I have just done these, and I thought I'd write up the job just in case anyone else wants to do it. Unfortunately no pictures, I wasn't that keen on wriggling under the car with my shiny Canon...
The first symptom of failing mounts is a strange feeling of "looseness" at the front. It feels like the engine is moving around as you apply and come off the power, but it isn't really. This gradually changes into a feeling that the clutch is going, and the car becomes hard to drive smoothly. The clutch seems to come in very hard, and setting off in 1st is jerkier than it should be. Then you get a slight knock when putting the power down. Time to have a look under the car.
Put the front of the car on ramps, and wriggle underneath. The front gearbox mount is next to the air filter box, and is a cylindrical lump of metal (it has rubber inside), and the box bolts to the centre of this. The obvious sign of trouble was that the mounting was off to one side - clearly the rubber was failing and the box had shifted. A very light tweak with a pry bar, and I got metal to metal contact. The rear one is hard to see, but again, a small tweak with a bar resulted in movement.
Time to get some new ones.
Here's how to do it, and what you need. For both, you need the front of the car up in the air, either on ramps or stands. Usual caveats apply about making sure the car is secure, you'd look like a pancake if it fell on you.
Front one. This is easy. You need a 19 mm socket, a 13 mm socket and an extension bar. Undo the big 19 mm bolt in the centre. If you have a finger between the box and the mount, you will feel it dropping, then it will stop and "hang" - it won't land on your head. Remove the 19 mm bolt. The undo the 3 x 13 mm bolts holding the mount to the body. The mount will now fall out. Put the new mount in, refit the bolts, job's a good un. Really easy job a "1 spanner" rating.
Back one. This is much more fiddly, as on my V6, the exhaust was very much in the way. Might be different with other engines. You will need: a 10mm and 13mm spanners (preferably ratchet), a 24 mm spanner and a 19 mm socket. Some WD 40 as well.
- The first job is to remove the little heat shield: 2 x 10 mm nuts. Soak them in WD40 for a while first, the threads will be corroded.
- Then undo the 19mm bolt in the centre of the mount, again, the gear box will not land in you head.
- Undo the 13mm bolts holding the mount to the body. Again, with the V6, you need to do this with a ratchet spanner. You could do it with an ordinary one, but it would take a long time.
- Now you have a loose mount, and it won't come out, there is not enough clearance between the body and the gearbox bracket. Hmmm.
- Follow the gearbox bracket back to the box, and you will find 2 x 24mm bolts holding it on. Loosen the bottom one - on the V6 you can't remove it because the exhaust is in the way. You can just remove the top one (1/8 of a turn at a time), and this allows the bracket to swing out of the way. The mount falls out, and you can put the new one in. As they say, refitting is the reversal of removal. A "2 spanner" job, as it is not hard, but fiddly.
The old mounts did not look too bad - a bit softer than the new ones, but certainly not broken. However, the car is transformed, the engine feels like it is attached, and the clutch is far smoother. A recommended job to anyone with a 10 year old 156...