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| 2 Taking car of your diff and gearbox In the road test review set out as ZTV8NOTE1 care was recommended with running in the back axle on the ZT 260 V8 models. Roger Parker has a ZT260V8 and provides his views and suggestions on taking care of your back axle and gearbox. (Aug 07) There are definitely differences between cars that go beyond components and must be from the way they are treated. As with any mechanical component a degree of considerate use and not looking to place harsh or heavy loads on components whilst they bed in is always a good policy. I took special care with my car to drive it sensibly without undue loading (not that this means the car is slow in respect to other traffic with the capabilities it has!) and also took the opportunity to have a rear axle oil change at 12 months and 12,000 miles. I use Castrol SAF-XJ 75W-140 fully synthetic oil designed for limited slip differentials and note it is a recommended MG lubricant for this application. The old oil came out 'looking' pretty coloured, but that is, I believe, the running in treatment mixing with the oil. I have also just changed the oil again at 34,000 miles which coincided with a need to change the front pinion oil seal which was weeping oil - not uncommon. Interestingly, when I first changed the oil I noted that the car would roll easier and that there was a clear but small improvement in the fuel consumption (which I monitor closely), plus a 'feeling' of the car being more responsive. As it was quiet and refined before I saw no difference in this area, but I know another ZT260V8 owner who did note a noise reduction. The original rear axle oil is not scheduled to be changed for 150,000 miles or 10 years from the MG Rover technical data, but the same axles are fitted to MG SVs and post 1994 Morgans, most TVRs, Holdens, V8 Vauxhalls and Lotus, Aston Martin and Pontiac models. The bottom line is that experience far greater than in MG circles has long dictated that a change of oil - and a change to the specially formulated Castrol oil, or one from Morris's or Redline developed also for the |
same applications - is very beneficial and on a more regular basis, such as every two years or 30,000 miles. Many titbits of information that I have gleaned show that the LSD often 'cuts up' the oil and a characteristic is that you get very light diff whine. It has also been said that the new diffs are coated at manufacture with a running in compound to aid the bedding process and whilst this is effective, then leaving this and any other deposits in the back axle oil from the bedding process for 10 years is unwise. Best to change the oil of a new diff after 5,000 miles, matching the engine oil change point for convenience. Incidentally, the gearbox oil is a scheduled change at 120,000 miles or 8 years and I would suggest it be changed much earlier, especially as the gearbox is best described as 'agricultural' and if anything needs to be carefully bedded in and treated well it is the gearbox not the diff. I have found most variation between cars to be in the gearbox, although general transmission noise and refinement varies considerably, with a noticeable poorer standard for the pre facelift cars. My car is silent and smooth and one of, if not the best, I have experienced in respect of refinement, yet others have clunks and whines. I expect that the advice from Ames back in 2004 is true and the differences I have noted reflect the different treatment the car has in its initial life. Another point on the gearbox issue is that it took a good 5,000 miles of considerate use to start to loosen up, and then as miles have been added the box has continued to improve all the way to the current 34,000 miles. I expect to change the oil soon in the gearbox (to Castrol TQ DIII) and wonder if the same advantage I found with changing to SAF-XJ in the diff will be repeated with a stepped improvement in the gearbox operation? Copyright
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I have found
this link interesting regarding differentials and the bedding in needed: http://www.diffsonline.com/techinfo/Differential%20break%20in.pdf | |