Hi All , I am working on a friend's car a 500r which has a 600cc engine in it ( presumably from a 126), the bell housing has the starter motor mounted on the side,so the bell housing at least is for 126 my question is I need an axle shaft 25 mm but according to Axel gerstl they are different for the 126 and 500. How do I tell the difference, on my box it's stamped 110F100 and 4107991 and then 7B.

The Fiat 500R had a 594cc engine fitted as standard (but with de tuned 24IMB carb) from new with a gearbox similar to the 126 in every respect except the 500R gearbox was fitted with the shorter 500 driveshafts.

following on from this...

Whilst 126 axles are longer than 500 ones...
Are the 126 wishbones different or are the mounts just further outwards to account for the wider track...
and at the front whilst the uprights are inter changeable are the wishbones?

I am led to believe that whilst the rear suspension arms are the same on both the 500 and the 126, those on the 126 they are mounted further out, hence the requirement for longer drive shafts on the 126 vis-a-vie the 500.
Again, the 126 front uprights can be mounted onto the 500 wishbones without any problem, but the wishbones themselves cannot be swapped--the inner wing mounting studs for the 126 wishbones are further apart than those on the 500, and the 'yoke' that the wishbone bolts to are thicker on the 126 than they are on the 500.
The engine number will tell you whether it came out of a 500R or a Mk 1 '126'

Tom... I hope you have written all this down... in a BOOK

the hobbler said:

I am led to believe that whilst the rear suspension arms are the same on both the 500 and the 126

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The 126 arms are longer. I've held both together with a view to use 126 ones to fit the 500. The suspension mounts are in the same location on 126 and 500 otherwise the gearbox mounts would be different.

MOD500 said:

The 126 arms are longer. I've held both together with a view to use 126 ones to fit the 500. The suspension mounts are in the same location on 126 and 500 otherwise the gearbox mounts would be different.

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Well I was just going to comment that if they were the same Axel Gerst has really different prices on them.....

El cargador said:

How do I tell the difference, on my box it's stamped 110F100 and 4107991 and then 7B.

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If you are fitting the box back into a fiat 500 then you need fiat 500 drive shafts. They are shorter. If the box came out of a 500 then it already has 500 drive shafts fitted.

Thank you for that correction "Mod500"---I will update the info in my notes; and it all goes to prove that at times you just can't trust an 'expert'!
I am correct regarding the front suspension---Initially my car had Mk2 '126' uprights with standard 500 top wish-bones but after the front-end rebuild where the body-shop had to fit 'fettled' '126' inner wings, I had to fit '126' mounting yokes and top wish-bones.

Hi MOD500 Reading up,I believe the 500R had the 594cc engine fitted from factory and therefore the gearbox would have been a 500 non synchro box with the shorter diveshafts coupled to a 126 bell housing (the starter motor position is on the left side) correct me if I'm wrong.

You are correct in that the 500R had the 594cc Mk1 '126' engine fitted (not marketed in the UK). According to my 'Haynes' workshop manual, the 500R had the '126'type gearbox (but with 500 drive-shafts) with synchro on 2nd, 3rd,and top gears. When it was realised that, due to its lighter weight, the 500R was quicker than the '126' (with the same engine), the powers that be at Fiat had the engine in the 500R slightly de-tuned by fitting a IMB24 carb (Weber) whereas the '126 had a IMB28 fitted.

BTW the car is a 1967, I was told it was an F. Sorry I said in earlier post it was an R. So if it's a 67 it must be an F right ???( it has front hinges ,round binacle) but a 600cc engine

MOD500 said:

If you are fitting the box back into a fiat 500 then you need fiat 500 drive shafts. They are shorter. If the box came out of a 500 then it already has 500 drive shafts fitted.

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I spoke to a friend who said he's used the longer 126 shafts in a 500 by shortening them, has done a few without problems ,your thoughts?

Personally, I only pay to repair things that are too expensive to replace.

in the UK drive shafts are not expensive, but machining costs are, so it makes more sense to buy new drive shafts

If they are expensive where you are but machining is cheap then it makes sense to repair the drive shafts.

a few things to consider:

1. are the splines worn? no point modifying driveshafts that need to be replaced.
2. who would weld the shafts for you? Will they sleeve them properly?
3. What is the price difference?

I probably have a set of new old stock 500 shafts if you need them.

the hobbler said:

Thank you for that correction "Mod500"---I will update the info in my notes; and it all goes to prove that at times you just can't trust an 'expert'!
I am correct regarding the front suspension---Initially my car had Mk2 '126' uprights with standard 500 top wish-bones but after the front-end rebuild where the body-shop had to fit 'fettled' '126' inner wings, I had to fit '126' mounting yokes and top wish-bones.

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I don't think this undermines your expert status. you have picked up far more than me over the years from the posts I have read! I started restoring my 500 from when I was 13 with access to cheap scrap fiat 126's, but not much of a budget to buy new parts, so every problem encountered met the first question 'Will a fiat 126 part fit?'

I learned which parts could be substituted and or modified whereas your experience within a garage environment, (the correct way to repair a car!) would use the correct parts from the beginning.

Without the pragmatic approach, with our limited budget, I'm not sure my 500 would be on the road so I don't regret the decisions taken and ironically, most of the parts swapped are widely regarded as upgrades these days. I'm 37 now and the car still works so I guess that's a result in one way or another!

El cargador said:

BTW the car is a 1967, I was told it was an F. Sorry I said in earlier post it was an R. So if it's a 67 it must be an F right ???( it has front hinges ,round binacle) but a 600cc engine

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It's all been said in parts by others; I'm no "expert" but the simple "fact"? that I've learned from those others and experience is that later Fiat 500s, possibly starting with some F's and L's and then (I'll wager) certainly into the R's, were fitted with what are commonly know as 25mm driveshafts but are sometimes listed (maybe more accurately) as 24mm.

The 126 continued with the 24mm diameter but had to be slightly longer because of the dimensions and geometry of the swing-arms.

So if your gearbox comes from a 126 and hasn't been modified, you need to replace the driveshafts with ones listed as suitable for a 500. It will still work with 19mm shafts but would be unnecessarly under-engineered

If it has already been running with the 600 engine the shafts are likely already to be correct.

Your original post says the gearbox is stamped 110F... From my experience (non-expert ) that might mean that the innards of the gearbox are those from the F/L range of cars because the gearboxes I have seen, which are of 126 heritage, all have 126AB stamped on various castings.. To be marked 110F might be the norm on the box of an original 500R and might explain the non-sychromesh thing despite the contemporary 126 having sychro. But it could be that someone has grafted an 500 box onto a 126 bellhousing.

Anyway, regardless of how much the previous ramblings ,might prove to be conjectural...you definitely need the shafts and matching drive-flanges labelled as 25mm/ 500 type.

Hi Mod500 yes the splines are very worn,but so are the gears. The owner is relunctunt to spend another 250€ on a repair kit. So trying to source a gearbox. She will have to use it till it dies. As I am in Spain so I don't think it makes economical sense for you to send me diveshafts unless they're cheap .thanks for your offer. But maybe interested in a gearbox minus bellend if anybody has one for sale