Question about 8.5 Rear end swap, rear spring swap, and car height - Team Camaro Tech
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post #1 of 15 (permalink) Old Mar 20th, 10, 10:25 AM Thread Starter
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Bryan
 
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Location: NY
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Question about 8.5 Rear end swap, rear spring swap, and car height

Last year I did a complete front end rebuild - New steering components, Hotchkis 1907F springs, bilstein shocks, and new rims/tires.

My current measurements are:
Front: Hub-Lip = 14.5" Lip-Ground = 26.25"
Rear: Hub-Lip = 15" Lip-Ground = 27"

Tires sizes:
Front 245/45/17
Rear 275/40/17

Now I plan on doing new rear springs, shocks, and new gears.
I currently have a 8.2 2.73 open diff.

I have a 8.5 open 2.73 rear available to me for $100. I want to add a eaton posi and new gears.

Since I am adding the new rear springs, I'm guessing the 8.5 swap is best since it's stronger, and will already have the multi-leaf perches. Will I have to change the shock plates?

My question regarding the springs - Hotchkis says the fronts should have dropped down to 13 9/16 - I'm at 14 1/2" They said if I go with the 2407C rear 1.5" drop springs - I will be about the same height as I am now. I really want more drop, but the 3" drop springs seem to be too much, and would require a change to the front springs - Hotchkis said they have new 3" drop coil springs coming and would not recommend cutting the 1907's with factory control arms. I want a little more drop but maintain a level stance.

My profile pic is as the car sits now. https://www.camaros.net/forums/member.php?u=29778

My questions:

What rear springs should I use? Hotchkis 1.5" or 3" or DSE 2"
Should I use the 2407C's and add lowering blocks?
Should I cut a 1/2 coil on the fronts?
The 8.5 is worth the $100 extra instead of upgrading the 8.2?
What do you think of the current stance in my profile pic?
I have read that swapping the 8.2 to 8.5 requires a driveshaft length change - Is this true?

Thanks for all the help!
Bryan
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post #2 of 15 (permalink) Old Mar 20th, 10, 03:43 PM
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

I would use the 1.5" hotchkis springs, if you need to go lower at a lowering block. If you go with the 3" you can't easily make it taller.
Wait to do anything with the front until you have installed the rear. And I think there was a post a while back where a few members listed the hub to fender lip measurements with hotchkis and 14"-14.5" sounds right. Search and it should come up.

You do not need to change to multi shock plates, but if you end up using a lowering block I would want the thicker, stronger multi shock plates.

And yes the 8.5 rear is worth the money for the added strength, and yes the driveshaft will likely have to be modified (I think shortened and possibly a new yoke for different u-joint)
I haven't yet installed or built my 8.5" but it sitting in wait...

Forgot to say, Nice car. Looks good
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post #3 of 15 (permalink) Old Mar 20th, 10, 08:37 PM
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T
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

I swapped in an 8.5" rear from 72 nova into my '69 last year, but I already had the Hitchkis rear leafs.

As far as the lower spring plates -- it's possible to get away with re-using the old mono-leaf spring plates, but the multi-leaf deals are a lot thicker and move the lower shock mount to the correct location. There are various re-pop parts that have had fitment issues with the shock mount at the wrong angle. DSE makes some nice parts that seem to have no fitment issues.

Apparently, sometime around '76, GM changed from the 1310 U-joint to the 3R U-joint, so you'll need to check what yoke is on that 8.5" you're looking at. If it's the 1310, you'll probably still have to have the driveshaft shortened by about 0.75" (cost me about $80). If it's a 3R, you'll have to choose between using a "conversion" U-joint or changing over either you driveshaft or yoke.

If you choose to go with the 8.5" rear and are going to get a new posi carrier anyway, consider stepping up to the 30-spline posi (which would also require new 30-spline axles). Per BGH (and others), an 8.5" with 30-spline axles is nearly as strong as a 12-bolt.
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post #4 of 15 (permalink) Old Mar 21st, 10, 12:26 AM
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shane
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

have you considered a detroit tru-trac. im in love with mine after having an open wheeler for a year. i have had no trouble with my 8.5 with 28 spline mosers and i thrash it all the time.

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post #5 of 15 (permalink) Old Mar 21st, 10, 12:27 PM Thread Starter
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Bryan
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Thanks to you guys that responded.

400Bird - Thanks for the comment. I need a better pic - That's a phone pic, and not a good one!

How can I tell if the yolk/u-joint is a 1310 or a 3R? Are they visually different enough I can tell?

gingerbreadman - Everyone has pushed the Eaton - what advantages do you see with the Tru-Trac? I'm street only - no drags, no road course.


Bryan
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post #6 of 15 (permalink) Old Mar 21st, 10, 01:02 PM
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

They are different enough to look at and tell, I just don't know how. Search and you will find the answer and pics.

And the Tru-track is a locker, goes clunk-clunk-clunk around corners. Eaton is a limited slip, better for the street in my opinion.
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post #7 of 15 (permalink) Old Mar 21st, 10, 01:39 PM
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shane
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Quote:
Originally Posted by 400bird View Post
They are different enough to look at and tell, I just don't know how. Search and you will find the answer and pics.

And the Tru-track is a locker, goes clunk-clunk-clunk around corners. Eaton is a limited slip, better for the street in my opinion.
it does not go clunk clunk. its completely quiet and uses gears instead of clutch style discs so it never wears out. ill post more later..going to work now.
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post #8 of 15 (permalink) Old Mar 21st, 10, 03:44 PM
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T
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Quote:
Originally Posted by Bryans68 View Post
How can I tell if the yolk/u-joint is a 1310 or a 3R? Are they visually different enough I can tell?
The 1310 yoke has cast-in "tabs" to locate the U-joint whereas the 3R has no locating tabs and uses internal snap-rings on the U-joint to locate it.

1310 has 1+1/16" diameter cups and 3R has 1+1/8" diameter

There are some pics here:
http://www.actionmachineinc.com/ujoi...ringguide.aspx

The TrueTrac is gear-based "torque sensing" LSD similar to the Zexel Torsen or Quaife diffs used frequently on road-race cars. It is very smooth and quiet and has no clutches to wear out. The TrueTrac tends to be smoother on tight corners, so I like it for the street (or if you plan on road-racing, autoX, etc.) The down-side is, the TrueTrac needs SOME traction on one wheel in order to make traction on the other. Some folks have reported not being able to make "two black lines" with the TrueTrac as a result, so the Eaton clutch-type posi may be a better choice for those who mostly want to go straight
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post #9 of 15 (permalink) Old Mar 21st, 10, 05:20 PM
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

I stand corrected on the tru-track, thought it was a normal locker.

Bryan, I don't know if my results are typical in the rear but I have hotchkis 1.5" drop leafs and 1" lowering block and no rubber isolators. From hub to the lip of the quarter I get 14.5" or so. I would search and see what others have seen, there is a thread with others' results listed.
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post #10 of 15 (permalink) Old Mar 21st, 10, 11:05 PM
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shane
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

bryan its a mouthfull but it is technically called the eaton detroit tru trac helicoil gear designed lim slip device

so if people are pushing the eaton i guess this comes in that category. the biggest advantage of the gear design is no wearing parts such as friction plates in other carbon plate devices. its an absolute breeze to install and can be removed in about 10 minutes for access to your axles. 1 snap ring,1 plate and then one loc-bolt and its out. i dont know of any disadvantages.

ps..... i absolutely have no trouble leaving two big black lines with it .

here it is right here on the eaton page in the first link.....
http://www.eaton.com/EatonCom/Produc...trac/index.htm
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post #11 of 15 (permalink) Old Mar 22nd, 10, 08:04 PM Thread Starter
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Bryan
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Shane,

Thanks for the link - I read their FAQ section.

Bryan
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post #12 of 15 (permalink) Old Mar 24th, 10, 05:42 PM Thread Starter
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Bryan
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

OK - Next question....

Considering I am adding Hotchkis rear leafs - Is it still worth swapping the 8.2 for a 8.5?
I'm running a 327 - and from my searching, the 8.2 will be fine. But I do need to buy the Eaton, gears, etc.

Is it best to swap anyways?

Bryan
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post #13 of 15 (permalink) Old Mar 24th, 10, 07:28 PM
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Are you ever going to have more power than the 327?
I would compare part priced to build both rear ends, they say the 8.5 is cheaper to build...
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post #14 of 15 (permalink) Old Mar 25th, 10, 08:32 AM
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Chris
 
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

I was in the same position 5-6 years ago. I found a guy rebuilding 8.5 10-bolts out of early 70's Novas and got a screaming deal on a fully rebuilt 8.5 with a posi, new 30 spline axles and new 4:10 gears. I just needed to transfer my brakes & shorten my driveshaft about 3/4".
I had debated on dumping money into my existing 8.2 10-bolt, but it would have cost more and would not have been as strong. Plus the 8.5 had the deep perches needed for my new Hotchkis springs. I am still using the mono-leaf shock plates with no issues (and see no reason to change them out). With the lower rear spring, the shocks are in the same range of travel anyway.
I'd ditch the 2:73 ratio unless you are competing on the salt flats or standing mile or something. 3:23 or 3:55 is a good all-around ratio if you don't have overdrive.

1969 Camaro
Electric Blue Lacquer Paint
355/400 HP, M-21 4-Speed, 8.5 10-Bolt 4:11 Posi
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post #15 of 15 (permalink) Old Mar 25th, 10, 03:44 PM
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Re: Question about 8.5 Rear end swap, rear spring swap, and car height

Probably best to make a new post over in the Trans & Driveline forum - I don't think the resident drivetrain "experts" come over to brakes and suspension much (no offense meant to anyone that posted, just think TLowe and Freddie should get a response in...)

As far as 8.2 vs 8.5 -- I agree (from what I've read) that if you're not going to strap on drag radials and go play hard at the drags, then an 8.2 is likely to live fine behind any "reasonable" 327. But... the 8.5 could be built stronger, so let's do some cost math...

If you're going to build up the 8.5" and you're going to need a new posi unit anyway, the 30-spline unit is the way to go -- beefier axles and a big part of the strength advantage of the 8.5" (at least based on what I've read, the 28-spline 8.5" is not much stronger than the 8.2...) Cost delta between an 8.5" and 8.2" posi is pretty much nothing.

OK, either way, you'll need/want a new gear set along with install kit and installation. Again, there's pretty much no cost delta between 8.2" and 8.5".

If you go with the 30-spline 8.5", you'll need new axles at a cost of ~$250. I'd probably recommend getting new axles for the 8.2" as well as this is good insurance (broken axles == baaad and 40-year old axles tend to be a little tired...) Once again, not really any cost delta here, but if you stayed with the 8.2" you could stay with stock axles and potentially upgrade later to "aftermarket" 28-splines...

With the 8.5" you will very likely need to have your driveshaft shortened. Cost ~$80. 8.2 should bolt right in.

With the 8.5", you MAY want to get multi-leaf shock plates. (I forgot about the fact that lowering springs tend to put the shocks back in their "normal" travel range.) Cost ~$70 for the pair if you get new plates.

Other than that, you have the cost of the 8.5" rear (minus whatever you can sell your 8.2" for). For me, I bought an 8.5" for $100 and sold my 8.2" for $75. Figure maybe $50 delta is more realistic.

Sooo, is it worth $80 + $70 + $50 ~= $200 or so more to have a stronger rear to you (even if you don't need it yet....)

For me, I wanted the TruTrac diff (which isn't available for the 8.2") and with plans to (eventually) go with a 383, I wanted my driveline to be pretty bulletproof... Plus I figured after the diff, axles, gears, etc -- what's another $200 on top of the $1000 I was already spending....
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