Hilton

I was just assembling the front shocks for my '89 and ran into an issue - a quick search turned up nothing on it.

The brand new plastic dust covers are sized slightly smaller where the shock rod goes through the plastic area, than the neck on the Koni shock rods.

Its possible to twist them down far enough, but it takes a fair bit of force, and the problem is that if I put them on the car that way, then I'll have problems adjusting rebound.

Its so tight, that if I were to try adjusting the Koni rebound on the car by pushing the shock rod right down, its pretty clear the rod will not come back up through the plastic dust cover due to binding.. and I'd have the ugly experience of lifting the car with the front shock undone.

My plan is tomorrow to go grab a 15.5mm drill bit, or possibly a 5/8"one (15.87mm), and ream out the hole in the plastic part beneath the metal spacer, so it's actually larger than the rod's 15.1mm diameter.

This may be a function of using brand-new dust covers (old ones were cracked, so I chucked them), but I figure it might save someone a lot of headache

As a side note, this wasn't an issue for the rears, as their covers are a different style and there's no way it can bind.

Dave928S

Thanks for posting Hilton ... I've got Konis

soontobered84

I've not had any problems with that on all the sets that I've installed. Maybe it's just the new batch of dust covers?

GlenL

Maybe it's meant to be a press-fit. It doesn't go on at all? Does the rod go down far enough to make the adjustment with the dust cover stuck firmly to the rod?

I was doing this a couple weeks back, off the car, and am curious.

Bill Ball

I don't understand. You don't want these covers to move on the shaft at all. They move with the shaft. They stay fixed high, on that lip near the top of the shaft, protected by the metal spacer from being crushed. Try compressing the shaft into the body with the cover (with the bumpstop and plastic "washer") installed there. It should engage the cam.

Hilton

The cover won't move - it is fixed on the shaft by the metal spacer built into it. The metal spacer ring sits between the shoulders and the washers/bushings above, to keep the top assembly the right separation apart, so is under a fair amount of load and won't wobble, move etc. You can see the metal spacer in the top picture in my first post - it sits above the area that binds.

The problem with the lower part is just the minimum internal diameter of the plastic body immediately below the metal spacer.

I noticed the issue when I was compressing the whole lot with a spring press to mount it up - and not enough of the threaded section was poking out the top of the dust cover to assemble the top washer and nut onto the shock to hold it all together. It was binding enough on the plastic that it just compressed the shock rod. I hadn't noticed it wasn't down the shock rod far enough as I'd just expected it to be a simple fit like on the boges.

The problem is with the new plastic dust covers I have, the lower passage, which is supposed to go down far enough that the metal spacer ring can rest on the shoulder, is fractionally too small. I can't get a measuring tool in there, but I'd guess its a 15mm diameter hole through the plastic, versus the 15.1mm shaft diameter. This causes the whole dust cover to sit about 21mm too high up on the shock rod.

It can be forced down; I used some grease, and a nut on the top of the shock rod so I could hold the rod up while twisting the cover down - however when I did that and could assemble the shock, there's no way in hell I'd be able to adjust the shocks' rebound setting whilst on the car, as I couldn't get the same kind of leverage to pull the shock rod up again.

I'll go measure the shaft on my old Boges and see if the new dust cover has the same issue on one of them.

Hilton

I just did some test assembly on the bench again to sanity check myself.

The cover definitely needs to be able to move up the shaft - by about 40mm (eyeball guess) to get the shaft down far enough to make the shock adjustment.

This is because of the rubber bellows spring (I'd call it a bump-stop, but not sure if it has a different name in the US?), which sits between the dust cover and the top of the shock body.

The cover is such a tight fit, I can't push the shaft through it downwards using my body weight (just under 200lb) - trying to get it to engage the adjuster. To get the cover off again, I had to pull and twist it whilst holding the shock rod still (and it was lightly greased).

Will go take some pics once the camera is charged to more clearly show the assembly issue.

jon928se

I suspect that when you depress the shock shaft to engage the cam the shoulders on the shaft will be below the level of the top of the foam rubber bump stop that sits loosely on top of the shock body. In fact this must be the case otherwise the shock would bottom out in use without the bump stop ever doing it's job.

Either the Koni has a slightly larger dia shaft than the boges or the plastic part of the cover has been made with a smaller than spec diameter. I would just use a round file to carefully open out the hole in the plastic. It shouldn't be a tight fit on the shaft anyway - that would just cause it to crack.

LEADASS

This may sound stupid, I'm not sure about the proper size/fit issue, but I drill a bunch of holes in a lot of different materials... When I drill in plastic, especially if there's already an existing hole that I'm enlarging, I find that if I put the drill in reverse it's more better. In forward with a high speed steel bit there's a tendency to walk... your hole's not as centered anymore. With the drill in reverse you're sort of burning the hole larger, the bit won't bight into the plastic (won't crack), and it tends to stay more centered. Just my two cents. Brian

jon928se

Good point Brian

I find that 50% of the time if you can't control the feed rate, the drill bit just grabs and produces a "thread" in the plastic with the same pitch as the flutes of the bit.

Bill Ball

OK, I guess you have to be there to see the problem. I had no problem going from Boge to Koni to Bilstein with the same dust cover and I was able to adjust the internal Konis while on the car with Carl's tool.

Tails

Hilton,
If you drill the plastic dust covers, first dull the cutting edge slightly of the drill by grinding a small chamfer across the cutting edge to stop the drill biting in.
Tails 1990 928S4 Auto

Hilton

Some pics and measurements..

The issue seems to be that the Koni's I have (bought from one of our suppliers a few months ago) have a slightly thicker neck than the boges. Its a small difference, but the dust covers fit nicely over the Boge shock, and need to be forced with the Koni.

As you can see, to adjust the shocks on the car, you'd need to push the rod down through the dust-cover and into the bump-stop.. then let it come back up through the stack to put the nut back on.

Reaming out the plastic bore slightly is definitely the course of action here - thanks guys for the tips on drilling the plastic.

A drill seems like the best choice - to make sure the material is removed all around the shock rod, rather than applying pressure on one side which may cause premature cracking.

soontobered84

I don't think you'll be drilling plastic. Inside the plastic collar is a steel sleeve that acts as a necessary spacer.

Hilton

The steel spacer is only about 15mm long.. and it doesn't need drilling - its ID is designed to stop on the shoulder.

The problem area is the 39mm deep section of plastic bore below the spacer, which has slightly too small a bore to fit over the shoulder to allow the spacer to sit easily/correctly on the new Koni's.

After seeing $$ prices on a 5/8 drill bit, I ended up using a 16mm boring bit I had knocking around. Worked a treat, and left straight walls all the way to the metal spacer, so there's no undue stress on the plastic when the stack is tightened up and the spacer compressed.

Given noone else seems to have had this issue, either I have a rogue set of Koni internally adjustables from one of our 928 vendors, or Koni have changed their tooling to use slightly thicker shafts, and I'm just the first to install them.

I found one of my old cracked original dust-covers and they have the same fitment issue on the new Koni shocks, so it appears the Porsche part isn't at fault.

Shocks are assembled now - hopefully I'm the only one to experience this issue, although I suspect not.