Jay Wellwood

So....I'm in the process of rebuilding Oskar and I'm on the suspension path right now.

Looking to convert to 944 turbo brakes/spindles/A-arms using M474 Struts/Shocks I picked up leaving the rear trailing arms intact for a more bolstered appearance.

Any input or experience to share?

TIA-

Debo18D

So the previous owner did this to mine. Love the look of the 16" wheels (which you will likely need to house the larger brakes) and the fact that it throws you through the windshield when you mash on the stop pedal. The one thing that he didn't take care of was the speedometer. The 924S uses a mechanical speedo and the 944T uses an electronic speedo. This past weekend, I pulled off the driver front hub and spindle, stripped it down to the bare spindle and modified it with the speedo cable channel. I am fortunate to have a Bridgeport milling machine in my garage and was able to work it out perfectly. If you don't have access to a heavy drill press, a milling machine, and the know how to do it, you should probably take it to a machine shop. You can bring in your 924 spindle as an example to show them what you need done. The other option is to buy a 944T speedo and cable and modify it that way although that seemed cost prohibitive to me. I can post some pics of the process if you would like. That is if you want a speedo, which running without would be the 3rd option.


Debo sends.

Jay Wellwood

Debo - if you wouldn't mind sharing the pics that would be great!

I've looked at this a bit in depth, and concluded that to preserve the factory Speedo, either using '86 spindles/hubs/rotors or drilling the 87+ spindle to accommodate the cable. Not sure of the impact of hollowing out the spindle for this, but apparently it is ok. Another option is to use a Speedhut GPS speedo with a similar configuration - or go with no Speedo

Debo18D

Sorry it took so long to get back with you. Been busy around here.

So here is the car at the start of the mod. Notice the grease cap has no square hole with a cable plugged into it. Also notice the speedometer cable doubled back and pushed through the bracket to keep it out of the way for the last year since I have had the car.










Here is the spindle and removed from the car and after the other parts have been removed. This is what you will have to figure out a way to hold in the vice. It isn't exactly perfectly square and easy to grab.

Debo18D

So the next thing that I did was get the spindle in the vise. I used an edge finder to check for square and also to locate the center of the spindle. After zeroing the X and Y axis, I zeroed the Z axis so I would know when the bit reached the depth I needed. I had used a brass rod to measure the depth on the 924S hub that was taken off so that I could use the same dimensions on the 944T hub that I was drilling. Also measured the diameter. I will edit this post with the dimensions when I get home and retrieve them. The outside dimensions of the 924S hub and the 944T hub are largely the same save for the extended tabs to mount the larger brake caliper and a beefier ledge that holds a rubber seal between the cable and the back of the spindle. This made me feel better about removing the material as it would be functionally just as strong as the 924S hub on thousands of those cars.

I used a short machine drill bit (size to be added here later) to get the hole started the first inch or so and then switched to a longer bit to get the depth needed. Total depth was 3.100" (will be checked and edited for accuracy later). Machined it nice and slow with a sharp bit and lots of oil and lube and it went through like butter.

Debo18D

Here are a couple of videos of the first cut. Nice and slow, lots of air and pauses for cleaning out chips. I am not a professional machinist by any gauge or ruler so those guys can probably add a ton of good hints for making it go smoothly.

Drilling


Final cleanout-

Debo18D

The next hole needed to be at the right angle and had to be perfectly on axis in order to meet up with the deepest part of the first cut. This was tricky as it was near impossible to get a good mount in the vise. A machinist could easily have used clamps to the T-slots of the table and not used the vise, but I am not that good so I went with what I knew and it worked out.

I measured the angle at approximately 16 degrees from the bore axis with some angle blocks so next step was to get the bore axis as close to straight up as I could when it was mounted in the vise.


15 degree angle block for reference.




Once I squared up the spindle as best I could straight up and got it locked down, I made sure that I was correct on the y axis. Luckily, when they machine this at the factory, there is a divot on the inside of the spindle that the lathe uses to index perfectly with the outside end of the spindle so they can spin it correctly on the axis. I simply used an edge finder to center the y axis on it and locked it down so it wouldn't move. After that, I angled my machine head to 16 degrees. I know that you can't completely rely on the accuracy of the gauge on the head of a 50 year old Bridgeport but I knew that it would be close enough in this application.

The 924S has a beefy ledge on the back that a larger hole is started in, in order to hold the seal that the cable goes through. (Pic of 924S hub to be added later). The 944T hub doesn't have this but I needed to machine at least a little bit in order to get a flat spot to start the drill on when making the connecting hole. Otherwise it would have hit the back of the spindle at an angle and deflected ruining my drilling angle. Used a carbide bit on this and it acted like it didn't even realize it was machining into something. Only took a few seconds to get where I needed it. Didn't have to go very deep and did it with the 924s hub in front of me so I could approximate where I needed to be on the X axis to make the right intersection. After this, I was able to use the same size drill bit that I did on the center of the spindle and just drilled it until it reached that depth that I had measured on the original.

Debo18D

As you can see, once the holes connected and made the channel, the cable fit perfectly and poked out the outside of the spindle.







Mounted back on the car.



Grease cap from the original 924S spindle with the square cut-out. The cable indexes and the clips to hold it in. From what the book says, I should seal this up with silicone also when I install the new speedometer cable that I ordered and am awaiting to arrive.






So that's it. The speedometer now works like a champ, save a little bouncing from being 32 years old. I'll fix that with a new cable next week. Amazingly accurate when tested against a GPS also.

Jay Wellwood

FrenchToast

Hopefully you're not planning on pushing the car very hard. The early hollow spindles break fairly frequently. Putting a hole in a late one, IMO, isn't a good idea. I'd sooner use a GPS speedo if one really is necessary.

Debo18D

I agree.




D.

mel_t_vin

Jay, do you have all the hard parts [hubs, spindles, calipers, arms] you need for this conversion?