something (probable just more weight to slow the car up) I can't feel the rear of the car lifting the inside wheel on slow corners as much, high speed corners ( 55-60mph!!!!!) stable at this time, if I fit a stiffer (thicker) ARB the rear of the car may want to slide or skip across the road surface, I do have an 18mm, 22mm and 25mm ARB with fitting solution for all but would like to have time to play with this setup so I can feel the change when I move on to a different ARB, project time, started it last Saturday and Sunday and 3 nights this week.
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Old 20-10-17, 04:43 PM   #2
vorsprung durch technik
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Looks impressive. Just in case you haven't considered it,how about the fwd B4 or B5 saloon estate arrangement?
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Old 20-10-17, 06:00 PM   #3
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Quote:
Originally Posted by vorsprung durch technik View Post
Looks impressive. Just in case you haven't considered it,how about the fwd B4 or B5 saloon estate arrangement?
Not sure if that would work.
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Old 26-10-17, 10:40 PM   #4
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Wee bit shocked at the lack of reply's to this post, but moving on, been out in the coupe a few times now and all Ok, decided the other day to move on from the Audi S2 15mm ARB to the original 22mm ARB fitted to the front of the the coupe and fit it to the rear on the mounts that I made, test drive was in the dry, it did take me a little time to stop turning in too early into corners, my timing seemed to be off, I stopped in a lay-by to gather my thoughts and try to understand what was happening, the only other time this happens is when I fit my two track tires to the front of the car and on the way up to Forrest Burn Hill climb the front of the car turns in nice and sharp but by the time I get there my turning in timing is OK, yes sounds daft I know but the only reason for turning in sharper is more grip at the front and that may be due to less roll at the rear, I can feel the rear end is flatter and feel no lift from the rear on the inside wheel mid corner, test drive in the wet is needed to confirm that no daft unpredictable snap away is present mid corner and to see if wheel spin on inside wheel is reduced on corner exit due to less roll on the rear, it is pants going round a roundabout turning right with lots of grip and then turning left lighting up the inside left tire to exit the roundabout as you accelerate away in the wet.
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