I'm rebuilding my 126 diffeential and have struck a couple of snags tonight that I'd appreciate some advice on.

First, and no biggie here, I found that the 500R axles I am using needed a small adjustment to make them fit. Specifically the axle trunions - or pins I think some people call them - had a very slight difference in their end radius to the original 126 ones. This meant I had to gently grind the pins down ever so slightly so that they fitted into the side gears. Anyone else had this issue?

Second, and this is the major issue, I appear to have too much play in the side gear pinion assembly. The side gears float in and out by about .5mm. I have 1.3mm bronze thrust washers fitted. These are what came in the differential from the factory and are the thickest ones listed in the parts book, but it would appear I need to either stack in some additional thinner thrust washers to take up the slack, or make/source a set of thicker thrust washers. Or I guess I could buy a new side gear/pinion assembly. Trouble is I have never seen either the washers or replacement side gears for sale and even a google search finds no reference!

Does anyone with any experience with this know if the .5m slack in the mesh is normal? I'd really like to reduce it so that the gear teeth are loaded up further towards the stronger root of the tooth. Also, with this amount of slack there is no effective rolling torque, which surely can't be right?

Cheers Roger

Roger,

I really don't have an answer for you as I have not rebuilt my transmission yet, but do you have a FIAT factory manual (not Haynes or Autobook)?
There are 8 pages in the Fiat factory manual on this adjustment.

John

Here is one of the pages showing an exploded view. They show 1.5mm as the largest shim.
John

Thanks John, yes, I have that manual. I had not noticed that it states 1.5mm as max oversize. My parts book says 1.3. It is kind of academic though because nobody sells them! The rest of the pages cover in detail the shimming of the layshaft to ensure the pinion and ring gear mesh properly (very useful, I've already been through that procedure) but give almost no mention of side gears. Since no-one seems to sell those either it looks like I may have to just get some thrust washers made to suit. I can't believe I am the first person to experience this?!

Cheers Roger

Hi All
I am currently experiencing the same issue as Roger had with his planet gear thrust washers.
Luigi has a dreadful noise coming from his transmission, I’ve run the car stationary with the wheels off the ground and in gear, when you stop one wheel rotating the noise gets far worse, leading me to suspect that the planet gears are worn.
Everything is now in bits and new planet gears have arrived but what should the clearance be on the side gears and how is it measured?
Any help/advice would be greatly appreciated!

The Mouse That Roars said:

Hi All
I am currently experiencing the same issue as Roger had with his planet gear thrust washers.
Luigi has a dreadful noise coming from his transmission, I’ve run the car stationary with the wheels off the ground and in gear, when you stop one wheel rotating the noise gets far worse, leading me to suspect that the planet gears are worn.
Everything is now in bits and new planet gears have arrived but what should the clearance be on the side gears and how is it measured?
Any help/advice would be greatly appreciated!

Click to expand...

I've been in there a few times but never thought about that or had to do it.
I wonder if you can do a dry assembly of the differential and get a feeler-gauge in the gap between the back of one of the planetary gears and its bronze thrust surface through the crownwheel carrier? If I'm reading it correctly, that gap should be 0.2mm.

If you have newly manufactured parts anything is possible, including it all being too tight. Unless you can get hold of some custom shims, maybe to fit under the shoulder of an existing bush, I can't think how you have any scope for removing excessive play if that is found. It's an intriguing but frustrating problem. Good luck with it; you sound like you know what you're doing. Personally, I would probably just assemble things as carefully as possible and hope for the best.

Thanks Peter, I’ll aim for 0.2mm.
Out of interest where did you manage to find that info, I’ve looked everywhere I could think of to no avail!
I’ve a set of cranked feeler gauges and a pair of 1.2mm shims on the way. I’ll put it all back together and see what clearance that gives and report back.

The Mouse That Roars said:

Thanks Peter, I’ll aim for 0.2mm.
Out of interest where did you manage to find that info, I’ve looked everywhere I could think of to no avail!
I’ve a set of cranked feeler gauges and a pair of 1.2mm shims on the way. I’ll put it all back together and see what clearance that gives and report back.

Click to expand...

I found the 0.2mm, (which is actually listed as the wear limit on "bevel side gears") on page 90 of the Haynes manual for the Fiat 500. So that may not actually be the gap I'm thinking it is. I'm sure there will be more detail in Fiat publications.

It seems that rather than clearances, the baseline measurement is done by measuring the turning torque needed on a driveshaft when the casing for the assembled diff. alone is locked in a vice....it's a bit beyond where my technical inclinations come to a terminus.

fiat500 said:

I found the 0.2mm, (which is actually listed as the wear limit on "bevel side gears") on page 90 of the Haynes manual for the Fiat 500. So that may not actually be the gap I'm thinking it is. I'm sure there will be more detail in Fiat publications.

It seems that rather than clearances, the baseline measurement is done by measuring the turning torque needed on a driveshaft when the casing for the assembled diff. alone is locked in a vice....it's a bit beyond where my technical inclinations come to a terminus.

Click to expand...

Hi Peter
Thanks for the info, that’ll teach me not to be a typical bloke! Need to read all the instructions/information next time.
I think, like you that the 0.2mm is not the measurement I’m looking for but what is listed on page 89 is the ‘standard’ bevel gear thrust ring thickness of 1mm, so that’s a great start.
I’ve got all new gears and a pair of 1.2mm thrust rings so I’ll get it back together and see how it feels, if it’s too tight I can always thin down the thrust rings to suit.
I’m out of action following a knee op at the moment so I’ll post progress when I’m allowed back in the garage!
Cheers Ian