Pre c35 gearbox oil leak

[Gotti]

My reconditioned gearbox have a small oil leak when i drive the car for a longer run.

It looks to me the oil comes from the second screw from the top near the right outputshaft gasket,you can see the oil.Can i unscrew this bolt and reseal without having some problems?

At first i was thinking it is leaking from the outputshaft gasket itself so i used a transparent gasket maker to find out the leak.I will remove that again.

Any advice welcome......Gotti

[Gotti]

I cant wait and jacked up the car for a closer look.

Now i know the bolt goes from the gearbox to the bellhousing.It wasnt very tight.....the thread in the bellhousing is damaged.The bolt looks good.

I have read somewhere the M7 should be torqued about 27Nm.Is that correct?I get only 10Nm before this screw turns over so i cleaned everything and used blue threadlocker and gasket sealant.I hope its now solved....but i am a bit annoyed.

I have checked all the other bolts and they seems ok.And no oil leaks somewhere else.

Should i be worried about that damaged thread,as i said before all the others are fine? 

 

[lotus-62]

so what is the strenght marking? an M8 in 8.8 has 25Nm but in 4.8 its only 13Nm.  if it is wet (oil) reduce with 10%  so 27Nm seems high for a M7 or is it 10.9?

btw is the bolt going into a cast aluminium treath? and how deep? 

i

[Gotti]

2 hours ago, lotus-62 said:

so what is the strenght marking? an M8 in 8.8 has 25Nm but in 4.8 its only 13Nm.  if it is wet (oil) reduce with 10%  so 27Nm seems high for a M7 or is it 10.9?

btw is the bolt going into a cast aluminium treath? and how deep? 

i

Yes,they all going into a aluminium thread!This is what i've found on pistonheads.....

I can,t find the gearbox torque settings in the service manuals,only the settings for the bellhousing to engine block and mounting brackets,calipers......

[lotus-62]

27Nm seems a lot to me for m7 (test on the bench with a m8 in steel and see how it "feels"....) is the aluminium already damaged?  why not helicoil it,   because of the bigger tread from the helicoil (or the like) you can put more torque on it

[910Esprit]

On a C35 box that screw does nothing, so no idea why its even there....   However, I also noticed that the threaded portion in the casting goes straight through to the inside and is approx 8mm deeper than the screw, so just put a longer screw in.   As its non-functional, you could also just 'glue' the old screw back in with an anearobic sealant and forget about it.     

As I say I've just, now, looked inside a C35 box, but not aware of any differences in this area, however, happy to be corrected

I wonder why it was removed in the 1st place?  Or have I misunderstood?  is it coming from the lower level plug?   (still suspect the longer screw may work tho)

Edited May 1, 2018 by 910Esprit

[Gotti]

Thank you both!

Its not coming from the lower level plug.

There is not enough place to get this thread helicoiled,i would have to seperate the bellhousing from the gearbox,but i dont want to do that.

This leaking bolt goes from the gearbox into the bellhousing thread thats what i understand.

I used blue thread locker and sealant and screwed it back(not very tight).I didnt have time to drive the car after i have done this.I hope its now solved.

When its not solved i will try a longer bolt,good idea!

I forgot to measure the length of this m7 screw while it was out.Does anyone know the length?

Many thanks.

 

 

 

 

[Gotti]

I drove the car today and the problem is solved now.

Btw the gearbox shifts perfectly,almost as good as my 10 years old BMW 

[lotus-62]

👍

[Gotti]

Another leak found!What is this hole for?Can i seal that hole with an anearobic sealant?

[Gotti]

It seems its only a plug for the reverse selector shaft.It looks like only the pre c35 gearbox have this plug.

I resealed that area with an anearobic sealant....now it looks solved.

[DaveyT]

Hi @Gotti,

Can I ask what sealant you used? I'm wondering if a PU like tigerseal or Masterbond (screen bond) would do it..

I have exactly the same issue, and although it feels like a blind hole, there is definitely oil coming out of it somewhere since I topped up to the full 3Lt as suggested by @dsvitesse1

lost probably 100ml during a 10 min setting up session, so revs generally below 1500rpm.

TIA

Dave

 

 

[Gotti]

I used the (Dirko) black sealant from Elring.You can use every engine or gearbox sealant.It should be oil and fuel resistent and good cleaning with brake cleaner.No leaking since i have done this (1000 km)

[DaveyT]

Thanks Gotti...

did you knock the plug out and reseal, or just backfill with sealant? (If indeed it is a separate plug that fills the hole in the casting...)

[Gotti]

I didnt knock the plug out

2 hours ago, DaveyT said:

Thanks Gotti...

did you knock the plug out and reseal, or just backfill with sealant? (If indeed it is a separate plug that fills the hole in the casting...)

 

[Gotti]

Dont press sealant into the tiny hole of the plug.

2 hours ago, DaveyT said:

Thanks Gotti...

did you knock the plug out and reseal, or just backfill with sealant? (If indeed it is a separate plug that fills the hole in the casting...)

 

 

[DaveyT]

But fill the larger hole? I assume this is to stop RTV getting into the 'box?

I prodded around in that centre 'hole' with a piece of wire, but it seems to be more of a recess than a through-hole?  so I'm guessing the oil is getting out from between the sides of the plug and the casting?

the breather is clear and doing its job correctly as far as I can tell..

 

[Gotti]

2 minutes ago, DaveyT said:

But fill the larger hole? I assume this is to stop RTV getting into the 'box?

I prodded around in that centre 'hole', with a piece of wire, but it seems to be more of a recess than a through-hole?, so I'm guessing the oil is getting out from between the sides of the plug and the casting?

 

Behind this plug there is the selector shaft moving.On my gearbox oil was coming out from the centre hole and between the sides.You only have to fill up the casting where the plug is pressed in complete with sealant.

[PrecisionMike]

On 09/05/2018 at 20:07, Gotti said:

Another leak found!What is this hole for?Can i seal that hole with an anearobic sealant?

That "plug" blanks off the cross drilling that retain the spring and ball which forms the detention function in the selector mechanism. There are two, on on each side of the box. The manual talks of pricing the plugs out but not sure how you'd actually do that. My intention upon reassemble of my box is to use a medium strength bearing retainer loctite.

Picture for reference.