Author - Pim25
Everything below is practically identical for the x60(x61) body.
As you know, part of our cars have a dependent rear suspension, and another part has an independent one (x40 axle, x41 independent).
There are advantages and disadvantages in both types. But there always exists a certain number of car owners who want to change the type of suspension on their car.
In this section I will try to be useful for those who have decided to replace the 'axle' with 'driveshafts' on a Mark II from series x30-40.
This is not a report - the information is presented more as recommendations for those who are firmly resolved to carry out the procedures described below, so there are no photos of the process itself. You won't find it exciting, and I did not aim for that.
It is quite possible that somewhere in my description you will notice inaccuracies or discrepancies, if not a constructive mistake altogether – please do not hesitate to write about this in comments! The more sensible remarks - the greater benefit for future users, I believe.
Before starting the work, read the process description thoroughly - assess your skills and resources, as well as the availability of necessary equipment.
The changes you make to the car's structure are irreversible – they cannot be undone in reverse order.
I draw your attention that most of the work is done under the car body which must be securely fastened!
Always work with an assistant who is not under the car and can help if needed!
During the process, you will have to deal with toxic fluids whose contact with or inhalation may cause severe poisoning and even death!
Ensure fire safety during cutting, cleaning and welding of metal - keep a fire extinguisher and sand close by!
Always take breaks in the work process and ensure good ventilation of the room!
Remember that the quality of your work directly affects the safe further operation of your car!
Do not rush to complete the work by any deadline – remember that in restoration we enjoy the process, and time works for us.
Attention! During modification, the following systems of the vehicle will be affected:
— Body
— Service brake system
— Parking brake
— Transmission
— Suspension
— Exhaust system
Initial overview: we have a car with an axle (dependent suspension) that we want to change for driveshafts (independent suspension) from a donor body.
Further, for brevity, I will call our car with dependent suspension ('axle') simply '40', and the donor's body with independent ('driveshafts') just '41'. The numbers are conditional, taken for convenience.
Diagram 1. Control arms, links, and stabilizer.
(1) - transverse stabilizer
(2) - stabilizer mount bracket
Diagram 1
Diagram 2. Large and small cross-braces.
(1) – double-threaded bolt
(2) – bushing with a 'ring'
(3) – the nose of the brace with a reducer mounting
(4) - transverse bushing
(5) - small cross-brace
Diagram 2
Photo 1. Features of independent suspension.
1 - Brake line manifold
2 - End brake line mounting brackets of the body (2 pcs)
3 - Parking brake cable bracket (2 pcs)
4 - Location of embedded bolt of main transverse beam (2 pcs)
5 - Threaded anchor for mounting a locknut with "link" (2 pcs)
6 - Covers with threads for small cross member and stabilizer (2 pcs)
7 - Stabilizer bracket
Photo 1
BODY
If you look into the trunks of cars standing next to each other, one with an independent suspension system and another with a live axle setup, you can notice some differences in the upper mounting points of shock absorbers relative to the wheel arch.
Also, there's a difference in the location of the top spring mounts (this is visible when looking under the rear fenders).
Moreover, the angles at which rubber bumpers are positioned inside the springs also differ. The bumpers themselves vary as well, along with the springs and shock absorbers.
All these differences stem from variations in construction and articulation of wheels (control arms) during movement of independent suspension systems.
Therefore, replacing these three points on the body (spring mounts, shock absorber supports, and bump stops) is the first step when switching from a live axle to an independent suspension system.
However, before starting work on our vehicle, it's necessary to disconnect the battery and perform the following steps:
1) Remove the exhaust system from the catalytic converter or tail pipe to the end;
2) Unscrew and remove prop shafts with intermediate support;
3) Detach parking brake cables;
4) Drain brake fluid from the system and unscrew the rear brake hose from the live axle;
5) Remove springs with rubber mounts and shock absorbers;
6) Remove the live axle assembly along with four longitudinal control arms and Panhard rod;
7) Disconnect wiring and hoses from the fuel tank, working both underneath and through a hole in the right side of the trunk floor (screwed on). For information about number and purpose of hoses see this link.
8) Remove the fuel tank and its filler neck. Before removing the fuel tank, drain the fuel! Loosen clamps on rubber hose connecting the tank to the filler neck (under right fender skirt). Then remove the filler neck separately via the fuel cap;
9) Disassemble and disconnect the fuel pump station from pipes and hoses;
10) Remove the rear compartment behind front seats entirely, including back door panels (or fully remove rear doors), along with carpeting on the floor;
11) Remove insulation from wheel arches and rear passenger side of trunk area from inside the car.
12) Clear out the trunk completely, including carpets and trim.
Now we can proceed with replacing the mounting points mentioned above. A positive aspect is that all three locations (spring mount, shock absorber support, and bump stop) are placed on a separate element welded underneath the body (we'll call it a 'half-sphere'). There's one per side of the car; clean them up and carefully drill with 9-10 mm bit (two elements per car and donor - total four), then detach using sharp metal tools (chisel, reliable pocket knife, old chisel, etc.)
Work starts from underneath right and left fender arches precisely along weld points – approximately two dozen on each side.
On the '41' donor you can drill straight through but for car '40', try to only pierce one layer of metal - specifically on half-spheres themselves, not touching body metal.
However, these half-spheres won't come off simply after drilling.
To remove them, first drill small cut-off cones mounted at the top of each fender arch from trunk side – here shock absorber shafts are fixed. These cones are double and formed by an outer cone placed from trunk side, and inner one inserted underneath essentially part of bottom half-sphere. Inner cone should be drilled second (on '40' car drill only one layer of metal - the cone itself!).
Now we can remove two half-spheres with cones from '40', setting them aside, and two half-spheres with cones from '41', which will be used further.
So at this stage we hold in hand four (actually six) elements from '41' that need to be welded onto the '40'.
If they show signs of corrosion on inner spaces - it's time to remove them and apply zinc primer. Unlike other coatings, it won't hinder welding of components to body metal. Don't forget to remove and set aside rubber plugs from large half-spheres – we don’t need these for now.
(Some point here you may cut off mounting ears for longitudinal and transverse control arm brackets on the car)
Clean up remnants of weld points on body and surrounding metal with a wire brush.
Fit and weld six components to the body.
(I know this can encompass several days’ work in just these few words - but be persistent and patient, and it will all come together. There's no going back now.)
For welding, we use a CO2 semi-automatic. We weld only along the circular edges of the holes in the parts formed by drilling points – thus obtaining something very similar to spot welding construction.
Note the sequence of welding: the external cone towards the trunk is welded last. Correctly orient the parts! The cones inside the trunk should be tightly joined at their tips and welded together.
To facilitate work with hemispheres, you can use extraction rivets which we use for securing the part in 3-4 points after precise fitting. After tack welding the part, the rivets can be removed (drilled out), and the holes filled by welding.
I predict your questions – 'Will parts from donor car model 41 fit to body model 40?'
Fortunately, yes! We just follow the path of the manufacturer who installed a different hemisphere depending on the type of chassis when welding the body at the factory. This applies also to cones and other discussed elements.
After welding, protect it from corrosion by sealing with adhesive and applying paint.
So we've changed the configuration of the upper spring and shock absorber mount, but welding work on the body is not yet finished!
WORKING BRAKE SYSTEM
The rear brake line setup for model 41 differs from that of model 40. The differences are as follows.
The bridge for model 40 receives fluid through a single hose which then distributes it along the bridge via a steel tube attached to the frame, reaching the wheels.
With the independent suspension of model 41, things get slightly more complicated. The main line tube connects to junction piece 1 (see photo 1) mounted on the underside of the vehicle. From the junction, two separate tubes run along the underside to the right and left wheel housings where they are secured in brackets welded to the body. From there, hoses extend down to the suspension arms. Along the plane of the arm, short pipes lead up to another bracket where the transition is made to hoses – these then transport fluid directly to the calipers. All pipes and hoses for the independent suspension setup are schematically shown on a diagram by link.
First, drill out brackets 2 from the donor body (it’s okay if you drill all the way through), carefully measure their location on the donor car, and transfer this position to model 40. Clean up that area down to metal, then weld the brackets in place as needed. After that, prime and paint these parts.
Somewhere near the end of the main brake line on the underside of the vehicle, find a point with an M6 screw thread and attach junction piece 1 from model 41 using an appropriately sized bolt. If no such point is found (or if the main tube does not reach), you have two options: a) extend the main line to the junction and then use tubes from the donor car, or b) install the junction in place of the end of the main line by drilling through the underside and securing it with a bolt from inside, followed by fabrication of new tubing for the left and right brackets.
How to lengthen brake lines and fabricate new ones is described here.
If there was an 'wizard' (brake effort regulator) installed on model 40’s master cylinder, connected to the bridge – it should be removed.
The dimensions of the main brake cylinder located in the engine compartment (with its reservoir for brake fluid) need attention. It's possible that a different amount of brake fluid would be directed towards rear drum brakes compared to front disc brakes during braking (depends on structure and stroke of piston),
This inconsistency may affect braking efficiency. In such cases, it might be necessary to consider replacing the main cylinder or its piston assembly with one from model 41.
PARKING BRAKE
The parking brake cables in their sheaths are also different for independent suspension – both in design and mounting method.
Firstly, model 41 has additional brackets welded to the body that secure the cable (inside the tunnel for the driveshaft).
These brackets should be drilled out from the donor car and transferred onto model 40. Measure their position carefully before drilling them out together with the bolted-on nuts.
The installation of the parking brake cables occurs after mounting the suspension frame with arms but before installing the drive shafts.
SUSPENSION
Regarding the mounting of the suspension, there is some work to be done and elements from the donor car are needed for welding.
Model 41's rear suspension design primarily involves securing the main crossmember (6) to the vehicle body using two powerful bolts (1). These unique bolts have variable sections with different threads on their bodies – large diameter thread at the first third, smaller at the last. They screw into a hole in the frame rail from inside the car, then secure the crossmember underneath with a nut and bolt of smaller diameter. However, model 40's body has no mounting point for this complex bolt.
So we go to the model 41 vehicle and see how it is done there. By cutting out a lid approximately 12x12 cm from the interior longitudinal frame rail above where these bolts were screwed in (guided by large holes with rubber plugs on the inside), we can see that inside there’s a bracket welded with nuts for our complex bolt.
What should we do? Correct – drill out the bracket together with its attached nut, which is approximately 10x10 cm and has bent edges.
But first, accurately measure the position of the complex bolt (actually its nut) relative to reference points on the underside of the car.
Now a similar 'opening up' of the longitudinal frame rail inside our model 40 vehicle is necessary. It’s recommended to remove a slightly smaller section than on the donor car – this may come in handy or you can cut only three sides and bend open (for easier reassembly).
The bracket with its nut from the donor model 41 must be placed into the opened area.
There are two possible options: a) welding it, b) securing it with several mounting bolts, leaving room for future adjustments.
Option one requires that all other suspension parts are already assembled and attached to the body. Option two allows some maneuverability in the future.
The exact positioning and fixing of these brackets at this stage determine the wheel's position directly centered within its arch (when viewed from the side) later on. An alternative approach could be trusting our measurements relative to control points.
However, precise duplication of the bolt’s (nut's) position is impossible due to differences in frame rail shape – model 41 has a slight stamping under crossmember bushings which we don’t see on model 40.
So this decision is yours. In any case, secure the brackets by screwing in complex bolts and fitting the crossmember underneath for accurate measurement between bolts.
Later (after completing suspension work), the cut-out 'lid' from frame rail of model 41 can be welded to our model 40 vehicle with its hole above the head of the complex bolt oriented correctly.
Now about the installation of the cross member itself. After putting on rubber washers and the cross member onto bolts under the nut, plates (2) (see Diagram 2) of a special shape are placed underneath the nut and it is tightened down. These plates have a "tab" that needs to be fixed to the body with an M8 bolt. The threaded inserts 5 (see Photo 1) in the body for this purpose exist, but just fixing the tab won't work as it cannot reach its mounting point by several centimeters vertically because there is no extrusion in the longitudinal rail "40" to fit the cross member and the shape of the rail itself is slightly different – so the silent block is placed a little further from the floor. A possible solution could be lengthening (welding an insert) the tab and some modification of its bending angle. However, this work needs to be done only after the complex bolt has taken its final position.
Moving on. To the 'front end' (3) (see Diagram 2) of the cross member is mounted a reducer, and from the reducer (through a powerful transverse silent block (4)) – a small cross member (5). This, in turn, should be fixed to the body with two bolts. But there are no threaded inserts for them on the body!
Next, look at Diagram 1. The transverse stabilizer (1) is mounted to links on the control arms by its lower ends, and at the top we need to fix it to the body through brackets (2) with rubber bushings. There are also no ready-made threaded inserts for these brackets in the longitudinal rails.
OK, let's go back to the body '41' and see that the required threaded inserts for mounting the cross member and stabilizer are located on a separate body element 6 (see Photo 1), kind of "encircling" the longitudinal rail – one on each side. This part also needs to be drilled out from the donor '41' and, setting it according to measurements, welded to our body '40'.
After welding these two elements we will have threaded points for mounting the small cross member and transverse stabilizer.
Upon completion of these actions, you can proceed with installing the donor suspension. After finishing installation, the inserts of complex bolts of the main cross member (welding work is done from the passenger side) as well as adjusting the plates (2) with tabs can be finally welded.
TRANSMISSION
The drive shafts from car '40' and donor '41' may turn out to be different in length, requiring their repositioning or choosing other more suitable drive shafts.
EXHAUST SYSTEM
The exhaust tracks on these bodies are also different. The main difference is that the track passes over the bridge axle on the machine '40', whereas on body '41' – under the suspension cross member. As a result, they have different shapes.
Moreover, engine types must match as well – this determines whether the exhaust starts from the left or right side under the floor and also depends on the presence of a catalytic converter.
CONCLUSION
If after reading all of the above you haven't lost your desire to test your abilities and skill, then go ahead!
After completing all the described work, your body earns the full right to change its index from 0 to 1 :), and you become the owner of unique experience – which, however, is unlikely to be useful for you in the future :).
Good luck nonetheless!
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