S-10 axles not fitting in housing

[Strokercutlass]

So I'm doing the 5 bolt conversion on my '75 Monza and have run into a problem......the rear in the '75 appears to be a 7.5" rear....dimpled cover, 2 long bolts holding the torque arm on. I picked up both a '77 Starfire rear for the backing plates since the '75 Monza rear used small brakes, and an 88-89 era 2wd S-10 rear end to pull the axles from....Now, the rear covers between the Monza and S-10 rears are IDENTICAL, BUT....the S-10 axles won't fit in the Monza rear....the S-10 axles are a larger diameter and won't go thru the side gears....

So...WTF is the issue here? Can I use the side gears from the S-10 rear and swap them into the Monza rear? Did I get a halfbreed morphodike rearend from either the S-10 or the one in the Monza? Everyone says this is such an easy swap, and somehow I've got a train wreck here.....

I've seen that all '71-'75 H bodies had 6.5" rears....I've seen that all Monzas have 7.5" rears...who knows the TRUTH???

Heres another funny thing...checked the axle code on the rear in the '75....DB, which shows a 2.56 6.5"....checked the code on the '77 Starfire rear....DY, 2.56 7.5" rear...both these rears look IDENTICAL....same covers, same 2 large bolts holding the torque arm on...S-10 axle won't fit in EITHER....

Axle measures 1.20" diameter on the S-10 axle splines, 1 115-1.120 on the Monza/Starfire axles....the other thing that doesn't jive is that this is a factory V8 4 speed car, but it isn't geared as such.....the H body library talks about 2.56's with a V6 4 speed, and 3.08's with a V8 4 speed....

Figured out some of it....28 spline axles in the S-10 rear......so WHAT S-10 rears have 26 spline axles? This rear is out of an older S-10, which is what everyone says to use, so how the heck do you know??

I'm gonna go curl up in a corner and bawl now.....

[Strokercutlass]

So heres another stupid question......I'm guessing I can use the 7.5" carrier out of the S-10 rear to go to 28 spline axles...EXCEPT the problem then becomes using a 3 series carrier in a 2 series housing, which wouldn't work either, since the S-10 rear I have for donor parts is a 3.42 rear, and the 2 series carrier cuts off at 3.08...

What about an S-10 rear with a 3.08 gear? Depending upon the year the axles would be 26 spline (direct fit) or 28 spline (swap axles and carrier, swap pinion bearing and pinion)....

And finally.....how EXACTLY can you ID a 6.5" rear vs. a 7.5" rear in an H body? Obviously the old tried and true "2 long bolts or 4 short bolts" theory or the "dimpled cover" theory isn't working on the rear currently in the Monza, since the casting number says 6.5", but physically and comparing to a 7.5" rear on the floor it's identical to that one....

[Monzamaddogger]

I tried to install a 7.5" Powertrax unit in my '75 Skyhawk...Wouldn't fit. The carrier was too small for it to go in. The side gears on '75s are smaller or something. I ended up putting in a posi carrier from another 7.5" You should be able to use the S-10 carrier or a posi one from some other 7.5" rear. I think you would have to use the S-10 gears on the S-10 carrier or you'd have to get the right carrier for the 2.56 gears.

[Strokercutlass]

And another odd thing...as I said, axle code shows it as a 6.5" rear....took a tape measure and eyeballed the S-10 rear I have...7.5" ring gear....crawled under the Monza and eyeballed the ring gear with a tape... 7.5" Now isn't that some strange business? The axle is coded out of Canada, the sequence number on the VIN is off from the body tag, I know the history back to 9,000 original miles (car has 18,900 on it now)....

I found a rear from an '84 s-10 not too far away on the locator with 3.08's, which means I should be able to use both the axles and the carrier and ring and pinion if I use the adapter bearing and such for the pinion....with 3.08's and the 25.7" tire I'm planning on, it should put the cruise rpm at 55 around 2200 RPM with the 4 speed...then hopefully I can find a lock right to drop in and it should be good to go for future engine upgrades to around 300hp....I don't want to build an all out drag car, just something that's fun to drive and has more than the original 100hp 262 that's back in the car now...

Sorry for the rambling.....it's Monday, I'm frustrated, and I'm ready for beer....lol

[cjbiagi]

I believe all 75 Monza's have a 7.5" rearend. My car is a 75 V8 4speed car and 2.56 rear gear was standard in 1975 with this combo. A 2.93 was offered as a option with the V8. I did the same swap using later Monza rear backing plates and 26 spline S10 rear axles that I ordered from Moser Engineering. I think you discovered the problem with the axles being later 28 spline versions. Once you start mixing and matching internal components you have to be careful, you can swap carriers but you have to use the correct series gears with the carrier in question. The other problem is Monza's use a slightly different pinion gear bearing diameter so you can't simply swap other 7.5" pinion gears into a Monza housing. You need to either machine the pinion shaft down to Monza specs or use a special conversion pinion bearing. Talk to Jim on this site (JD Race), he builds rearends for a living and does a lot of H body ones. He can set you straight.

[ROB]

You need to use the earlier S-10 axles, from the 82-88ish years.

[monzaz]

And another odd thing...as I said, axle code shows it as a 6.5" rear....took a tape measure and eyeballed the S-10 rear I have...7.5" ring gear....crawled under the Monza and eyeballed the ring gear with a tape... 7.5" Now isn't that some strange business? The axle is coded out of Canada, the sequence number on the VIN is off from the body tag, I know the history back to 9,000 original miles (car has 18,900 on it now)....

I found a rear from an '84 s-10 not too far away on the locator with 3.08's, which means I should be able to use both the axles and the carrier and ring and pinion if I use the adapter bearing and such for the pinion....with 3.08's and the 25.7" tire I'm planning on, it should put the cruise rpm at 55 around 2200 RPM with the 4 speed...then hopefully I can find a lock right to drop in and it should be good to go for future engine upgrades to around 300hp....I don't want to build an all out drag car, just something that's fun to drive and has more than the original 100hp 262 that's back in the car now...

Sorry for the rambling.....it's Monday, I'm frustrated, and I'm ready for beer....lol

Now you are on the right path...lol. So you could keep the 28 spline axles with the 28 spline carrier from the s-10 and your good... You will need to use 3.23 -4.56 if it is a 3 series carrier the 4.3 2wd s-10 rears are usually 3.08 (2 series carrier) 1990 -2004 are all 28 spline 7.5 1995-2004 4.3 5 speed s-10 usually got the 8.5 optional rear.

The power trax MUST be bought for the correct carrier there are 3 different ones. 10 bolt 7.5 1982-1985 (26 spline 2 large window open non posi carrier) 10 bolt 7 5/8" 1986-1988 26 spline (redesigned spider gears found in the monte carlo rears with v8 engines and other cutlass and GRAND prix with v8s one big window and small back window case) Then there is the 1990-2004 7.625 28 spline unit camaros s-10 etc. large window and small rear window just like the 7 5/8 late 80'2 26 spline unit.)

Hope this helps. Please remember you can catch me at www.jdrace.com for diff questions if i fail to answer here quick enough.

Sorry for the late response. Jim
JD

[Strokercutlass]

So JD, I have a question.....

Obviously the 28 spline axles are a better choice, but how do you get away with using the 3 series 28 spline centersection in the 2 series/low 3 series 26 spline housing? I know in my 8.5" rear in one of my Cutlasses, I had to use a ring gear spacer when going with 4.11's in my 2 series carrier...

If the carrier break is at 3.08 and lower (numerically) and 3.23 and up numerically, how do the two come together? I could use the 3.42's currently in the S-10 carrier, but will they work in the 2 series housing? I guess 2-300 rpm at cruise speed isn't a huge difference, and would keep the car in the powerband better.....

Nevermind, I think I've got it...as long as I use the correct matching centersection and gears, I should be ok....the housings are the same, it's the carrier and how the ring gear positions on it that matters, right?

[monzaz]

Man ---you sure like to answer you own questions...lol.

You can use the 28 spline axles with the correct 3.08 and higher ratio (2.73 2.56 2.41 etc.) These are in the 4.3 s-10 rears alot of times as the 4.3 did not need the LOW steep gears to get the truck moving. Also camaros had 2.73 gears in alot of the cars 7.625 1990-2002 era those too will bolt right into the monza 7.5 rear.

So there are MANY MANY ways to do this you just have to keep your carrier series stright if you are reusing your 2.56 monza gears you will need to find a 2 series carrier 28 spline period.

IF you are using the 3.42 s-10 gears and need the 26 spline side gears and axles you will need a spacer for that 2 series carrier to hold the 3.42 gears AND the conversion pinion bearing and race (WHICH I HATE by the way...) Just have me machine your set...better choice...

If you want to use the 3.42 and the 28 spline axles you will need the 28 spline carrier 1990-2004 and just the pinion conversion bearing and race set.

TIP - you can not use the s-10 backing plates with your monza/Hbody...the backing plates are a different offset then the h-body 9.5 x 2 backing plates. The wheel cylinders will hit and the drum will rub the backing plate ...that is an understatement...THEY just WILL NOT BOLT ON PERIOD!

ALL 7.5 and 7.625 gears and carriers are interchangeable between 1975-2004 s-10 camaro firebird g-body cars. Posi open all does not matter.
BIG difference is the h-body has the 1.375 pinion shaft and the rest of the GM 7.5 world is 1.438 pinion shaft diameter...AND the pinion spline count on the monza is 25, where as the rest of the 7.5rear gears are 27 spline...Using a chevy NOVA 1976-1980 7.5 pinion yoke will cure the problem or you can use the s-10 yoke with a conversion joint will also do the job...PLUS the s-10 yoke is a better stronger designed yoke.

Well I hope some of this has helped.

IF you need personal help on the phone etc. just call i am here to help plus i HAVE AXLES ALL THE TIME FOR THIS CONVERSION

Jim
330 659 7117
JD

[Vega Guy]

I've got a 6.5" posi and a 7.5" non posi for both vega and s10. Any way to put the posi into the 7.5" rear or put the 26 spline axles into the smaller 6.5" posi rear?

[monzaz]

I've got a 6.5" posi and a 7.5" non posi for both vega and s10. Any way to put the posi into the 7.5" rear or put the 26 spline axles into the smaller 6.5" posi rear?

nO- CAN NOT BE DONE. sORRY.

Use the 7.5 Vega housing and build it. Sell the 6.5 to someone who needs a restoration rear. Jim