Technical Gearbox Rebuild 2nd Gear Synchro Unit

Currently reading:
Technical Gearbox Rebuild 2nd Gear Synchro Unit

Joined
Dec 27, 2014
Messages
1,133
Points
363
Location
Ripon
Greetings All, I'm having a tad of a problem with the proper assembly of the 2nd gear synchro unit:mad: Having stripped the box, cleaned, inspected and started the re-assembly I found a circlip with the synchro unit:confused: As you all can see the first pic shows said circlip in what I think is the correct position, but, now the housing where the 2nd gearshift fork fits will not move (slide) along the unit due to the circlip fouling (second Pic) the unit(n)(n) Does Anyone have a pic or assembly schematic that shows how the circlip is located please?
I have found out that the 'circlip' is in actual fact the 'Synchro Spring' but I still need to know how it fits please???????
 

Attachments

  • DSCN2604.JPG
    DSCN2604.JPG
    904 KB · Views: 171
  • DSCN2605.JPG
    DSCN2605.JPG
    965.7 KB · Views: 84
Last edited:
It's a long time since I worked on one of these gearboxes, so my memory may be suspect, but....

I think that spring goes inside the 3 metal plates that the synchro sleeve fits over, i.e. to push the 3 plates/blocks (can't remember what they're called, possibly blocker plates?) outwards. It might even be possible to wind the spring into position from it's current position and then tuck the bent end under one of the blocks?

Idk if this is any help,

Al.
 
It's a long time since I worked on one of these gearboxes, so my memory may be suspect, but....

I think that spring goes inside the 3 metal plates that the synchro sleeve fits over, i.e. to push the 3 plates/blocks (can't remember what they're called, possibly blocker plates?) outwards. It might even be possible to wind the spring into position from it's current position and then tuck the bent end under one of the blocks?

Idk if this is any help,

Al.

Al, Thank you, Thank you, It was doing me ed in:bang::bang::bang: When I next have a moment I'll do what you suggest (y) I think that this is one lesson well learnt - apart from the excuse "It came off in me hand Sgt Major" One must take more care, and it would have been a bit of a laugh (not) had I finished the rebuild and found the spring afterwards:eek::eek::eek:

Ian.
 
That is a tricky little part and from memory you need to assemble the spring so that the up stands line up with the grooves in the sliding sleeve. I assume that there is an up stand at both ends. The steel syncro sliding keys do get filled with crud on the inside and are worth cleaning out if you want everything clean inside. I have stripped a couple of boxes in the past where that spring ended up mangled in the bottom of the gearbox but if you check that the gears change OK on assembly I am sure it will be fine.
 
That is a tricky little part and from memory you need to assemble the spring so that the up stands line up with the grooves in the sliding sleeve. I assume that there is an up stand at both ends. The steel syncro sliding keys do get filled with crud on the inside and are worth cleaning out if you want everything clean inside. I have stripped a couple of boxes in the past where that spring ended up mangled in the bottom of the gearbox but if you check that the gears change OK on assembly I am sure it will be fine.

Al, Dave, Thanks for the input - appreciated. After a lengthy fiddle getting the spring into place - result(y)(y)(y) But I must say what a faff it is with lining up the second gear selector rod too. :mad::mad: You need an extra hand.:rolleyes::rolleyes:I am confident that the synchro is assembled ok and I will give it a good selection run with lots of oil(y)(y) Thanks again chaps.

Ian.
 
Just a quick note for anyone rebuilding a 126 BIS gearbox with the higher ratio Diff and Pinion. All of the gasket kits I have seen only supply two oil seals for the gear selector shaft and the clutch actuating arm (small rubber O rings) Please note that the BIS gearbox gear selector shaft requires TWO you will need to find an extra O ring for the rebuild(y)(y)(y)

Ian.
 
These all came from 126 gearboxes. Some later gearboxes have a small lip seal, some one or two o-rings.
 

Attachments

  • image.jpeg
    image.jpeg
    1.3 MB · Views: 35
Update on the BIS box conversion - well, I got ALL of the gears and bits together in the correct order (y)(y)(y) New seals all round, new drive shafts (25mm) and the THIRD 126 bell housing fitted a treat :D:D Or so I thought :mad::mad: Because when I finished the assembly of the bearing retainers and tightened up the nuts the differential locked up tight - AGAIN:mad::mad: All I can think of is that the BIS gearbox casing is not compatible with a 126 bell housing. I've tried three different bell housings and the last one was a great fit in the critical area between the casing and bell housing for the bearing retainer, but no, the BIS box has very slightly narrow external sides on the casing and this causes mis-alignment when the bearing retainers are up tight. So :bang::bang::bang::bang: Decision time - take it all apart and use the 9/39 pinion/crownwheel in my existing box (y)(y) luckily I only need to rescue the pinion as the diff is complete with new drive shafts, but it will mean another strip and rebuild - deep joy (n)(n) just think - all those bearings, gears, synchro units, shims and things to mess around with - engineering bliss !!!!!! In the end I'll have a complete disassembled gearbox of spares :rolleyes::rolleyes::rolleyes:

Ian.
 
Finally got my box out of the car, and apart from being somewhat mucky - oil leak from selector shaft (n)(n) everything seems to be in order - even all the rubber parts are good to go (y)(y) we shall see what the internal situation is when I get the time to inspect!!! I did notice that the driveshaft couplings were well and truly shot :eek::eek: The pic shows the internal face with the rubber oozing out (it's been cleaned off too) the rubber mess is semi liquid and awful to remove, fitting the correct socket is difficult as the coupling rubber centre has contaminated the nut area too preventing a good purchase on the nut :mad::mad::mad: I'll have a think about removing more mess before attacking the nut when time allows (n)(n) I didn't have any indication of wear in the couplings either?????

Ian.
 

Attachments

  • DSCN2622.JPG
    DSCN2622.JPG
    1,008.8 KB · Views: 36
Looks like someone was a little over enthusiastic about lubricating the splines on the drive shaft. Seen that before and not a pretty sight. I use some really heavy duty graphite grease that stays where you put it. If you are going to put a lot of power through those couplings it might be worth fitting the tripod mechanical ones.
 
Looks like someone was a little over enthusiastic about lubricating the splines on the drive shaft. Seen that before and not a pretty sight. I use some really heavy duty graphite grease that stays where you put it. If you are going to put a lot of power through those couplings it might be worth fitting the tripod mechanical ones.

Hi Dave, Yes the 'Tripod' would be the answer, but where to purchase ??? Cannot seem to get an answer from the makers and prices are very high elsewhere, I guess I'll have to be 'kind' when I drive (n)(n)(n)

Ian.
 
I've fitted the tripod "cv" joints - cost £230....is that dear??? I know that they will handle my rough treatment better than the fragile originals.
This tuning malarkey is expensive - even on a tiny car
 
I've fitted the tripod "cv" joints - cost £230....is that dear??? I know that they will handle my rough treatment better than the fragile originals.
This tuning malarkey is expensive - even on a tiny car

Hi Andrew, yes a malarkey it certainly is :bang::bang: The last quote noted for the full CV kit on the 'MOTOMAX' web site is € 138.00 but the kit has been unavailable for while now. So, where to get a full kit for the least wedge - Anyone know of the cheapest supplier :confused::confused:

Ian.
 
MOTOMAX made a set for me at that price I recall....they now sell at £230 on eBay!
Search fiat 126 and they pop up
 
R Proietti (fiat500.cc) do them for £70 a side
 
I think that you will find that the 'Proietti' price is from 2012!---it will cost a bit more than that now. Ritz Handels GMBH list both the single CV joint per side kits AND the 2 CV joints per side kit---(which at E650+ per kit, is probably for the racers only). There is a u-tube film of how to fit the CV kits and one on the MOTOMAX site. (y):)
 
At the risk of gatecrashing a thread that's addressing a specific problem, can I pose a related question to the learned classic 500 brethren?

During the winter I'm toying with the idea of making one last fundamental modification to my car. It's already be "Abarth-ised" in the engine, carb and suspension departments and, earlier this year, I converted to front disc brakes. I'm now thinking of introducing a syncrho gear box as one last core modification.

I'm still not 100% convinced. I like the character of the crash box and I don't mind the double clutching element to the driving experience. That said, a nice, smooth box has an appeal. Also, there does seem to be a fluid link in that area that I can't get rid of!

Here are my questions:

1 - What's the best approach here? A switch to a 126 gearbox? I've also read that you can change the gears in the standard box and add synchros, but the actual gears are slimmer and more susceptible to wear?
2 - Assuming the above is a new (refurbished) 126 box, I gather I need a new bell housing. But do I also need to switch driveshafts etc?
3 - What about gear ratios? Now the BhP has been improved, and the engine has more power and torque, should I also be looking at changing the top end gearing to improve performance/reliability up towards the top end? I'm not too concerned about increasing speed, but a different gear ratio might help with reliability?
4 - Any advice on how/where to source the parts that I'd need?

Again, sorry to gatecrash the thread, but thought it would be better than starting a new one!

Pete
 
Last edited:
I have a 126 gearbox mated to the 126 engine in the back of my 500, and I still (mainly out of habit I will admit) double de-clutch on down changes. Whatever engine you have in the back of your 500, the bell housing on the gearbox must match THE ENGINE. It is not a difficult job to swap them over (500 to 126---126 to 500). If you fit a 126 gearbox you will have to fit 500 drive-shafts--the 126 shafts are too long. It is a job to be done when swapping bell-housings. I would recommend that you fit the thickest of the 500 drive-shafts (24 or 25mm, depending on how the supplier describes them). The BIS diff ratio is slightly higher--a tuned 500/126 engine will pull it with no problem, and it will reduce engine revs at higher road speeds. You will also have to ensure that the starter matches the gear-box---they are different in location and fitting vis-a-vie the 500/126.
As to supply of parts, gearboxes and starters can be sourced from e-bay, and all the other parts you will require can be obtained from the normal sites---Axel Gerstle, Leo van de Laan etc. I am aware that the clutch hasn't been in your car for long, but I would suggest that you fit at least a new centre plate when you have the engine/gearbox out (which you will need to do to do the gearbox swap). (y):)
 
Update on the BIS box conversion - well, I got ALL of the gears and bits together in the correct order (y)(y)(y) New seals all round, new drive shafts (25mm) and the THIRD 126 bell housing fitted a treat :D:D Or so I thought :mad::mad: Because when I finished the assembly of the bearing retainers and tightened up the nuts the differential locked up tight - AGAIN:mad::mad: All I can think of is that the BIS gearbox casing is not compatible with a 126 bell housing. I've tried three different bell housings and the last one was a great fit in the critical area between the casing and bell housing for the bearing retainer, but no, the BIS box has very slightly narrow external sides on the casing and this causes mis-alignment when the bearing retainers are up tight. So :bang::bang::bang::bang: Decision time - take it all apart and use the 9/39 pinion/crownwheel in my existing box (y)(y) luckily I only need to rescue the pinion as the diff is complete with new drive shafts, but it will mean another strip and rebuild - deep joy (n)(n) just think - all those bearings, gears, synchro units, shims and things to mess around with - engineering bliss !!!!!! In the end I'll have a complete disassembled gearbox of spares :rolleyes::rolleyes::rolleyes:

Ian.

Hi Ian, I had a similar issue when mating a 126 box with a D bell housing.
My issue was that the 2 locating pegs meant that the 2 casings didn't line up perfectly. I had to file the pegs slightly until the 2 halves lined up. The main issue is that the 2 halves must make a perfect circle otherwise the bearings will not fit. There is enough tolerance in the bolt holes for the casing to dealt with the slight adjustment when tightening the cases.
However I believe your issue is possibly the width of the 2 casings being slightly different. So when you tighten the 2 bearing plates up they are either clamping at a very slight angle causing a problem or they are clamping too tight onto the bearings due to a reduced width.
Ideally the 2 casings need to be the same width - this would require machining the wider one down to the width of the narrower half - could mean you need to strip the box again:eek:
Or could you make 2 gaskets out of card or even thin brass sheet that will take up the difference between the 2 halves. These will need to be applied with a good amount of sealer because the bearing covers use a rubber o ring to seal them from leaks and chances are if your 2 halves don't match you are going to experience oil leaks from the flanges as well as the standard oil seapage from the gaitors and gear selector seal. (Even with new ones I still get some!)
 
Hi Ian, I had a similar issue when mating a 126 box with a D bell housing.
My issue was that the 2 locating pegs meant that the 2 casings didn't line up perfectly. I had to file the pegs slightly until the 2 halves lined up. The main issue is that the 2 halves must make a perfect circle otherwise the bearings will not fit. There is enough tolerance in the bolt holes for the casing to dealt with the slight adjustment when tightening the cases.
However I believe your issue is possibly the width of the 2 casings being slightly different. So when you tighten the 2 bearing plates up they are either clamping at a very slight angle causing a problem or they are clamping too tight onto the bearings due to a reduced width.
Ideally the 2 casings need to be the same width - this would require machining the wider one down to the width of the narrower half - could mean you need to strip the box again:eek:
Or could you make 2 gaskets out of card or even thin brass sheet that will take up the difference between the 2 halves. These will need to be applied with a good amount of sealer because the bearing covers use a rubber o ring to seal them from leaks and chances are if your 2 halves don't match you are going to experience oil leaks from the flanges as well as the standard oil seapage from the gaitors and gear selector seal. (Even with new ones I still get some!)

Hi Sean, thanks for the advice I think that you have hit the nail on the head. Even if I do have the gearbox casing or the bell housing (or both :eek:) machined to fit together I still cannot be sure that the leaks you note wil be prevented and with the bearing support plates being in a different location the settings for the diff pre load and drive shaft turning torque will have to be reset :bang: I know that the existing gearbox is sound and providing I don’t make a c**k of changing the pinion and crown wheel it should be all ok(y)
I’ll have to get on with the job when back from my travels and include some tripod cv joints too(y)
Ian.
 
Back
Top