TheSamba.com :: View topic - Type 3 Swing axle to IRS conversion. (Plus Kafer bars)

Wed May 08, 2013 6:10 pm

Hello all, here's a rundown on my experience doing an IRS conversion on my 66 TS Fastback. (Australian built). It's an ongoing project of mine. Basically I'm focusing on rejuvenating and upgrading my chassis as much as possible for a healthy 1916cc street motor.
So I decided to do an IRS conversion on my Fastback. Many people have many different ideas on why or why not to do this but let’s just say I prefer it to swing axle and leave that kind of discussion for other threads.
Because it's a removable rear sub-frame with frame horns much like a beetle I figured I'd hang onto those framehorns and construct the IRS trailing link pivots rather than try to install the late model IRS beam (without frame horns) and try to weld the rear engine mounts on the inner rear guards like the later model type 3's. People say those later ones are prone to cracking and warping at the rear engine mounts once you start increasing the power. To be honest, I can't confirm from personal experience. I just went with what a few experts with experience had told me and that was to make the swing axle rear sub-frame into an IRS and keeping the framehorns as the way of supporting the motor and gearbox.
As a final supporting brace I added the Kafer bar truss (torque tubes as some people call them) to help stop the frame horn tips from flexing under hard acceleration. Instead of doing this you might consider a Berg rear engine support or even installing the rear engine mounts from a late model in addition to the frame-horn IRS mod but I tend to always pick the hardest route.

So I started with the Swing axle, (see chassis below, a lot has changed since this pic though). Got lucky and found a spare rear sub-frame from a Squareback very cheap. So I'm doing the work to that then swapping out my original one later. Keeping the original in the back shed for historic preservation. I believe the one I’m working on was from a wrecked squareback because it has some reinforcing underneath the torsion housing tube done from factory and the torsion bars are slightly thicker in diameter. (bonus). You will see it further down in the work thread.

Next, I bought a donor IRS rear end from a later model wreck. This will give me all the necessary hardware. I also bought some aftermarket pivot boxes but decided I would cut the originals off the donor susp' because I preferred the angle they met the torsion housing tube at. It meant that less metal would be cut off the frame horn using original pivot boxes and so I felt more comfortable because it looks more like a VW original design like you would find on an IRS Beetle. I will warn you though, cutting the pivot boxes and grinding them is no fun. I could not work out an easy way to do it. It's just hours of work with a grinder.

See here: Cut out the boxes with excess metal.

Now somehow hold the pivot box and grind off the excess tube section from BEHIND the tube section being sure to only grind the tube off and leave all the original pivot box metal intact so that it will fit snugly against the new torsion bar housing with no-gap to fill with weld. (I held the pivot boxes on a bench vice using the IRS jig)
Grind, grind, grind, repeat for hours ….. (Note: I did not use the die grinder in the background for the bulk grinding. I used an angle grinder. The die grinder was merely used to chamfer the edges in tight areas to accept the weld better.

The IRS jig test fit:
This custom pivot jig works: (Custom made, hired from a vw shop (in Sydney Aus) who know their stuff). I was going to make one till I found out it could be hired. It’s solid as

(Note, if you're borrowing a set, bolt them up to your donor rear susp' just to check everything's in alignment and the pivot boxes are on the money before you cut them out. Also write on the pivot boxes left/top, right/top. Will help later when you forget.)

This JIG does not work for type 3: It is an off-the-shelf item made for Beetles. The difference is clearly obvious. It hits the shock tower and is prevented from finding the correct position.

Now for some notching.

THIS PART IS IN CAPS (NOT BECAUSE I AM SHOUTING BUT) BECAUSE IT IS IMPORTANT. GET EVERYTHING UP OFF THE GROUND BEFORE YOU START CUTTING. YOU NEED TO BE WORKING AT A COMFORTABLE HEIGHT SO THAT YOU CAN GET A LOOK FROM ALL ANGLES when the pivot box is touching the frame horn.
Measure about 100mm, (verify all my measurements yourself please.) cut the inner join off back to the torsion tube up to the front of where the pivot box.
Check the pics. The notched-out hole in the side of the frame horn for original pivot boxes will be a lot smaller than if you were installing aftermarket pivot boxes. You need to cut a bit then test fit the jig with the pivot box bolted in. Leave the pivot bolt just a bit loose so the pivot box can rotate into the natural position when it hits the tube.
Important: USE A RECIPROCATING AIR SAW OR SIMILAR TO DO THE DETAILED CUT. NOTHING ELSE WORKED FOR ME.

Estimate where you need to cut then make a smaller hole than that estimation. The closer you get to a perfect fit the smaller your cuts need to be. When you get real close use a sanding disk on a grinder to give you the ability to trim a very small amount at a time. Remember, welding big gaps is not ideal. 1-2mm gaps are ok for tig welding but more than that is not ideal because bigger welds require more heat and that can lead to cracking at a later time.

TIP: Put a few washers on the outside bolts where you will attach the jigs to the torsion housing. You will be inserting these bolts and removing them a lot over the course of this exercise so lube them up and make life easier.

Once the first side is perfect, (expect anywhere from 1 to three hours work) ensure that it fits neatly without any forcing any of the bolts holding the jig in position. You can opt to tap the metal surrounding the hole in the framehorn with a hammer to push it inward if you are close and could not be bothered cutting it to perfection but I opted to sand the metal down till it was near perfect.

Note: The area on the top frame horn metal near the pivot bolt exposes the pivot bolt a little and needs to be raised so that you don't inadvertently weld the pivot bolt in the process. A little massage with some pliers and a hammer. Note: The top of the frame horn is thinner metal to the bottom half of the frame horn. I'm guessing that's because the top is in tension with the weight of the motor so it doesn't need to be as heavy gauge.

To do the second side we take a template from the first side and spray the outline with any old paint to get the shape. Don’t assume the hole is going to be exactly the same size. Cut it a tad smaller then do same as the other side. Cut and test fit till you get it perfect.
Here’s some pics. Metric rule used but only as a rough guide. Confirm your own measurements please.

Final pic is where I bolted pivot boxes on and it’s ready for welding.

KAFER bar construction:

At this point I’m going to construct a Kafer bar support truss to stabilize the frame horn tips. I figure that since I’m going to get the pivot boxes professionally welded I might as well get the Kafer bar setup tack welded myself now with the MIG and then give it to the professional TIG welder as a complete job.
First I sourced 1.5” chromoly tubing for the cross bar and 1” Chromoly for the diagonals. Also 4 clevis joints for the 1 “ tube. The rear diagonals will be removable. The rest will be welded.
Source a Heavy Duty rear trans mount to weld the tabs for the clevis joints. I chose an Empi one but will be welding it the entire way round
Bolt the engine up to the trans (My old engine finally comes in handy for something.) This will give you ability to see where the Heater boxes and the starter motor are positioned so you can miss them. This is also the reason why I opted to make my own. I want to retain heating and I was unsure if the ready-made kafer bar setups would work. It’s also a lot cheaper to make since I’m already paying a professional welder to do the work on the pivot boxes.
Weld in the cross bar. I chose to sit it on the shoulder of the shock tower. Much like the pivot boxes you need to be obsessive about maintaining little to no gap when cutting the Kafer bar tubes.

Final note. The front diagonals are not tacked in position yet. Deliberately left them loose for the welder to weld the pivot boxes first. Since the welder is a custom racecar frame builder he also recommended that we weld a plate next to the pivot box where the diagonal connects to the top of the frame horn. I beleive they call this a 'foot' for the tube. The metal on the top of the frame horn is relatively thin so it will spread the loadand tension of the Kafer bar diagonal brace.

The Subframe is currently at the welder. I will edit with finished pics very soon. (just got the call that it's ready so should have a few pics up tomorrow.)
Cheers.

Wed May 08, 2013 7:56 pm

Nice work! That setup will hold up to a lot more than a 1915 :evil:

Wed May 08, 2013 10:33 pm

Really nice work there!

Thu May 09, 2013 1:33 am

Thanks for this detailed write up! I am going to do the same for my 1966 Fasty. I already prepared the pivot boxes (from an IRS Beelte - they are exactly the same). I was struggling a bit with the jigs, but the design you used looks good to me, I will "copy" those. I have 2 IRS subframes lying around, so I can check the jig geometry before I start working on my "Ex"-Swingaxle subframe.
Keep posting your progress!

Thu May 09, 2013 7:21 pm

Thanks for the replies. Will keep you posted. Picking it up from the frame builder/welder today so will have picks soon.

A worthy note; even with all this preparation he worked another 5 hours on it with welding, dismantling, assembly and minor fabricating. I am very excited to pick it up now. I believe that I still saved a significant amount by doing the prep work myself (probably about $800 - $1000) even though there is 5hrs of professionally charged work in it. There is no point adding the hourly rate of the work I was charged because it is different rates all over the world but by comparison the framebuilder's welding charge was about 20% more than an average welding contractor. In the whole scheme of this project I find that was money well spent because he was absolutely in tune with how important the geometry and strength of those pivot boxes are to my car.
In all honesty I also think that framebuilder's are happy to have you do the hard 'grunt' work as I call it in preparing the parts and trial-fitting the parts so long as you don't take the 'near-enough is good-enough' attitude and hack it all together then expect them to work miracles.

Yeti69 wrote: Thanks for this detailed write up! I am going to do the same for my 1966 Fasty. I already prepared the pivot boxes (from an IRS Beelte - they are exactly the same). I was struggling a bit with the jigs, but the design you used looks good to me, I will "copy" those. I have 2 IRS subframes lying around, so I can check the jig geometry before I start working on my "Ex"-Swingaxle subframe.
Keep posting your progress!

Yeti69 I believe it is the best design both for type 3 and beetles. Make sure you use very thick metal plates. At least 10mm. When you tighten up the 4 outside bolts the plate (if too thin) can easily distort leading you to believe the pivot box is sitting in the right position when infact it may have been snagged on a piece of metal and caused the whole jig to deflect when you tighten the bolts up. You can see the difference in thickness between the custom jigs and the ready-made jigs. I believe that the lighter weight they are then the more careful you need to be that it is not deflecting. To be safe, the outside plate should find its home flatly against the outside of the torsion housing without even tightening the bolts. I will also say again, you need to leave the pivot bolt just a little loose so that the pivot box can move freely enough to find it's natural angle on the torsion tube housing.

Thu May 09, 2013 8:14 pm

Excellent write-up/diy! I'm going the other route by welding some Berin(?) chromoly frame horns onto a IRS subframe, but I'm planning do up kafer braces just like you did. Spare time has been eluding me :(

Thu May 09, 2013 10:06 pm

Thanks supaninja,

supaninja wrote: Excellent write-up/diy! I'm going the other route by welding some Berin(?) chromoly frame horns onto a IRS subframe, but I'm planning do up kafer braces just like you did. Spare time has been eluding me :(

I'm sure those frame horns will be a solid solution.

The Kafer bars I made are really quite light weight due to the 4130 tubing. Around 3kg of tube and connectors. Hopefully not too light but the frame-builder who sold me the bar stock and the one I'm using for the welding didn't see any immediate problem with it. Also I think the distance between the top of the shock tower and the intersection of the diagonals at the top cross-bar will give the whole setup a small degree of downward flex. This distance was necessary to get the clearance for the heater boxes but I think it may also add a small degree of flex which might be a good thing overall.

I actually still wanted a small degree of flex in the whole setup. Just my personal opinion/hypothesis. I think there can be a point where it gets a little too stiff for a street car. I learnt this with my experience in cycling and owning many different bike frames. My favourite bikes are the chromoly ones that absorb the road vibrations better instead of the large diameter alloy tube bikes which typically have less flex, stiffer larger diameter tubing and a more bone-jarring ride.

Thu May 09, 2013 11:21 pm

I just put a honda motor in my bus and had to build a engine cradle to hang the motor. I used 3/4" 4130 tubing and it is really quite strong and light. I think you'll be fine.

Fri May 10, 2013 2:12 am

Update.
Picked up the rear sub-frame from the welder. See pics below.

5.5 hrs worth of welding and fabrication in addition to all the prep work I did. It's really a far better welding job than I could have done.
I am very pleased with the results. The reinforcing plates next to the pivot boxes where the diagonal meets the frame horn were an addition.
So was the additional welding of the Empi HD rear trans mount. Although it's heavier guage steel it was a little light on welds we thought.

Here's the pics. The Mohr mid mount is just placed under the frame in pics below. They don't require any welding. Was going to use a Berg mid mount but to be honest I like the simplicity of the Mohr style one.

Fri May 10, 2013 5:21 am

fucking ace! well done my man 8)

Fri May 10, 2013 8:22 pm

Thanks Vlad. I'm very excited to get to this milestone.
There's a dirty ol' chassis in my garage waiting for a lick of paint now.

Sat May 11, 2013 5:54 am

Update.

I panicked a little tonight second guessing my measurements so I had to test fit it under the car to ease my mind.

Notice in the last pic - the right side front diagonal bar touches the small cylindrical electrical component next to the right side hot air flange.

Can anyone tell me what that component does? I can't remember how that was wired and couldn't find a reference pic in the manual. Just looks like a junction to me but I don't know. Power to the starter motor perhaps? I'm just guessing. Whatever it is I can only make out the marking 6V and SS-610.

Looked like it was screwed in an arbitrary spot with sheet metal screws so should be no trouble relocating it. Anyhow removed it and everything fit like a glove.

My heart stopped for a few minutes there cause I couldn't work out why the subframe bolt holes weren't lining up properly with the body mounts.
It's all good now. Phew.

Sat May 11, 2013 6:02 am

thats a external solenoid for starter motors, since VW don't use this bin it.

problem solved. :wink:

Sat May 11, 2013 6:09 am

vlad01 wrote: thats a external solenoid for starter motors, since VW don't use this bin it.

problem solved. :wink:

Thanks mate. Had me stuffed. yup i'm converting to 12 volt anyway with a new 12v starter motor and a single wire 60amp alternator so there's gonna be a little non standard wiring to get sorted at some point.

Sun May 12, 2013 6:58 pm

So I was browsing the forum and found this thread.
Is that gadget I removed for clearance a Hot Start solenoid as detailed in this thread?
http://www.thesamba.com/vw/forum/viewtopic.php?t=555140
If so, would it be fair to say that it has a reasonable purpose and I should look at installing a new one later on when I do the engine bay wiring?
I don't want to introduce phantom problems like that guy had when his car was periodically hard to start.

Sun May 12, 2013 8:36 pm

Guys call them hot start solenoids. VW cut a huge corner by not using a starter relay IMHO. Without the relay ALL of the current needed for the solenoid to engage the starter goes through the ignition switch, which will shorten the life of the switch. That being said I have yet to get motivated to install a starter relay on either of my VW's :oops:

When you do it use a relay rated for at least 40 amps.

Sun May 12, 2013 10:42 pm

supaninja wrote: Guys call them hot start solenoids. VW cut a huge corner by not using a starter relay IMHO. Without the relay ALL of the current needed for the solenoid to engage the starter goes through the ignition switch, which will shorten the life of the switch. That being said I have yet to get motivated to install a starter relay on either of my VW's :oops:

When you do it use a relay rated for at least 40 amps.

Thanks for the advice. Will be sure to do that when the time comes.

Mon May 13, 2013 4:34 am

supaninja wrote: Guys call them hot start solenoids. VW cut a huge corner by not using a starter relay IMHO. Without the relay ALL of the current needed for the solenoid to engage the starter goes through the ignition switch, which will shorten the life of the switch.

If this is such a bad idea (not using a relay), how did GM get away without using one? I work on a lot of different GM's, and none of them have a starter relay. Is it because their switch is more heavy duty?

Mon May 13, 2013 4:49 am

Bobnotch wrote: supaninja wrote: Guys call them hot start solenoids. VW cut a huge corner by not using a starter relay IMHO. Without the relay ALL of the current needed for the solenoid to engage the starter goes through the ignition switch, which will shorten the life of the switch.

If this is such a bad idea (not using a relay), how did GM get away without using one? I work on a lot of different GM's, and none of them have a starter relay. Is it because their switch is more heavy duty?

probably?

on a side note all my GMs have starter relays but then again aussies did things differently as always.

I recommend using a relay, then the type 3 switches will last a lot longer.

Mon May 13, 2013 6:28 am

GM's probably have way shorter wires from battery to switch to starter solenoid compared to a VW :D