Rear end is a what?

[Merlin]

I have been slowly working on my Astro van since health issues are with me for life it is going really slow. Right now it is on blocks and I am about done with doing the front end stuff, bushings and all but I stopped short of some because I am thinking hard on doing a steering change to a Rack and Pinion.
Now to what is going on. My question is I have a 1989 Chevrolet Astro R/S van that I am working on and something seems wrong. The rear end in it is a 12 bolt rear end. I asked the first owner if he had it changed and he said that it came that way from the factory. He never had any work done on it except to change out the Brake shoes one time. Since he is the original owner and I am the second owner something is not right, in a good way. No where can I find anything that says an Astro van ever came with a 12 bolt rear end. What brought this up now is I am working on the suspension and was going to up grade the rear brakes and replace gaskets, seals etc. I have them and was ready but they are not going to work with this rear end since it is different in size. So my question is this, are the outer ends the same size as the normal 10 bolt, that is what should be there? They need to be so the brakes will fit. I know the seals and gasket won't work. I have read here till I am going blind I did a search and nothing came up on it. I haven't taken it apart yet to be sure. No tag and nothing in the van says anything about what the van has in it, and since it isn't right, or is it, I know it could be several different rear ends except the original guy says it is the one it came with. If all fails I will wait till the rest is done and then open it up and get the info. I was hoping to have all the parts here to be able to put it back together in short order but maybe the car gods are against that. Any help please? Yeah I know a 12 bolt is much better than the 10 bolt but parts are going to be different and maybe hard to get since I don't think it should have been there from the get go. I have all the paper work that the first guy had done on the van and nothing shows the rear end being worked on other than the brakes.

[Smiliesafari]

Over many years GM guilt several different 12 bolt rearends. Some pics would help a lot on identifying what you have. I have never heard of a factory 12 bolt in an Astro or Safari, so we have a mystery.

[doyoulikeithere]

If it is a 12 bolt, someone has shoe-horned it in there for certain, at some point.
Rule 6B... PIX... Show us this 12 bolt installed...
If it is a 12 bolt, bonus!

[Merlin]

Sorry no camera it died and haven't replaced it yet, but it is a 12 bolt. I will have to take it apart to find out what it is I guess. Have to get the front back on the ground as my garage is not large enough to have room around it to work with both ends up on stands. Strange part is the original owner swears that it came with what ever is under it.
I did some more research in the tech books I have and like I was sure of no Astro ever came with a 12 bolt, at least that I can find. I was thinking maybe something to do with the R/S setup as those do have a few things that are different from the regular Astros but didn't see anything. I am going to take a stab at calling the original selling dealership and see if they have anything on this particulate van as they are the ones that have done all the work on it before I got it. If they will check their records on it and see if they did it for some strange reason. It does have the small off set that the normal 10 bolt has and it looks like it has been there a very long time. Not sure if they will do that or not but I am going to try calling them tomorrow.

[doyoulikeithere]

Does your GT still have the rear swaybar?
Before you call them, you might like to write down the VIN number, and also, if it is original, you can probably look in the glovebox, and record the RPO codes.
All of the codes on that white sticker have a definition that you can look up, and they are coded in such a way that you can sorta know what they might refer too, by the letter they start with. For example, Axle ratio codes all start with a G, so does the locking vs open differential (G80/GQ1) Anyways the point is that GM would have 2 G codes for the rear axles, on the RPO sticker.

I dont think my 90 Safari GT has a 12 bolt, I wish! If it did I would sure go looking for a TPI 350 & World Class T5 5 speed from a 90's Camaro.

and rule 6b says I gotta heckle ya for no pix!! Lol...

[Merlin]

My Astro is a 1989 R/S not GT, the GT is GMC, but about the same thing. Any way here goes. The sticker that is supposed to be in the glove box is not there. So I do not have any RPO codes. The rear sway bar is there and looks stock. I took a high pressure washer to it last night so I could see if there is any numbers on the axle it's self, none found. When turning the tires with the back of the van on stands it does have some kind of posi in it. I am going to take the cover off today and with all that I can find I am going to call the dealership to see if they have any idea how it got there. Since the original owner swears they are the only ones that have been under the van or did any work of any kind to it. I have a stack of repair orders that came with the van, from day one until he sold it to me, I went through again last night to see if it mentions anything and it doesn't. Only good thing I found in the repair orders is the van did have rear brakes put on and it gives the GM number of the shoes. That will come in handy if I never find out what this rear end came out of so I can at least replace them. I am really curious about this now and happy, wouldn't you be I mean a 12 bolt is a good thing.

[Merlin]

Well the question of what and how did this 12 bolt get in the van is still a question. I talked to the repair manager at the selling dealership and he looked up the life of the van. No where does it say that it had a rear end anything done to it. Only thing done to it was rear brakes as far as the back of the van is concerned. He said that as far as he knows a Astro van never came with a 12 bolt rear end, which we all were pretty sure of. So no help there.
I did open it up and it has a posi, which I was sure of by turning the wheels, and it is a 3.73 ratio rear end. Only numbers I can find on the axle is on the top on the passenger side and it is a 752 G. I can't find that as any help in all the places I looked up.
So I guess I will never really know how or where it came to live in the van but it is a good thing after all it is a better rear end than the 10 bolt. It just might be a little harder to get parts now and then. Thanks for helping and if any one has any other ideas please jump in and let us know. Thanks again back to the drawing board I guess.

[brokenwrench]

I would count again, then get a friend to count. The Safari rear ends have an axle offset that I do not think is on any late model 12 bolt rear ends. there is an 8 3/4 12 bolt in car and truck configurations but they have not been made for a long time. the truck one was last made in 1982. there is no factory substitute that would swap in.

[Merlin]

I agree but the rear end is a 12 bolt. Believe me I counted it several times and had a friend count it too. The gasket on the back looks like a truck gasket, the car and truck used different shapes. So I am going on the idea it is out of a truck. The offset is no biggie everyone knows it is fairly easy to cut one and make it work. After cleaning more I can tell it is welded different than a stock rear end. The factory only welded the spot weld holes up and this one is welded all the way around both sides at the pumpkin.
What started this was I was going to get a better brake setup. Either a disk or the 11 inch drum, favoring the disk since one member here has a set to sell. Now plans have changed at least for a little while. It has drums on it now and measuring the size it is not the 11 inch it is a little over 10. Any idea from that what it might have come out of. All the lists I have found including the dealership here in town doesn't show a drum that uses 10 inch brakes?

[brokenwrench]

I agree but the rear end is a 12 bolt. Believe me I counted it several times and had a friend count it too. The gasket on the back looks like a truck gasket, the car and truck used different shapes. So I am going on the idea it is out of a truck. The offset is no biggie everyone knows it is fairly easy to cut one and make it work. After cleaning more I can tell it is welded different than a stock rear end. The factory only welded the spot weld holes up and this one is welded all the way around both sides at the pumpkin.
What started this was I was going to get a better brake setup. Either a disk or the 11 inch drum, favoring the disk since one member here has a set to sell. Now plans have changed at least for a little while. It has drums on it now and measuring the size it is not the 11 inch it is a little over 10. Any idea from that what it might have come out of. All the lists I have found including the dealership here in town doesn't show a drum that uses 10 inch brakes?

rear brakes generally only do 20% of braking, you will not find a noticeable difference if you add bigger drums or discs. irrespective of how much money or time you spend on the rear brakes, it is ultimately the ABS and tires that determine improved braking as the factory setup has the ability to lock the wheels and ABS will always stop you from doing this.

if you truly have a 12 bolt, and it has been shortened, how it happened is interesting but irrelevant. does it have aftermarket axles? I would be more worried about someone shortening the axles and welding them.

more effort than you think to sweat the axle tubes out of the housing. I used to do this on Dana rearends for race cars, fortunately everyone wants Ford 9 inch configuration now.

[Merlin]

This van is a 1989 and doesn't have ABS. I don't think any 1989 did but I could be wrong. I have one other one, it is a 1989 R/S also, in storage and it doesn't have ABS either. I know most of the braking is done by the front but doesn't every one want better? I know I do I want my van to be different in some ways. Ways that others may have done but that you don't see every day. As far as making a rear end narrower yes not for the untrained but I have done it several times and it really isn't that big of deal if you have the right equipment to do it. I did at the time as I worked at a dealership for years. Who ever did this, and I would still love to know who and when but I doubt that will happen now, did a good job as it is now apart and the axles are done right no welding on them. It looks to have been done like a pro would do. Oh yeah no offense but not every one wants a F--d 9 inch. I want my Chevy all Chevy. Yeah I know the F--d thing is supposedly stronger but this van will not see 1000 H.P. or even be on a track more than a few times if that. Street is where it will live only a little stronger than a stock one and I hope to say better in some ways if not every way. If I was building a race car maybe a F--d 9 inch but since I am not a fan of that product I would probably use a Dana, guess you did to at one time brokenwrench, they are strong. My van that was stolen and wrecked had a Dana and it was fine and it had some power no not the 1000 H.P. like the big guys are building now, wouldn't that be nice to be able to do, but it had more than most. Miss that one but then again it wasn't legal on the street here in Calif. so guess it is ok like I have a choice in that. So on with the build and thank you for the knowledge brokenwrench and the others here. Nice to know people here are willing to help out and every one here seems to be. Part of the reason I am looking to change all this stuff is this will probably be my last ride like this that is built by me. I am getting to old for this and the body says no more all ready. Thanks again to all.

[brokenwrench]

This van is a 1989 and doesn't have ABS. I don't think any 1989 did but I could be wrong. I have one other one, it is a 1989 R/S also, in storage and it doesn't have ABS either. I know most of the braking is done by the front but doesn't every one want better? I know I do I want my van to be different in some ways. Ways that others may have done but that you don't see every day. As far as making a rear end narrower yes not for the untrained but I have done it several times and it really isn't that big of deal if you have the right equipment to do it. I did at the time as I worked at a dealership for years. Who ever did this, and I would still love to know who and when but I doubt that will happen now, did a good job as it is now apart and the axles are done right no welding on them. It looks to have been done like a pro would do. Oh yeah no offense but not every one wants a F--d 9 inch. I want my Chevy all Chevy. Yeah I know the F--d thing is supposedly stronger but this van will not see 1000 H.P. or even be on a track more than a few times if that. Street is where it will live only a little stronger than a stock one and I hope to say better in some ways if not every way. If I was building a race car maybe a F--d 9 inch but since I am not a fan of that product I would probably use a Dana, guess you did to at one time brokenwrench, they are strong. My van that was stolen and wrecked had a Dana and it was fine and it had some power no not the 1000 H.P. like the big guys are building now, wouldn't that be nice to be able to do, but it had more than most. Miss that one but then again it wasn't legal on the street here in Calif. so guess it is ok like I have a choice in that. So on with the build and thank you for the knowledge brokenwrench and the others here. Nice to know people here are willing to help out and every one here seems to be. Part of the reason I am looking to change all this stuff is this will probably be my last ride like this that is built by me. I am getting to old for this and the body says no more all ready. Thanks again to all.

i agree on the 9 inch obsession, but what people want, and who pays......, plus they are so easy to set up and great for race cars as you can swap out the center between runs. class racers run 750 hp through 10 inch rear ends with no problems, however, it is only the housing that they use. if you stick in a detroit true track ($400.00) new gears ($150) new axles ($325) and the bearings and setup kits ($200) for a little over $1000 you have an indestructable rear end. My shop can actually do this cheaper than using factory parts. ( subtract 30 to 40% mechanic prices)

if you upgrade brakes on the rear, add an adjustable proportioning valve, $30 to $60 so that you can fine tune the brakes front to rear bias.

[doyoulikeithere]

Just FYI, My GT is a 90 and it has ABS.
It uses vacuum boosted brakes just like the 87-89, not a hydro boost like the newer ones have.

Not sure if Vacuum Boosted ABS on the 90 was GT/RS specific, or not...(like the sway bar is)
Might be an easy upgrade if you can find a 90 to steal ABS parts from.

What year did the hydro boosted brakes begin?

[Merlin]

I know the nine inch is easy to set up and if you have a reason to change gears a lot it would be the one to get. I am just a die hard Chevy guy and want to try and keep this van a GM product at the least. I would say All Chevy but I put Cad tail lights in it. I wish I had thought about it before though as I think a set out of a Chevy truck around the 1972 would look cool but it is done and I doubt I will do over. At least not now.
I was thinking about using an adjustable proportioning valve, since you recommend it to I think I will when I change the brakes. Not sure now what to put in it since it is different from what I thought it had. I have to say that it was a nice surprise though.
I really do not know when the hydro boosted brakes began being used. Any one else know for sure?

[Merlin]

I was looking in my FRM and it says that the vans I have should have ABS. Now the one in storage is not surprise that it might have been taken off as it is missing a few things that I knew about so this is just another thing missing, I guess. The van that I am working on the ABS is missing too or at least from what the manual says it is missing as I went out and looked for the things it is supposed to have to make it work and nope not there. Another mystery I guess. Isn't it fun working on our rides? I wonder what else I will find missing?