G50 Transmission Repair

[MaxDiesel]

My car's had an annoying problem for a couple of years now where it intermittently jumps out of 2nd gear under engine braking - often just when you don't want it to. It's the main reason I've not done a track day yet so I've finally decided to bite the bullet and see if I can fix it......over the last two years I've tried replacing engine/transmission mounts and adjusting the gearlever but none of these have had any effect so I'm resigned to it being an internal gearbox issue - probably synchromesh related.

 

So here goes - I'm hoping this doesn't become another epic rebuild thread - more a "quick fix"

 

Last time I removed and refitted my engine I had the front wheels on the ground which meant the car was at a very steep angle - this time I decided to get the front wheels up in the air as I wanted to drop the engine & transmission in one go. In order to avoid the issues with jacking one end and then the other I made up some timber front wheel stands with integral wheel chocks - secured together with some monster timber screws. I parked the car on some bits of 6"x2" then jacked the front up and dropped it on the wheel stands, then jacked the rear all the way up in one go - the wheel stands held the front firmly in place

 

 

All ready for the drop:

 

 

 

It took ~2hrs to disconnect everything - much easier this time as I only fitted it all last year Then Tim S gave me a hand with the drop this afternoon.

 

A little while later:

 

 

It was probably the smoothest engine drop I've done - I've previously just removed the engine on VWs and my 912 but it certainly seems easier to remove the whole lot in one go on a 911.

 

I made a start on stripping the transmission but ran out of time - also I'm not exactly sure what I'm doing as Bentley manual doesn't cover the G50 and I know a lot less about gearboxes than I do engines....

 

 

Has anyone on here ever rebuilt a G50 and does anyone have the Porsche workshop manual that covers the G50 ?

 

Cheers

 

Matt.

[tim s]

How did you get the gearbox on that stand after I left?

[MaxDiesel]

How did you get the gearbox on that stand after I left?

 

With difficulty..... I fitted stand adapter to gearbox, then put stand up against the wall, lifted the bellhousing end until the adapter tube just rested in the stand tube, then lifted the other end of the g'box and pushed - there was a point half way up when I thought I wasn't going to make it ! Will see how my back is in the morning

[tim s]

With difficulty..... I fitted stand adapter to gearbox, then put stand up against the wall, lifted the bellhousing end until the adapter tube just rested in the stand tube, then lifted the other end of the g'box and pushed - there was a point half way up when I thought I wasn't going to make it ! Will see how my back is in the morning

[burgundyben]

Matt - Hope the gearbox is an easy fix.

 

Your garage....I'm ashamed of the state of my garage right now, its a tip. Looks like someone lifted mine up and shook it!

[jevvy]

Cant really help much with the gearbox issue but I do have a little bit of garage envy! Also how come your engine looks cleaner coming out than mine does when being fitted?

 

I'm sure I saw some decent stuff on pelican recently about DIY G50 rebuilds but you have probably already read all that

 

Good luck wit the mish and take lots of snaps.

[MaxDiesel]

I'm sure I saw some decent stuff on pelican recently about DIY G50 rebuilds but you have probably already read all that .

 

Good luck wit the mish and take lots of snaps.

Cheers - sounds like I better have a search on Pelican.

 

(BTW the garage isn't normally this tidy - I had to have a major clear out last W/E so I could repaint the floor...)

[Tripe]

Matt, you can download the factory workshop manual from the Cannell site HERE. Hope he has the G50 supplement on there for you.

[MaxDiesel]

Matt, you can download the factory workshop manual from the Cannell site HERE. Hope he has the G50 supplement on there for you.

Thanks Jeremy - I managed to download the 964 G50 workshop manual from Cannell - it looks like the 964 box is vitually identical apart from the nose casing & mount.

 

I've made a bit more progress on the strip tonight - the main success being getting the two main shaft nuts undone - one 20mm and one 40mm. Having read a couple of Pelican threads it seems most people use an air gun to get them undone and then lock the shaft to torque them up at the end (140Nm & 250Nm !) so I'll still need to make up a locking tool. It took a little while with my air gun and the pressure wound right up to get the large nut off:

 

These are the two main nuts:

 

 

I've then removed the reverse "loose gear" plus guide sleeve and synchro assembly - the synchro plates look ok so far:

 

 

 

The pile of bits on my work bench is slowly growing:

 

 

Next job is to get a long arm puller on the fixed gears before I can remove the main gear casing from the diff housing.

Edited March 23, 2010 by MaxDiesel

[sladey]

Interesting thread

[MaxDiesel]

Made a bit more progress tonight...

 

Borrowed a hydraulic puller from work to get the fixed bearings and gears off:

 

 

 

Then removed the main gear casing:

 

 

 

I guess the good news is there weren't a load of broken bits lying in the case, all the main gears look fine with no real signs of wear to the teeth. The internal shift gate mechanism looks v. complicated - I'm hoping I don't have to distrub this

 

Definitely need to spend some more time studying the Porsche manual now so I know what I'm looking for....

 

A few more bit to clean up also:

 

[coxy]

Top work Matt, your garage is just too clean. (note: even blocks stacked tidy in the corner) Whats your background to start something like this? Keep it coming.

Edited March 24, 2010 by coxy

[REX]

+1 Other than the shed envy I love your threads Matt, keep it coming.

[coxy]

 

Ps. How many chinese takeaways do you get through per rebuild?

[MaxDiesel]

Ps. How many chinese takeaways do you get through per rebuild?

Lots ! I find you need to have a few of the Large Special Fried Rice tubs as well as the regular size

Edited March 24, 2010 by MaxDiesel

[Andy Young]

This is superb and scary stuff. I had always thought that G50s were a back to specialist job Good luck

 

Andy

[Dr Rock]

This is superb and scary stuff. I had always thought that G50s were a back to specialist job Good luck

 

Andy

They are: unless you're MaxD

[MaxDiesel]

This is superb and scary stuff. I had always thought that G50s were a back to specialist job Good luck

 

Andy

 

Its definitely scary stuff - I'm finding this more daunting than any engine rebuild I've done... the selector mechanism looks like its been scaled up from a Swiss watch! The way it takes the input from the single shift rod and translates this into the other three shift rods is impressive.

 

I think I may yet need to get some help from a specialist who's familiar with G50 boxes...

Edited March 25, 2010 by MaxDiesel

[burgundyben]

I'm finding this more daunting than any engine rebuild I've done

 

I'm with you there, 'boxes are much more complex than engines.

[coxy]

May be of intrest Matt.

 

Not G50 though.

 

 

Edited March 25, 2010 by coxy

[MrPerkles]

Its definitely scary stuff - I'm finding this more daunting than any engine rebuild I've done... the selector mechanism looks like its been scaled up from a Swiss watch! The way it takes the input from the single shift rod and translates this into the other three shift rods is impressive.

 

I think I may yet need to get some help from a specialist who's familiar with G50 boxes...

nice job Max,give the bainbridge a call if you need help,he builds them dry to set the exact & correct tolerances required

[MaxDiesel]

Made a bit more progress on the gearbox - also had a half hour lesson on gears and synchros from one of the transmission engineers at work - I now know what detents, dogs, and engagement teeth are ! Apparently the it's the slight "negative rake" on the engagement teeth that actually hold the gears engaged under postive or negative loads.... when these wear it can cause it to jump back out of gear:

 

 

Based on what I've been told I haven't found anything wrong yet - even the synchro plates are OK. I've got a meeting up in the Midlands this week where our transmission guys are based so I'm going to throw all the bits in the Passat boot and see what they think.

 

I've now stripped the box down to the diff case, I'm not planning to disturb the diff but will probably replace the output shaft seals:

 

 

The insides of a G50:

 

 

1st/2nd and 3rd/4th gear set (5th and reverse are in the nose casing), plus selector mechanism:

 

 

I'll see what I find out this week.... in the meantime I'm getting stuck into all the other while the engine's out bits...

[Andy Young]

Superb work lots of people watching this with interest keep the pics coming. I will be fitting the new clutch kit this week so the old friction plate is waiting for your call

 

Andy

[MaxDiesel]

With a bit of help from my transmission colleagues in the Midlands it looks like we've worked out what wrong with my gearbox

 

The good news is all the really expensive bits are in good condition - selector sleeves, gears and synchro hub assemsblies.

 

The 2nd gear issue looks to be down to a combination of two things - a bent 1st/2nd gear selector shaft and worn detent grooves in the same shaft.

 

The first thing that pointed to this was the wear patterns on the 1st/2nd gear slector fork - this showed the fork was acting at an angle on the selector sleeve:

 

 

This usually means a bent fork.. we check the fork and its OK, we then checked the shaft and its bent by over 1mm:

 

 

It's bent in a way that means it pushes the selector fork further into 1st gear than it does 2nd gear - allowing it to only partially engage in 2nd when there's less load (under load the angles on the enagaement teeth pulls the teeth togther).

 

This in turn has meant the selector shaft hasn't always been in its fully enagage position... resulting in wear to the detent grooves which define the shift locations, a spring loaded pin rolls into the grooves depnding on which gear position you're in:

 

 

So a new selector shaft is required - the fork should be fine to re-use. The shaft is £90 from Porsche so not too bad - the only other bits being a £50 gasket set and some new oil.

 

Fingers crossed it'll be going back togther next week - its going to be fun heating the gears to the right temperature in the kitchen oven and then legging it back down to the garage !

[jevvy]

Nice work maytee - good luck putting it all back together.