Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Wed Jun 08, 2016 4:51 pm Post subject: Double steering damper Modification for 411 and 412
|Double steering damper modification for VW 411-412
This is actually a REALLLY good handling modification for your type 4. I have about 60,000 miles on this particular modification.
First…why would you do this…and what does it help?
1. The 411/412 and super beetle strut suspensions of their day are notoriously deficient in castor angle. That alone makes then susceptible to “bump steering” where small, hard raised bumps like rocks cause directional changes and “tramline” directional changes where the tires follow grooves in the pavement excessively.
With no other changes……having a larger overall volume…..not necessarily stiffer (an important difference)…can help a lot with shocks primarily from rocks, that jar the wheel in your hand.
[b]NOTE: this is not a substitute for more castor. This will not prevent larger bump steering and does little for tramlining. But if no other changes are made to an otherwise stock suspension….it greatly cuts down on steering wheel jarring especially going through curves on rough roads.[/b]
By this I mean…you do not necessarily want to go to a gas charged damper or one with stiffer valving settings. Those can negatively affect the self-recentering of the steering gearbox. You want the same valving but a larger volume damper to have more stabilizing leverage…..of the same level….not stiffer action.
2. To do that….its normally a simple matter of going to a larger diameter damper with the same valving. There are many aftermarket examples of this type of unit for other cars. I recently read where Koni even made adjustable units for some cars so if you needed stiffer or softer valving you could dial it in.
But…there is no room for a larger diameter unit on the 411/412, and you would still need to find one with similar valving and then add the mounting hardware.
This is NOT …repeat NOT….a fix for the “shimmy” syndrome found in VW 411/412 and supper beetle with struts.
That syndrome is caused by a stack up of tolerance and material issues. Not to get heavily into it here but the “Shimmy syndrome” is caused by small gaps/tolerances in this range of parts:
• Slack between strut rod and bearing or loose bearings
• Slack between cartridge and strut body or loose strut body top allowing cartridge to have axial movement
• Wear, flexibility or looseness in the idler arm
• Wear, looseness in the center link rotating pins
• Slack/movement in control arm bushings and radius arm bushings
• All of the above leveraged by poor alignment to toe-in and camber due to improper weight in front end while doing alignment
• All of the above leveraged by slightly bent or spread wheel rims.
• Worn out steering damper and not enough castor angle leverage all of this
• Poor wheel balance makes all of this worse. Because of the setback and centerline of our rims, if any wheel weight is large than .75 oz….have it split in half and applied opposite to each other on the inside and outside of the rim. This helps to damp a “helicopter” style oscillation it can cause.
In general, the shimmy is caused by no one item. The tolerances and gaps are really quite small between most parts (though they can be fairly large on a worn out idler arm or center link)….but wheel condition, alignment angles and road conditions will basically set up a vibration between parts that allows the wheels to oscillate at a specific speed range.
This modification allows you to add two exactly the same stock dampers side by side. It uses a pair of brackets. The original damper still fits the two same mounting points on the subframe and centerlink bushing. The 2nd damper lays alongside it to the rear spoon style.
IMPORTANT INSTALLATION NOTES:
1. I am not giving exact locations for the holes drilled in each bracket. Since there are at bare minimum three different shapes of the reservoir end and the neck end of various makes of these dampers, each fits a little different.
Fit the one you are using up to the bracket and mark the center points through the part and then drill the holes.
2. These brackets are cleaned up, more robust copies of my original brackets. The original brackets were made of scraps of steel and a lot of filing and grinding to fit. The side to side spacing of the two dampers took a bit to get right and is important and correct….but the original brackets could have been slightly differently shaped in other respects and still work perfectly.
The L-shaped jog of the center link end bracket….may not need to be that way. But it worked perfectly in the first version……so I copied it. I cannot remember if it needed to be there. I did not want to re-engineer the part. I know….how Soviet of me to slavishly copy details no matter how worthless!
From the top:
TOP: The red one is a new/recent build, Mexican “IP” brand part. 411 425 021 A also lists 22205 part #. Uses a 10mm X 1.0 thread instead of normal 10mm x 1.5 thread in the center link connector end. Construction looks a little crappy but it seems solid and the dimensions are correct.
Middle: Large reservoir Brazilian Cofap brand. Uses part # 22005
Bottom: German made Boge brand. Has a really stout and wider center link end. I have had several of these at one time or another which is why the gap on the subframe end is wider than it needs to be for the part I am currently using. It fits all of these.
Part 411 425 021 A and part # 1-0031-22-748-0
1.25” X 1.25” X 0.125” common angle iron. You can use thinner angle iron as well and possibly even 1” x 1” angle iron. It’s what I had handy.
VHT epoxy spray paint (optional)
Drill press or hand drill with various bits
Angle square and ruler
Dremel Tool with cut-off wheels
Centerlink/passenger side bracket:
Here are the general views of the bracket. Do not be alarmed by the milled out, keyhole shaped hole in this bracket. The original 10mm hole I drilled was a copy of the old bracket which was using a different brand of centerlink so it fit differently. This configuration allows me to bolt all three brands I have here into the bracket.
For reference, here is my old bracket on the left and the new one on the right. Yes…the old one was made from a spare Thermo-time switch bracket and worked quite well.
Subframe/drivers side bracket:
General views of the subframe bracket. It’s as simple as it looks…but fitting up is important (more on this too come).
Here are the new bracket and my original angle iron bracket for comparison. The bent leg on my old one……is important….and I will get to that when we talk about fitting. It was purposely bent to fit a different brand of damper that I installed later on.
Installed parts/bench assembly with the centerlink for fit:
Here are assembled views of the centerlink end (passenger side). There are some critical features of the bolt length and thread for the damper that connects to the center link bushing and of the fit between bracket and the reservoir end of the 2nd /outboard steering damper (the right hand one in this picture).
I did not remember the importance of this notch until I installed it here. It just turned out that the thermos-time switch bracket was perfect with a little grinding. I was being lazy and got lucky.
Because of the angle to the pitman arm and idler arm that the center tie rod creates….and the fact that the driver’s side end of the steering damper is bolted to the subframe….and has only a little play in the rubber eye bushing both on the subframe end and for the centerlink rubber bushing, there is a slight twist to this assembly.
If you use a complete plate that covers the whole top of the rubber bushing of the center link…as the unit twists slightly on the bushing the plate impinges on the top of the center link on the steel and does not allow flexing and starts to wear the centerlink. So the notch in the centerlink end plate is somewhat important.
You can see this from the two views above
Some general assembly views of the driver’s side subframe bracket. The left hand damper in the last picture above is the one that bolts directly to the subframe.
General sub-assembly layout
Attached to the subframe in the general location. Approximately centered here.
Drivers side sub frame attachment
Passenger side centerlink attachment
Full extension for a hard right turn
Full extension for a hard left turn
THE most important bracket fitting considerations:
For this conversation the damper that actually bolts to the subframe and the centerlink in the original damper position…we will call the primary damper and the new damper that bolts to the brackets will be the secondary or outboard damper.
CRITICAL UNDERSTANDING OF DAMPER FUNCTION:
even in the normal single damper configuration….in order for the damper to work to prevent the small steering oscillations that happen from rough pavement, small gravel etc….the mounting MUST be rigid.
If there are any small gaps between the bolts and the steel bushing tubes, slack in the bolts or worn out/cracked rubber bushing either in the subframe mounting end or the centerlink bushing end…..that small amount of slack causes a minute delay before directional pressure comes to bear on the damper piston.
Add to this….the centerlink movement..…which is what the damper is actually damping…..is attached directly to the steering knuckle at each end. If the angle of the steering knuckle arm is taken out of the picture you have a 4.5” lever, bearing across the pivot point of the ball joint axis….leveraged across a 13.3” long tire radius (half the rim diameter plus sidewall width).
Slack in the parts of the steering damper linkage….as little as .015” to .020” is equal to 2.95 times that gap when measured at the tire leading edge.
So….a stack up of gaps due to bolt or bushing wear or slightly loose bolts…of 0.015” will cause a movement of 0.044” at the leading edge of the tire BEFORE there is any control exerted by the steering damper. That’s a little short of 1/16”…and does not sound like much….but when multiplied/leveraged by castor or camber changes, toe-in changes due to speed and many oscillations per minute at road speed..…can lead to significant harmonics in the steering wheel.
The double damper configuration is no different.
Issues with centerlink end bolt fitting AND BOLT TYPE:
In order to have no geometry and leverage issues the center link end mount (the most important mount because the centerlink is the moving part needing to be damped)….MUST be locked together as a unit.
In the diagram above, the bolt, the steel bushing tube and the threaded end coupler of the damper rod……are outlined in yellow as a unit…..because they MUST be linked tight as a solid unit. In order for this to happen the factory parts book specifies using a “J” type internal toothed lock washer that bites into the bolt head and the bushing tube to lock them together. The bolt must also lock solid into the damper rod threaded coupler
The built-in PROBLEM and THE FLAW:
Since there MUST be some small amount of angle/geometry change to the damper body and rod as the centerlink moves back and forth…..the steering damper pivots freely on the subframe mounting end bushing tube, around the bolt that attaches it to the subframe.
BUT….in order to actually pivot or change angle….the damper body must be free to move/pivot on both ends.
This means that at the centerlink end…..if the bolt head and steel bushing are locked together as a solid unit by the lock washer ….then the only way this joint can pivot is if the threaded coupling on the end of the damper rod is loose…which is not possible if there is clamping force all the way through the stack up from coupling, through the steel bushing to the lock washer sandwiched at the bolt head……or the steel tube MUST spin in the center of the rubber bushing…..which is the way it was set up from the factory.
This wears the bushing out somewhat but works.
The big problem is that over the years the vast majority of cars have lost the proper "J" type tooth toothed lock washer and or have the wrong length bolt.
It’s common with lots of driving to have to tighten the attaching bolt every 3-5K miles because it works loose. It’s also not uncommon to have the bolt fall out.
The original bolt was 10mm x 40mm length. The bushing eye in the centerlink is 25mm, the threaded coupling on the rod end is 14mm and the washer thickness should be about 1mm +/-.
In this dual damper setup….the subframe end of the steering damper that is the primary…meaning actually mounted to the subframe…will NOT be allowed to pivot anymore because the bracket will wear against the subframe. Instead, the second pivot point will be where the rod end of the new outboard damper bolts to the bracket.
"J" type internal toothed lock washer similar to that used by the factory.
A much better method of locking the rod end of the primary damper:
We will use a partially threaded bolt that has just enough threads to fill the 14mm of the threaded coupling on the piston rod and lock up solid so it can be torqued.
This must leave just enough unthreaded bolt length between the rod coupling and the bolt head to fit the steel bush and a high strength SOLID flat washer…which is 26mm total.
A 10mm DIN 931 bolt of 60mm length will have variably 26 to 34mm of thread depending on who makes it. Either will work.
If it has 34mm of thread…..cut the bolt off to 40mm. This will thread 13-14mm into the rod end, leave 25mm for the bushing and 1-2mm for washer between bolt head and bushing.
Or if it has 26mm of thread, cut the bolt length slightly longer and use a thicker washer between the bolt head and bushing.
Either way the object is to lock the bolt solid in the rod end and allow the bolt to pivot internally in the steel bushing just like on the subframe mounting end. Just make sure it’s a dead fit on all of the mating surfaces.
The slightly simpler but less elegant method is to use a fully threaded 40mm DIN 933 bolt and heavily distort the thread where you want it to lock against the rod end coupling. The only long term drawback (and its minor) with the fully threaded bolt is slightly more wear from the threads to the ID of the steel bushing.
Setting and locking proper damper geometry:
In the picture above, the two dampers with their assembled brackets must be LOCKED together to form two separate “dog legs” as is illustrated by the black bars with the red corner lines.
The lower damper is the only one physically linked to the subframe on the right end and the centerlink on the left end. The two green dots….one on the left end of the lower damper and the right end of the upper damper present the bolts that are the two pivot points for the damper to change geometry….remembering that the bolts on the primary (lower) damper are locked solid and the steel bushing tube of the primary rod end…rotates about the bolt….while the right end is locked so it cannot pivot anymore…instead extra movement is allowed by the rod end of the outboard damper between bracket and rod coupling.
The two red dots represent the mounting bolts for the brackets to the dampers. They are used to bolt the damper rock solid hard to the brackets with no movement between damper and bracket.
You will notice that the windows I cut in the angle iron are slightly oversized. This is too allow various brands/makes of damper to fit. This is a picture of the mounting of the outboard extra damper on the centerlink end bracket.
In order to lock the damper up solid to this bracket as previously mentioned, cock the damper slightly in either direction and bring the damper reservoir into hard contact with the bracket and tighten the mounting bolt. This will lock the bracket and the outboard damper into a single unit as per the previous picture/diagram.
On the reservoir end of the primary damper where it mounts to the subframe bracket, I used a standard arbor shim (1.5” OD X 1.0” ID X 0.040” thick) to make a spacer between the end of the damper and the face of the bracket.
I left a little extra “meat” at the bottom of the window so the bushing does not make contact with the bracket plate to allow a bit of out of plane, bushing flex which is required. You will notch a washer with the Dremel or file of the appropriate thickness as a spacer between bushing and bracket.
Finished views with shim and spacer.
NOTE: the nut on the bottom of this is simply to hold it together for the picture. The bolt in this picture will be threaded into the subframe
This is the outboard/new damper mount to the centerlink end bracket. You will notice that I have a forged washer under the bolt head, and one under the nut. This is to insure that the steel bushing is locked up solid between the two washers, the nut and the bolt head as a unit to clamp the plate. This will still allow some out of plane flex from the rubber of the bushing but essentially locks the damper to the bracket plate solidly.
An important final clarification:
This is the subframe end bracket. The right hand bolt holding the rod end of the new/outboard damper to the bracket…is using the wrong bolt and missing a washer. It’s all I had at the moment.
I have to prepare a new bolt with proper thread length. This picture is here to remind you that this bolt is the other pivot point. By pivot I mean only a few degrees on each bolt. This bolt, just like the one diagonal to it that goes into the other rod end and mounts it to the bushing in the centerlink…..must have threads that bottom out in the rod end threads so that the bolt can lock up solid.
The thickness of the washers must be adjusted so that there is only enough slack in this stack up for the coupling to flex axially and not move up or down in the direction of the bolt.
This is a really cheap and easy modification that is very effective but the key is in the bolts and hardware and proper fitting.
Joined: November 24, 2008
Location: Des moines Iowa
|Posted: Thu Jun 09, 2016 4:37 pm Post subject: Re: Double steering damper Modification for 411 and 412
I realized reading through that it was a little vague about how long the bolts should be and where to get them.
Everyone's bolt lengths will be a little different because your angle iron brackets will be slightly different thickness, your washers will be slightly different thickness and even the forged rod ends and eye bushings are different by .005" to .015".
Just remember that for the primary damper...meaning the one that is in the original position with one end bolted to the subframe and clamping the new bracket between it and the subframe.... the subframe end gets locked down rock solid so that the new bracket and the bushing eye cannot move around.
Its opposite end....the rod end...must be able to move just a little bit but must be locked solid to the bolt so it moves a little like a control ...no slack between washers bushings and bracket.
The secondary damper...the new one...is bolted up the same way....rod end with a locked bolt but allowing a few degrees of movement and the bushing end of the damper bolted rock solid to the bracket allowing no movement.
Here is how I set and made the bolt length for the rod ends:
This is the drivers side bracket that bolts to the subframe. The damper in the picture is the original damper or primary damper. The rod end eye goes in that hoe above. The bolt and two forged washers are shown. Its 1" long bolt to start with (actually about .85" under the head).
So put a washer above and below and insert the bolt and hold this stack together tight.
Mark the bolt thread tight up against the washer all the way around with a Sharpy marker.
Where the tweezers are pointing to...one thread higher is where I will actually distort the thread with a punch. I would rather have to make a slightly thicker washer if necessary.
Lock the bolt up tight and peen the threads hard.
Like this but do this all the way around in at least three points on the same line...do not follow the thread up....work around the line.
Test fitting...I was a little sloppy and forgot to trim the bolt to length a little before I started but it is not an issue on THIS END...it will be on the centerlink mount point.
During test fitting make sure you have distorted the thread enough to torque the bolt to at least 20 ft. lbs. so you know it locks.
This is the finished assembly. Notice that Instead of two thick washers...one on top of and one below thee bracket.... used two medium thickness washers.....and a little work with the file...to make sure that when the bolt is torqued into the rod end.....this stack up has no slack between washers, bracket and rod end....but is movable with about 5-8 lbs of torque.
The same fit and measurement technique is used on the long bolt on the center link end of the assembly. I made this diagram for it because the stack up is a little different......and the measurements in mine will be different than yours.
There will only be enough room on the bolt head side of the stack up...bellow the centerlink....for ONE washer in the stack....so you have to be more exact on this end. If you have more than about 0.080" of washers between the bolt head and the centerlink....the bolt head MAY drag on the subframe. No much room either below or above this area.
As you can see....the rod ends only need to change angle by a couple of degrees. This is about double what they will ever move.
By the way...all of the brackets, assembly and bolt fitting for this modification should be done on a workbench. This assembly and even just a single damper is a finicky hassle of process to install under the car anyway.
Make sure it all fit together first. Then jack the the car up on stands with wheels off he ground and ignition unlocked so you can turn the steering gear to get the best access.
You will bolt the subframe end on first...but do not lock the subframe bolt yet. Position the rod end on the centerlink end, insert the insert your washers, use a small rod to align all the holes and the brackets...and then screw the bolt up from below.
Trust me....getting the centerlink end all aligned and then threaded ...will take 20 minutes of laying on your back. Its actually the same process for the stock single damper...so get comfortable.
Joined: July 01, 2004
Location: Ridley Park, PA
|Posted: Sat Jul 02, 2016 8:48 am Post subject: Re: Double steering damper Modification for 411 and 412
|Wow, wow, wow- thanks for this Ray- your knowledge needs to be collected into book form!
'74 412 wagon
(3) '74 412 2dr. sedan
'73 412 2dr. sedan