The Stovebolt Site Forums The Shop Area The HiPo Shop 6 lug rear from chevy tahoe

Has any one used one of these an their AD, Task Force, or Art Decco trucks? Any info on the wheel spacing? Seems like these axles come with appropriate ratios like 3.73 or 3.23 and give you the option of adding lockers.

John

They are awful wide.

yeah I know but they I have found a complete rear with 3.73 locking rear and disc brakes in new condition. Not sure what it would cost to have it cut. It looks like whatever I chose to do there will be some level of customizing.

read:
http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=011182;p=1#000003

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=011238;p=1#000003

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=22;t=002711;p=1#000000

rear ends that fit
http://www.chevytrucks.org/tech/rear_ends.htm

why spend lots of money on having the rear end tubes cut and rewelded, buying new axles & ??? cause it's tooooo wide. there are many that you should only cut the old hangers off and weld your new hangers on to fit your truck!!!!! I had my gearing changed cause that equipment/parts are readily available.
disc brakes can be always be added if you plan on going THAT fast. the rear brakes on my stock HD 1977 burb rear are 2.75'' wide.
they stop pretty good.

my .02

thanks for input. I am just looking at all my options. I agree about not having to cut the rear end... however it doesn't look like it is ez to keep the 6 lug pattern and have the gears you want and have disc brakes. Rear disc brake kits seem to be expensive if you can find them... I know it is possible to get axles from the wrecking yards that have the backing plates and brackets, and see if I could make something work.

Trailblazers are 6 lug but I believe the bolt circle is 6 on 5. Our older chevies and jimmys are 6 on 5.5... same as the new chevy full size

big~daddy
there are several gear sets that chevy uses. your basic choices are 3.08:1, 3.40 or 3.43 to 1, 3.73:1, 4.11:1 in the 10 and 12 bolt rear end range. these are about 60'' wide and make a very good swap for AD's. That covers quite a bit from towing to freeway use.
http://www.drivetrain.com/gm8.875car.html
http://www.chevytrucks.org/tech/rear_ends.htm
I have disc's on the front. my rear end is from a 77 burb, 4x4, heavy duty brakes @ 2.75''x 11.032'' dia.
so after you read the chevy link you can decide. disc's are nice all the way round but do you really need them on the rear.
I have 6 lug disc up front (matches my rear) and the rear is 2-3/4'' wide brake shoes. Power master. WHAT more could you want to stop!!!!!!!
my rear axle /spring perch offset is 2-1/2'' NOT the 1 - 1/2'' the kits come @.
again my .02

Are you planning on converting to disc brakes in the front any time soon? If so, you might want to go with an axel that has the same bolt pattern as the disc brake conversion. If notice teh 5 bolt on 4 3/4 circle conversion kits are a few hundred dollars cheaper than the 6 bolt kits.

Then width might come next, though I'd argue rims come next. Width is tricky. Your axel might be 62 inches from wheel mount to wheel mount, but what is the backspacing on the original rims? Is the mount plate right at the middle of the rim (50/50). Do you have a 6 inch wide rim and thus 3 inches of back spacing? Well... then you'll have three inches of wheel and rim on the inside of hte backing plate and 3 inches on the outside. What if your new rim is 8 inches wide with 6 inches of back spacing? That means you'd have six inches on the inside of the mounting surface and a 62" wide axel will be too narrow because the inside of your tires will rub against the frame and inside of the wheel well. For that reason, it is better to find the bolt pattern you want (i.e. to match your front axel OR what you plan to do to the front axels in the future, such as a disc brake conversion or Mustang 2 IFS). Then buy the rims you will actually put on the back of your truck and measure the backspacing. Then measure the original axel and do the math, taking into consideration the back spacing. My original axel is 62 inches, I need a 65" axel due to backspacing on the modern rims and tires I'm using. Don't forget that tires count too. Your rim may have the right backspacing but if the tires extend beyond the rim width it must be considered.

Once you have the width figured out and you know the gear ratios in the transmission you can figure out what gear ratio you need in the rear end so that in all gears you'll have shift points and rpms your engine can handle, taking into consideration it's power band (the rpm range it has the most power at and can handle (usually 2200-4000 with a 3/4 cam), and what you want to use the truck for (commuting, hauling a trailer, strip racing...) I'd guess you'll probably come out somewhere in the 3:43-3:73 range. You decide what gear range by calculating the tire height, transmission ratio, speed you want to travel, and rpm range you'll be comfortable with, which is easy using any number of online 'calculators'. My 235-75R15s are 28 inches high. In the back I went to a 275 60 r-15, which is wider and still 28" high. The height of the tires impacts the effective gear ratio, a smaller tire has a higher numerical gear ratio on the same axel with taller tires. So, 25 inch tires are 3:73 and 28" tires are 3.4x (roughly...)

Now you know the width of the axel, the bolt pattern and the gear ratio (s) you are looking for. Go to the junk yard and start looking under cars. Ideally, in my opinion, you'll find a positraction or limited slip differential that meets the characteristics you are looking for. It doesn't really matter if its set up for coil springs because you'll have to cut off the existing mounts and put on new leaf spring mounts (aka perches) right where you need them anyhow, since most axels won't have the mounts in the right place or the mounts won't have the right pinion angle to match your new transmission. I bought a 4" grinder from Harbor Freight for $15, a pack of cut of wheels and grinding stones and went to work cutting everything off the axel tubes and grinding them down. It took me about 3 hours to do it all, including cutting the 'ears' for the coil spring locator/tracking bars on the pumpkin and painting the whole thing with rattlecan Krylon black.

It is no big deal to bolt the new perches in there, line everything up, mark the axel with the right location and right pinion angle, tack weld the perches in place or mark the axel and then pull it out and weld it or take it somewhere to be welded. Setting the pinion angle is easy too. The idea is that the angle of the tranmission/crank shaft is the same as the angle of the axle. Basically they are paralell, or within a few degrees. This is necessary for the u-joints on the new drive shaft to work right and not wear out too quckly. It's very easy to set the pinion. Measure the angle on the tranny, put the 'inclinometer' ($10 from sears) on the axel and turn it til you get the right angle, mark the axle (or tack weld) and then make it permanent. Don't feel comfortable doing that? Bolt the axel in and drive it to a driveline/spring shop and let them do it for about $50.

Having spent a fair amount of time digging through the boneyards, I can tell you that I found lots of 5 on 5 posi rear ends (5 bolts on a 5" diameter bolt circle) under Caprices. 5 on 5 is a standard ford bolt pattern too, so if you've got (or are going to have) 5 on 5 in the front, consider the the famous ford 9" differential because it is easier to swap gears in than the chevy rear ends. The 9" is also a stronger rear end because it has bolt in axels instead of the c-clip system chevy uses. The 9" also came with 5 on 5 rear discs under lincolns. Another advtage to the 9" is asthetics. Since it has a pumpkin that bolts in from the driveshaft side, from behind it looks like the original axel.

The most common Chevy rear axel you'll run across is the 10 bolt. A true 12 bolt is better but harder to find in a 5 bolt posi configuration. There are faux 12 bolts to watch out for that have 10 bolt ring and pinions inside, generally they are newer and not under chevy vehicles. There are also diffences in the GM 10 bolt rear ends that you should be aware of. They don't all use the same diameter ring gear and some diameters are more expensive to replace/repair than others. Check speedwaymotors.com for replacement ring and pinion sets to figure out what the desirable diameters are and then figure out which year differentials those diameters came in, and skip cars that aren't of those years.

Another thing to keep in mind is the rear brakes, do you want rear drums or rear discs? If you go with drums try to find 12" drums with the widest shoe you can find. 11" drums are nice too. Stay away from anything with less than 11" diameter because it is easy to find 11" and why take less rear braking than you can. If you are looking in the bone yard, mix and match if they'll let you. For example, you found the axel you want with 11"x2 3/4 drums that have grooves in them. Find another set of 11"x2 3/4" and switch them before you pay. Another thing you might keep in mind is the e-brake cable. Measure the one on your truck and look at it. The cab end of it is threaded. GM makes a cable like that but it doesn't come under every car. Find the ones you want and put them on the axel you are going to pay for before you buy it at the boneyard so that you get everything in one fellswoop, rather than just grabbing the axel and getting home to discover the brake drums need to be replaced and you've got to buy e-brake cables. Keep in mind that brand spanking new drums are only about $40/apiece from napa. Wheel cylinders are cheap too, as are springs, shoes, brake hardware and brake lines for newer brakes.

How can you tell if an axel is posi? If both wheels are off the ground spin one, if the other one spins in the same direction its POSSIBLY a posi, or someone has welded the spider gears inside the axel. If they don't both spin in the same direction, it might be a posi but it is probably worn so badly that it'll need lots of money to repair it. If both tires spin in opposite directions, it definately isn't a posi. Another way to tell is if the differential has a tag on it saying 'use only limited slip fluid'. Those are often missing so no tag isn't a guaranty it isn't posi. By the way, there are two types of posi's, conical and clutch. The conical is rarer and harder to repair. The clutch type is much more common and fairly easy to repair, relatively. Some people argue the conical or gear driven version is 'better.' I'm sticking with clutch driven so I can find parts in another 20 years.

Is there anything wrong with a non-posi axel if it has good brakes, the right bolt pattern and the right width? Nope. Just like the brakes though, if you can find a posi for the same money why settle for less. There are lots and lots of posi's under sedans and station wagons and cadillacs. Look at the caprices and trucks, if they've got the right width, brakes and ratio.

How do you figure out the gear ratio and how do gear ratios work? Gear ratios are the number of turns on the drive shaft to get the wheels to turn once. 4.11:1, the engine turns 4.11 times to get the tires around once. Higher numerical ratios are better for higher rpm engines with lower torque. Lower numercial gear ratios are good for highway driving and higher low end torque engines. Just like the tranny, too high and you are wrapping out the engine, too low and you don't have enough power. A 2.08 rear end behind a four cylinder might not even move, a 7.6 rearend (like what comes under dumptrucks) is good for moving slowly with lots of weight. There are two ways to figure out the ratio: First, mark a spot on the inside of one drum and the backing plate. Turn the pinion/driveshaft enough times to make the tire turn ten times. Divide the number of turns on the pinion by 10. (i.e. 34 pinion revolutions to 10 tire revolutions is 3.4x:1). The most sure way to determine the ratio is to pull the cover and count the teeth on the ring gear and pinion gear and divide. What about the ID numbers stamped on the passanger side of the axel tube? You might decode them online, but it'll probably take you longer than if you just do the math. Can't you get the rear end width/brakes you want and change the gears? Changing ring and pinion gears is alot of work and requires special calibration tools, unless you are talking about a ford 9" which has a removable pumpkin. You can buy a pumpkin with the gears you want and swap it into your axel in about an hour, really. Thats why the ford 9" is popular with racers! They can change gear ratios depending on the track/competition/etc... I"m using a 12 bolt posi with 3:73 gears.

Last but not least is the drive shaft. Now that you've got the tranny and differential in place you measure the length from the back of the tranny to the pinion of the axel. Go to a junk yard and get yourself an axel of that length with a transmission yoke that matches the one on the tranny($15 around here). Take it to a driveline shop and get the u-joints replaced to match your pinion and then have it balanced. Bolt it in and you are done. You could save yourself a little work by getting the yoke that came on the transmission, but if you didn't it's no big deal. Also, you could make sizing the drive line a two stage process. Go get a yoke, make sure it fits, measure the distance from yoke to pinion and then find a drive shaft and have it all put together. It is important that when you measure the length of the driveshaft you have all the weight in the truck it'll usually have, ie the engine, front clip, cab and bed. The weight on the spring will affect the height of the front and back of the truck which will impact the distance between the tranny and the axel.

nm51, a lot of good info in your post. I was concearned about possible offset issues in the wheels and tires. I have also seen lots of ford 9" parts available. Never thought much about looks, but you are right the 9" does look like the stock rear.

thanks
John

The Trailblazer rear is essentially an S-10 unit,
and the bolt pattern is more like 6 on 4 3/4
instead of the standard 6 on 5 1/2.