How to flush out a 75W/90 manual gearbox

londonTiger

This thread relates to this thread but I'm creating a new topic as it's a bit of seperate topic altogether,

basically trying to change the gearbox oil from a closed box manual gearbox.

A lot of people are simply draining the box and filling it with new oil. Now I'm sure just draining and filling it will get rid of most of the crap. But having observed kitchen sinks many times I know that the heavier deposits don't actually drain away completely, they're too heavy and just sit at the bottom and don't budge. I'm qworried that if I just drain and reful, the bigger bits of metal will remain inside.

I want to flush the gearbox out. The cheapest method would be to just use a garden hose to inject water into the fill hole, and flush everything out. But that risks damaging the internal by rusting the internals and steam damage if water remains inside.

i'm thinking of using using some kid of pump that will recirculate the drained oil back in the fill hole and then back out again.. So i can get more of the big lumps of metal out.

atrixblue.-MFR-.

your not going to get all the oil out in the box unless its removed completely and rotated to allow the litre or so drain out that will be left over if it was to be done in situ.

if there lumps of metal in you have to question the state of the box in first place and its symptoms before hand and think whether a reconditioned box is needed.

i dont know whether you would gather much force to lift the chards off the bottom of the box in situ or by removal with use of a "pump".

i wouldnt put water in the box with use of pressure washer or hose pipe either iinstant disaster waiting to happen.

colino

Easiest and safest way is to do the drain/refill cycle a couple of times with a drive beforehand to heat up the transmssion oil. Don't worry, you'll spot the difference from old to new, old tranny oil stinks.
Don't remotely think of steam/pressure cleaning or anything else. You'll both damage seals and start off corrosion where it shouldn't be.

[Deleted User]

Chances are, if there are "bigger bits of metal" in it, the box is ready for junking.

rxbren

take it for a drive let the oil warm up then change it
there isnt alot you can do about the deposits any other additives you add may do more harm than good and dont put any water in there thats an expensive disaster waiting to happen
if your worried about swarf being in the box you can get a magnetised plug

Norman_Castle

I know that the heavier deposits don't actually drain away completely, they're too heavy and just sit at the bottom and don't budge. I'm qworried that if I just drain and reful, the bigger bits of metal will remain inside.

If the heavier deposits sit at the bottom and don't budge they will not affect your gearbox.

londonTiger

Norman_Castle wrote: »

If the heavier deposits sit at the bottom and don't budge they will not affect your gearbox.

well the bumps on the road will unsettle it IMO.

I'm going to run the drained oil through the system a couple of times to complete get rid of all the crap build up. Is there any way to filter the drained gearbox oil crudely? it's 75w/90

marlot

Check the drain plug - it might have a magnet to collect any swarf.

sun-n-moon

Do you need to change the gearbox oil? I thought modern cars do not need this doing. I've never changed gearbox oil in any car and never had a gearbox problem.

GolfBravo

sun-n-moon wrote: »

Do you need to change the gearbox oil? I thought modern cars do not need this doing. I've never changed gearbox oil in any car and never had a gearbox problem.

Yes. The transmission oil loses viscosity and breaks down over time, significantly decreasing the ability to prevent wear. Plus you have all those metal bits floating in your transmission doing further damage.

Definitely worth changing manual transmission oil somewhere between 75K and 100K miles.

atrixblue.-MFR-.

londonTiger wrote: »

well the bumps on the road will unsettle it IMO.

I'm going to run the drained oil through the system a couple of times to complete get rid of all the crap build up. Is there any way to filter the drained gearbox oil crudely? it's 75w/90

if theres fragments of metal more than the size of a 5p peice in there you should be very concerned indeed.

you dont even know whether there are peices in there so your speculating to say the least.

in the dense mixture of the oil fragments hardly move put a socket in a tub of oil seal the top and mimmick going over a bump by shaking it shaprly itll hardly ever move!.

gearbox oil is not like engine oil in wich its consumed as quick or thins as much due to the heat.