Fox front suspension, maybe Audi 4000, maybe Audi B3, maybe combo of both? by 90quattrocoupe

By diyauto
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Fox front suspension, maybe Audi 4000, maybe Audi B3, maybe combo of both?

Compliments of 90quattrocoupe @


I know a lot of stuff has been written about various methods to lower Foxes. So I am not going to cover that. 

A lot of us think in terms of VW interchangeability, when we think of modifying the Fox. I have a tendency to think of Audi, when I think of modifying the Fox. I have had a couple of Audis and think along those lines. One of the reasons I bought a Fox vs a different older VW. We have a car that is using late 70s and early 80s Audi technology. Think Audi Fox and early 4000. So I started collecting a few parts, for a Fox project I am working on. Nothing written on the project, but this is something to think about. 

The Fox axle uses a outer CV joint that uses a 68mm bearing with a nut on the end this very similar to other VWs and early Audis. The Audi4000 uses the same type outer CV. The B3(Audi 80/90) uses a 75mm outer CV with a bolt holding the axle to the hub. But the big difference is, the 89 to 92 B3 has two piece struts. I hate one piece struts. A pain when it comes to changing springs, shocks, and upper strut mounts. 

So below we have a Fox axle. 


A litte closer look 

So this next picture has the B3 outer CV joint attached to the Fox axle. 


As you can see the CV slips right on the Fox axle. Uses the same little circlip to temporarily hold on the CV as the Fox CV. Instead of using a nut, the B3 uses a bolt to hold the axle to the hub carrier. 

In the next picture, we have a side by side comparison between the Fox Strut and the Audi B3 Strut. 


From this picture you can see a couple of things.  
(1) Late B3 strut is a two piece. Great thing. 
(2) The B3 lower spring perch is exactly the same as the Fox lower spring perch. Good thing. 
(3) Even though the Audi B3, 4000, Coupe and Fox all us the same shock insert, the B3 tapers at the top, and the Fox does not. Good/Bad thing? 
(4) The B3 and Fox use the same tie rod end.  
(5) The B3 tie rod arm is a little over 1 inch lower on the strut than the Fox tie rod arm. This could be a good thing for a lowered car. 
(6) The B3 Strut is about 1/2 shorter than the Fox strut. So you get a 1/2 drop just using the B3 Strut. 
(7) One problem is the ball joint. The B3 uses a 19mm ball joint vs a 17mm for the Fox. This problem could be solved by using a lower 4000 control arm which can use either a 17 or 19mm ball joint. 

A problem does occur if you use the B3 strut. The hub is designed for a 4X108 rotor. And no, there is no replacement 4X100 hub that will fit(not that I have found one). But this is not and unsolvable problem. You can have the hub drilled and threaded to 4X100. Offset the holes 90 degrees. 

The B3 comes with the upgraded G54 girling brakes, so you can have the 256mm rotor slotted to 4X100. The B3 hub carrier also allows the use of the G60 girling brakes, with would allow you to run the 276mm front brakes. You cannot do this with the Fox strut, without paying a couple of hundred dollars for the Sirocco front brake adapter. 

The hub itself for wheel fitment is the same for either a 4X100 or 4X108 wheel. 57.3mm. So with the hub mod as described above, you can still run your VW wheels. 

Next chapter will have a comparison of a Fox lower suspension vs a Audi 4000 lower suspension

Greg W.


A little update. I am still waiting for the machinist to drill and tap the hubs. Also slot the rotors. But here are some pictures with updates on fitting up.

The next couple of pictures are a comparison between a 4000 4 cylinder subframe and Fox subframe. Both top and bottom.


This next picture shows why you just can't use the 4000 subframe on the Fox. The frame mounting locations are in a different location than the Fox.

The next pictures shows a Fox control arm attached to one side of a Fox subframe and the 4000 front control arm attached to the other side. This 4000 front control arm is from a 4KQ. The 4KQ front control is also the same front control arm as the later 4000 FWD and the early B3 arm. So you can use either. You can tell if you have the right one, as it has the rubber grommet for the 4000 sway bar. We will get into that later.

As you can see the 4000 control arms will bolt up, using either the Fox control arm bolts, or the 4000/B3 control arms bolts.

I assembled one of the struts to show what parts I used from the varies cars to get one put together.

In a previous post, I noted that the Jetta springs are almost identical to the Fox front springs. Just upside down. Since I found a set of Neuspeed springs for a jetta in the junk yard for cheap, I am using them. The neuspeed spring is a little tight fit on the lower spring perch, but it does work with a little persuasion.  

This picture shows the front springs in there normal set up.

The next picture shows the Jetta Neuspeed spring flipped.


I used a Koni shocks from a Audi CoupeQ(same as 4000 or B3 shock), the neuspeed jetta springs, the B3 snubber and cover, the Fox upper spring perch, Fox strut mount, and B3 nut(a little larger than the Fox one).  

This picture shows the strut assembled and all the parts laid out that were used to put it together.

This picture shows a little mod I made to the Fox upper spring perch. Upper spring perches rarely come with location tabs. Bottoms do, upper don't. So I added a couple. I like to know that the spring is located properly.

The Audi 4000 4 cylinder subframe weighs 18 lbs. Even thought the Fox subframe is slightly smaller, it weighs 22 lbs. It is made out of a heavier gauge metal.

Next update when I get my hubs and rotors back.

Greg W.


Made a beginners error. I didn't check everything. I made an assumption that was wrong.

4000 control arms unless modified will not work on Fox subframe

I didn't compare the Fox control arm directly with the 4000/early B3 control arm.

See anything wrong in this picture. I do. The 4000 control arm is longer than the Fox control arm. Using the 4000 and Fox 17mm ball joints, I measured the bottom side to the center of the ball joint from the rod I inserted in the bushings. Difference. Approximately, 1 inch.

Now even though the 4000 ball joint has slots in it and the Fox control arm has slots, I could not push in the 4000 ball joint far enough in on the Fox arm to make up the difference. I should have thought about it before, since the 4000 is a wider car than the Fox.

Well, maybe the Fox subframe is a little narrower at the control arm mounts than the 4000. This would help a little.

No, the Fox gods were not with me on this one. With the 4000 subframe being a 1/4 inch narrower, this makes the problem worse. So I am dealing with approximately 1 1/8 inch to much control arm length. Well, I could modify the 4000 control arms(I really like the idea of using 4000 sway bars), or I could build my own arms. But I want this to be as close as possible to bolt on, so others may be able to use without a lot of fabrication.  

So I look at the ball joints for all three cars. Fox, 4000 and early B3.

Now these ball joints are very similar. The Fox ball joint does not have slotted mounting holes as the Fox control arms has the slots. But other than that, the B3 19mm is very usable. This may even allow a little more variation in camber. The ball joint uses a plate on the top for the fox, ball joint bolt up. I will probably use a second plate on the bottom. On the Fox, the bolts are pressed into the plate. On the B3 the bolts are separate. I will use the B3 system, as the bolts are higher strength.

Well, that is where we stand at the moment. I have my hubs and rotors back from the machinist, so more stuff to come. Need to put new bearings in the hub carriers, and put in the hubs.

Greg W.