Rear end noise

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jfarr
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Rear end noise

Post by jfarr » Sat Aug 10, 2019 7:27 am

The ‘74 has developed a ticking sound that is coming from the diff. You hear it as you roll to a stop. My mechanic put the car on the lift and found that there is play in the diff when the driveshaft turns as well. At speed, this ticking becomes a growl.

I’m not familiar with what’s in the differential. Obviously at least two gears, but what else should I be prepared to replace in there?
Jody Farr
Worthington, PA
1974 Fiat Spider 1800
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miker
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Re: Rear end noise

Post by miker » Sat Aug 10, 2019 8:25 am

I would treat this as a cooperative winter project between your mechanic and Jon Logan and Midwest 124. Your mechanic could remove the snap rings holding the two axles in and pull out the pumpkin. Send it to Jon for rebuilding or exchange for a known good used one that your mechanic reinstalls. I think the differential rebuild process and the parts availability are a barrier to normal mechanics.

You could also consider a 3.9:1 new pumpkin, but these are out of stock at the moment at Autoricambi.

Also, post in "Parts Wanted" for a 4.3:1 pumpkin used. It's a commonly held-on-to part from scrapped Spiders. I had one for a long time on the shelf until someone needed it.
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
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Re: Rear end noise

Post by jfarr » Sat Aug 10, 2019 8:52 am

miker wrote:
Sat Aug 10, 2019 8:25 am
I would treat this as a cooperative winter project between your mechanic and Jon Logan and Midwest 124.
Great idea. I'm traveling out to see Matt at Midwest-Bayless next weekend so maybe I'll reach out to Jon to see what he might have available on the shelf and fall back to this plan if he's out of stock. Thanks!
Jody Farr
Worthington, PA
1974 Fiat Spider 1800
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Re: Rear end noise

Post by kgfiske » Sat Aug 10, 2019 9:55 am

Jody, If you are interested, I have a used 4.3:1 and a hard to find 4.1:1 differential that would bolt into your 74. I'm not too far away in the Akron area.
Regards
Kelly Fiske
Akron, OH
78 Spider
82 Spider Turbo
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Re: Rear end noise

Post by jfarr » Sat Aug 10, 2019 1:59 pm

kgfiske wrote:
Sat Aug 10, 2019 9:55 am
Jody, If you are interested, I have a used 4.3:1 and a hard to find 4.1:1 differential that would bolt into your 74. I'm not too far away in the Akron area.
Regards
I might be. What would I have now? The service manual I have lists a 4.3:1 but AutoRicambi lists a 3.9:1.
Jody Farr
Worthington, PA
1974 Fiat Spider 1800
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Re: Rear end noise

Post by MikeGreer » Sat Aug 10, 2019 4:39 pm

Jody, the 3.9:1 that AR has is the same gearing that is in the new style rear end in the spider 2000. Stock on the '74 would have been the 4.3:1. The 3.9 would lower RPMs on the highway. The 4.3:1 used to be available as a new pumpkin, I'm not sure if it still is. This is a fairly easy r&r, unless you're like me, in which case, while it's apart I should do half a dozen other things. Flex joint, u-joints, center bearing, axel bearings and seals, oh what rage heck, ss brake lines, Koni's, I just don't know when to quit.
45 years with a spider, that's a long time
Restoring the '79 for the second time, you're never finished ;)
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Re: Rear end noise

Post by kgfiske » Sun Aug 11, 2019 8:48 am

The 4.1:1 differentials were used on the 124 Coupes. The one I have is from a 71 or 72 Coupe. It's I nice compromise between the 4.3:1 and 3.9:1 rear ends. When I ran it in my 78, I found it actually made my Speedometer much more accurate. I have since gone to a new 3.9:1 differential, but have coupled it to a 2 Liter engine with a bit more power than the original 1.8 Liter set-up.
Kelly Fiske
Akron, OH
78 Spider
82 Spider Turbo
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Re: Rear end noise

Post by jfarr » Sun Aug 11, 2019 8:59 am

kgfiske wrote:
Sun Aug 11, 2019 8:48 am
The 4.1:1 differentials were used on the 124 Coupes. The one I have is from a 71 or 72 Coupe. It's I nice compromise between the 4.3:1 and 3.9:1 rear ends. When I ran it in my 78, I found it actually made my Speedometer much more accurate. I have since gone to a new 3.9:1 differential, but have coupled it to a 2 Liter engine with a bit more power than the original 1.8 Liter set-up.
I've noticed my speedo reads about 4mph slow at 60mph. I wonder if I don't actually have the stock diff in this car.
Jody Farr
Worthington, PA
1974 Fiat Spider 1800
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Re: Rear end noise

Post by miker » Sun Aug 11, 2019 9:52 pm

What size tires do you run?
MikeR (mirafiori.com since 1995)


1977 Fiat 124 Spider
Previously owned:
2012 Fiat 500 Prima Edizione #236 (now owned by my son David)
'86 Bertone X1/9
'81 Fiat Spider 2000 #236
'78 Fiat 131 four door
'76 Fiat 128 4 door
'74 Fiat 128 4 door
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jfarr
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Re: Rear end noise

Post by jfarr » Wed Aug 14, 2019 11:01 am

miker wrote:
Sun Aug 11, 2019 9:52 pm
What size tires do you run?
I'm running 205/50-15 tires on Volumex wheels.
Jody Farr
Worthington, PA
1974 Fiat Spider 1800
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