#21  
Old 05-19-2004, 04:36 AM
bigcatmike65 bigcatmike65 is offline
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Thanks. Looks great

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Old 11-22-2006, 10:43 AM
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Default Rim fitment

Let me first start off by saying thanks to "arowhed" and everyone else for the great information listed in this post. My question is this.... I have a 1966 Grand Prix and I believe that in 1966 the rear axle was lengthened by approximately 3/4 of inch on either side... How does this affect the rim recommendations? Also, there is a difference between back spacing and offset, so what is the offset of the wheels when the rim has 5.50 inch of backspacing. I am trying to figure out how much clearance is in the front so I don't have to cut off the factory fender skirt attachments... Any help is greatly appreciated. Thanks.

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Old 12-07-2006, 11:55 AM
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Bump...

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Old 12-07-2006, 03:18 PM
mike nixon mike nixon is offline
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measure your diff backing plate to backing plate just under the chock mounts and i'll do the same for my 65.

while you're at it measure the center of the shock bolt to center of shock bolt also. i curious if they relocated them at the same time.

mike

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Old 12-07-2006, 04:30 PM
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65 and 66 are exactly the same rears and axles. I have both rears and they have the same measurements.

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Old 12-07-2006, 04:56 PM
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As far as I know the 66 B body Pontiac rearend is exactly the same as 65...axles shafts from 65-70 B body are fully interchangeable..I have 1968 Catalina shafts in my 65 housing right now. Rearend width is 65.50" inches brake drum face to brake drum face.
Lower shock bolt mount location unchanged as well, at least between 1965 to 66.

I believe backspacing and offset are confusing terms, so to clarify, if you take my modified rear rims, without a tire on them, and lay them face down on floor, set a 3' or longer straight edge across back side edge, and measure down from it to the point where rims will contact brake drum, that distance is 5.50" .....and if ya measure down to the ground through one of the spoke holes, that is exactly 9". (which means a 15 x 8" rim is actually 9" wide overall, and 8" wide bead to bead)
What I di was cut most of the "ring" off a pair of 15 x 7 Rally II, leaving only the centers, shipped them to Stockton told them to put 15 x 8 rings on them with 5.50" backspacing. They shipped them back, in bare steel, for $100 each, plus shipping. Really, from the outside of the wheel, they still look like stock 15 x 7, as far as "depth"...because even though the rims were widened 1 extra inch, it is all to the inside, therefore adding 1 extra inch to the backspacing as well.

If you modify your rims like I did mine, there is NO WAY you can retain the factory fender skirt latches. Even stock 15 x 7 Rally II will rub the tire sidewalls on the latches.

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Old 12-07-2006, 07:25 PM
mike nixon mike nixon is offline
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with the info that's been provided in this thread about b/spacing and mods required to get wider wheels on these cars i'm going to stick this thread here and copy it to the suspension forum.

i think it'll save a lot of questions in the future.

mike

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Old 12-11-2006, 06:48 PM
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great sticky!

so 8 is the widest..

but what about tallest wheels capable?..

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Old 12-12-2006, 12:22 PM
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65-66 B body wheelwell will accommodate a little over 30" tall tire before ya start rubbing the wheel opening towards front of car. So whatever wheel diameter\tire size combo you want to run, max tire diameter is still gonna be around 30" tall.

As for wheel height specifically, I've only experience with the stock 15" x 7 and custom 15 x 8 Rally II, but....I would bet a very low profile (short sidewall) tire on a 17 or 18" rim would allow the rim width to grow to 9", due to much less tire sidewall bulge beyond the rim's width, that low profile tires usually have. Also, with a taller rim, the lower shock mount\bracket will fall INSIDE the rim's inner diameter, which may make moving it unneccessary??

For test fitting, anybody got access to a 17(or 18, 19?) x 9 rim with around 6.500" backspace and 5 x 5" bolt pattern?

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Old 12-12-2006, 02:14 PM
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Okay, here is what I have and it's no where near conclusive, as I am still working on it. I have a 20x8.5 (9.5 inch total width) rim. I have a 66 GP and the offset of the rim is +14mm (approx. 1/2 inch). I figure that the backspacing is approx. 5.25 inches with this setup. The rim has a 255/50 R20 tire on it currently (which doesn't buldge that much). With this setup I have 1/16 inch in the front by the wheel well and 1 15/16 on the rear to the frame rail (car is not being driven, I am going through it and making it mine). The shock tower is not an issue as there is plenty of clearance with this size rim.

I also have a 65 Full-size posi rear that is going into the GP. From articles I have read the 65 full-size axle is 3/4 inch shorter on either side, although all the mounting is in the exact same place for 1966. The way to tell it is a 65 compared to a 66 is to stick two fingers in between the backing plate and the lower control arm (?). If two fingers fit it is a 1966 rear, if they don't it is from a 1965. I am hoping this is true because I am looking forward to the rim being recessed 3/4 of an inch to give me more of a centerline. If the rim is recessed the 3/4 of an inch then I calculate I can get a 285 on the rear, but (and this is a BIG but) I will have a little over half an inch on the backside of clearance and a little under 1/2 inch of clearance on the front. If I stick with a 275 tire I will have over 1/2 inch on the front and the rear with this combination. The tire would be a 275/45 or 275/50 R20.

Sorry to be long-winded but I truly love this site and it has provided me with an exceptional amount of information that until now I have not really been able to contribute much to.

Does anyone know how much clearance should be maintained on the outside and inside at a minimum? I am planning on using Poly bushings to limit the amount of axle travel. My friend, who knows Pontiac's pretty well, said to leave atleast 1/2 inch on either side.

If anyone wants I can post some pictures, just tell me what you want to see pictures of.

Thanks.

Larry "Kid Skid"

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Old 12-12-2006, 07:36 PM
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Again, pretty sure there are NO differences between 65 and 66 fullsize rears. 65-70 B body all use the same bolt-in axle shafts (9783561, same part for Right or Left side), differentials\ring and pinion gears(within three different ratio series), brake drums, backing plates, etc. I have a Hollander Interchange manual that confirms this. Can you show us this article you mentioned that supposedly outlines differences, becasue I am quite curious to see it.

Now....Rear axle HOUSINGS are different between the following year groups among B body: 65-67, 68, 69-70, I think the main difference being coil spring perch size, not anything to do with axle shaft length.

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Old 12-12-2006, 08:44 PM
mike nixon mike nixon is offline
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kidskid is describing the differences in "a" body axles.

my hollanders states the same thing ase arowhed's.

i actually have a 69 impala 2dr i'm considering cannabalizing for my /gp to have disc brakes and a 12 bolt. per hollanders it'll work.

mike

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  #33  
Old 12-13-2006, 02:27 AM
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I'll check the axle that I got that I think is shorter. Are there some numbers or something that I can look for that would identify the axle? I am pretty sure when I bought the axle it was advertised as a full-size 65 axle. If it is the same length I am going to have to re-think my wheels... If nothing else I am having a blast with the old pontiac... it's been in my family 41 years... thanks for the info and I will post what I find. I will also look for the article I found, probably confused what I read... wouldn't be the first time with pontiac stuff.

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Old 12-13-2006, 10:40 AM
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I checked the axle late last night (early this morning at 2 a.m.) because I couldn't wait. Arowhed and Mike Nixon both are right, the axles are the exact same length. There is one very important difference though... the 65 is a posi unit! That's probably what I bought it for, although I would love for it to be shorter because now my wheels won't fit right! I guess I am going to have to go back the drawing board and find some wheels that measure up! Thanks for the help to both of you and I will post pics when I can figure out what to do next...

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Old 12-13-2006, 10:56 AM
mike nixon mike nixon is offline
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you could have the axle you have narrowed, but the wheel's will probably be cheaper.

i guess i'm spoiled with that stuff as moser engineering is located about 8 miles from me.

mike

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  #36  
Old 12-13-2006, 11:29 AM
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Mr Nixon..living only 8 miles from Moser, eh? VERY interesting! Do you get a "locals" discount??
Kidskid, from what you described above, looks like your gonna need a wheel with at least another 1" of backspacing. Post some pics of the front and rear clearance as is, if possible.

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Old 12-13-2006, 12:06 PM
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on the discount, i have no clue as i run my stuff thru my business.

i do know local stuff gets priority on the job list!

and yes it's handy.

mike

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  #38  
Old 12-21-2006, 03:02 PM
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What is the minium amount of space to leave between the wheel well and the tire and the frame and the tire? Where can I get poly bushing kits for a full-size 66 pontiac? Arowhed, I believe that you left aporoximately 1/2 inch on either side of your wheels, is that enough space? Have you had any rub issues? I believe that you used poly bushings, did you also use boxed arms? Thanks.

  #39  
Old 12-31-2006, 01:03 PM
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Sorry for late reply, holidays ya know! Rear control arm bushings are from Competition Engineering, the kit is availble through Ames Performance.
I have 1/2" inch inner sidewall to frame and outer sidewall to whel well, but that required wheelwell sheetmetal modifications and removal of factory fender skirt latch assemebly, as well as some trimming on the fenderskirts.
1/2" is not really enough, as I do still get very occasional rubbing, but is is very slight..not enough to damage the tire. 3/4" to 1" would be ideal but I was willing to cut it extra close.
I don't have boxed control arms on the car right now but do have a pair waiting to be installed...not really all that necessary unless you a have very healthy engine and steep rear gear.

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Old 12-31-2006, 03:09 PM
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arowhed, you wouldn't happen to have the competition eng part #'s for that bushing kit handy would you?

i want poly-graphite bushings for mine when i upgrade the suspension on mine.

mike

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