Hi all. I have a 3.73 8.5 10 bolt rear axle today and although the car goes like crazy up 'til 60 it's not exactly a pleasant ratio for daily driving so I'm going to change it to a more reasonable ratio. The engine is no monster and if I get 300 bhp out of it I'm happy so strength shouldn't be a problem with an 8.5 as I understand it. What I'm wondering (even after looking through this forum) is if it's easier for me, not a shop, to change the gears in this axle or if I should replace the whole axle? Worth mentioning is that although I've been a petrolhead for 20 years, I haven't taken apart one single rear axle during this time. Also, what ratio should I aim for? TIA.
Hey Jim, now I know how you got to 9500+ posts. p I'll replace the period with a question mark on my first question btw.
If you mean to ask if it's easier to change the gears yourself, I'm going to stay on the cautious side & say no. The first couple of jobs I did, I had someone with lots of experience looking over my shoulder, and it was a good thing, too. Not to say it can't be done on your own for the first time, but you need to be accurate and precise with side bearing preload, pinion depth, backlash, gear mesh pattern, etc. Having someone experienced do the job is a good way to go, they could have you ready to go in an afternoon. I also think 3.08 is a good choice, maybe 3.23:1 but no more. I don't remember where the ratio cutoff is with your current carrier, I'm hoping you can get to 3.08:1 without changing carriers. Devon
Easier to swap the whole rearend IMO. If you change gears you'll probably take the whole rear out to do that work anyhow, it's simpler to have a complete unit ready to install afterwards. A gear ratio is difficult to recommend without knowing what kind of driving you do. I have a 2.56 and would recommend that if you do a lot of 75 MPH highway driving like me. -Bob Cunningham
It looks to me that you have the perfect gear for a trans change! If you install a 200-4R you will have the best of both worlds. The 3.73 wil let you accelerate with the best of them ,and the .67 overdrive gear in the trans will make it into a real cruiser. It is practically a "bolt in" operation, and will make a great set up. I have a 200-4R in my 72 GS and my 69 Sport Wagon and Love them :beer :beer
I'm hoping to do a lot of highway driving with it in order to visit friends, family and various meets but it'd be nice to outrun or at least keep even pace with all the ricers at the redlights. @The Old Guy: Sounds like an interesting option (assuming it's an automatic). What kind of money am I looking at for a 200-4R? Anyone else have an opinion about the 200-4R?
Nevermind my previous post; I've done some digging and found out that I can most definitly not afford a 200-4R, at least not this year. I'll keep looking for 10 bolt 8.5 axles instead.
I'll disagree with what most people are saying, I think it's far easier to switch out the gears. Especially If your're going to switch it on carrier.
Well, as I haven't gotten my manuals yet I don't really know how much work that's involved in changing gears. I'll dig around the net for some info though.
This might give you an idea about what you're up against. Don't underestimate the need to do this right, otherwise you'll turn new parts into trash: http://www.automedia.com/Swapping/RearEnd/Gears/res20020501gs/1 http://www.motivegear.com/tech_info/R_P_instructions.html http://www.thedirtforum.com/differential.htm http://www.drivetrain.com/ringpinioninstal.html Devon
Correctly setting up gears is by no means a walk in the park. Sometimes the occasional installer/"mechanic" will get lucky, many times not. Been quite a few times I've thought doing a video on the pitfalls & common to not so common screw-ups. Seen them all. Even with such a video, I doubt many one time installers would want to invest the $$$$ to have all the tools & specialty fixtures. Set-up new or go used rear... IF, you have someone who is very well versed in setting up ring & pinions, ie, builds rears all the time, buy a new set of US Gear-Strange 8.5's, have them shipped over, & have them correctly set up. If not, keep watching for a non a/c '71-72 Skylark or Cutlass that might have some decent 3.08's. Out of over four hundred '71-72 8.5 A-body cores I've disassembled, nearly all had 2.56's or 2.73's. Even with a 35 year old used rear, expect to have to have new pinion bearings, carrier bearings, races, new crushsleeve, & nut installed. Care has to be taken that used gears are in really good shape & pinion depth & correct B/L are recreated. Recently, I built a '66 3.31 Chevelle 12 bolt posi rear with decent used 3.31 gears. Had to have this ratio & none avail new. Patterning out the gears & getting what I perceived as an optimal pattern, always takes quite a bit longer with used gears. New US Gear 3.42's would have taken a few hours less time to correctly set-up. Hit the target depth, affirm a good pattern, & go. With unknown used, I'm always crossing my fingers :shock: that rear will be quiet, & thats after building over a thousand GM 10 bolts @ 12 bolts. Got to run. trying to find the best BBQ in KC p Got Posi? :3gears: Roger
Thanks for the feedback Devon and Roger, I'll see what I end up doing but it leans towards a "new" axle and having someone skilled go through it to make sure it works as it should.
I decided to revive this thread as a rear end change is looking more and more likely. As mentioned previously in this thread the 3.08 8.5 rear axles are quite rare and if I find one I most likely need to rebuild parts of it just to make sure it hold together. What other options besides 8.5 do I have if I want to go for a 3.08 ratio? What would the set of US Gear-Strange 8.5's that Roger mentioned cost?
Not sure what it would cost to buy & import a set of new US Strange 8.5 gears to Sweden. New US Strange 8.5 gears are typically avail in the US for $165 to 175 a set. Got Posi? :3gears: Roger
Hey Roger. Thanks for the info, now I know what the gears cost and that's a start. Do you any thoughts on using another axle than 8.5, 10-bolt if I want to get a 3.08 ratio?
Martin, Just can't advise against the 8.5 A-body rear. Superior pinion support, stock tapered bearing bolt-in axles, along with a huge amt of parts from the aftermarket, make the 8.5 the 10 bolt to run & to build for hp use. Every year I ship out dozens of nice unchewed axles for fellows still running earlier sealed bearing 10 bolt rears. Many have rears that have spit out axles & damaged a rear 1/4 panel & outer wheelhouse. If I was overseas & on a tight budget, the only other 10 bolt rears I might consider in a cruiser type '64-72 A-body would be a - '70-72 Pontiac 8.2 10 bolt (also used in 70-72 Grandprixs) -'70 type "O" Olds -' 70 Buick 8.2 Reason, all have tapered axle bearings, not the problem prone sealed axle bearings. Unfortunately, the Olds type "O" & the Pontiac 8.2 are the only such rears avail in 3.08 ratio. Hope this helps. Got Posi? :3gears: Roger
Thanks for the feedback Roger. Since you're the resident rear-axle guru I'll take your advice to heart and keep looking for a 8.5 10 bolt. :TU:
I've been trying to get a bearing on how much I should pay for a complete 10 bolt 8.5 axle by looking at eBay and this forum and also what axle I can use. As for the price; $750 + shipping seems to be the standard asking price for a posi rear end in good shape. I haven't seen any non-posi so I'm not sure what those are (or if they do exist). I'm not sure how much difference the ratio makes either, I only saw one 3.08 axle that was rebuilt to a posi and that was $375 + shipping. As for what year/make/model I haven't been able to figure it out exactly but it seems as if any BOP from 69-73 should fit my car. Any thoughts on this?
x2, keep your rear, and save up fot the trans swap, LOTS of GM cars in the 80's had them, even chevrolet. when all is said and done, you'd be much happier with the end result.
