WALTSTAR

The aluminum bushings I received were not cylindrical from top to bottom but have a flange that locates the rack against the chassis so that there is no vertical movement. These in the pictures are different from what I received, but hold the rack up like the right side of your fourth picture.

Carl Fausett

Yes, our mounts are not as long as the steering rack casting is thick, and that is by design. Others manufacture their steering rack bushings to hold the rack still purely by concentric location (which is likely to fail as the power steering rack is a casting and therefor inconsistent. Hence, the use of rubber mounts by the factory to make up for the irregularities in the hole sizes).

Our mounts use less of a concentric mount and more of a clamp mount. While some concentricity occurs (we also lightly touch the outer walls of the steering rack holes with our mounts) the true clamping in location is done by clamping the mounts under the plate and by clamping the steering rack to the engine cross-member. That is why our mounts are a little shorter than the casting - to make certain that the first thing to clamp against the engine cross-member is the steering rack, and not the steering rack mount.

ROG100

Stop shopping at WalMart for your materials 8>)

MjRocket

LMFAO!!!...Roger i luv you brother!

Carl Fausett

Yeah, that must've been it.

Delrin comes in many grades. My experience with it indicated that its tolerance to pressure plus abrasion was poor. The steering rack beat it up in no time.
I have now learned it is not recommended for applications involving high loads plus impact and/or abrasion, which was consistent with my results too.

Here are some of the grades : http://dupont.materialdatacenter.com/profiler/7MblW/

GregBBRD

It's really interesting about how different people/different vendors head down different roads and think that is the only path.

Carl had poor wear issues with Delrin bushings once (not made by me, BTW) and doesn't like them. I read this thread about someone installing solid aluminum bushings in their street car and just shake my head, wondering how the he!! they expect that to ever work.

Different people. Different ideas. Different theories. Different products.

To me, mounting one of these steering racks in solid aluminum bushing on a street car is one of the poorest ideas ever. Unless the bushings are a very tight press fit into the holes (or welded into place), they are going to move around and wear on both the rack and the bushing....that is absolutely a given. Additionally, that lower crossmember is attached to both of the frame rails, where the suspension is attached. It has to be continuously flexing...which, by definition, has to twist the steering rack, once it is solid mounted in aluminum.

Neither one of these is a good idea, in my mind.

Pieces made and used on a racecar differ from those made and used on a street car. It is important to realize this distinction.....because there is a tremendous amount of difference between the two. I'm guessing that on Carl's racecar, the front suspension is attached to the roll cage and has other added pieces to make this entire area of the car stiffer. He might get away with solid mounting of his rack on his racecar (but I'm betting there is grey aluminum "dust" coming out between the rack and his bushings.)

ZF and Porsche designed the rack bushings to absorb movement, for a reason. If they thought using a solid chunk of aluminum was a good idea, they would have made the "ears" solid and drilled a 10mm hole through the ears and been done with it. Saved a whole bunch of money...

Addressing the "Delrin failed very quickly" thought: I just checked with Mary about our Delrin steering rack bushings. We've made and sold over 1200 of them....with zero returns and zero comments about wear....over a 10 year period of time. Roger buys them 50 sets at at time. Roger stands behind everything he sells 100%. If there was a problem, he'd be talking to me about it. (Jim Corenman has a much better design and I'd love to make bushings using his design, but the cost is higher.)

Do I expect Delrin bushings to last forever? No. They are supposed to absorb vibration, load, twisting, and shock. They are a type of plastic. They are going to deform, over time...it's a nature of the application.

Am I right? Is Carl right? Is either one right?

In the end, you have to apply logic to what you are doing, and make the best choice possible.

jcorenman

I'm just going to leave this here, for discussion purposes. The problem with aluminum bushings is, well, everything. The problem with Delrin is that you are tightening structural bolts against plastic, which flows under pressure. The factory bushings incorporate steel sleeves of the proper size, so that the bolts tighten against steel and form a structural box with the crossmember and lower plate. But the problem with those is that the rubber bushings deteriorate over time, and provide more compliance than some might desire even when new.

So why not a steel bushing to tighten the bolt against, a Delrin bush for a bit of isolation, and a urethane compression washer to accommodate the uncertain dimension of the cast rack foot? (Have a look: the rack foot is machined on the ID and bottom surface only, the thickness is as-cast).

Details here: https://rennlist.com/forums/928-foru...ml#post7202909

These particular bushings were put in service 6 years and 80K miles ago, on our GT. I just had occasional to check them and they looked the same: No change, no wear, bolts still torqued as they originally were.



I've thought about having some made, and talked to some of our parts vendors, but they will have to cost more and folks seem happy with plastic.

GregBBRD

^^^^^This is the way it needs to be done!^^^^^

worf928

What, if anything, is being considered as a means of keeping the steering arms from moving non-axially in the rack housing? This is what dominates in the 'wobbly' steering feel world and is something that is not dealt with in the typical rack rebuild.

Carl Fausett

Greg - a good post and I mostly agree with you.

Dave C: you are right too; a lot of "vibration" issues are not the steering rack mounts fault. It will not cure a bad alignment, a rack with bad outer bushings, a bad tire, or an out-of-balance tire. I have had cars in the shop that were obviously aligned while they had bad steering rack bushings, and now that the steering rack is properly located (in a new location), guess what... the toe needed to be checked and reset. SOP

Carl Fausett

Consider the variables offered just between driver and car.

Owner A installs Delrin bushings, has 255 fronts, and drives like its his pride and joy. He'll be fine with Delrin mounts all day. But if he was to install 275's and he's that guy that likes a good onramp/offramp setup - he will likely deform his Delrin with the heavy side loads the tie rods will impart to the rack.

Owner B installs aluminum steering rack mounts. He likes to feel the seam in the pavement, he throws his car into corners, and he too is running the 275's or 295's in front. Aluminum is the better choice for him.

This is my explanation for why we get different feedback for essentially the same part. One guy has no problem with Delrin mounts and likes them. Another guy has no problem with aluminum mounts and likes them. Different cars, tires, drivers, and expectations.

Remember: there is a huge rubber vibration isolation disc in the steering column itself (see pic in post #27 of this thread), so if you install EITHER Delrin or Aluminum steering rack mounts, and swear you can feel a vibration, it has to be pretty bad. Have it checked out.

WALTSTAR

The 928 was designed as a luxury sports car if I am not mistaken. Surely a good reason to mount the rack with very minimal isolators is the luxury component. The isolators are minimal because of the tight German tolerances (think Luger) and the inherent rigidity of the platform. I would like to add that the cradle that the rack mounts to probably does flex somewhat under heavy load, but some of us arent going to track the car and DO make every effort to avoid potholes and bumps where possible. The mounts that I bought were perfect in their fit and index as well as their snugness around the bolts. Although the rack is not meant to be structural, I would think that rigidly mounted to the cradle it would tend to act in concert with the cradle (as a system-as it were) and would probably not be compromised if the car were not on the track. As far as vibrations, its a sports car first (for me) and Ive removed everything I think superfluous. I cherish road feel.
Just my two cents.