73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: choptop on April 21, 2010, 06:45:34 pm
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ok guys heres the story. Last year the rear axle cratered in my red truck. The pinion nut came off and trashed the gears. I swapped the axle with one from a parts truck (85 blazer) just to find out it was bent. Well I acquired a 12 bolt (free) to replace the 10 bolt with and upon inspection today, I found the 12 bolt is a 3:07 (43:14) and I need 3:73 to match the front axle.
Whats best route?:
1) use original housing and axles and swap in ring and pinion and related parts from bent axle
2) rebuild 12 bolt with new ring and pinion
Ive attatched a pic of the 12 bolt and have questions there:
what is the spring setup in the middle for?
will it swap and work in the 10 bolt axle?
Are the back plates and drums the same on the 10 bolt and 12 bolt? I need drums for the 12 bolt and the ones on the 10 are brand new
Thanks guys for your help, Im trying to get this done before a show on the first of May
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if you want to go to a show, why not stick it on, and drop the front shaft off, so you can go, and figure it out afterwards.
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springs=Posi
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You'll need a conversion U-joint. You have a limited slip differential so that's a plus. Get a 12 bolt truck ring and pinion along with an installation kit. I can't remember if the backing plates will swap over from the 10 bolt to the 12 bolt but I think they do. It's been so long since I did that I honestly forget. I'm sure someone else will chime in on that.
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dont forget the straps for the rear end, if yours didnt. i had to buy some today
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You'll need a conversion U-joint. You have a limited slip differential so that's a plus. Get a 12 bolt truck ring and pinion along with an installation kit. I can't remember if the backing plates will swap over from the 10 bolt to the 12 bolt but I think they do. It's been so long since I did that I honestly forget. I'm sure someone else will chime in on that.
Best place/price for ring and pinion w installation kit? Chris, do you have them?
Howlinwolf, what straps are you refering too?
Thanks guys
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Give these guys a try
http://www.ringpinion.com/
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Thanks, that brings up another question. it sasy "this is a thick gear set for 3:42 and down carrier"
Is that numerically down or gear ratio down. Since mine is the 3:07 gears, I assume I need the other gear set. Is that right? Sounds like a dumb question, but it doesnt make sense to me.
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If they were smart they would be referring to numerical.
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where my u joint bolts to my rear end, there are 2 straps or clamps or whatever that bolt it on. just make sure you have the right side.
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where my u joint bolts to my rear end, there are 2 straps or clamps or whatever that bolt it on. just make sure you have the right side.
Gotcha, and thanks for pointing that out. I do need to get some
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If you have a 3.42 or numerically-lower (like your 3.07 ratio) then you would need a 'thick' gear set to run the 3.73 gears. I went through all that last year.......3 times :-\
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Thanks guys, that what I needed. I tried to swap axles on the 10 bolt today, but the housing has to be bent because it binds up severely when it meshes with the inner spline, plus, its a 3:07 gear as well. So, if Im gonna have to buy gears, it may as well be the one with the limited slip. Ill start on it tomorrow. Im gonna redo the bearings and seals. Ill probably just run the 3:07 for next weekend because I dont think I have enough time to order and install the gears before then.
This leads to new questions:
Will the u joint straps from any of the 12 bolts work? I have a few, but they are 5 bolt axles. If not, where to buy?
What lube do I need to run with the limited slip?
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Vile, hook a dummy out please and tell me which install kit I really need please>
PK GM12T or BK GM12T or the master YK GM12T
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You can run regular 80w90 just add the friction modifier. U-joint straps can be bought at any auto parts store. http://www.rockauto.com/catalog/raframecatalog.php?carcode=1296121&parttype=10437&a=FRc1296121k634492
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If you want to replace all of the bearings go with this one http://www.ringpinion.com/ProductDetails.aspx?ProdID=391
If you want to just replace the R&P go with this one http://www.ringpinion.com/ProductDetails.aspx?ProdID=564
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Thanks Vile, I owe you one. Can I run the front shaft as long as its not put in 4wd? I want it at least complete for the show even if the gears arent changed. Ill have to change the gears after the show
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What transfer case is in there?
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np208
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As long as you're in 2wd you won't have a problem
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Anyone know the pn for the straps? The ones the parts store gave are not right. The strap is ok, but the bolts that go with it are only about 1/2 in long and way too small in diameter. The only other ones they showed are the u type clamps. Our Chevy dealer is a waste of time.
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What year is the rear end?
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These are for a 77 12 bolt
(http://info.rockauto.com/getimage/getimage.php?imagekey=634433&imageurl=http%3A//info.rockauto.com/RB/kit81000-007.jpg)
Part #: 81000
Weight: 0.15 lbs.
Features & Benefits : Replaces lost or damaged U-joint straps, precision engineered quality.
Notes:
Bolt holes center to center 1.58"
http://www.rockauto.com/catalog/raframecatalog.php?catalog=42&partnum=81000&a=FR42-81000
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Thanks Vile, thats the pn I got, but they dont look anything like that. Back to the parts store in the a.m. Should be ready to put the rearend tomorrow if all goes well. Thanks alot.
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what are the axles out of...
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The one I am rebilding is supposed to be out of a 77 Blazer.
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got the rearend in, and have two problems. One, the rearend is still forward about 3/4 in on the right side. I know the pins are lined up in the lift blocks (took it apart several times just to make sure)maybe its the block itself because the pin in the spring to the rear hanger is the same distance on both sides, but the axle is about 3/4 in forward on the right, Uggh this is turning into a chore.
and to ad to that, the orignal brakes on the 12 bolt were 2 inch wide, and it didnt have any drums on it when I got it. To add to that delima, all of the parts stores show the same drum for a 77 or a 85. My question is, does anyone know if i can just use the 10 bolt axles drums and upgrade to the 2.75 wide shoes? I didnt try to put the wider drum on to see how it fits the backplate, but I will be shortly.
someone has also changed the backplate on one side so there is not access to the adjusting screw for the drums. I just wanted to see what you guys thought.
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What do you mean it's forward 3/4"? Do you have the lift blocks both pointing the same direction? Are you measuring it with the springs loaded or unloaded?
As long as the backing plate holes line up just swap over your backing plates and drums.
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Thanks Vile, I should have did more checking before I posted. If the backing plates are changed, then the wider drums will work. Everyone keep this in mind for future purposes. If you want to upgrade from the 2 in wide brakes to the 2 3/4 in brakes, just swap out the back plates, shows and drums. Fortunately for me, I found a set of drums for the 2 inch brakes. It didn't come up under the 77 parts list, but it did for the 75 No telling what year the rearend is actually from.
As far as the axle being off center, it was checked with the load on it, and both are in the right direction (short side toward the front) I checked it over and over to see if I had a brain fart and did something wrong. The tire is visably forward on the right side, so I checked it out. Keep in mind, I see stuff that most people do not, I'm picky on stuff like this. I had the same problem with the last axle, but thought it was just because it was bent. I measured it off of the rear shackle just in-case the bed was throwing me off, but got the same measurements every way I measured it. The pin in the spring to the center of the spring eye is the same on both, so I am thinking the blocks are different. I may try to check them tomorrow, but since I'm running out of time, it may have to wait until I do the gear swap. Its not grotesquely out of line, but it is noticable to me.
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I would measure from the pin to the center of the spring hanger on both sides and mesure from the pin to the frame height on both sides.
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I will do that. Im wondering if the rear shackle just hasnt settled. I havent driven it yet, and I didnt compare the two to see if they are at the same angle. I know that could cause some issue. The biggest thing is the tire lines up with the body as veiwed from the rear now. With the other axle, you could see the front of the right tire tilted in in the front. Ill know tomorrow and will post the info with some pics. Thanks Vile
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well, as normal parts people do, they told me they had the drums when in fact they did not. The ones they had were for a 5 bolt 11x2 drum. So,I just swapped the entire brake assembly, including backplate from the 85 10 bolt to the what apears to be 75 12 bolt. Everything bolted right up without any modifications. So now, instead of having 2 inch wide brakes I have 2.75 inch wide brakes which I figured would help slow the 35s alot better. (duuhh, I know) No one for miles around has the 2 inch wide drums, but the 2.75 are everywhere, and are half the price. No all I have left is install new rear cover gasket, hook up the shocks, fill the diff with oil, and that part is done.
Next question, when I pulled the drive shaft to install the new u joint, alot of fluid came out. Now, insert dumb question here: Is this from the transmission or the transfercase? Do I need to fill it up thru the tranny dipstick as usual, or do I need to fill it thru the transfercase? This is my first 4x to work on, so things are new. I assume it just dexron/mercon tranny fluid, at least thats what it looks like.
On the ujoint make a note and dont do what I did. I pulled the caps that werent being installed in the driveshaft yoke, and set them aside so they wouldnt get damaged. I then installed the ujoint thinking I was doing good since it went in real easy, just to find out I put the short side of the ujoint in instead of the long side. Didnt pay any attention to it until I slid under the truck with my buddies (the red ants) and realized what I had done. What a goob! Fixed that, and all went well from there. I guess I now have a nice set of blasted and painted backplates for 2 inch brakes to take to the swap meet this year. I'll post pics tomorrow when I get it finished, then off to the show.
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Top off the transfer case through the fill plug with ATF on level ground. It should be just below the fill plug. Don't you just love dealing with the highly intelligent auto parts people that waste your time? Take some carb clean to those ants and a lighter. Show them what a real fire ant is!
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Funny you say that, fortunately for me Oldyeller bated them this morning, but there was a few stragglers wandering around. I had a can of brake clean, shown in pic, that was just for them. It worked great, but I didnt do the lighter part.
Where is the fill plug at?
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If it's a 208 it's the higher up 30mm plug
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Do I just fill it up til it comes out like the rear diff?
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yes just below the fill plug hole is good.
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Thank you sir
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Well, I got it finished in time, but just barely. The brake trouble set me back a full day ( or nights work you might say) I apologize for the pics, but I will get better ones up when I can, and post a few of the show. Thanks again for all the help.
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Looks great!
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Thank you. When we get back, I'll order my 3:73 gears for the rear, and then strip clean and paint the front axle to match. I couldn't get a chrome diff cover in time so I just painted it black and replace the bolts with new silver ones from Home Depot of all places. I did it just for a quick detail until the chrome ones could be ordered, but I'm starting to like the contrast look of it. Anyone else think I should keep it instead of the chrome covers?
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Definitely keep it black!
I've been wanting to try one of these
(http://www.cleargearz.com/images/IMG_0840.JPG)
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You want to try what? 20 shocks? Oh, the transparent cover...
Chrome don't get you home!
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Ive been curious about the see thru covers myself. Definately something different. The shocks are cool, but way too many for my taste and too much cost for my budget as well, especially with as many trucks as I have. All in all, it went well. Its amazing how many people dont even notice the extended cab, but I was successful in getting the word out to those cool enough to like squarebody trucks.There were a couple of real nice ones in the show, and even more in the burnout competition. I'll post those pics when Oldyeller gets them downloaded. The truck drove good once I got all the vacuum leaks sorted out. It amazes me how a vacuum leak can take a great running truck and make it run horrible. Ive never had any engine troubles with this truck until yesterday. It has always started and run great,even without the choke hooked up (which I didnt realize until yesterday) I will be removing the smog junk next and delete a bunch of vacuum lines. One thing is for sure, the front sway bar needs to be hooked back up, its kinda like riding in a rollercoaster.
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Yes I meant the clear meatball cover.
There's nothing wrong with chrome unless it's that cheap made in taiwan garbage. I've got so much chrome on my bike if you look at it in the sun you'll go blind.