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Blown differential going 60mph

3K views 21 replies 10 participants last post by  giulia_veloce 
#1 ·
Hello Everyone
I was driving my GTAM clone yesterday cruising around 60mph when suddenly my differential blows out. It spun me 180 degrees and luckily I didn’t hit anyone or anything.
I have recently replaced the transmission and am unsure if this has caused any stress on the diff or if it is just from years of abuse.
The diff is a welded race diff with an AutoDelta sliding block.
From what I am learning, I cannot simply bolt on a normal diff if I want to keep the sliding block . And to service the diff, I needs to be done with a factory diff jig.
Can someone with experience servicing sliding block differential give me some in site on the steps needed to repair .
Thanks in advance

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#2 · (Edited)
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#5 ·
A note in the GTA section may get you started. Sounds like you will need to rebuild what you have or modify another good condition, street diff.
If you are in SoCal, I would recommend G&S Gears in Huntington Beach for a rebuild....
 
#6 ·
Fwiw, I was running a welded diff in my race car (750 Giulietta, 175/70-15 Avon tires) . In a regular winter inspection cracks were found in the welds that lock the spider gears. A few bits had broken off but no big chunks. I’m sure driving around in the paddock with hot sticky race tires (tight cornering). I’m sure had I gone on with this diff a big piece may have cracked off and jammed the diff.

I imagine street use with big tires would greatly increase the likelihood of the high stresses that will fatigue the welds.

So, my philosophy is welded diffs should be regularly checked for cracked welds.

Finally l: I had a diff seize up on me in an old Jag (80mph on an overpass ). Instant oversteer. After some really good tank slapping I got her stopped on the shoulder, pointing straight forward, 12” from the guard rail. Used up all my good Karma. A diff shop run an old hot rodder rebuilt the diff with all new guts. If your case is ok I’m sure yours can be rebuilt. Good excuse to change to LSD.
 
#7 · (Edited)
First, you need to disassemble it to see what damage is done and where.
Pictures? Welded diffs often un-weld themselves and break axles. I suspect the former...

Since your diff must be a 101/105 smaller unit, Your choices for repair are limited to setting it up with a "open" diff or finding an old LSD that was sold for these cars. Or weld up another. If the Pinion and ringear is undamaged(?) you could just weld up another "carrier".

I`ve built several LSD units for these small diffs using the larger LSDs from transaxle cars . But smaller 101/105 axles must be welded and re-splined & shortened to fit the larger drive plates in the LSD. There are some old post on the BB from "Subtle" on his which I built using carbon fiber coated clutch plates.

But in any event setting up your diff is going to be difficult to get it correctly patterned to keep wear from being excessive as well as noisy.


\The Sliding Block was not a good handling location device. Jon Norman converted his GTA to a Panhard location design to improve handling.

He had an article in (I think) the Alfa Owner Magazine (AROC USA) some time ago.
 
#8 ·
My Ausca spider had a 5:12 GTA sliding block center which Kweck converted to a 5 link. I broke the Jack Beck built 4:56 LS I used to replace the GTA center as the partially locked GTA 5:12 was nasty other than for track. Pinion teeth broke but did not catch in the ring gear as speed. Richard Jemison built the installed replacement. I have not broken that one. It IS street friendly.
 
#10 ·
You trust those? After 30,000 miles where will you get parts?
 
#11 ·
Yes it makes you 100% dependent in them.

I haven’t heard terrible things about their LSD longevity, and I have one in my race car. So I’m hoping they are durable. If mine breaks and we can’t get or machine new plates etc then I have my refreshed welded rear end as a backup. It’s sometimes more fun to drive than the LSD because of the need to overcome extra push. The only time I didn’t like the locked rear end that much was in cold and rainy racing.
 
#12 ·
The tried and true assembly is the 1750/2L LS unit because MANY were made, and parts from used should be available well into the future. It worked well, and many builders know how to set them up for both street and race use. The smaller unit does fit into the late 101-1600-105-1600 case without machine work, but if you apply considerable POWER as many do, while the smaller unit appears attractive, it is not as robust as the 2L unit. It also is NOT a version of the more durable, adjustable lock-up, GTA unit, with the bigger half shafts. Some racers might prefer the old GTA assembly, but they have not been available for years, and like the unit being discussed, component parts now must be fabricated if broken. None of this is true with the 2L assembly, which has the larger half shafts. If you have ever snapped off the splined end of a smaller half shaft, racing, and at speed, you make some interesting ground loops before stopping. My friend Dave Brengle has an educational video somewhere on the BB vintage racing his Mom's great spider. I first saw this car at Ausca, when Dave's mother had it there for some work. Mine was there then too. Anyway, the video shows just how much fun can be had snapping a half shaft at speed. Dave had a front and rear facing go-pro running at the time. It's an exciting video. Also why I use the bigger assembly behind my GTA engine in my spider.
The above is only my opinion from my own experiences over time.
1637203

This is never good...
 
#14 ·
But... in 2065, there will still be more 2L parts around than those for the 'lil LS unit.
Fortunately, I won't be around to fix either one.
 
#20 ·
I think it all depends on if you plan to keep the car... FOR YEARS. Short term, new is always better, long term, sometimes, not always, old.
 
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