Hobbes Posted March 21, 2009 Share Posted March 21, 2009 Hello everyone, I apreciate a little help here. Tried the Tech section and endless internet search, but I am stalling.... I want to change the gears in my differential. From my half rotten buildsheet I could find following: - (something unreadable) 7 278 ratio axle (but I can only find 2.73 gears?) - g80 positraction all confirmed by finding the limited slip tag, and doing the rough counting driveshaft vs wheelturn. Plus my rearend looks untouched so I am assuming it to be the original setup. BUT there is no way I can find that stamped number on the passenger side of the axle. I have a friend who has the knowlegde and will help doing it. I wouldn't touch that myself after all I learned by reading about that. But I am in charge of getting the parts. He only advised to choose the Richmond Gears. To get to the point: 1 - Am I right assuming a 8.5" axle? because there is also a 8.2" one 2 - will my carrier hold a steeper ring and pinion? So far I nailed these two parts: ring and pinion installation kit 3 - This will be a street car. Is the 3.42 too radical? I was told I shouldn't go over 3.5... Or should I go one lower to 3.23??? I just know with that 2.78 the car doesn't fullfill my expectations at take off. And the highspeed loss is ok since it is no fun at all to drive fast with it. 4 - last one: the speedometer won't be correct. I read changing a gear in it can fix it following a formula. Can't find it right know. But that's for Miles. My tach is in Km.. Any advice there??? Anyone done the speedometer gear change? Can I do it knowing the right ratio or should I give it away? Hoooooo...loong text and a lot questions. I am happy for any input. I need to order soon to have it for sure in the hotel when I am there. Next month 17.-20.04 I am for a short trip in NY killing two birds with one stone: Mom gets her daughter-time-Trip to the great NY and I see a chance to get parts without expensive shipping costs and time By the way, I would be up to a coffee/beer in NY if anyone happens to be there to talk some gas... Janin Quote Link to comment Share on other sites More sharing options...
Guest XXXXXXX Posted March 21, 2009 Share Posted March 21, 2009 Hey Hobbes, I went from a 2:73 Single track rear to a Richmond Posi unit with 3:48 gears. I love the way it launches! Both tires burn! I hate single wheel burnouts. I don't drive very fast either so the RPM @ 60 MPH is not too bad. No tach so I can't tell ya the RPM,sorry. Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 21, 2009 Author Share Posted March 21, 2009 Hey Ken, thx for the input. I was a little undecided since I read a recent post here from someone going back to a lower gear ratio because he didn't like the steep gears.... And a single tire spin is not a burn out in my diccionary...positraction is a must! burn baby, burn.... JAnin Quote Link to comment Share on other sites More sharing options...
Guest XXXXXXX Posted March 21, 2009 Share Posted March 21, 2009 Janin, You won't like the 3:42 ratio on the Autobahn but around town and out on the back roads those gears are fun. Quote Link to comment Share on other sites More sharing options...
monte70car Posted March 21, 2009 Share Posted March 21, 2009 is your rear a 10 bolt or a 12 bolt (bolts that hole the rear end cover on)? If you have a 2 something gear now the carrier will not carry anything bigger. Limited slip is still a posi. just that the other wheel will kick in after a few seconds. One thing I don't see is what type of trans. is it a 350th or the 400th? Even though you speedo and tach are in km it should still use the same speedo gears like a mph car. a mid 3.xx something gear would be idea you might want to look at a 3.55 or maybe a 3.73 gear, anything higher then a 3.73 you will spend more time at the gas station then on the street. Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 21, 2009 Author Share Posted March 21, 2009 Hey Robert, You are right. Important info missing. Here it comes: got a TH350 and a 10 bolt rear. The tag at the rear states to use correct fluid for limited slip. The buildsheet says G80 - Positraction ?! And like I said, there is no way to read digits on the axle. Heres a pic of the rear with the limited slip tag. Both tires spin the same way, there is no delay when we tried while the back was lifted up. The carrier question bothers me, because I can find little sidenotes in the catalogs like: 2.73 and up or 2.5something and down carrier. Since my buildsheet says 278 ratio axle I am assuming the carrier for the bigger gears equipped with the lowest one. But just not sure and not wise enough how to find out. Any ideas? Janin Quote Link to comment Share on other sites More sharing options...
Guest XXXXXXX Posted March 21, 2009 Share Posted March 21, 2009 Janin, have you tried emailing Richmond gear with your question yet? They may be able to help you. Quote Link to comment Share on other sites More sharing options...
bobsmc Posted March 21, 2009 Share Posted March 21, 2009 i know a quick way to tell if it is a 8.2 vs. 8.5. the pinion nuts are different sizes. that is the nut behind the u joint. the small one will have a 1-1/4" nut and the larger one will be 1- 3/8". not 100 % on the sizes but 99%. hope this helps. bob Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 21, 2009 Author Share Posted March 21, 2009 Hey Bob, that is an approach to try. I have the dilemma though, that I don't want to tear the rear apart. We still need the Monte to drive to the friend's garage and I hoped to get the parts before that. Have there been 8.2" axles on the 70s Montes in the first row? In worst case I have to take off the driveshaft to look up that pinion nut. But that at least saves me from opening the differential. I also wrote a mail to Richmond Gears, asking about that carrier. In my summit catalog it has NO sidenote about carriers. Just seems as if with the 8.5" axl it should fit...if I have a 8.5"..... uargh....too many ifs and whens... Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted March 22, 2009 Share Posted March 22, 2009 Hobbs, follow this link then go to this page rear axle tech page Quote Link to comment Share on other sites More sharing options...
kc8oye Posted March 22, 2009 Share Posted March 22, 2009 if you have overdrive, the 3.55 gears are a GREAT choice.. if you don't have any plans for over drive.. I'd stick to lower numerical gears. btw.. 10 and 12 bolts does NOT refer to the number of bolts in the cover.. while for the monte's it just happens that the 10bolt does have 10 bolts and the 12 has 12.. 10 bolt or 12 bolt actully refers to the number of bolts holding the ring gear on the carrier. when you start talking about other axles like 14 bolt truck axles.. it doesn't always hold true. Quote Link to comment Share on other sites More sharing options...
overdrive Posted March 22, 2009 Share Posted March 22, 2009 Janin, this link may help, if you haven't already seen it. There are some more threads at the bottom of the page. I also found this: The best way to identify an 8.5 is to remove the cover and inspect the ring gear bolts. If the head of the bolt requires an 11/16-inch wrench (7/16-inch bolt diameter), then its an 8.5. If the ring gear bolt requires only a 9/16-inch wrench (3/8-inch bolt diameter), then its an 8.2-inch rear. Be aware that the ring gear bolts on the 8.5 are lefthand threads. Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 22, 2009 Author Share Posted March 22, 2009 Hey all there... thx for the support on infos. Bones, your axle code pic is from a storybook where the world lives in peace Frustated on all the confusing different axle options and not yet willing to open the differential or getting off the driveshaft, we grabbed the steelbrush and looked everywhere. Now it gets spooky : number found on the drivers side facing to the rear.... plus it is shorter than expected. At least from the code list on the Tech info site it states the strange gearing of 2.78, which is also stated in my buildsheet. I hope someone here has a secret book with information he would have to kill that one that sees the book.... Because with that number still I am not sure weather it is a 8.5" or 8.2" axle and if the carrier will hold up those richmond 3.42 gears I am dreaming of... Janin Quote Link to comment Share on other sites More sharing options...
monte70car Posted March 22, 2009 Share Posted March 22, 2009 Janin I did some looking and you are not dealing with a chevy 10 bolt rear end. You have a BOP rear end http://www.oldsmobility.com/10bolt-tech.htm going by the picture you posted of your rear end and the one on the link I post it looks like you have a 8.2 rear B or P Axle 11 1/2" Irregular Cover - 10 Holes 8.20" Diameter Ring Gear 1.438" Diameter Pinion - 27 Splines "B" or "P" Axle Only Non C-clip type 64-70 Olds F-85 64-71 Tempest/GTO 67-71Firebird Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted March 22, 2009 Share Posted March 22, 2009 BOP stands for... Buick Oldsmobile Pontiac someone may have swapped rear axle at some time, more than likely you will need a new carrier Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 22, 2009 Author Share Posted March 22, 2009 Monte70car and Bones, thx for quick reply...and OUCH... that is definately not what I wanted to hear...new carrier with posi and gears that are hard to get... That rips an unexpected hole in my pocket... I will definately have to unbolt that diff-cover trying to find proof for you guys being wrong... But at least now I can start looking for proper parts...OUCH, my eyes...that can't be true, they must have forgotten a decimal point there... I just wish my junkyard was filled with different cars than VW Golf2, Opel Astras, Fiats, Renaults and all that stuff that is sooo wrong frontdriving... So far I appreciate all the secret book hints and info-tips. I will be back...when the differential is open with some pics and probably some more questions. Great Place Here, Thx! JAnin Quote Link to comment Share on other sites More sharing options...
kc8oye Posted March 23, 2009 Share Posted March 23, 2009 alllright.. thanks for the info.. when I change my diff fluid this spring I'm gonna check on those ring gear bolt sizes and figure out which pinion yoke I need to order for 1350 ujoints Quote Link to comment Share on other sites More sharing options...
Monte7071 Posted March 24, 2009 Share Posted March 24, 2009 As stated above that is a BOP 8.2 rear. What year is your car I had a 70 Monte one owner that had a 8.2 BOP they are a completely different rear bolt in axles and I belive the brake shoes are even different. Quote Link to comment Share on other sites More sharing options...
alex's72fgmc Posted March 24, 2009 Share Posted March 24, 2009 BOP rear ends were substituted from time to time on the line. just fyi Quote Link to comment Share on other sites More sharing options...
kc8oye Posted March 24, 2009 Share Posted March 24, 2009 I ddin't know kph speedo's were available for the 1st gen monte's? even my car from canada had an MPH speedo.. but if it's a factory replacement tach, it should still be setup for 1,000 rev's per mile. Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 25, 2009 Author Share Posted March 25, 2009 Hey there, for the skeptic among you, here is a pic of the buildsheet, with the readable info on axle, posi, auto level and smallest engine... plus the axle codes info on the Tech section lists the "xc" code, with the odd ratio of 2.78 So I still think it is the axle with which the Monte rolled off the assembly line in 1970. I know these are odd combinations, but hey, this car went straight from factory to switzerland. Km/h speedo plus a original GM but funny swiss/german version of the owners manual. And as a side note: this may be the smalles engine in the Monte line, but it is HUGE compared to engines out there at that time. If I just compare my 1300cc VW Bug from 1968 with the MOnte, it must have been a monster on the streets. The two cars seem decades apart technical wise, not only 2 years... At the end another question: I did some homework on the BOP parts. With posi-carrier for gearing I want, ring and pinion and rebuild kit I am facing easily 800USD... I am wondering what used/rebuild Chevy 10 bolt axles go for in the US? I am just trying to figure out pros and cons of rebuilding my BOP axle or get a 10 bolt chevy one where parts are cheaper and there is more available.... Here in Europe they are hard to find or very expensive due to the small market. Shipping wise for items that big, I am not concerned, because I get freight benefits since I am working for an airline. I would roughly pay 1,2Euros/kilo (1Kilo around 2 Pounds) once the axle is within an bigger/international airport... I appreciate any input... Janin Quote Link to comment Share on other sites More sharing options...
Monte7071 Posted March 25, 2009 Share Posted March 25, 2009 It looks like your car was pretty loaded from the factory. I would try to get a Chevy 10 bolt they are cheaper and a little stronger. But if you want to keep the car original I would keep the 8.2. Its hard to read some of the build sheet but it looks like you have power bench seat power windows locks block heater trunk release defogger tilt and map light and some other options. Does the car still have all these options. Quote Link to comment Share on other sites More sharing options...
Hobbes Posted March 25, 2009 Author Share Posted March 25, 2009 Hey Monte7071! Yep, all options are there. Or at least a trace of it. The only things missing: -window washer monitor (completely gone, but lookig to get one!) -power trunk: wires cut, but hardware still there (also looking for parts to restore it) -air ride system was there but cut off at the wires and airline. That option was out of my league to make it work again, so I sold it to a member here to fund some of the other parts I needed) except for the factory clock and above stated everything works, all the litle map trunk whatever lights,power bench, windows...it amazes me! I just repaired the rear defogger...it was only dirty... Well, to be honest: I have no clue what an engine block heater looks like but I stumbled across it deciphering my buildsheet.. Axle wise: like I said. I am right now balancing the pros and cons. Pro: -original axle -good shape (assuming the total (1)17800 km = 63600mls from the speedo reading is right)and feels tight -I have it Cons: -parts are hard to get -very expensive!!!!!!! -just not the gearing/carrier I want Can you just give me a rough estimate on used/rebuilt 10bolt chevy axles? Online on the official vendors places I see prices like for a rebuilt one with my dream specs for around 1500USD. If those are the numbers I have to count with, I guess I stay with my BOP. Janin Quote Link to comment Share on other sites More sharing options...
overdrive Posted March 26, 2009 Share Posted March 26, 2009 You have the only 70 that I know of that came with dual exhaust and a 2 barrel! Your car has some nice options. I see you even have the AM radio with 8 track tape player. What is the first option, the one above the electric door locks? I'll see what I can find out about the Chevy 10 bolts. Dan. Quote Link to comment Share on other sites More sharing options...
overdrive Posted March 27, 2009 Share Posted March 27, 2009 Here is a link to a rebuilt 10 bolt for sale. The rearend in this ad may not be what you want, but this guy can probably answer any of your questions and he can build any GM rear that you need, if he doesn't already have it. Quote Link to comment Share on other sites More sharing options...
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