Hey Hambers I just wanted to ask people’s opinion on some different diffs for a daily driven 53 Chev with a 300hp SBC. I went and bought a GM 8.5” 10 bolt out of a Firebird the other day and looking at it/carting it around has made me think I may have gotten too much diff for this car. I know they are tough as nails but I’m just wondering if it’s too big and heavy. I want to keep this car light if I can as it all helps when you drive it around all the time. I currently have a Holden HQ Salisbury diff in there but it has to be replaced anyway as it has the wrong diff ratio and the bigger ring and pinion Salisbury gears aren’t interchangeable. I haven’t pulled the Salisbury out yet but it looks like a lighter diff, and would be enough - strength wise I think. I’m at a cross roads of what to go with. Does anyone know the weight difference between these diffs? If they were essentially the same weight I’d go with the GM 10 bolt but I think it could be wayyy more diff than I need. Basically if you would want to keep things light, efficient and practical behind 300hp what diff would you opt for in this car? Cheers in advance! J Sent from my iPhone using The H.A.M.B. mobile app
What ratio are you after? You may be better going to a Commodore / Falcon BW 78 as parts for the other 2 aren't that common down here. I have a Salisbury 3.08 Limited slip behind a 350 in my 55 and have only split the LS housing once so far. Open centres are stronger in the Holden Salisburys.
The 8.5 is a cross of both 10 bolt and 12 bolt. I wouldn't worry about it's weight. As asked above, "what ratio?" would be of more concern.
Either 3.55 or 3.73 is what I’m going for on a T5 with 0.63 OD and 27” tires Sent from my iPhone using The H.A.M.B. mobile app
Then your saying you have no idea what ration the Firebird rear you have has in it? It's ratio will say keep or move on. Ratio's start at 2:56. Not what you'd want behind an OD trans.
It has a 3.08 which I’ll change to a 3.55 or 3.73, but I’m not concerned about doing that until I can figure out which diff design will suit my needs better Sent from my iPhone using The H.A.M.B. mobile app
A Salisbury is a good strong diff. I’m just trying to figure out the weight difference mainly Sent from my iPhone using The H.A.M.B. mobile app
I have Camaro discs up front on this thing. The Salisbury I’ve been running has drum brakes Sent from my iPhone using The H.A.M.B. mobile app
Not for any reason other than having a well matched drive train. I don’t want to be lugging around a whole bunch of extra diff weight if it’s not necessary
Well ,,, GM thought it was a good idea to pair that rear end with a 300 hp engine in a firebird. Does that count for being a "well matched drive train"? The first thing to figure would be the load on the rear end. Take the weight of your car, then the low gear multiplied torque available at the tire contact patch, (Engine torque X first gear ratio X rear end ratio / tire radius gives you ft lbs of torque thru the rear end.) and the traction factor you expect out of the car. See how that all stacks up comparing your car to the Firebird and the other proposed rear end donor. You certainly could get the car around with less substantial parts, just drive it like there's a raw egg between your foot and the accelerator. Castrating the power off your 300 hp small block would be another way to motorvate around with less substantial parts. Neither one sounds like much fun.
As far as it being matched to a 300hp Firebird, Didn't GM put these 8.5's in just about everything for a time there anything from 175hp 305's up to the big blocks? The 8.5" "corporate diff" being a one size fits all compromise between 8.2" and 9". So, 300ft-lbs (est) X 2.95 X 3.73 = 3301.05 ft-lbs. Divided by 2.25 ft (27" wheel) = 1467.13 ft-lbs of torque at the wheels. Am I doing this right? I see what you mean. Going lighter/weaker wouldn't be doing me many favours aside from perhaps a small drop in parasitic loss. It just seems like an immense chunk of iron, but I guess I'm over thinking things.
Tire radius, 1.125 Yes GM used that designed rear in a lot of stuff. They have pretty tight guidelines they needed to fall into as well. MPG, ride quality, and longevity as well as bottom line profits. That means that over all weight, un sprung weight, strength were all considered over the cost of the thing or fitting something larger or smaller.
Never broke a 10-bolt in a lt. wt Model A, just thought they were less strong than the 12-bolt. Don't know about the Salisbury.
Yes, you are over-thinking things. Whatever the weight difference is (minimal) you have 300 hp. And if you put a couple of friends in the car, the difference in weight of the two rear ends (not your friends') is not going to matter. A race car needs a "well matched drive train". You just need a suitable gear ratio.
The subject of weight difference has come up before between 8” and 9” Ford axle ***emblies. In the discussion it was claimed there is about 29 lbs difference between the two. I would think that would be close to the difference in the OP’s comparison. Ray
Since you brought it up. Last night I searched several forum's and with out exacting numbers being said. The weight difference between the 10 bolt and 12 bolt wasn't very much. This would mean the 8.5 would fall some where in between.
I am not familiar with what exactly the Salisbury rearend is? Is the Salisbury rearend the late model GM withearing surface 7.625 ring gear? That was used in countless vehicles with 300 or more hp. I always thought it seemed light weight for the higher power V8 applications. The 8.5 10-bolt is a good string rearend that can hold up to much more than 300 hp. That I am familiar with, it was the GM rearend of choice during the 70's and into the 80's. Only real drawback to either the 7.625 or the 8.5 are both have c-clip axle retainers, and both use the axle shaft as the wheel bearing surface. Might want to verify the axle wear in the bearing area on that 8.5 you picked up.
I think that "Salisbury Axle" is a term often used to describe not only a specific brand name, but also a type of axle construction that was originated by Salisbury, so far as I know a British company. The characteristics of it are that it has a cast center section which incorporates the differential carrier. The axle tubes are pressed into that housing. We all know the type....common to Dana/****er, GM 10 & 12 bolt, etc. The common alternative design is the type used by Ford 8 and 9 inch axles, most GM vehicles prior to 1965 and Mopar 8 3/4"........all of which have pressed steel, welded housings and removable differential carriers. The term 'Hotchkiss' comes to mind and I am uncertain if it applies to the axle housing described immediately above or applies to the suspension type where the drive axle ***embly is attached to the ch***is by parallel leaf springs. Ray
^^^^^ Enter that diff name and not just one type will appear. The first time I heard that diff mentioned here on the HAMB some time back. It turned out to be a 7.5 via a picture. To me Salisbury is like only saying Rear End.
My point is that ‘Salisbury axle’ is a term used to describe a type of axle ***embly design and construction, named for the company that invented it......not it’s specific size or capacity. It has also become common to describe, or identify type of design, of any axle brand name that uses the same design features. For instance, a GM 10 bolt axle ***embly is a ‘Salisbury type’ axle because of it’s design characteristics, though it was manufactured by GM or one of it’s suppliers, not the Salisbury Company. Think ‘Kleenex’ or ‘Scotch Tape’, in reality brand names, but commonly used to describe a type of product, made by other manufacturers, that looks and functions the same as the original brand name item. Ray
Things are different in other parts of the world http://gbrutah.com/product-catalog/cs-differentials-overview/history-of-land-rover-differentials/
In Australia there was a Holden banjo diff, then the Holden Salisbury diff. In HQs and the like. They are a 10 bolt diff, but not to be mistaken with the GM 10 Bolt. Which I believe is heavier duty, but there's not much info out there comparing the two it seems. Even the weight of a 70's Holden Salisbury is debated...
Thanks for the link. That inspired me to do a further search and I found this this.... http://www.gomog.com/BLAIR/tech/rearend.html It seems I was incorrect about the Country of origin of Salisbury, but on the right track in general as to the design features that are characteristic of this axle design. The ****er (Dana) axles began as Salisbury in the US, not the UK, but eventually found their way there..... Ray
Damn good read ! Part 2 goes over the "Salisbury" Part 1 http://www.themotorhood.com/themotorhood/2015/12/8/the-ultimate-guide-for-diff-buyers-part-i Part 2 http://www.themotorhood.com/themotorhood/2015/12/8/the-ultimate-guide-for-diff-buyers-part-ii
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