Running in a rebuilt gearbox. Is it necessary?

[Salvi139]

Hi all, just had my manual gearbox on my Clio 197 fully rebuilt a couple of weeks ago, and the garage informed me that it needs to be run in: driving gently for approximately 1000 miles. I know that engines need to be run in after a rebuild, but I haven't seen much about gearboxes being run in. Has anyone had any experience with this? I mostly use the car on the weekend, so it's going to take a long time to get up to 1000 miles. I want to know if other people also run in their gearboxes after they've had a rebuild or had a new gearbox put in. Thanks

[GreenV8S]

Yes, that's normal in my experience. I'm sure you can get away without it (how many cars off the production line go through a 'running in' process?) but the people who've rebuilt gearboxes for me in the past have recommended a short running-in period and I can see how it would help the various bearing and meshing surfaces to go through a gentle polishing before you give it the gyp.

[Salvi139]

Thanks, that makes sense. I haven't driven it so far anyway. I may just drive it like a learner for about 500 miles before starting to use it normally

[GreenV8S]

Salvi139 said:

I may just drive it like a learner for about 500 miles

I treat it as a gradual process where I gradually work up to normal driving, rather than something you have to maintain until you've reached the milestone.

[Salvi139]

GreenV8S said:

Salvi139 said:

I may just drive it like a learner for about 500 miles

I treat it as a gradual process where I gradually work up to normal driving, rather than something you have to maintain until you've reached the milestone.

Oh ok, that makes more sense actually. Cheers

[rambo19]

I would also change the oil after 500 miles.

[stevieturbo]

I can see little reason doing that would be needed. There isn't really much in a gearbox that needs run in as such.

What exactly was this rebuild and what did they change or replace ?

[littleredrooster]

As a time-served Millwright, I replaced bearings in various bits of machinery as a matter of course for some years (before moving into management) and can attest that there is usually no option to run anything in.

Buggered bearing - strip down - replace bearing - rebuild - press 'Start' button - go to max design load in probably 0.2 seconds. And the majority weren't in an oil bath, either!

Don't worry about it - if it helps your conscience, keep your foot off the loud pedal for the first ten minutes.

[Salvi139]

In terms of what work went into it, it's a full rebuild. They stripped and rebuilt the existing gearbox, some of the synchros were apparently gone. It's a common issue with this age of RenaultSport. So some of you think that it doesn't need running in? Some people told me the seals and gaskets and other internals need time to properly settle in, like they do for a new engine. But because I haven't heard much about running in a new gearbox, I just wanted to see if other people also bother with doing it

[littleredrooster]

Salvi139 said:

In terms of what work went into it, it's a full rebuild. They stripped and rebuilt the existing gearbox, some of the synchros were apparently gone. It's a common issue with this age of RenaultSport. So some of you think that it doesn't need running in? Some people told me the seals and gaskets and other internals need time to properly settle in, like they do for a new engine. But because I haven't heard much about running in a new gearbox, I just wanted to see if other people also bother with doing it

This is just a gearbox rebuild though, isn't it? The main bits of an engine which need bedding in are the piston/bore/rings group and camshaft lobes/followers, and (to a lesser extent) plain bearings on the crank, but as there's no metal-to-metal contact with those, it actually makes little or no difference (I wrote a paper for my Eng qualifications on lubrication of hydrodynamic bearings). Seals and gaskets don't need running in, although a couple of heat cycles may help to 'settle' paper gaskets.

[Salvi139]

littleredrooster said:

This is just a gearbox rebuild though, isn't it? The main bits of an engine which need bedding in are the piston/bore/rings group and camshaft lobes/followers, and (to a lesser extent) plain bearings on the crank, but as there's no metal-to-metal contact with those, it actually makes little or no difference (I wrote a paper for my Eng qualifications on lubrication of hydrodynamic bearings). Seals and gaskets don't need running in, although a couple of heat cycles may help to 'settle' paper gaskets.

Yes, just the gearbox got rebuild. Ok, it's interesting you say that. Maybe these garages say you should be gentle for the first few miles so that you won't need to use their warranty (they've given me a 12 month warranty)

[richhead]

in the old days engines needed to be run in to help the piston rings seal properly, now days tolerances are so good that it is largely not required, as for gearboxes well there is no need, on race cars we often change gears between sessions they then get used flat out.

[Salvi139]

richhead said:

in the old days engines needed to be run in to help the piston rings seal properly, now days tolerances are so good that it is largely not required, as for gearboxes well there is no need, on race cars we often change gears between sessions they then get used flat out.

It's funny you mention that, that's exactly what I was thinking about before I posted this. Because there's no mention of racecars having their gearboxes run in. But then again, their gearboxes are designed to ensure extreme wear and tear. So on the whole, everyone seems to be of the opinion that it's not necessary to run in a gearbox