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Walt Fricke's Avatar
 
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Oh - I now remember that you can (or could) purchase the 930 crossmember mounting piece. I think it came with a little bit of sheet metal as well, so one would cut out the old one, weld in the sheet metal piece on the bottom to fit the specified cut, and then weld around where the "nut" protruded into the area behind the gas tank. Stock is welded there too, but the 930 I think just stuck up a bit farther.

Otherwise, I don't believe the sheet metal in that crosswise tunnel area was modified at all. No need, as things still fit, if tighter than before.

Walt

Old 06-26-2010, 11:58 PM
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I was proposing the anti-dive angle being added within the custom bearing housings themselves, for use with the stock 1971 crossmember.

I have just had the Rebel Racing bearings installed in my car. They feel great. The old Urethane had a tremendous amount of stiction which caused a harsh ride (which I previously attributed to dampers, sway bars, torsion bars, or other things). Now the ride is smooth, stable, and silent.

The configuration of the RSR bearings I used are with spherical washers on the front only. This angles the front mount down relative to the rear, adding some anti-dive while also correcting small suspension pan misalignments.

The car has not been aligned or corner-balanced so I have only made a short drive around the block to (not) hear the bearings. I will report on any anti-dive effects I might somehow actually feel after the first shake-down spin around the canyons.



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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-27-2010, 12:34 AM
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The formula at the bottom is referencing the previously defined variables around post 31 or 32.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 06-27-2010 at 12:37 AM..
Old 06-27-2010, 12:35 AM
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I'm a little late to the party, as usual, but here's a little info from the 930 Service manual, page 50-4.

"In comparison to the type 911, the carrier pin of the type 930 Turbo is 21 mm higher. This has caused changes to the floor/frame assembly in the area marked in white.

The Border on the wheelhouse and floor plate is cut about 70 mm higher than the central area, to allow accessibility."

And here's a pic of that area from my 930 showing the step above the carrier pin:



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1986 911 Turbo
3.3L, K27HFS, Tial 46mm, TurboKraft Intercooler, 964 Cams, Monty Muffler, MS3Pro Evo, M&W Ignition, Zietronix WBO2 Data Logger, Wevo shifter, coupler and motor mounts.
Old 06-27-2010, 06:41 AM
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Quote:
Originally Posted by Flieger View Post
I have just had the Rebel Racing bearings installed in my car. They feel great. The old Urethane had a tremendous amount of stiction which caused a harsh ride (which I previously attributed to dampers, sway bars, torsion bars, or other things). Now the ride is smooth, stable, and silent.
Those are sweet looking!

I went through several sets of poly-graphite bushings on my old 1972 years ago, fitted those POS bushings several ways, and even cut channels and installed grease zerks. The problem was, I could fit them perfect for the summer, and they would be sloppy in the winter, or perfect in the winter and too tight and 'creaky' in the summer. There was no in between.
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1986 911 Turbo
3.3L, K27HFS, Tial 46mm, TurboKraft Intercooler, 964 Cams, Monty Muffler, MS3Pro Evo, M&W Ignition, Zietronix WBO2 Data Logger, Wevo shifter, coupler and motor mounts.
Old 06-27-2010, 06:48 AM
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With increased spring rates of today's race cars it seems trying to add anti dive to the front of a 911 is not going to make much difference.

Back in the day I believe Porsche's torsion bar limit was something like 22/29's so the suspension had a lot more dynamics going on.

With 400lb plus front springs v 200lb upgraded torsion bars, there is probably more spring rate remaining in the tires.

I suspect spending ones effort on the camber dynamics (camber curve and as effected by caster and bump steer) and shock dynamics might be better spent.

Just a guess.
Old 06-27-2010, 08:14 AM
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Well, I have 22/27 torsion bars and even though the car is 2000 pounds without driver, I still feel a good bit of dive and squat.

Also, you can run softer springs for better road holding over bumps or to tune the roll stiffness front to back, then use some anti-dive like an anti-sway bar in the fore/aft direction to limit dive and squat.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-27-2010, 10:49 AM
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I was wrong in guessing the Turbo A arm (lower control arm) was the same as the stock 911. They are a different part number, though I have no idea just what is different.

Here is what I was remembering about how the chassis mount differs (it is what WinRice is quoting).



Looks like there was no turbo specific replacement part for this part of the chassis, so the shop manual showed how to modify the regular 911 panel.

I don't think you can achieve much in the way of anti-dive if you don't raise the rear of the A arm. Of course you could lower the front even more, but that has other consequenses.

And with a stock A arm, rasising the rear can only be done by raising the cross member, no? Not really enough room to move a bushing up? The steel crossmember is interchangeable with the aluminum one, so if you get the mount raised the steel member will work.

Those gorgeous Rebel Racing mounts look like they are centered where the stock mounts are. So how can you lower the front mount (I see you can align it with the clever washers) without causing a bind in the rear? How do you dip the axis of the rears? Chuck touts the small urethane cylinder in the Elephants as giving some alignment compliance, but these don't seem to have that.

With a 935 style front lower suspension you could raise the front pivot up based on how you designed that part of things. I plan to put a slug into the stock "cup" part to hold the pivot bolt. When eventually I get on the stick and fabricate a 935 style front for my car I may put the pivot up as high as I can get it without other interference issues. It would allow the front mount to move back up (better ground clearance, though so far that's not been an issue), but also would allow the A arm to regain more of a down angle.

Walt
Old 06-27-2010, 01:05 PM
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Talked to Clint today, I was mistaken. The bearings I have are an early version. The current configuration will use spherical washers on front and rear mounts, with the rear dimensions relived appropriately to allow for angularity to the crossmember. The front is then spaced down. This will provide the anti-dive angle. Sorry for my misunderstanding.

Best Regards,

Max
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-28-2010, 05:20 PM
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Max

Please let us curious ones know when the improved rear assembly is in hand.

It is easy enough to see how using those two piece hemispherical washers will allow the spaced down front bearing to tilt to match the A arm fore/aft angle. The long slots in the front in stock configuration are for allowing for variances in fore/aft mounting position. But they will also allow some degrees of rotation in the needed plane, one supposes. This would mean that spherical washers are needed on the underside as well as on top?

I'm not immediately coming up with how one could do this at the rear. On the early RSR Products version, the "slotting" is in a side to side orientation. Besides, the rears are basically fastened in place by their fairly tight fit into the aluminum (or steel) cross member. The vertical bolt holding everything together just kinds of keeps them there.

If you slotted fore/aft, and reduced the vertical diameter, you could put sphericals top and bottom inside the housing? But the housing is cylindrical, etc.

Coilovers make all this so much simpler, as you can just weld rods into the ends of the A arm and use spherical bearings in the carriers (if you don't go whole hog with the 935 setup). My track car came with coilovers, so I never had to weigh pros and cons.

Walt
Old 06-29-2010, 11:07 AM
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Clint runs coil-overs and that is a big percentage of his customer basis- 935 suspension/coil overs.

These bearings work for torsion bars, however.

Clint makes products in batches as demand dictates. He has a few sets of early bearings left and the next run will be the anti-dive version. If you say you want the anti-dive version, I am sure he will go ahead and place the order to the CNC machine shop earlier.

The way he described them to me was that the top and bottom of the rear housing would be relieved/thinner to allow the spherical washers to be used and to give clearance to the crossmember as the housing is tilted. I can find out more details if you wish, I did not see the CAD file for that configuration. I believe the way you describe the slotted bolt hole is correct.

I also suggested to him boring the hole in the rear housing at an inclined angle relative to the horzontal plane (something like the CAD image I posted earlier). This could always be another possibity if it were to be proven a more simple/better design, considering the abilities of the CNC machine.

Yes, the spherical washers are used on top and bottom of the front mount and will be used on the top and bottom of the rear mount. They are optional but I am using them. I have the early steel crossmember.

This picture is Clint's car with coil-overs. They are the prototypes so he plugged the torsion bar hole temporarily with a piece of cloth. The production version for coil-overs comes with a proper plug.


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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-29-2010, 11:43 AM
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Just pure curiosity for me.

The SC has to remain "stock" so it stays in its proper race class. And the track only car has anti-dive, no A arm concentricity issues, is slated for a home brew 935 setup at some point, etc.

There might be a market for home brew 935 setups. One of the cost items on those is a replacement cross member. I think I have figured out how to keep that stock piece and modify the existing steel cup inserts to hold a pivot bolt, though I am working on how to prevent the slight rocking of the insert when not fixed by the stock or similar A arm's use of the front mount to prevent that. You give up some design flexibility (longer rear A arm length, higher pivot), but I think not much for the lighter weight and increased adjustment the 935 system allows.

A shop owner has satisfied me that spherical rod ends are strong enough in the threaded area to serve as lower ball joints. But one wants the tube connecting LBJ with chassis pivot to be bent at its outer end to keep the ball joint more coaxial with the strut.

But I am wandering off of anti-dive. And I suspect most would, if lusting for the 935 setup, prefer to save up their pennies in a piggy bank and just buy one of the several on the market and bolt in a tested system.

Walt
Old 06-29-2010, 11:59 AM
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Near the bottom of the page here: Suspension2 he says he has a 935 suspension for sale. He does the strut modifications for coil-overs for any suspension configuration.
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 06-29-2010, 12:09 PM
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I am looking for more info and photos of the rear crossmember area. How is the sheetmetal bump different to allow the crossmember to be raised? I need to find out how far the centerline of the bushing is raised, ultimately.

The front spacers are 10 millimeters, is it?
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/

Last edited by Flieger; 10-11-2010 at 06:42 PM..
Old 10-11-2010, 06:39 PM
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I'm not following the rear crossmember question. Wasn't it covered in this discussion, with pictures? Rear up 13mm, front down 6? Per Bruce Anderson. You only need to raise the mount portion of the sheet meta, and weld the mounts in at the higher level. Unless you shortcut this and just modify the bottoms of the crossmember mounts and leave the sheet metal alone.

There is enough room above the rack in between the mounts to have the rack go up that amount. Though not much more, so the rack raiser spacers have to go, as I recall.
Old 10-11-2010, 09:36 PM
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So one can raise the crossmember 13mm while using a sock 911 chassis? I am having a hard time understanding if the crossmember can be raised. Do you have to mill off part of the "stand-off" area?

911S A-arm Bearings rear
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911S
1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 10-11-2010, 11:33 PM
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Flieger,

When I looked into this I concluded the sheet metal is different so that is what I belive so far.

I to wondered if the cross member might be different but it dose not seem to be.
Old 10-12-2010, 08:42 AM
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Max

The factory cut out the sheet metal in approximately the area where your flash overexposed it and it appears whitish, and dealt appropriately with the top end of the "nut" mount, which penetrates the trunk area sheet metal, and moved it up the 13 mm.

I posted the page from the shop manual which shows where to make the cuts, though it didn't copy too well and the dotted lines for cutting are hard to see.

The other way is the Fricke short cut, which involves cutting off the standoff, recreating just enough of a ring to socket into the recess in the top of the cross member so the bolt isn't doing the locating or taking all the shear, and not messing with the rest. I think a good welder/fabricator could do a good job of this. My rings cracked when I got into a racing incident and I had to reweld them.

I don't believe the 930 had a different cross member. I think a lot of us hot rodder racers would know were that the case. We all know about the turbo bananas in the rear, etc. A look at a parts catalog for an '80s pre-964 tub 930 would confirm or deny this.

Walt
Old 10-12-2010, 10:50 AM
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Thanks Walt, that is a good description. I understand now.

I am working on a project for easy anti-dive on a 911, hoping to have just the bearings do it, no big chassis mods needed up front.

BTW, while it is overexposed, the chassis is painted white, actually.
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1971 chassis, 2.7RS spec MFI engine, suspension mods, lightened

Suspension by Rebel Racing, Serviced by TLG Auto, Brakes by PMB Performance
http://www.flickr.com/photos/max_911_fahrer/
Old 10-12-2010, 11:17 AM
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I guess you could whittle down the ride height adjuster and move the pivot up. Half an inch might be tough to get, though. Even with coilovers so you could toss the adjuster.

I've thought of moving the pivot toward the center, to lengthen that leg of the A arm. But I am not sure that would produce any worthwhile gain in suspension characteristics.

I've also wondered what the effect would be of changing the fore and aft axis of the A arm. Because most, if not all, 935 style systems leave that front pivot in the same horizontal location. And some of them do move the rear pivot in, which will change that axis.

Walt

Old 10-12-2010, 11:28 AM
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