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Re: Muncie M21 parts (23/33)
 12/1/16 6:02pm
gtr1999
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CHESHIRE, CT - USA

Vette(s):
1969 350 4 spd drop top 1972 350 auto coupe


Joined: 5/2/2016
Posts: 61

Graham
You probably know this but if you change from a 4 series gear, in this case 456's to a 3 series, 355's, you're going to need a new 3 series posi case. Also the speedo drive and driven gears, you might have addressed that I only scanned over this thread.
 
Gary


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Re: Muncie M21 parts (24/33)
 12/2/16 6:28am
Grahamred70
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1970 convertible in red 350


Joined: 10/6/2015
Posts: 83

Cheers Gary, yes all sorted got a new diff with new crown wheel and pinion set, went for an Auburn unit and Nitro gears so hopefully it all goes together OK, not looking forward to shimming the pinion shaft, any suggestion for a starting point for the shim size? I don't want to have to pull the bearing off more than necessary.
I ordered the speedo gears from Autogear and gave them all my specs so hopefully my speedo will be good at last, at the moment it is seriously too fast shows about 110 when I'm really doing 70!
 
Thanks
Graham


|UPDATED|12/2/2016 3:28:45 AM (AZT)|/UPDATED|
Re: Muncie M21 parts (25/33)
 12/2/16 1:15pm
gtr1999
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CHESHIRE, CT - USA

Vette(s):
1969 350 4 spd drop top 1972 350 auto coupe


Joined: 5/2/2016
Posts: 61

An Auburn is a cone type posi, ok but not as strong as an Eaton. They do cost less and are not rebuildable. If you are building the diff for under 400hp and just street driving it should be ok. If more hp and hard use I would reconsider using the Auburn.
 
Nitro Gears?  Please specific some more detail. I am not familiar if that is a brand name. The only gears for the vette that I am familiar with are Tom's (only USA made one left), Yukon, Richmond, Motive and those are all imported.
 
 


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Re: Muncie M21 parts (26/33)
 12/4/16 3:52pm
Grahamred70
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1970 convertible in red 350


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Hi Gary If I can get to the original 350HP I'll be happy so the Auburn should see me out.
These are the diff gears http://www.nitro-gear.com/GMVET-355-NG-p/gmvet-355-ng.htm they come with a 2 year warrantee so they should be OK I'm only a weekend cruiser so if they're as good as they make out on their website I'll be good.
What do you suggest for a starting shim for the pinion shaft Gary?

Many Thanks
Graham
Re: Muncie M21 parts (27/33)
 12/5/16 5:09pm
gtr1999
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CHESHIRE, CT - USA

Vette(s):
1969 350 4 spd drop top 1972 350 auto coupe


Joined: 5/2/2016
Posts: 61

I am going to take a guess here and say those are reboxed Tom's gears. Did you get them in yet?
 
I am setting up a set of Tom's 355's now in fact, I ended up with a 026" pinion shim.
 
Look close at them when then come in. If there are a couple of yellowed patterned teeth, take pictures on both sides for reference. Then look at the side of the RG and see what is stamped I there, if you see made in USA and a "G" in a shield logo they are Tom's gears.


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Re: Muncie M21 parts (28/33)
 12/5/16 5:27pm
Grahamred70
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1970 convertible in red 350


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Hi Gary, yes I got them earlier in the year ready for the winter, I'll have another look I know there are some etched markings so they're a matched set will have another look later.
Graham
Re: Muncie M21 parts (29/33)
 12/12/16 8:55am
Grahamred70
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1970 convertible in red 350


Joined: 10/6/2015
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Got my diff. all stripped at the weekend bar the pinion shaft which my friend pressed out for me this morning, good to have friends with a 60 ton press!
All good so far, I haven't cleaned the internals yet but they all look in good condition, just got to find someone who needs them and offset some of my expenses.
Side shafts were both good, no mushrooms on the ends and snap rings safely in position, the crown wheel and pinion are both genuine GM, if what I'm seeing is a date stamp they are from 1967 so must have been NOS when fitted or else the PO swapped out the whole diff from another car.
I had to helicoil one of the mounting holes as it was stripped, I did expect that as someone had fitted a nut and bolt in that hole but so far no nasty surprises.
While I was in my friends shop this morning I had him drill the bottom for a drain plug, I have a magnetic one on it's way.
 
Graham
Re: Muncie M21 parts (30/33)
 1/11/17 4:55am
Grahamred70
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1970 convertible in red 350


Joined: 10/6/2015
Posts: 83

gtr1999 said: An Auburn is a cone type posi, ok but not as strong as an Eaton. They do cost less and are not rebuildable. If you are building the diff for under 400hp and just street driving it should be ok. If more hp and hard use I would reconsider using the Auburn.
 
Nitro Gears?  Please specific some more detail. I am not familiar if that is a brand name. The only gears for the vette that I am familiar with are Tom's (only USA made one left), Yukon, Richmond, Motive and those are all imported.
 
 

Hi Gary, apparently the Auburn diff is rebuildable, I was reading the bumf that came with it and apparently they do a rebuild kit which has all the internals, new cones, gears, etc. but as I say I hope it will last for a good while!

Graham
Re: Muncie M21 parts (31/33)
 1/11/17 1:05pm
gtr1999
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CHESHIRE, CT - USA

Vette(s):
1969 350 4 spd drop top 1972 350 auto coupe


Joined: 5/2/2016
Posts: 61

Interesting on the rebuild kit, I hope you don't need it.

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Re: Muncie M21 parts (32/33)
 4/30/17 8:38am
Grahamred70
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1970 convertible in red 350


Joined: 10/6/2015
Posts: 83

Finally it stopped raining and I could get  out for a little run for Drive It Day, all good, the taller diff ratio has made a big difference, pleased I changed the first gear ratio as I think the original might have been a bit too tall.
Speedo seems to be about right, haven't checked it against sat nav yet but revs seem about right for the indicated speed.
The composite spring I fitted during the job is a big improvement on the steel original and at last the car sits level, I haven't a clue what poundage it is but ride is much better, also the adjustable strut rods made setting up the camber a piece of cake.
Thanks
Graham
Re: Muncie M21 parts (33/33)
 1/20/19 3:04pm
Grahamred70
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1970 convertible in red 350


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Posts: 83

Update after a year of running, change of diff ratio was well worth it, makes cruising much more relaxed, had a bit of a whine but this has quietened down with a bit of running so guess it is running in nicely.
Only problem I have now is with the clutch adjustment, I fitted a new LUK clutch kit complete as the upgraded input shaft had different splines, I fitted the new release bearing supplied with the kit but retained the original ball stud and release fork.
Problem I now have is that in order to get the clutch to disengage I had to wind the adjustment all the way to the end of the thread so I don't even have room for the second lock nut! I didn't remove the ball stud so I don't know what length it is but can see there are various lengths ranging from 1 3/8" to 1 13/16" so perhaps I need a longer one but whatever it is the gearbox will need to come out again :-(
Graham