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 Post subject: Rear swap issues
 Post Posted: Mon Feb 20, 2017 7:47 pm 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
Posts: 34
I picked up in 8.5 out of a 1984 olds Hurst to swap in got the old 7.5 out and started building up the 8.5 as it was all tore apart in pieces. The first problem was it was missing a pinion yoke so I got one from a gear place but for some reason the seal surface is much too large for the seal that came with the overhaul kit that's the first issue so just wondering if there's two different pinion yoke SEALS or pinion yokes? The next issue comes with the wheel bearings I ordered the wheel bearings from the same gear place but the axles that buddy gave me to go with the tore a part 8.5 the bearing section measures 1.4 inches and is much too small for the bearings that came from the gear place I'm starting to wonder if I got the wrong axles or did I get the wrong bearings?

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 8:36 am 
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Location: Canton Mi.
Are you sure you have an 8.5 - the parts you got were for an 8.5(specific to 84-87) - I believe the wheel bearings for 7.5 and 8.5 are the same and you should have 28 splined axles.


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 8:48 am 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
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It's definitely an 8.5 from an 84 old hurst as far as the housing goes. It does have 28 spline axles as well. It was missing gears, pinion yoke, carrier and all bearing. Basically was a housing with main caps but he had what he thought are the axles as well so I took em. I found an article that talked about two different sizes for wheel bearing so I'm guessing I have the wrong wheel bearing size for my axles.

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 6:19 pm 
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Location: Cudahy, WI
General Motors is all about parts interchangeability. I doubt you have the right axles. GM wouldn't make 2 different size bearings (or seals for that matter) for a rear end that was only in a handful of cars. Just make sure the axles are correct. I would assume the 2 different sized bearings were probably for the 7.5" or 8.5" rear. Since the diameter of the axles are different, they might use different bearings. Or maybe I'm completely wrong, and they use the same bearing, but I wouldn't think so. The Grand National rear should be identical to yours, too.

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1978 Malibu Coupe SBC TH350
1979 Malibu Coupe BBC M21 4 speed the "Big Gun"
1979 Malibu Coupe LQ9 TCI 6X
1979 Malibu Wagon 305 TPI 700R4


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 6:45 pm 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
Posts: 34
I guess for starters I would like to find out what all the dimensions are for standard 8.5 axles The way this whole transaction happened I wouldn't be surprised I have the wrong axle but would need some numbers to confirm.

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 7:39 pm 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
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Well to add a little mystery to it all buddy isn't sure if it was outta of a grand national now. But it for sure is a 8.5 housing with the square protrusion on bottom and does have extra ribbing on the pinion area compared to my 7.5. Also does not have the diagonal cover. Other than center section it's all the same as my 7.5. I just bought wheel bearing and seals for a 7.5 and they do fit. So it seems like it's a center section from a 8.5 but with tubes from a 7.5 or something

Also not that this is very scientific but the axles do seem to belong by going how everything is painted

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Tue Feb 21, 2017 10:04 pm 
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Location: Cudahy, WI
Looks like I could be wrong. I looked real quick one Rockauto for replacement bearings, and sure enough, the same part numbers are listed for all years of turbo Regals, Malibus and your Cutlass. Says the 2.250 O.D./ 1.400 I.D bearing will fit both the 26 spline 7.5" rear, OR the 8.5" 28 spline rear. BUT, then there's also another larger bearing that's 2.530 O.D/ 1.620 I.D that says it's for the 8.5" 28 spline rear. So, wtf?!? That's why I have a guy who builds all my rear axles. I don't have to deal with this, lol.

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1978 Malibu Coupe SBC TH350
1979 Malibu Coupe BBC M21 4 speed the "Big Gun"
1979 Malibu Coupe LQ9 TCI 6X
1979 Malibu Wagon 305 TPI 700R4


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 Post subject: Re: Rear swap issues
 Post Posted: Wed Feb 22, 2017 7:24 pm 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
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Yeah its been a dousie. But I do got it figured now. It definitely took 7.5 wheel bearing setup. The pinion also I had to remove the outer sleeve that was on there for it to fit my seal that came with the overhaul kit. So far I'm day number 2 of setting it up. It's kinda too bad the axles are smaller but at least I have the better ring and pinion advantages of going from a 7.5 to 8.5.

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Thu Feb 23, 2017 11:37 pm 
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Daily Driver

Joined: Tue Dec 29, 2015 11:02 pm
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Can anyone she'd some light on which side I should really be concerned about for a pattern? Drive or coast. Seem like my drive ain't bad but my coast is way on the toe

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1980 malibu- 408 sbc, th350, GN 8.5 3.73


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 Post subject: Re: Rear swap issues
 Post Posted: Sun Mar 12, 2017 7:26 am 
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MalibuRacing Junkie
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Location: Upstate NY
The pattern has to be good on both Sides! I'm no good at setting them up, don't ask me which setting to change LOL

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'78 bu, 350/310 hp, M-21. Now with a GN 3.42 rear and Detroit Tru-Trac, Xtreme rims, grey bucket seat Monte interior


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 Post subject: Re: Rear swap issues
 Post Posted: Sun Mar 12, 2017 10:11 pm 
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Overall length (wheel mounting surface) should be around 58-58.5" I believe, and the shock mounts are on the rear side of the axle (right behind the lower trailing arm mounts).

I got a B-Body rear, but that's going to be its own little special animal... it will have to be shortened, but if the bearings are bigger than a G-Body then I'll keep the B-Body parts. The lower arms I'm not too worried about the fit, but if I have pinion angle issues from the uppers being too short (read they need to be shortened about 3") I have a 3-link idea in mind.

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