Axle joint compatibility 500 F L R 126 and 850..?

Matt Zerega

Passion, not Practicality.
After a recent exchange with someone about the rubber/aluminum axle flex joints on early Fiats, I became intrigued by the tripod and CV joint conversions. I came across one conversion kit that advertises compatibility with the "Fiat 500 F L R and 126." But..will it fit the 850?

A bit of sleuthing indicates that both the 500 and 126 flex joints have 22 internal splines and what appear to be 24 mm OD axles...which are the same as the 850. The only difference between the factory and CV conversion joints photo is the fact that the 850 ones skip a spline at each 180 degrees in the ID; the 850 axles themselves do not. With these observations, I went ahead and placed my order. I'll find out soon enough if the modified CVs fit.
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Matt Zerega

Passion, not Practicality.
Nope :( If one were to pound of the CVs hard enough to drive them all the way home, they would become one with the axle shaft...forever. In addition, the spacing between the fastener holes (for the CVs it's 42 mm...whereas on the Fiat 850 it's 46 mm). These $267 Fiat 600 CVs do not fit the 850 axles, stub axles or axle sleeves ...and will soon be for sale on the FS&W forum for some lucky <edit> owner of a vehicle with 42mm spacing between the axle-sleeve fasteners and a spline profile that looks like the image on the right (in yellow, below) </edit>.
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boxy02

True Classic
A 600 owner buying these would not be lucky - they're for a 500.
The description states otherwise, is it incorrect?
(Translated from google):
“preassembled kit pair of constant velocity joints, better than tripods but at a lower price! (A kit includes 2 pieces, for 1 car)
From November 2020 new improved version!!!
Modification for all 126, 500 FLR, 600, do not require modifications on the axle and wheel hub, replace the original joint including specific grease and screws, the brand of grease may vary based on availability.
Recommended for original engines, mandatory for tuned engines!
Replacement of the original joint which is easily damaged, the sliding joint will not wear out because there is no more rubber that strains axially, especially with tuned engines. There are no changes to be made, just disassemble the old joint, remove the spacer ring and fit the new joint after filling it with grease. Reassemble the nut with the right tightening torque and lock it. Reassemble the axle shafts.

OUR EXCLUSIVE PRODUCTION, MADE IN ITALY

AUDIO DERIVATION

LIST PRICE €250.00”
 

Dave Bassett

True Classic
I posted a YouTube vidoe of an 850 Sedan race car build in Italy and one of the modifications was universal joints, from new part as I recall. I'll look for it again if needed.
 

fiatfactory

Steve Cecchele
The description states otherwise, is it incorrect?
It may not mean the same model of 600 you do... there was also a 90's model Seicento?

neat solution though, wouldn't be hard to engineer a similar item with the correct P.C.D to suit the 850 axle flange.

SteveC
 

Matt Zerega

Passion, not Practicality.
If you find the URL, please do post it here or send me a private message. I'm shooting for 100+ HP and I'm not optimistic that the stock rubber couplings will tolerate the kind of driving that will tempt my right foot.
 

boxy02

True Classic
It may not mean the same model of 600 you do... there was also a 90's model Seicento?

neat solution though, wouldn't be hard to engineer a similar item with the correct P.C.D to suit the 850 axle flange.

SteveC
I measured the bolt holes on my flex couplers and they’re 42mm center to center, I have 22 splines on my stub axle shaft and the peaks of the splines are flat like on the CV. I’m 99% sure they’ll work for my application. I’ll report the final analysis when I fit them on my 600D. Thx!
 

boxy02

True Classic
An update on the CV joint journey:
They index on the splines, but won’t slide on as they should. Upon closer inspection of the valleys of the splines in the CV, they appear to be more of an acute angle compared to the angles of the peaks of the stub axle splines. So close. I’m going to seek out an axle machinist and get some advice whether they can be machined to fit or not. Oh well, I had to try. If all else fails, I can go back to the original flex couplers and be on my way. Thanks for all the insight and warnings, let the cascade of “I told you so” fall.😂
 

fiatfactory

Steve Cecchele
Someone here must have a 500 or a 126 that these will fit straight onto?

I know Ricardo has a little yellow 500... the standard rubber / alloy couplings don't fail often with about 20hp though...

SteveC
 

NM850

True Classic
An update on the CV joint journey:
They index on the splines, but won’t slide on as they should. Upon closer inspection of the valleys of the splines in the CV, they appear to be more of an acute angle compared to the angles of the peaks of the stub axle splines. So close. I’m going to seek out an axle machinist and get some advice whether they can be machined to fit or not. Oh well, I had to try. If all else fails, I can go back to the original flex couplers and be on my way. Thanks for all the insight and warnings, let the cascade of “I told you so” fall.😂
Can’t know unless you try.
 
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