964: bump steer correction

[kurquhart]

This has been discussed in several threads recently, but I thought I would still share my experience.

I dropped my car off at Mirage International this morning for bump steer correction. The kit makes for some serious eye candy; more pics to follow after install.

Evo uprights:



ERP tie rods; may require 993 steering arms:



AP Racing discs, 13" diameter requires radial spacers for the calipers.

[Bill Verburg]

Nice move, no more caliper adapters, lighter upright(can you get a weight on the steel 964 uprights?)

What size rotor is that? Looks like maybe a Wrightwood hat?

[Ag02M5]

Like to see the final product. Still high on my to do list.

RT

[kurquhart]

Originally Posted by Bill Verburg

Nice move, no more caliper adapters, lighter upright(can you get a weight on the steel 964 uprights?)

What size rotor is that? Looks like maybe a Wrightwood hat?

The rotor is 32mm by 13", custom made for Mirage by AP Racing. The hat is indeed Wrightwood, with Big Red offset. Several local cars are running this combination with good results.

I will try to get you some weights.

[Ag02M5]

By big red offset on the rotor hats, you mean 965t or 993tt? I am guessing you/they know what you are doing but you will need the 993 rotor offset with the evo upright rather than that of the original 965 big red.

RT

[kurquhart]

Originally Posted by Ag02M5

By big red offset on the rotor hats, you mean 965t or 993tt? I am guessing you/they know what you are doing but you will need the 993 rotor offset with the evo upright rather than that of the original 965 big red.

RT

Yes, 993TT offset for the new uprights. My current rotors are 965 offset with the stock uprights and caliper adapters.

[Tom W]

I'm also a big fan of the EVO uprights. I had them added to my car to get rid of the horrible bump steer I had once the car was too low for the stock 964 parts. We will be cleaning the rust off in the near future ... I also went to full monoballs and, while no photo, floating rotors with aluminum hats.

[kurquhart]

Originally Posted by Tom W

I'm also a big fan of the EVO uprights. I had them added to my car to get rid of the horrible bump steer I had once the car was too low for the stock 964 parts. We will be cleaning the rust off in the near future ... I also went to full monoballs and, while no photo, floating rotors with aluminum hats.

My bump steer is not too terrible right now, but that is because my car is not as low as I would like (it will be after we are done with this conversion). We are also changing all the bushings for monoballs, so the front end should be very sweet.

[Bill Verburg]

Sounds like a nice setup. Don't forget the back and m/c.
Any particular reason you guys went w/ the ERP tie rods instead of the factory RS pieces?

From what I have learned the struts need to be 993 versions. T/F?

Any other pieces necessary?

I know that when I changed to the RS/GT2 uprights it made a big difference. I would imagine more so on a 964.

[Tom W]

Bill: My suspension was put together by the folk at Jerry Woods/Smart Racing. I wanted the ERP monoballs all around in addition to the EVO uprights and I assume the tie rods were easier to source as they are a normal Smart Racing product (you walk from one garage bay to another and pick them up rather than trying to order it and wait for deliver from Porsche). I know Rich said they did a bit of additional fabrication to get the geometry they wanted given my cars ride height.

It made an incredible difference in my car. Before the changes the car would dance and dart and move all over under heavy braking. It was a diabolical beast to the extent I really worried about contact when I had someone right next to me going into the corners. After the changes (using the same alignment specs) it became a joy to drive.

[kurquhart]

Originally Posted by Bill Verburg

Nice move, no more caliper adapters, lighter upright(can you get a weight on the steel 964 uprights?)

964 steel upright is 12 pounds w/ bearing.

Originally Posted by Bill Verburg

Sounds like a nice setup. Don't forget the back and m/c.

I had already upgraded the rear brakes and M/C to 993 spec, plus the 60 bar P/V.

Originally Posted by Bill Verburg

Any particular reason you guys went w/ the ERP tie rods instead of the factory RS pieces?

The ERP tie rods were used instead of factory RS for two reasons:
1. the vertical portion comes in several lengths which can be custom fit for any ride height
2. no rubber anywhere

Originally Posted by Bill Verburg

From what I have learned the struts need to be 993 versions. T/F?

The 964 struts worked fine w/ no modifications.

Originally Posted by Bill Verburg

Any other pieces necessary?

The 964 steering rods needed to be changed to 993, as the threads are male and female, respectively.

A-arm bushings were replaced with ERP monoballs.

One of the drop links was replaced with a length adjustable link to eliminate any pre-load.

End result: less than 20 1/1000" toe change over +/- 1" vertical travel.

[Ag02M5]

Originally Posted by kurquhart

The 964 struts worked fine w/ no modifications.

One of the drop links was replaced with a length adjustable link to eliminate any pre-load.

Very interesting.

I was under the impression that the EVO upright is 1 mm wider. The struts I have on my 964 would definitely not fit if the upright mounts were wider. Any chance you could measure them precisely?

Also, what were the bolt sizes?

What drop links were used? Link?

Thanks!

RT

[kurquhart]

Originally Posted by Ag02M5

Very interesting.

I was under the impression that the EVO upright is 1 mm wider. The struts I have on my 964 would definitely not fit if the upright mounts were wider. Any chance you could measure them precisely?

I don't have calipers, but the spacing is approx. 17.5mm.

Originally Posted by Ag02M5

Also, what were the bolt sizes?

Appear to be M12.

Originally Posted by Ag02M5

What drop links were used? Link?

One side is 964 RS, other is a ordinary heim joint (red in first pic above).

[rcwaldo]

Originally Posted by kurquhart

The ERP tie rods were used instead of factory RS for two reasons:
2. no rubber anywhere

Kris, a lot of nice hardware there! One thing I want to mention is that the inner section of your toe link mount is rubber isolated. If you wish to stiffen those two pieces up (one each side of the steering rack), there have been a few people do this over on Rennlist recently in the 993 forum. One is a super simple and effective way to do so via roll-pin.

Question: at your outer toe link connection to the upright, is there a cone feature on the tapered spacer that mounts into the upright?

[Bill Verburg]

The 993RS/Evo mounts are 18.3mm thick.
the upper mount hole is 12mm
the lower mount hole is14mm
the holes are matched to the 993/993RS bolts 12x1.5x50 upper/14x1.5x55lower

964 uses 4x 12x1.25x90 bolts(the 90 maybe a typo in PET)
964t uses the 2x 12x1.25x90 upper and 2x 14x1.5x55

[Ag02M5]

Originally Posted by Bill Verburg

The 993RS/Evo mounts are 18.3mm thick.
the upper mount hole is 12mm
the lower mount hole is14mm
the holes are matched to the 993/993RS bolts 12x1.5x50 upper/14x1.5x55lower

964 uses 4x 12x1.25x90 bolts(the 90 maybe a typo in PET)
964t uses the 2x 12x1.25x90 upper and 2x 14x1.5x55

I think you are mostly right. The figures you gave are for the 964t with 3.6. The 3.3 turbo uses 12mm bolts top and bottom.

Cheers.

RT

I am going out to put a caliper on the 964 upright.

[Ag02M5]

The 964t 3.3 upright appears to be 18.3mm also. So indeed the 964 strut shoud work. Though in the case of the the 3.3t and the c2, the lowest bolt hole would have to be enlarged to 14mm.

The 964t 3.6 strut should work with the EVO upright as is.

Guess the mystery is solved. 993 struts do not look to be requred for the EVO upright.

[Bill Verburg]

Originally Posted by Ag02M5

The 964t 3.3 upright appears to be 18.3mm also. So indeed the 964 strut should work. Though in the case of the the 3.3t and the c2, the lowest bolt hole would have to be enlarged to 14mm.

The 964t 3.6 strut should work with the EVO upright as is.

Guess the mystery is solved. 993 struts do not look to be required for the EVO upright.

Good to know, thanks for contributing!

So to sum up, it appears that 993 or 993RS/Evo uprights will bolt on to the 964 strut w/ the caveat that 964n/a will need to enlarge the lower bolt hole from 12 to 14mm.

That's great news for 964 owners that want to get rid of or not use caliper adaptors w/ the bigger 993 calipers, and/or want to use 993 or 993RS/tt rotors.

[kurquhart]

Originally Posted by rcwaldo

Kris, a lot of nice hardware there! One thing I want to mention is that the inner section of your toe link mount is rubber isolated. If you wish to stiffen those two pieces up (one each side of the steering rack), there have been a few people do this over on Rennlist recently in the 993 forum. One is a super simple and effective way to do so via roll-pin.

That is good to know. I guess I need to rephrase from "no rubber" to "less rubber".

Originally Posted by rcwaldo

Question: at your outer toe link connection to the upright, is there a cone feature on the tapered spacer that mounts into the upright?

Sory, but I'm not sure I understand your question. If you look at the second photo at the beginning of the thread there is a side view of the ERP tie rod - does this help?

[kurquhart]

Originally Posted by Bill Verburg

Good to know, thanks for contributing!

So to sum up, it appears that 993 or 993RS/Evo uprights will bolt on to the 964 strut w/ the caveat that 964n/a will need to enlarge the lower bolt hole from 12 to 14mm.

That's great news for 964 owners that want to get rid of or not use caliper adaptors w/ the bigger 993 calipers, and/or want to use 993 or 993RS/tt rotors.

Sorry to be away from this thread for so long, but a three day track weekend beckoned.

I (finally!) bought some calipers today and measured the four mounting points on the 964 uprights. They were all different, varying from 17.95 to 18.15mm.

I spoke to my mechanic about the 14mm lower bolt hole. He used the 12mm bolt at the edge of the 14mm hole to get a little extra negative camber. Since it is torqued down around 100 ft-lbs, he doesn't think it will move.

I, however, am a little worried that the 14mm bolt was used by the factory to resolve a weak point in the mounting, especially in the context of 18" wheels. Does anyone know if this lower 12mm bolt is at risk of breaking in this application? If so, we will drill the strut and use a 14mm bolt.