1977 rear gear swap

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1977 rear gear swap

Post by Dinomyte on Sun Jan 19, 2014 11:06 pm

I've stated looking for parts to swap my stock 2.56:1 gears out with 3.42:1,  this will get up and go.

I thought from all the reading I've done here and elsewhere the specs of what I've got are 10 bolt 8.5" 28 spline with a series 2 carrier.

I know I'll need a series 3 carrier for the 3.42:1 gears, or special thicker ring gear to go on the series 2 carrier, but the BIG question is . . .

Is that a 8.5" 28 spline 10 bolt under the car? or how do I figure it out ? (preferably with out removing the cover.)

thanks.
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Re: 1977 rear gear swap

Post by dynchel on Mon Jan 20, 2014 12:38 am

'77 is a questionable year, Chevy was preparing for the new down sized malibu's for '78. I believe the 7.5 was available (maybe exclusively?) I don't know.  I know a former coworker who had a '77 Monte that didn't have the 8.5.  Maybe someone else can chime in on what to look for.
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Re: 1977 rear gear swap

Post by Dinomyte on Mon Jan 20, 2014 10:18 am

I forgot to ask earlier, can the 8.5 be installed in place of the 7.5 if that's what I've got. I'm thinking not but I'd rather know for sure.

I have a line on a 8.5 carrier with 3.42:1 gears for $50 - and it's complete.  For 28 spline axels.
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Re: 1977 rear gear swap

Post by ant7377 on Mon Jan 20, 2014 11:43 am

My 77 Monte has an 8.5,I would bet yours does too. You can Identify it by what the cover looks like,Im sure its on the web someplace,If I find a chart Ill post it for you.
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Re: 1977 rear gear swap

Post by driveit on Mon Jan 20, 2014 12:03 pm

Found this.

The page below is where it is located.
http://www.chevellestuff.net/qd/rear_axle_info.htmhttp://www.chevellestuff.net/qd/rear_axle_info.htm

Looks like there is a lot of info on there.
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Re: 1977 rear gear swap

Post by Dinomyte on Mon Jan 20, 2014 6:09 pm

After more searching, I found this image,



Is it accurate?  Could there be exceptions to this? or is it 100% true ? at least to identify one or the other.

The big issue is that there are reputable sources (Hemmings etc) that say 8.5" and others that say 7.5".
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Re: 1977 rear gear swap

Post by bracketchev1221 on Mon Jan 20, 2014 9:13 pm

A 8.5 carrier will not fit in a 7.5 housing. But you can swap an 8.5 housing into a car that has a 7.5. As for which you have the cover tells it all. The 7.5 is more square and the 8.5 is round with the 2 lugs underneath.
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Re: 1977 rear gear swap

Post by Dinomyte on Tue Jan 21, 2014 5:16 pm

Thanks for everyone. I just crawled under the car and as per the pictures and everyone's comments it's an 8.5" . . . so likely original, and so 28 spline axels.

Does anyone have a part number for the series 3 carrier, or dimensions, I know that 2.73:1 and lower gears need the series 3 carrier which is thicker, but don't know how big either series 2 or 3 are and can only find part numbers for posi carriers . . .

Thanks again.
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Re: 1977 rear gear swap

Post by Joe73 on Tue Jan 21, 2014 6:10 pm

No reason to OEM on the carrier unless its cheaper for you. Much better units out there than the factory stuff. Auburn, Eaton to name a few. And a new ring and pinion and bearing set isnt too expensive either.
As for factory, Monte SS has 373's out back. If you going used and would like that ratio, grab it out of a monte SS.
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Re: 1977 rear gear swap

Post by bracketchev1221 on Tue Jan 21, 2014 10:55 pm

Joe73 wrote:No reason to OEM on the carrier unless its cheaper for you.  Much better units out there than the factory stuff.  Auburn, Eaton to name a few.  And a new ring and pinion and bearing set isnt too expensive either.  
As for factory, Monte SS has 373's out back.  If you going used and would like that ratio, grab it out of a monte SS.

But the monte ss was a 7.5" rear. I used one in my 79 that I had.
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Re: 1977 rear gear swap

Post by dynchel on Tue Jan 21, 2014 11:07 pm

I think grand nationals had a 8.5.
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Re: 1977 rear gear swap

Post by Joe73 on Wed Jan 22, 2014 8:23 am

Back in the day I pulled a monte 3.73 set up and put it in a 72 cutlass. I also pulled a grand national 3.42 set up and put it in a 71 chevelle. Got me if there were 7.5's in those cars. I also put a monte SS quick ratio box in the 72 cutlass. If I remember correctly the hose needed an adapter and a restricter because of the pressure difference and thread difference. But it bolted right in.
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Re: 1977 rear gear swap

Post by Dinomyte on Wed Jan 22, 2014 9:40 pm

Hay guys - all great information, thanks.

Replacing the whole rearend is more than I'm willing to take on. Gears / baerings / seals etc is a good project for me. I'll post pics when I get started, after the winter.

I pick the thing up tomorrow.

Somebody I know suggested a diff locker. Any body got experience with them? I'm wondering what's happening when you go around a corner and your wheels actually turn different amounts?
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Re: 1977 rear gear swap

Post by dynchel on Wed Jan 22, 2014 9:56 pm

Dinomyte wrote:Hay guys - all great information, thanks.

Replacing the whole rearend is more than I'm willing to take on. Gears / baerings / seals etc is a good project for me. I'll post pics when I get started, after the winter.

I pick the thing up tomorrow.

Somebody I know suggested a diff locker. Any body got experience with them? I'm wondering what's happening when you go around a corner and your wheels actually turn different amounts?
I have a Richmond powertrax locker. It works well and was pretty easy to install. (I found a video of Stacey david's gears where he showed step by step how to install it) look for it on you tube. That said it is a bit noisey when it locks and unlocks...not real loud but you hear a audible click. It handles a bit different (and the instructions have a disclaimer not to let anyone not familiar with the car drive it). It sends power to the tire with the most traction (opposite of a open rearend). My car has a built trans that chirps the tires when it shifts gears, if I make a left turn it chirps the left tire.
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Re: 1977 rear gear swap

Post by Joe73 on Wed Jan 22, 2014 10:58 pm

To install a rear is a bolt in with the hardest part being bleeding the brakes.
Installing new gears and bearings is definitely more time consuming and requires somewhat specialized tools and a good attention to detail. You will need a bearing press, inch pound torque wrench for setting pinion load, ft. lb. torque wrench, dial indicator, and dial calipers. And marking compound should come with the gears to set tooth mesh pattern.
I like to use this for setting the pinion depth easily. And saves times and doesnt waste your crush collar.
http://www.ratechmfg.com/pinion%20setting%20tool.htm

Definitely take your time doing it or it will grenade or whine badly.

Good luck with it.
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Re: 1977 rear gear swap

Post by bracketchev1221 on Thu Jan 23, 2014 9:23 am

Joe73 wrote:To install a rear is a bolt in with the hardest part being bleeding the brakes.  
Installing new gears and bearings is definitely more time consuming and requires somewhat specialized tools and a good attention to detail.  You will need a bearing press, inch pound torque wrench for setting pinion load, ft. lb. torque wrench, dial indicator, and dial calipers.  And marking compound should come with the gears to set tooth mesh pattern.  
I like to use this for setting the pinion depth easily.  And saves times and doesnt waste your crush collar.  
http://www.ratechmfg.com/pinion%20setting%20tool.htm

Definitely take your time doing it or it will grenade or whine badly.  

Good luck with it.  

I agree with Joe here, if you can find someone to help you get them. Replacing the housing is a much simpler task than doing the gears for someone that has never done one. Even still, if you can swing it, pull the housing on your car and set it up on jackstands and do it out from under the car. It is much easier setting up a ring and pinion in a comfortable position than under the car on your back.
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Re: 1977 rear gear swap

Post by thatfnthing on Thu Jan 23, 2014 10:24 am

Yeah, I though I would do my own, too, but after investigating what was involved and learning all the ways it could go wrong, it made more sense to have the 4x4 shop down the street do it for me for a few bucks. It's done right and I had it back the same day.

It's a great skill to have if you're going to be doing a lot of them. If it's only once, it's better to have someone who already has that skill do it for you, 'cuz you can waste a lot of time and money figuring it out on your own.
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Re: 1977 rear gear swap

Post by Dinomyte on Sun Jun 01, 2014 7:15 pm

After reading all this and not acting on the gear swap just yet I've found the following...

3.23 posi, 10 bolt, Auburn posi unit. new bearings and seals (includes new upper control arm bushings) bolt pattern is 5x4.75. Built by reputable mechanic.

The width from inside backing plate to backing plate is 55 1/4 inches.

The big question is what do I need to look for / know before saying yes?

And some questions I've got.

1. what are the loops over the rear?
2. will this get me a ticket because I can lay a pair of tire marks 40' long?
3. this looks different than the 8.5" under my car, well at least the cover looks different or is it just looks? Mine looks just like the last pic.

Here are the pics he sent.







This is what the rear in my car looks like now.  At least the cover it has those two "cut outs" at 3 & 9 o'clock.
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Re: 1977 rear gear swap

Post by bracketchev1221 on Sun Jun 01, 2014 7:22 pm

That looks like a 8.2 out of an early car.
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Re: 1977 rear gear swap

Post by Dinomyte on Sun Jun 01, 2014 7:38 pm

Will it bolt in? and work with minimal issues or should I just forget it?

I'm not worried about staying original, but it seems like an easier job than doing the rear gears.

Or should I just wait to find one from an Impala SS 1995 vintage and get disk breaks too?
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Re: 1977 rear gear swap

Post by bracketchev1221 on Sun Jun 01, 2014 8:45 pm

I'm sorry looking at it again I think it's an 8.5 for a 73-77. I think you may have stumbled on to something. Let me check tomorrow but you may be in luck.
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Re: 1977 rear gear swap

Post by Joe73 on Sun Jun 01, 2014 8:47 pm

bracketchev1221 wrote:That looks like a 8.2 out of an early car.

I agree, yours does look like an 8.2 rear.  Wonder how that got in there.  

Take a look here about half way down for Gm rear axle cover/housing pics. http://www.crankshaftcoalition.com/wiki/Rearend_identification

The rear your looking at is definitely an 8.5".   It has the big blocks in the casting at the 5 and 7 o'clock position when viewed from the rear.  Its also definitely a chevy rear.  See how the axle tube tapers narrower right where it meets the brake backing plate?  That means its a "C" clip axle which chevy used.  BOP axles are dont taper at the backing plate.  Their axles bolt in from the ends which is a real nice feature to me.  No chance of your axle walking out if the rear goes bad.  Been there twice.
That sure is alot of undercoating on that rear your looking at.  It also looks like it was undercoated because it has a substantial rust issue.  And it is also missing the brake lines.  

Those loops up top are for your upper control arm bushings.
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Re: 1977 rear gear swap

Post by Dinomyte on Sun Jun 01, 2014 9:32 pm

Sorry guys I just grabbed a photo from the internet that had the same cover as I remember.  I think I need to role under the car and take a better look, it's just the two details in the cover at 3 & 9 o'clock that I remember and now that you comment on it being an 8.2" it may have just been my quick picking of a picture.

As for the one I'm looking at it's been painted with POR 15.  Is this good / bad / other?  I don't know what POR 15 is for, but have noticed that a number of people doing body work use it.

thanks
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Re: 1977 rear gear swap

Post by dynchel on Sun Jun 01, 2014 10:44 pm

Por stands for paint over rust, it is a very good product if used correctly.
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Re: 1977 rear gear swap

Post by Brainstain on Mon Jun 02, 2014 6:45 am

At one time I was told that the 2.56 housings were smaller than the 2.76 and up housings and that fears wouldn't fit in them. I'm not sure if there is any truth to this or not?

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Re: 1977 rear gear swap

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