Quote:
Originally Posted by Bonefishblues
I can't recall many (any?) examples of 'boxes being killed this way. Can you cite some - it would add weight to your point? Note we're not discussing say 200+K cars, where my advice would be (has been) to do nothing, and run until it fails.
I had no qualms about performing a full change last month, on the direct advice of Graham at Horton Cars (126K miles, 6-speed, Q8 ATF, good for 3309 & 3324 specs)
|
I had my own ZF 4HP22 that turned previously smooth changes into either horrendously slurred or very harsh and violent changes after doing a flushing change. Also how many people do you honestly think would admit to the fact their box has died because the method they used to change the fluid was too harsh?
Many wouldn't even know because the advice from manufacturers (who have a vested interest in your old box failing) and the likes of Haynes who produce workshop manuals -
often based on manufacturers advice - says to do a flushing change.
Most people would put it down to the box being old and often already having problems before the fluid change. Doing a sympathetic series of part-changes gives the box time to recover before getting the full motherload of new fluid.
On a higher mileage car this is the only way to do it. My current 760 with 215k when i bought it had slurred changes and generally sluggish performance. After a series of 4 part-changes it was much smoother, livelier and a later part-change about 8 months later saw it back to very rude health, changing imperceptibly no matter the load/speed/throttle opening.
Now with nearly 230k on the clock it's still just as good but due another part-change in the near future, as is my other beast but that only has 114k on the clock.
It's not just ATF and auto boxes that benefit from having fluid sympathetically changed.
Many moons ago when i was the maintenance dept in a factory producing medical equipment with all plastic parts injection moulded in-house, the largest of the injection mould machines started overheating regularly. My first instinct was the hydraulic oil but because the management were loathe to spend the money on having new oil in it (in fairness it took about 500L) and the old oil pumped out, i had to go through the motions of refurbing the heat exchangers on it over a series of weekends, going through all the other cooling options, fitting fans to the oil cooler etc etc.
Eventually when it was still overheating, they agreed to change the oil. Luckily for me, they scheduled it while i was on a very rare week off so although i didn't get to witness the truck pumping out the old oil or the labour of adding 500L by hand from 25L drums, a few days into my holiday i got a phone call - could i please come back in and fix the machine? Turned out it had blown several seals due to the old oil being so thin and losing its additives that kept the seals moist and supple. Instead of 1200T clamping pressure, it would barely manage 120kg!
New seals fitted, circulated the oil round the machine for the rest of the day just gently moving everything and no more problems.
Next machine that started overheating, they wanted to do another "all-in-one-go" oil change. Luckily this one was only about 100L capcity so i convinced them to invest in 2 more drums than they thought they needed and one weekend emptied the first 50L of old oil. Ran it up and cycled it through to get the seals moistened again before monday and being hammered into non-stop production.
Following weekend similar but i completely emptied it (bear in mind it had run a week at full bore without overheating but with the new fluid reviving the seals as it went) and refilled with fresh fluid. Ran it up and got it all bled through, new filter and cleaned the oil cooler out.
No problems at all with that until the gearbox wore out - at the time the machine was 30 years old and it was a sacrificial brass gear inside a gearbox with mainly steel gears - got a new gear made and fitted, all good.
I've also known steering racks pop a seal after a flushing change on the PAS fluid (usually ATF) so these days i use the "turkey baster technique" to do several part-changes a week or so apart then one a year to keep it fresh.
Using a large syringe (~200ml) or a turkey baster (hence the name but syringes work better) empty out the PAS fluid reservoir. Discharge into an empty white plastic pot (Pot Noodle containers are great for this) then refill with fresh fluid. Start engine and turn several times lock to lock to bleed the PAS, check/top-up the level and repeat weekly until the discharged fluid remains clean - usually 3-4 part-changes worth. The white pot shows all the dirt as it settles on the bottom, the true colour of the fluid as it is shaded but has enough reflected light inside to see and is a good way to assess the condition/colour of the fluid.
These are just a few examples, not just of auto boxes but other items that rely on hydraulic presure - the most recent one i've had was while renewing the (long overdue) brake fluid on my other beast, the master cylinder seals popped.
Half expected because it was so overdue and luckily i had a spare M/Cyl so not a great problem but needs rebleeding again due to me forgetting one small but important part of the bleed procedure on the second bleed (needed a second bleed because the M/Cyl went) that left some air in the front calipers.
I'll do that when i renew the rear pads sometime soon after they land with me.
That aside, any car with approaching 100k miles or over, a series of part-changes on the box is always the safer option. Cheaper and easier than changing the box, not to mention the inconvenience of being without a car while waiting for another box to come available!