Converting a 4x4 SUV to the Ultimate Track/Street Car

Jeff Curtis

Eastern Vice President/Track Chairman
First Settlers Region - PCA

Upon purchasing my 1991 Grand Prix White 964, I thought what many other 964 owners did, "Why does this thing look like a 4X4??"

So, my recent purchase soon found me on a mission with two goals in mind:

1. lower the car for appearance and better handling
2. complete "stage I" of a transition to the ultimate street/track car

Researching the various products ranging from just lowering springs to a Stage III Racing shock/spring setup yielded a decision to purchase what I refer to as a "middle of the road" setup. After all, I wanted to have a car that could survive on the street, driving it to work and back, running errands, etc. - and still be great a great handling machine at the 10 plus track events I attend each year.

I ordered a set of Bilstein HD (Heavy Duty) shocks and H&R sport/lowering springs for a 965 (Turbo). Mind you, I had plenty of discussion on the Rennlist boards in regards to why Bilstein didn't make a "sport" shock, but instead, an "HD" version, which basically is a "sport" version without the proper title. The decision to use 965 sport/lowering springs from H&R was purely mathematics, I wanted a little more stiffness than the 964 springs would provide, which is about 25-35 pounds more per corner...and I had heard from a buddy of mine in California that this would work, and had been done - on HIS 964. Also, the "progressive rate" springs offered by H&R provide a less harsh ride on the street than some of the other products offered on the market. So, there you have it, what I thought was the ultimate "middle of the road" setup for a 964.

What follows is a DIY procedure for the installation of my new Bilstein HD shocks and H&R progressive rate 965 "Turbo" sport/lowering springs. While I made an attempt to list pertinent details in the installation process...I also assumed that anyone attempting this procedure will be fairly mechanically inclined, so I'll make an attempt to be moderately detailed.

Please note that many steps in this procedure are dangerous, due to the nature of preloaded springs and the fact that you will be working under a 3000 pound vehicle for part of this procedure. Please make any and all attempts to maintain a safe working condition and utilize what any mechanically savvy person would label as “common sense”.

List of Materials, (hopefully I have included everything)

Special Tools

Ensure you warn your friends, neighbors, and loved ones, including the dog - that you don't want to be bothered, for a WHOLE day, and that you will have LARGE tools on hand in case this warning is not heeded! Save the beer for your post install celebration dance, you'll need 100% of your wits about you! Zoloft and Paxil tablets MIGHT be a consideration as you may possibly endure bouts of disappointment that grow into deep depression...just kidding...as you learn that those 10mm allen bolts WONT budge. (Are you getting the idea I had a little trouble with these??)

One thing, while you may be able to scoot that floor jack of yours under the car prior to lowering...keep in mind that you have to retrieve that jack once you're finished! Suggestion: Make a set of four 1ft. long 2” x 8” pieces, 45deg. bevel one end. Once you’re finished with the front install, before lowering the vehicle, place one of these pieces under each tire…same for when you are finished with the rear! This my friend, is a valuable hint learned from experience...don't ask! (Thank God I have a sense of humor - and TWO floor jacks!)

One more thing: this procedure was written from memory, basically "off the cuff" as one would say, so, while some steps may not be the ideal way, they were done MY way. Some steps or details may be omitted due to lack of memory -or- things I just DIDN'T want to remember!

Please enjoy my attempt at helping you, the "Do it Yourselfer" perform this procedure.

Let's begin!

Installation Procedure for front shocks/springs:

1. Jack vehicle up, via jack pads located directly behind front wheels. You can jack one side, or both up, it won't matter...after all, you can only do one side at a time! -secure vehicle with jack stands, NOT on any suspension point, for obvious reasons.
2. Disconnect brake line retainers, the encapsulated speed sensor for your ABS and anything else that "borrow" the shock housing for a mounting point. You will have to separate the fittings for your brake lines where the rigid line meets the flexible rubber one.
   Tip: This is a good time to upgrade to SS braided brake hoses. Assemble the brake lines for the meantime, for the purpose of not draining your master cylinder and consequently leaving brake fluid all over the floor...you will STILL have to bleed your brakes when installation of the front struts/springs is complete.
   
   
3. Here's where you grab your biggest 1/2" drive torque wrench and 10mm allen socket I told you to purchase, WELL before you attempt this procedure. Attempt removal of 10mm allen bolts that secure front struts to the wheel carrier. Don't remove bolts all the way, just break them loose at this point.
    
4. Note: these two bolts are responsible for your CAMBER adjustment for front-end alignment, this is a good thing to know. As you loosen them, your wheel carrier will likely adjust itself to the most positive camber side of the adjustment...this is okay. Again, DO NOT use an impact on these! Are you starting to get the idea that this is where I went wrong?? While it didn't appear to damage my socket, it did wear out the allen bolt hole where the allen socket went...this caused LOTS of trouble being that no other attempt at using an allen-type tool was productive from that point on...requiring the use of a drill, a punch, a chisel and LOTS of four letter words. Too bad I didn't have the camera at the ready for this segment of my ordeal. As you can see, the "School of Hard Knocks" is multi-faceted.
   Support the wheel carrier, I used a floor jack with a block of wood atop the saddle and placed it under the "hat" of the brake rotor, preload the carrier, just a little. The next step will require this, as you will be releasing the top support mechanism for the strut/spring assembly...and you don't want it to fall, causing potential damage to your wheel carrier assembly and fender well.
5. Enter front compartment and pull back/unsnap the carpeting in the vicinity of the shock you are removing. See the four nuts surrounding the large one? You are going to undo the four smaller nuts using a 13mm socket - remove them completely, washers too. Leave the larger nut alone for the meantime.
6. Slowly release the preload you have on the strut/wheel carrier assembly, being attentive to the fact that the upper part of the strut assembly is not connected to the vehicle anymore. You should be able to lower the carrier assembly all the way down to full extension without any consequences...use good judgment here as I can't remember anything that would cause a problem. You may have to remove your swaybar link?
   Tip: Your strut spring assembly may release from its upper attachment while lowering the wheel carrier, if not, kindly assist it with a rubber/plastic mallet BEFORE lowering wheel carrier to full extension. There should be a seal installed that provides quite a bit of "stiction" holding the strut assembly to the upper body mount/shock tower.
7. Once the strut assembly is completely released from the shock tower and wheel carrier is at full extension - remove the 10mm allen bolts completely, being sure to catch the nuts/washers (were there washers?) off the end of them and having one hand on the strut assembly...guess why?
   Notice that I have my front rotors removed in some pics, I was changing out my rotors at the time and though some of the pics would show more if I left them off.
8. Carefully guide strut/spring assembly out of it's position, place unit on one of those old blankets, stand up and do your best "celebration/touch-down dance"...at this point, in my opinion, you have just completed one of the most difficult parts of the procedure, well maybe, don't get too excited just yet.
   
9. Now, this is your first chance to use that handy-dandy impact wrench of yours. Use it to remove the nut that retains the hat assembly...you will NOT need a spring compressor for the front shocks, although please use one on the rears!!
   Tip: If you do not have the use of an impact wrench, you can always opt for a piece of leather, a pair of vise grips and a socket/ratchet. The provision for an allen wrench at the top of your strut shaft will be basically useless as the nut is on there pretty good and the concave shape of the hat makes it fairly difficult to get a good grip with a combination wrench, either end. Use the leather to prevent damage to the shaft from using vise grips.
10. Once the hat is removed from your original shock/strut assembly, set aside the various washers/spacers, rubber bumper, etc. in correct order or removal.
11. Remove spring and unscrew spring perch from body of shock, transfer spring perch over to new shock assembly - unless you already have spring perches for your new shocks, some shocks do not come with these...my Bilsteins did not. ***Your originals will be completely reusable and likely compatible with your new shock.
    Note: If you are using lowering springs from H&R, you should have a note inside the box describing how you need to obtain the proper bumpers -or- trim yours down, I just followed the guidelines for trimming my originals, nice and simple. For a Porsche C2/C4 you will need to trim off ¾”. Also, unless you have ordered new boots, you will be reusing those as well.
    Assemble the new strut/spring assembly just how your factory unit was, ensure spring perch is installed correctly, flat part down, offset facing upwards, orient spring per instructions provided, this is especially important with progressive rate springs. *Tip: Again, you should not need the assistance of a spring compressor to assemble the front units and this is where your impact wrench comes in handy again, tighten nuts that retain the hat until good and snug, I don't recall a torque value, nor did I use one.
    
    This is a good time to stand your new assembly on end, step back and admire your new creation, beat your chest and do your best Tim Allen impersonation!
     
12. Navigate your new shock/strut/spring assembly into the wheel well, inserting top end first and install the four 10mm nuts that secure the assembly to the top strut mount, finger tighten only at this point.
    
13. Using your floor jack, position the wheel carrier to where the holes line up for the two large allen bolts that secure the bottom of the strut assembly to the carrier, install lower allen bolt with corresponding nut, finger tighten only. Then, by the procedure I was using, I placed one lug nut on the lug closest to the 12 ‘o clock position, then took a 19mm deep socket and a ½” ratchet, basically using it as a lever, I muscled the wheel carrier up until the second allen bolt hole lined up and placed the other allen bolt through, finger tightening with corresponding nut on the end.
     
14. Tighten the four 10mm nuts at the top of the assembly to 27ft lbs.

15. At the bottom of the assembly, notice that the upper allen provides camber adjustability, the lower just holds everything together. Adjust the wheel carrier assembly, via floor jack, so that the upper allen bolt is pretty much in the middle of its adjustment range and torque both allen bolts to 100 ft lbs. I use my car on the track quite a bit, so I put 150 ft. lbs of torque to the allen bolts once I had my car aligned on a machine…so far, so good. (fingers crossed)
    Again, do NOT use an impact on these bolts!!
    
    
     

16. Once again, separate the brake line and place in applicable support tab mounted on strut assembly, then install speed sensor/ABS sensor harness/wiring into their proper locations.
    Tip: The plastic retainers that connect the speed/ABS sensor wiring to the strut assembly have a removable "apple core" of sort. With "core" pushed out -or- removed from plastic retainer, press retainer into position, once into position, press "core" in to hold retainer in place. IMPORTANT - Remember, because you had to separate the brake lines to properly install the front strut assemblies...you will have to bleed your braking system!! While installation of the rear shocks do not require separating of any brake lines, it is a good idea to bleed them as well. Once I was finished installing the front strut assemblies, I hooked my pressure bleeder up and bled the front lines only. I then put the front wheels back on the car and prepared to install the rear assemblies, bleeding the rear lines after completion.
     

READ AHEAD TO REAR SHOCK/SPRING PROCEDURE AS YOU MAY WANT TO LEAVE THE FRONT END SUPPORTED WITH JACK STANDS!!

Rear Shock/Spring Removal and Installation

Alrighty then, by now you've apparently made it out alive with the installation of your front strut assemblies - was that hard?

Relax, in my opinion, the rear shock assembly removal and installation is NOT as difficult, but it is several times as dangerous!! This is where you will need the assistance of a spring compressor.

Ready?:

1. Raise rear of vehicle and place securely on jack stands. I placed the jack stands under the jacking pads, forward of rear wheel well and directly behind the door. Careful, as you tend to turn your 964 into a "teeter-totter" in this situation, so if you have a set of four jack stands, this is where they become helpful as it would be ideal to leave the front end on jack stands.
   Tip: Use discretion when raising the rear of the vehicle if your front is still on jack stands. I used my big floor jack and a piece of 2x4 under the engine to jack up the rear of the vehicle all at once, vice one side at a time...besides, how would you place your jack stands under the jacking pads if your floor jack was there?? If you figure that one out...let me know.
2. Remove: airbox lid/filter element on right hand side of engine compartment, heater blower motor/down tube on left hand side. The procedure I used said to remove the rest of the air box…I did NOT find this necessary…but then I have average hands.
3. Place a jack under the trailing arm, with very little or no preload, just so when you release the top of the shock from the vehicle, there’s not a sudden release of tension.
   
4. Using a 13mm socket, 3/8” ratchet, and an extension, or assortment of…remove the three nuts holding the shock to the vehicle, being careful to keep track of the washers and nuts. NOW is the part that pretty much required the use of an impact wrench in my case…remember this bolt is in there at a 147 ft. lb torque value…plus all the corrosion that helps it stay there!
5. Set your impact wrench on reverse, place a 26mm impact socket on it and remove the bolt that attaches the lower shock mount to the trailing arm. Be careful, be sure to have one hand on the shock as it may fall upon removing the bolt form the trailing arm…mine were still held firmly in place by the plastic hats that retain the spring.
6. Wrestle rear shock/spring assembly from body of vehicle……once again, do your best “ARGH ARGH ARGH” as you place the assembly on the floor. I figure it best to remove both shock assemblies at the same time.
7. USING A SPRING COMPRESSOR <hint hint> attach spring compressor to spring in a matter that allows you to compress the spring. Adjust tensioner on spring compressor so spring obviously has NO tension on retaining hat.
8. Again, this is a good time to use the impact…remove the nut securing the hat to the shock assembly, remove hat assembly making sure to set any washers aside for proper reinstallation. You will only need the retaining hats off of your original factory shocks! Unless you have purchased new ones…in that case, well aren’t we just loaded!? At least you’ll save some time being that you won’t have to disassemble your original rear shock/spring assembly to scavenge the retaining hat. Again, YOU may need to reuse the spring perch/adjuster off your old shocks, my new Bilsteins came with them.
9. Remove spring compressor from old spring and compress new spring as necessary and place onto new shock, ensure you have spring properly oriented as to top/bottom.
10. Place retaining hat atop spring and screw on nut – by hand! My Bilsteins came a new nylock nut as I’m sure your choice of shock will, due to the fact that you’re only supposed to use a nylock nut once…you did know that…didn’t you?
11. Tighten nut, I found a torque value that stated 43lbs…but that value was out the window being that I used my impact on this. Go ahead, YOU figure out how to tighten that nut to spec, without the shaft rotating excessively!
12. The factory manual says to lubricate the upper strut mount/retaining hat with tire assembly compound…you tell me, WHO has some of THAT laying around? I sprayed mine with some soapy water, as did the person who wrote the procedure that I used had.
13. Install new rear shock/spring assembly into upper mount/receiver in vehicle…this is where it gets a bit tricky as you have to align the studs properly, before inserting the assembly because the plastic retaining hat/mount fits snugly inside the receiver in the vehicle, so once you push it up in there, you pretty much aren’t able to rotate it as to line up the studs with their corresponding holes…so patience is a virtue!!

14. If you left your jack under the corresponding trailing arm, then you should be in the ballpark for placing the lower mounting bolt and threading it in by hand…you will likely have to incorporate a little adjustment via floor jack to get the hole lined up good as to be able to thread the bolt in properly…do NOT cross thread! Your trailing arm is aluminum…and costly! Finger tighten bolt as far in as possible at this point.
    

15. Place washers/nuts on upper shock mount studs…tighten to 15 ft. lbs <91, 27 ft. lbs on 1991 and later models.
    Tip: Use a long flat tipped screwdriver, place the washer/nut on the screwdriver shaft, properly oriented, holding washer/nut in place with fingers, place tip of screwdriver blade on top of shock mount stud and release washer/nut as to “slide” them into place…leaving screwdriver in place, attempt to start the threading of the nut onto the stud, repeat for remaining washers/nuts. This may save you a few bouts with four-letter words and such…keep a magnet handy.
16. Tighten lower shock mount bolts to 147 ft. lbs. – it might be a good idea to use anti-seize on these bolts, so they’re not as hard to get out next time!!
17. Perform your best mental check list:
    -Brakes bled?
    -Brake lines snug?
    -Retained properly?
    -Flexible brake lines oriented correctly as to not snag –or- bind with front wheel movement?
    -All speed/ABS sensors in place?
    -All nuts/bolts torqued correctly?
    -ANY LEFTOVER PARTS THAT SHOULDN’T BE??
    
18. Lower vehicle, ensuring you have all jackstands, wood blocks, etc. clear of the vehicle.
19. Assemble heater blower motor assembly on left hand side of engine compartment –and- airbox/filter assembly on right hand side.
20. WASH YOUR HANDS!
21. PRIOR to starting vehicle, manually pump brake pedal until firm…this ensures there are no surprises when you back out of the driveway!!

Now that you have successfully completed this procedure, and have experienced a successful test drive, give yourself a pat on the back with one hand, with the other – dial your local P-Car alignment facility to schedule a four wheel alignment/corner balance.

Oh yeah, give your dog, wife, kids, whatever, a big hug…not necessarily in that order – well, you gotta hug the dog first! …and of course, go for that beer you’ve needed ALL DAY LONG!

Jeff Curtis - jefc@mindspring.com
Eastern Vice President/Track Chairman
First Settlers Region - Porsche Club of America