Even MORE gearbox trouble: any ideas please?

stuby · Post by **stuby** » Sun Apr 21, 2013 7:40 pm

My opinion (for what its worth ) is that if I'd parted with £3200 for a job that wasn't quite right when completed, I'd be pretty naffed off too and I wouldn't have settled with the specialist posting me a seal in the hope that it'd solve his problem, i.e. a rectification. My advice to you would be to pick up the phone, explain your concerns and see what he is prepared to do about it to sort it out. Why should you be 3k out of pocket for something that is not right ??

just my opinion ( to which I'm entitled)

Stu

911hillclimber · Post by **911hillclimber** » Sun Apr 21, 2013 8:14 pm

This is my feeling, and I'n racing now for the next 3 weekends, so to get the box out and shipped will be a push. I have an 11 hour day job too!

Away from my emotions on this, I hope things are sorted, but it will be another month gone before I can be sure if it all works.

To the thought I have to deal with this myself, my questions still stand.

From what I can tell nearly the whole box has to come apart to free the shaft and the first gear is matched to it.

The basic issue is the seal does not seal, but wears rapidly. The oil leaking after 50 miles is nowhere as bad as at 201miles but it was running down to the lowest point of the box ready to drip off at 50. At 201 the mess is 'wide-spread' and was getting to the new competition clutch...

The parts were leak-free before the strip down, so as a first step I'm considering to get the seal lip well away from the wear already there, where the black ring is by drifting the seal far deeper into the tube but keeping the body of the seal still in the tube land.
Easy to say...and there are already two wear marks from previous seals.

Then all the way to re-install and fingers crossed (like I was last week) that it seals.
It is a lot of work to trial and error time and again. If it leaks, then:-

The shaft is scored and I have to find a good one (with gear) or repair what I have.
I doubt that there will be a set sitting on the shelf anywhere so another box off eB@y and transfer everything over?

Surprising what a £6 seal can do. At least it is not a mag case box like in the Lola.

What I fear is to have the box apart at the specialists, find the shaft is scored and have the situation where the box is in a million pieces, needs a £1000 part and building back up, another £500 and 4 weeks at least. I end up paying all the way.

Another way is to re-grind the journal and find an 'undersized' lip seal.
Actually, that would work well, but full strip, machine shop, rebuild, bill to me.

That does appeal and is possible with a bit of research and would not weaken the shaft.

Bit more positive.

Dingbat · Post by **Dingbat** » Sun Apr 21, 2013 9:43 pm

Hi
I would be pretty miffed off if I had parted with a load off cash and seemingly got nowhere, I would suspect that the first seal was installed a little dry and burn't with the first few miles of use, as to why quite so much oil is coming out is a bit odd as the level should be below the shaft, I guess its spraying around the bell housing and dripping out when stationary, and despite your efforts without removing the black ring I suspect it grabbed up on the new seal and damaged it, I would take a careful look at the clutch assembly as with that much oil spraying around it could well be contaminated and you don't want to be putting it all back together and finding the clutch slips. As for getting the box apart its not that bad but you will have to make a tool to lock the shafts, I made mine from the centre of a clutch plate and a bit of strip metal that goes to one of the mounting stud holes, its necessary to undo the reverse gear etc from the front end of the box, with the gears removed the main body of the box comes off and your then faced with the insides and selector forks etc, this is a job for a workshop manual and a sheet of clean paper to lay all your bits on, and eventually you can pull the shaft out to polish it up, if your not changing any parts and put back what you remove it should not throw anything out,

reverse gear

innards

pinion with the input shaftabove it, the selector forks could be marked on the shafts prior to dissembly maybe a scribed line each side, if your clutch is soggy I might ask Mr man if he would cover the cost of a new one.

911hillclimber · Post by **911hillclimber** » Sun Apr 21, 2013 10:17 pm

Thank you for those details.
I have a 1/2 worn centre plate and I'm no stranger to a MIG welder, so that covers that.
The thought of getting the forks back in the right place is a bit daunting.
does the CWP need to come out?

The seal was lubricated before going together at the rebuild stage, but that black ring says it all. The lip had disappeared to a flat about 2mm wide.(comparing by eye to a new seal.)
My box is the 205th box rebuilt and it changes gear really well, such a shame I have this stupid issue.

When I split the box off after the '201 mile' point, the oil was just getting into the inside of the cover plate and flywheel.
Most of those 201 miles were above 3000 rpm.(motorway driving)

The thought of a tear-down is a bit depressing, so tempted to chance a rubbing over the journal with 800 wet or dry or rather wet with oil and put it all back again...
I would change the O ring in the guide tube and seal with 571 as an extra.

smallspeed · Post by **smallspeed** » Mon Apr 22, 2013 9:19 am

911hillclimber wrote:so tempted to chance a rubbing over the journal with 800 wet or dry or rather wet with oil and put it all back again...

800 wet and dry is far too coarse, the requirements for transmission type lip seals is normally in the +/-0.1mm diameter tolerance range, and a surface finish/roughness of 0.2-0.4Ra which is 1-2 micron scratches. This needs a very-very good ground finish or a lapped/superfinish surface, so any kind of wet and dry will not work.. it is important that the surafce finish is in the right range though, and not too smoot aswell; it will not hold oil against the seal whcih will cause it to burn out..

was there any refinishing done on the shaft at the time of rebuild? anything at all can have an effect, so if they guy wet-and-dried it, polished it, centerless ground it, etc., it could be wrong.. it should be "to spec" and in the required range of values to work correctly

a couple of avenues to check before tearing into the box..

a) is the shaft straight (ie not bent)
b) the correct size
c) the correct surface finish
d) centered in the tube which the seal fits into

..all of this (excl. the surface finish) can be done fairly easilly with a magnetic plunger type gauge and a micrometer, if everything appears to be correct then i might be able to help with surface finish measurement depending on how far away you are from w.leic

911hillclimber · Post by **911hillclimber** » Mon Apr 22, 2013 12:53 pm

That is interesting and why I stopped trying to remove the black mark (presumably from the previous seal) off the shaft journal.
When celuose thinners failed (on a Kimwipe paper) to move anything I decided to stop and try to set the position of the new seal deepr into the box to allow the new lip to run on a virgin part of the journal. Doing this is much harder than saying it.

Perhaps I should have said my approach was 800 grit rubded across each other to kill the 'high spots', but you cannot get truse radial 'scratched' on the journal surface this way due to poor access.

I was going to dull the 800 paper this way, whet the journal with oil and wrap the paper round the journal. With an old seal slide that ove the 'tube' of paper and twist as radially as I could so the compresion of the lip seal would apply an even concentric pressure. I bulked at this with the thought the paper or fragment might tear off and drop into the CWP!

This all gave rise to the question what to actually do.

The Specialist is a VERY experienced guy and his previous rebuild of my 915 boxes have been perfect.
I'm sure this shaft was spack-on as he assembled things.
Chances are the lip seal lacked lubrication on assy. I actually do not know.

I obviously need to find a solution to this silly problem the easiest way preferably not involving a full strip to re-grind the journal a 0.1mm or less to clean the surface.
I imagine any shop that grinds crankshafts can face the shaft and micro finish as you state.

As to your questions on axial alignment/concentricity:

The box was leak-free before the rebuild. This re-build about 50K miles old after a full pro rebuild at 60K miles after a driver induced failure.

The latest re-build inc all new bearing in the box and the shaft was very free of clearances when the box went in.
After 201 miles it was the same!

To set the seal such that the lip is on virgin journal is crucial, but that is hard to do with certainty, pulling the drivetrain time and again is no joke hoping that things will work for the next 50~K miles.

Lubrication of the seal in duty is dependent on the seal being drowned by splash off the CWP. The micro scratches of the surface allows a small lub of the lip contact area.
Does the surface really need concentric scratches as opposed to random 'orbital' scrathc surface?

Is an abrasive scouring pad too harsh,; this was my other method to remove the black ring on the journal.

Of course, all this may be wrong!
What if the oil is leaking from the tube/O ring seal!

When you take the box out the oil has migrated to the inside of the bell housing and it is impossible to tell exactly the source of the leak.
All I can say is the ring was present when I took the tube off after the major leak.
The oil is very searching when hot.

I appreciate you help!

Bruce M · Post by **Bruce M** » Mon Apr 22, 2013 2:18 pm

I'd echo previous statements.

The only thing I can add to this is it would be worthwhile inspecting the pilot bearing very carefully. This is a key support for the input shaft.

haasad · Post by **haasad** » Mon Apr 22, 2013 3:28 pm

Graham, obviously I don't have the detailed surface finishing experience of small speed but I have rebuilt one or two gearboxes of various types and sizes (admittedly not a 915 though) I would be perfectly happy to polish out the surface of the shaft using worn 800 or 1200 wet and dry used with wd40 or similar as long as I could get all the way round. It may be possible to make a ring shaped tool on a rod you could bond some wet and dry onto the inside diameter and run it round the shaft.

It would be nice to find the seal tube was the problem? Totally off piste but could you fit two seals one standard and back it up with a narrower one if you were really stuck. It seems a shame to strip the whole new box for what could be essentially a service item.

Just to reiterate I'm 1000% sure a phone call will get the help you need.

Can you tell I'm home sick and bored......

911hillclimber · Post by **911hillclimber** » Mon Apr 22, 2013 5:43 pm

Andy: not 1/2 as bored as I am with ALL things Porsche/911.

I think I said above or elsewhere, my plan was to 'dull' 800 grit paper against each other (or use 1200) and wrap a sleeve of it over the shaft. Whet the whole lot with oil (though WD 40 is a good/better idea) and then slide the old seal over that paper. Gently turn the seal/paper to burnish the surface clean.
I am worried the paper will rip and drop straight into the CWP!

As to two seals, the USA boys actually do this using a 'dam-seal' on the shaft dia just ahead of the lip seal (clutch side). I have tried to find details but cannot quite translate that term to English, but i think it is a thin lip seal or even a V seal.

The specialist has emailed and will have the box back and resolve the issue.

It is important this is said as some of you know the specialist and I want this to be clear.

I am racing the Lola 4 weekends in a row starting this weekend, so not sure when I can strip it all out yet again and get the box to him, a 5 hour round trip for me.

I had planned to have the 911 race-ready if the Lola breaks (I have very little confidence in it) so at least I can continue the season in the 911, back to my roots, but that reserve has now gone for a while.

That Triumph Spitfire 1500 is looking better every day I spend on Porsche things.

Barwaut · Post by **Barwaut** » Mon Apr 22, 2013 5:58 pm

Hopefully the specialist will set it right now.

911hillclimber wrote:The box was oil tight before it came apart for a slightly crunching 2nd.

But I never get it, people tinkering so much with stuff that's pretty hard to get it right ánd expensive most of the time.
It was just a naughty 2nd gear, it's a 40 year old car.
These boxes are very well engineered, you could have driven it for years without more trouble...

911hillclimber · Post by **911hillclimber** » Mon Apr 22, 2013 6:41 pm

When we stripped it down (at the specialist's shop) the wear and damage was significant.
The bearings fell out of the case (should be a shrink fit), 3 brake bands were gone, and the parts tally came to £2200

£340 to do the case that was done badly by another reputable specialist who told me to go away when the bearings would not fit in the case repair, and so on...

Beware!

haasad · Post by **haasad** » Mon Apr 22, 2013 6:48 pm

That is excellent news and frankly never in doubt. Where did you see the info about dam seals I'd be interested just for curiosity ?

brembo · Post by **brembo** » Mon Apr 22, 2013 6:53 pm

Don't think the two "specialists" you refer to should be linked in the same post. The specialist who rebuilt the box, is going to put things right, regardless of who's to blame.

Bruce M · Post by **Bruce M** » Mon Apr 22, 2013 8:13 pm

The US trick is to drill the guide tube and fit a non-contact seal. That way if the main seal leaks, the oil get caught by the dam seal and diverted out the hole, away from the clutch.

Bruce M · Post by **Bruce M** » Mon Apr 22, 2013 8:15 pm

Btw, was the case repair only to the main bearing bore or did they repair the input shaft bore too?

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