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cheshire911
Estoril


Joined: 10 Jun 2012
Posts: 3849



PostPosted: Tue Sep 10, 2019 3:49 pm    Post subject: Reply with quote

I saw this thread and thought - "this is going to be interesting. A DIY gearbox rebuild with different internals from a slave box?"

Mike at Sports & Classic knows these boxes well and is setup with all the tooling to do the jobs on gearboxes and diffs. I doubt anyone could DIY a proper rebuild of the box or diff as there are numerous calculations involved and specialist tools required and a heavy press (as well as specialist know-how) - though there will be an opposing view that says these are just mechanical gearboxes that any competent mechanic can rebuild - and they can with the specialist tools and experience.

It will be interesting how this finishes up - fully DIY'd or at a specialist with all the internals to rebuild using the tools for the job and the proper settings - backlash, heights etc.
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Martin996RSR
Nürburgring


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PostPosted: Tue Sep 10, 2019 4:37 pm    Post subject: Reply with quote

If any forum member can figure out how to measure and set up the required shims, it's Mistercorn.
 
  
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MisterCorn
Dijon


Joined: 08 Jan 2011
Posts: 7266
Location: Nottingham, England

2004 Porsche 996 Turbo

PostPosted: Tue Sep 10, 2019 4:46 pm    Post subject: Reply with quote

Martin996RSR wrote:
If any forum member can figure out how to measure and set up the required shims, it's Mistercorn.


I will be doing my best to get a service manual or equivalent for it, but initial searching has not been fruitful. Dammit, myself, and Infrasilver are all on the case....

Sorting the relevant tools is another issue, but by far the biggest problem at this point is getting the basic information.

MC
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 10, 2019 10:26 pm    Post subject: Reply with quote

cheshire911 wrote:
I saw this thread and thought - "this is going to be interesting. A DIY gearbox rebuild with different internals from a slave box?"

Mike at Sports & Classic knows these boxes well and is setup with all the tooling to do the jobs on gearboxes and diffs. I doubt anyone could DIY a proper rebuild of the box or diff as there are numerous calculations involved and specialist tools required and a heavy press (as well as specialist know-how) - though there will be an opposing view that says these are just mechanical gearboxes that any competent mechanic can rebuild - and they can with the specialist tools and experience.

It will be interesting how this finishes up - fully DIY'd or at a specialist with all the internals to rebuild using the tools for the job and the proper settings - backlash, heights etc.


I totally respect Mike and the work he does on our gearboxes, he's the No1 name for me in the UK when talking gearboxes and obviously he has to guarantee all his work plus he wouldn't want any come backs so has to make sure the gearboxes are 100% correct, especially in a race car.

People have rebuilt these gearboxes themselves without a lot of the specialist tools but the main tool being the press which is needed if you are replacing the spinning bits, everything else is fine tuning to a certain extent. I will plod on and see how far I get with this and keep researching to see what more we can find out?

I know people have fitted diffs etc into used gearboxes without a problem but even so I will be measuring up both the gearboxes to see what differences there actually are between the two if any at all. And in the end if it all goes wrong I can get the box rebuilt by someone else, I just enjoy trying to find out how stuff works and then also if I can fix it, the same as I do with everything. Current list of jobs for this week, Rebuild G96 gearbox, Seat Ibiza Timing chain, a washing machine repair and 944 Sunroof slipped worm gear.
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sportsandclassic
Approved Trader


Joined: 21 Apr 2008
Posts: 275
Location: Nether Alderley Cheshire


PostPosted: Wed Sep 11, 2019 5:35 am    Post subject: Reply with quote

Morning,

As you say above one of the tools you need is a very heavy duty press.

We run a 75 tonne press with all the press plates that support the gears, so you can press them on and off safely without damage.

The amount of gearboxes we get through that have come from other places especially gearbox rebuild centres that are damaged is staggering.
They cause more damage than the original fault and in the end it costs the customer more.
We must have at least 3 gearboxes a month brought into us in plastic boxes, partially stripped and the garage / specialist have come to the end of what they are prepared to do, the funny thing is most of these are customers that we have spoken to previously and given a price to do the job and for what ever reason they have not brought the box into us, sometimes it’s a financial decision other times it’s simply because we can’t do the work for 4-6 weeks so they go with the garage that has pulled the gearbox out and sent off to their “go to” gearbox specialist repairer.

We have actually financially wrote a few gearboxes off due to chipped and damaged gears, that could of been avoided if the correct press tooling had been used.
We have seen things welded to the gears and slots cut into the gear collars so they can pull the gear off the shaft, seen some things that really I do wonder what goes through people’s minds to get to that point.

There are differences in casings, machining, bearings and gears. They all have tolerances. There are also a range of shims available from 0.5mm - 1.60mm just for pinion bearing. Input shaft bearing shims from 1.2 to 2.5mm, differential shims from 1.5mm to 2.8mm. That’s just the 996/986 gearboxes. I bet we would have over 40 shims per shaft and and at least double that for the differentials.

We also custom grind shims for special applications, like gearboxes that run aftermarket differentials with billet aluminium side covers. Sometimes the diff work alone can take us anywhere from 4 - 6 hours. We have invested heavily in tooling, we also use clam shell style pullers that can pull a bearing off a differential with out damage to the bearing cage/rollers as on some applications there is no clearance behind the bearing to pull on. Although I admit this is more aftermarket applications we do still use the puller for 996 turbo gearboxes as clearance is very tight on the larger differential carrier bearing.

I can remember my very first pinion bearing replacement that I did £200 for a press tool...! I had no idea I would be using it again and again. Borrowed all the setup tooling and a friends 50 tonne press. Worked through it and sorted the gearbox out. After that I had another one and another one so we took the plunge and invested around £10k into the gearbox side of the business for tooling. A 50tonne press arrived and that served me for around 10 years, I finally bought an air assisted 75tonne press to make the job easier as pressing those gears off and back on can be hard work.

To do the job right the pinion height needs to be checked and the diff needs setting up, all clamping pre tensions need doing to input shaft bearing and pinion bearing. Differential rolling torque setting and finally backlash between crown wheel and pinion head gear. That’s just basic gearbox fundamentals.

Mike.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 17, 2019 1:59 am    Post subject: Reply with quote

Thanks for your in depth explanation Mike regarding these gearboxes, they do seem to be very fiddly in respect to setting them up. I was looking at the amount of shims that are available on PET and there are loads of them.

I haven't got my current gearbox out quite yet as I've been away for a few days but I got very close today before I stopped what I was doing.

I was just about to undo the last bolt from the bellhousing and then slide the jack under the car to take the weight when I spotted a shiny part on the gear selector bars weight, I then realised it had been rubbing on the driveshaft/CV joint for what looks like for a while.

I deduced that this was where my 3rd gear noise was coming from and I sent Mistercorn some pictures, but we both couldn't work out why other gears weren't making the same noise. I connected the gear shift cables back up to the gearbox to check how it actually shifted, it was then I realised when in third gear (and 1st and 5th) this weight is actually furthest away from the driveshaft so this couldn't be the problem noise but then I ran out of time today in the end with finding this so will have to carry on finishing getting the box out on Tuesday now.

Some pictures of what I thought was my problem, I guess the gearbox does still need stripping down after-all. Its strange that I hadn't noticed the noise from this rubbing previously though, will have to work out why that weight is so close to the driveshaft when it obviously wasn't before once I get the casing off.

You can see the clean part of the CV joint and where it has been rubbing on the shifter weight.



And it's worn into the same shape as the CV joint.


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Last edited by infrasilver on Fri Sep 20, 2019 1:41 am; edited 1 time in total
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 17, 2019 9:02 pm    Post subject: Reply with quote

Got my gearbox off today and stripped it down, it was indeed 3rd gear making the noise and I found 3 teeth missing on 3rd, two together and another on the opposite side and they were all stuck to the magnet in the base of the gearbox. I just need to weight up what path to take now.

I'm guessing a bad shift may have caused this but I don't remember a bad shift? There is no other damage or wear on any other internal parts.






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sportsandclassic
Approved Trader


Joined: 21 Apr 2008
Posts: 275
Location: Nether Alderley Cheshire


PostPosted: Thu Sep 19, 2019 7:30 am    Post subject: Reply with quote

Has that gearbox been apart before ?
The reason I ask this is that normally when the teeth break off like that is because they have been chipped previously when the gear has been pulled.

Take a picture of the shift arrestor detent please. (The pin that is held in with a spring and a M18 threaded plug with 8mm Hex drive. If you can measure the roller in the end of that...

Mike
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Sep 19, 2019 9:57 pm    Post subject: Reply with quote

sportsandclassic wrote:
Has that gearbox been apart before ?
The reason I ask this is that normally when the teeth break off like that is because they have been chipped previously when the gear has been pulled.

Take a picture of the shift arrestor detent please. (The pin that is held in with a spring and a M18 threaded plug with 8mm Hex drive. If you can measure the roller in the end of that...

Mike


Yes Mike, both have been rebuilt, my spare box had Input shaft, new 2nd gear and the major bearing, the other box that was in the car was reconditioned but I don't have any info of what was replaced, although looking at that input shaft it also looks quite new.

It also makes perfect sense that a gears teeth could be weakened by the amount of force applied to it, I did check the teeth today that had broken off but there were no chips noticeable on them. It has done quite a few thousand miles with this gearbox attached.

I have measured the roller as you suggested, I see what you are saying with this, if it is worn it may lay the shifter bar over more. I will wait for your reply in relation to whether it is worn or not from the diameter (picture below) but I also have a feeling it may have been bent somehow the last time it was remove/installed?




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infrasilver
Fast & Furious
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Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Sep 19, 2019 10:32 pm    Post subject: Reply with quote

While I was at it I also inspected the flywheel, I found the spec for this DMF and it should only rotate 2 teeth of the starter ring or 6 degrees, it was easier to mark the middle position on the teeth and move the flywheel in either direction.

The DMF manufacturer part number is 415 0102 10



It's moving around 3 teeth so is out of range and will require a new one.





I also checked the RMS and IMS seals but these are fine so I won't be disturbing them.


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Last edited by infrasilver on Fri Sep 20, 2019 1:45 am; edited 2 times in total
 
  
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Marky911
Magny-Cours


Joined: 04 Jun 2009
Posts: 2640



PostPosted: Thu Sep 19, 2019 10:36 pm    Post subject: Reply with quote

Nothing remotely useful to add, but great work. thumbsup
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Mon Sep 23, 2019 8:33 pm    Post subject: Reply with quote

I've been busy over the weekend and at the end of last week trying to see if I could get my 3rd gear swapped to my current Pinion shaft at very short notice but this wasn't going to happen, some people could get a 2 day turnaround but after speaking with them they didn't have the really heavy press to actually do the job. The reason I was looking to swap the gear over was that when I had a closer look at the spare pinion end I saw a little pitting and thought it may damage the crown wheel over time but I decided I would fit it anyway just so that I had a 3rd gear for my upcoming road trip.

When I got back to the garage I tried to fit the spare gear set to my current box but when trying to fit the bearing it was sitting proud of the casing and on further investigation the two pinion bearings are actually different in design. My current one has a recess in it and sits further into the diff housing, the spare pinion is just a regular faced bearing so sat proud of the housing.

There is around a 2mm difference in depth for the bearing although I'm sure I've only ever seen one part number for this bearing. Also I'm sure this spare box came from another 996 Targa of a similar year to mine?

Hopefully some picture can explain this better than me.









And the shims from each pinion bearing.



The recessed bearing housing.



How I pulled the bearing in, slowly with half turns on each bolt in turn, pulled in quite nicely in the end, it just took a little time.


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Last edited by infrasilver on Mon Sep 23, 2019 9:08 pm; edited 1 time in total
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8474
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Mon Sep 23, 2019 9:04 pm    Post subject: Reply with quote

I have now made the decision to put my original internals back into my original casings as I have run out of time to get the car fixed for this coming weekend. I'll just have to go back to missing out 3rd gear for a couple of thousand miles. frustrated

I have refitted the gears and selector shafts but I'm currently having trouble getting the casing to seat fully with the bellhousing part. The selector shafts seemed to have all lined up and both the rear bearings but I'm struggling to get the selector pivot arm wheel on the middle selector shaft, they seem to be getting in the way of each other. I only tried for around 40 minutes today so will have another go at it tomorrow, there must be a sequence or knack of getting it all lined up for it fit? I've not read of anyone having problem with this as long as they have lined up all the selector shafts? Question

I've had all on getting the middle selector shaft to line up while fitting the casing.



As close as I got today.


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FRP
Albert Park


Joined: 30 Apr 2014
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Location: Middlesex


PostPosted: Tue Sep 24, 2019 5:49 am    Post subject: Reply with quote

Goodlick Chris....we know you will get there in the end !
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
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Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 24, 2019 9:13 pm    Post subject: Reply with quote

FRP wrote:
Goodlick Chris....we know you will get there in the end !


Eventually yes but back to square one at the moment although it has been a good learning curve.

I watched MC's gearbox video last night and noticed his Pinion bearing also has the recess and his is a 3.4 gearbox but again I only have seen one part number for this bearing? I'm just wondering the origin of my gearbox?

I spent another 3 hours today trying to get the nose seated over the gears, there are 8 elements to line up , 5 selector rods, 2 bearings and one selector roller wheel and all are unseen once you get the majority of the nose over the gears. The main issue is the main gear selector in the centre, it moves about somewhat when dropping the nose over.

I used a couple of screwdrivers to line it up again and also some cable ties in various ways but when I did get it to go over the 5 selector rods the roller wheel that moves the first selector shaft fell off, this happened several times and I had to remove the nose each time, when I managed to get the wheel to stay on I seated the two faces and found the gear selector didn't work, it was stuck solid, so off it came again, this also happened a few times, I lost count of how many times I had to remove it.

This is the offending roller, I held it in place with engine rebuild lube as this is quite sticky but even then it fell off a few times.



I did eventually get the casings seated and sealed (used Loctite 5900) but this was a ridiculous amount of time just to put something back that takes 3 seconds to remove, if you don't count the undoing of the bolts. Hopefully it won't take so long next time.

So the gearbox will be back to it old self when its fitted, with a noisy 3rd gear and I will have to revisit all this again when I get more time.
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 17065
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue Sep 24, 2019 9:42 pm    Post subject: Reply with quote

Not back at square one - you removed the 3 broken teeth which had a very good chance of munching the whole box and your diff. too.

Dodged quite a bullet there Chris Thumb

Good luck in getting it sorted.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
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Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 24, 2019 9:53 pm    Post subject: Reply with quote

Alex wrote:
Not back at square one - you removed the 3 broken teeth which had a very good chance of munching the whole box and your diff. too.

Dodged quite a bullet there Chris Thumb

Good luck in getting it sorted.


At the base of the gearbox there is a huge magnet, all 3 were firmly stuck to that and there was no chance of them coming loose but it should go quicker now its lighter?
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Alex
Le Mans
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2000 Porsche 996 Carrera 4

PostPosted: Tue Sep 24, 2019 9:57 pm    Post subject: Reply with quote

I'd just be wary of it shearing more off. When my diff. sun gears lost a few teeth, my wheels kept locking up. I'm surprised there's no other symptoms than a chatter in 3rd.
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infrasilver
Fast & Furious
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Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Sep 24, 2019 10:17 pm    Post subject: Reply with quote

Alex wrote:
I'd just be wary of it shearing more off. When my diff. sun gears lost a few teeth, my wheels kept locking up. I'm surprised there's no other symptoms than a chatter in 3rd.


That's all, at the moment... the the pinion into your diff has larger teeth so would be an issue and I guess the pinion teeth would just pass the missing ones and not mesh correctly when it came across the next available teeth making the car lock up.

I'm just missing 3rd out (going 2nd to 4th) which is a pain but my only option at the moment with the limited time I had/have. I was doing the same in Spain too but should have gotten around to fixing it much sooner than I did.
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