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Old 11-06-2012, 05:39 PM   #1
peytonracer4's Avatar
Join Date: Jan 2010
Location: Valparaiso, IN
Posts: 7,756
My Ride: '00 328i
OFFICIAL: ZHP steering thread

I'm making this thread so that the facts can be clearly laid out for anyones use.
this is info regarding the notorious "zhp steering rack"
for a while some people believed that the zhp had a special rack just for that package. however, people were finding steering racks with the same part number on regular 330s. so these are the facts to clarify.

The 330 zhp only received the steering rack with the part number 7852974712

the regular 330s could receive 3 different steering racks. how bmw chose these cars, we do not know. but the numbers are
and a non ZF label from TRW with unknown part number.

this means that a zhp can only receive the 712 rack, but there are a number of regular 330's that would receive this rack as well. like i said, we're not really sure there's a pattern to which cars received what rack.

all we can be sure of is that the 712 rack is the zhp rack that people talk about.

all of these racks have a ratio of 13:7:1
this means the lock to lock will be 3 turns for any 330. but what makes the 712 (zhp) rack different? that will be explained in the following quote from the rack doctor. the internals ARE different despite the same ratio. this is what contributes to the better feel in the zhp, and some zsp, 330s.

at this point, we do not know how many 330s got the 712 rack and how many got the other two racks. all we can be sure of is all zhps have the 712 rack or should have it.

note: this information is regarding 2001+ 330s. earlier 330s will have different racks and part number that are not discussed in this thread

Originally Posted by The Rack Doctor View Post
Hello I am reluctantly chiming in here in hopes that I may lend a point of view from a technical standpoint. I have had several PM's, e-mails, and phone calls asking me to explain this dilemma over the ZHP Rack. If I may say ahead of time I have no desire to argue fight debate or anything else about the subject I am simply going to try to explain this as it was explained to me By ZF engineers at the AAPEX Expo. as I too (after 26 years of building the rack and pinions) don't claim to know "EVERYTHING" and at times have questions that I need answered. If anyone would like to debate the information please contact ZF.

I am not here to make anyone right or wrong simply offer tech help when I can this is what I always thought that the forums were for a community of enthusiasts trying to help one another.

I took a little time to break down a few pinions to let you see what's on the inside and how they work.

YES the 330 and the ZHP rack share the same turn ratio (3.0 turns let's keep it simple) the racks function differently by the strength of the torsion bar that runs through the center of the pinion (or in simple terms the spool valve ..... I have heard 1000's of names for the pinion)

I am adding a few pictures to try and explain how the units are different I am aware the pinions are not BMW pinions as they are only for the purpose of illustration .

The easiest way to put it is the torsion bar is different in the ZHP rack. As torque is put on the pinion the the more fluid is passed through the pinion. The stronger the torsion bar the more the sport feel. (this is also where the famous over boosted steering comes from a weak torsion bar)

Below is a simple illustration of how a rack works. The torsion bar runs through the center of the pinion (in simple terms the pinion is the brain of the rack it tells the pump when it is turning (torque) give me more pressure to turn the wheels)

The next picture shows the pinions as they would have been removed from a steering rack

The next picture shows the barrel of the pinion taken off with teflon rings still attached

The next picture shows the barrel close up I wanted to show how small the fluid holes are in the pinion so I used a ball point pen for illistration. I wanted to show this so installers will have a better understanding of the importance of flushing the system out prior to installing a rack and pinion. It takes very little to clog these small holes

Ok Moving on the next picture shows the pinion broken down by components the thin bar that runs through the pinion is the torsion bar. This is where the units differ.

The next picture is just a closer look at the torsion bar. Side by side again with a ball point pen so you can get an idea of the size of the torsion bar in the pinion

The last picture is the assembled pinion with a down view so you can see where the torsion bar is in the pinion while it is assembled

I would like to take a moment to thank the forum members for your valued business. I Hope you find the information helpful and we can agree that simply because a rack and pinion has the same turn ratio does not mean that they all perform the same, much the same as on the E36 models the standard E36 and the 96-99 M3 racks have the same turn ratio the racks perform differently. I have a good friend that works for a BMW salvage yard and he tells me that he sells the M power engine covers all the time for people to slap them on their 2.8 L engines we all know that what happens internally is what makes the difference. Adding a ZHP shift Knob to your car does not make your car a ZHP.

We at Rack Doctor go to great lengths to separate these units rather than lump them all together so that when you order a rack you will get the specific rack you are looking for.

Thank you for taking the time to read through this, and again I hope you find it informative. I hope I have explained it well enough, feel free to shoot me an e-mail if you have any questions, or give me a call I will try to help whenever I can.

Be well

Rich (aka the Rack Doctor)


Originally Posted by The Rack Doctor View Post

I have NEVER said that there was a difference in the 712 tagged racks THERE IS NOT...... NUFF said a 712 rack is a 712 rack

There were 3 different racks used on the 330

1. a TRW rack this rack was manufactured by TRW and has NO TAG rack is stamped T R W

2. a purple 678 tag rack with 3 turns

3. a yellow 712 Tag rack also with 3 turns

I questioned what is the difference between the 678 tag and the 712 tag and was told the torsion bars were different giving a different feel. (not going to post the same dirty pictures all over again)

The gear in the 678 tag and the 712 tag are slightly different as well

Based on the 100's - 1000's of cores returned from customers based on what they order and tag numbers given to me on the phone on top of countless hours at core suppliers (where racks are tagged from junk yards) and hours buying cores in junk yards over 26 years. this is the data I have come up with.

What I have seen is anyone who has claimed to have a ZHP has ALWAYS sent in a 712 rack as a core apparently there were other packages as well that shared this rack I have even had a 712 rack returned from a 323

Yes I agree the 678 tag was also used in the 325 that would be why they have the same part number on my site as well (hmmmmmm weird)

The racks I "WAS" intending to break down were the 678 tag vs the 712 tag and never the 712 vs the 712, they are the same to think otherwise would be silly. I don't think this was EVER a debate. I was simply trying to convey that from all of my resources physically touching, holding, handling, building, and sometimes cuddling with rack and pinions as well as discussions with other builders also in the industry for 25 + years that there were 3 rack and pinions used on the 330's

1. TRW Rack (rack is stamped T R W )
2. Purple 678 tagged racks
3. Yellow Tag Tagged Racks

To answer an earlier question there is another yellow tag this was on the earlier 330 (2001) and was tag Number 599 this would be the same as the 643 tag (silver) a 3.4 turn unit.

Once again I was simply trying to help and seems some people get it and some don't... I am only posting again to point out that I DID NOT claim the 712 racks were different only that there were different racks on the 330 models if I have not explained this well enough then I am sorry.

Be well
Rack Doc

I am no expert. but i think we can all agree that rich is based on his years of experience and evidence presented. i will post pics of both the yellow and purple rack tags for reference purposes just so you can see what they look like if you do not know.

i really hope this clears things up for some people, especially people searching and learning this for the first time. i hope this is an end all post.

if anything needs to be added or edited i will do it at my digression.

**if the mods want to move this to general and sticky it, so be it. but if that's the case it should be locked to avoid another episode.
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Last edited by peytonracer4; 11-06-2012 at 06:03 PM.
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