Removing the downpipe and catalytic convertor
Dropping the undershields
1 As with most jobs when working under a Discovery 3, the engine and gearbox undershields are unbolted. This gives access to the front of the downpipe.
Leak source
2 Soot on the pipe and cross-member was visible before the undershields came off. Now we see the source of the leak, on the flexible section above.
Unbolting the propshaft
3 The bolts and the washer plates holding the front propshaft to the front diff and the transfer box are removed, but the prop will stay there for now.
Transmission crossmember
4 To extract the prop, the crossmember needs to be removed. We needed heat to release the two seized nuts and bolts at each side. Bolts are left in for now.
Transfer box support
5 This single long bolt securing transfer box to its mounting bracket on the transmission crossmember is now removed, withdrawing it through its bushing.
Unclipping
6 Before the transmission crossmember can be removed, the fuel solenoid, hoses and multi-plug need to be unclipped from the rear of the crossmember.
Detaching shield
7 Attached to the front of the crossmember is this heat shield which protects the fuel filter. This is held in position by three bolts, and needs to be removed.
Supporting the weight
8 Before removing the crossmember, we fit a correctly rated transmission jack bolted to the underside of the transmission for support after the crossmember is removed.
Crossmember out
9 Once the transmission is safely supported, the four loose securing bolts are removed from the chassis mounting brackets and the crossmember pulled down and out.
Propshaft out
10 With the crossmember now removed, the front propshaft can be lowered, then pulled backwards to remove it from under the vehicle.
Nuts to release
11 With the crossmember and propshaft removed, we are able to look upwards to see the three manifold nuts (arrowed) that secure the downpipe in position.
More heat shields
12 One of the manifold nuts can be more easily accessed from the wheel arch, once these three sections of heat shield have been removed.
Spanner access
13 We can now reach the outside exhaust manifold nut, but it’s seized so we need to heat it to avoid snapping the stud and causing a bigger job.
More heat needed
14 Other nuts are reached from below. All three fixings may need warming to remove the nuts without shearing the studs. The old nuts should be discarded.
Moving down
15 Lower down the pipe, the exhaust clamp which is securing the front downpipe section to the rear pipe of the exhaust system now needs to be released.
Unhook
16 This hanger rod is unhooked out of its rubber hanger which is linked over the chassis rod. A spray with penetrating oil helps to ease the rubber off.
Pipe seizure
17 The front section of the exhaust pipe is often seized into the rear section of the pipe, in which case, cutting the pipe is often the only option.
Removing the pipe
18 With the front downpipe disconnected front and rear, it can be pulled off the manifold studs and then manoeuvred backwards to extract it from the vehicle.
Removing cut end
19 With care, and after a bit of effort and pulling, the remaining cut short section of the front exhaust pipe is worked out from the rear section of the pipe.
Minor defect
20 Apart from the failure of the woven flexible section at the front of the pipe, the remainder of the pipe and the integral catalytic convertor appear serviceable.
Thread care
21 Before installing the replacement front downpipe and catalytic convertor, the manifold stud threads are cleaned and a new exhaust manifold gasket is fitted
New nuts
22 The new downpipe is eased onto the manifold studs, taking care not to damage the threads, nor to dislodge the gasket. New nuts fitted, but not tightened.
Rebuilding
23 The rear of the front pipe (exhaust paste applied) is slid into the rear section. Now, the three manifold nuts are torqued up, and the rear pipe clamp tightened.
Clips and shields
24 The job is now a reversal of dismantling, ensuring bolts and nuts are torque-tightened. Prop, transmission crossmember and transfer box bolt are fitted before removing transmission jack.
Not pretty yet
25 Fuel solenoid, hoses and multi-plug are now clipped back onto the crossmember, the heat shield bolted back into position, and the undertrays refitted to complete the job.