Hey!
I just got a sweet deal on a 9 bolt posi rear which was originally a disc brake rear($25). Part of the reason the price was so good is that the brake components are all gone. I figure this is ok, because I still haven't done anything to my rear brakes in my car (stock J65 discs on the original '84 3.73 geared open 10 bolt) so I've got a clean slate to build a decent braking system out back. Anyway, I was just wondering what you all would recommend going with. Should I just try and get stock thirdgen PBR stuff for it, LT1 stuff, or LS1? I searched and found out the LS1 stuff is a little bit of work to install on the 9-bolt but that it is doable, do you think it'd be worth the extra work, or would stock/LT1 be just as good? Also, anyone have any ideas on where I can get the axle retainer bolts for this rear, would standard grade 8 hardware store bolts work or are they some sort of unique design? Finally, any thoughts on where I could get the rubber inspection cover plug? Thanks for any and all suggestions and help!!!!!

-Paul

 

Have you got backing plates for it?

 

I'm not sure since I haven't picked it up yet, but I'm going on the assumption that it won't have backing plates, then if it does, it'll be a nice surprise I didn't worry about asking too many questions (since it was only $25 lol), aside from making sure it had a 3-series posi carrier in it.

 

I'd go with the LT1/1LE style brakes...the LS1s will be a big hassle to fab up and install and the LT1/1LE PBRs will bolt right on. As for the retainer bolts, use Grade 8 3/8"-16 bolts around 1" to 1 1/4" long. For the drain plug. I think www.9bolt.com has them or you can do what I did...install a Moroso drain plug on the stock cover.

https://www.thirdgen.org/techbb2/sho...ighlight=cover


Ed

 

Thanks for the advice....I was kind of leaning toward the LT1/1LE style setup, for exactly the reasons you listed. Great info on the bolt size, and I'll check into the cover plug stuff. Thanks again!!

-Paul

 

Should the hard lines and/or other miscellaneous pieces be gone, you might find part numbers in the following thread:

https://www.thirdgen.org/techbb2/sho...hreadid=249098

JamesC

 

Excellent! Thanks a ton, lots of good info there!

 

2 other quick curiosity questions. Is the prop. valve the same in my '84 with 4 wheel discs as it would be with the later style PBR/1LE/LT1 discs, or do I need to get a later style or aftermarket adjustable prop. valve? Also, whenever I get to installing this rear if I run Mobil 1 80W90 in it will I have to put limited slip additive in also, or does the Mobil 1 have that stuff in it already? When I swapped to posi and changed the gears in my '69 GTO I just used the Mobil 1 but I want to make sure that it'll be ok without any additive. Thanks again for the help guys!!

-Paul

 

Check the the first link inside my link above, and you'll find info concerning the m/c and combo valve, which "may" be helpful. Most of the guys, including me, run Mobil 1 75-90 with GM posi additive.

JamesC

 

Thanks again James...sorry I should have checked out the links in that post more thoroughly Bummer, it looks like I'll need the MC and the prop valve to set up newer rear brakes properly. What's the reason behind this, do you know? Is it because the iron rear calipers sucked so much that GM ran more pressure to them and the newer calipers won't require as much pressure, or is there some other reasoning behind having to swap out the MC and prop valve? Maybe this is info I should search for lol Thanks again!!

-Paul

 

Well, I did some quick searching and it looks like I can keep my MC...since I've got the '84 J65 I've got the MC with the larger bore, so I think I actually like the idea of keeping it better than going with the smaller bore. I'll just get a PBR vintage prop. valve or grab an adjustable one once I get everything else set up!

-Paul

 

Ok, another quick question. I picked up the rear last night and everything looks good, especially for the price. Now, I also bought a complete LT1 rear brake setup off ebay and it's coming with the caliper brackets and everything. Will I be able to use these brackets (backing plates, right?) or am I going to have to modify them or get totally different ones to bolt it all up to the 9 bolt rear? In this picture from that thread you referenced me to, is it just the bolt pattern that's different or is the diameter of the center hole different between the two brackets?


Sorry for all the questions, but thanks again for all the help!!

-Paul

edit: here's a link to the ebay auction for the brakes I bought so you can see the brakets that are coming with them http://cgi.ebay.com/ebaymotors/ws/eB...tem=7922638166

 

Those backing plates will not fit your 9 bolt, you'll need 9 bolt plates for them to fit. Other than that, you should be OK...you may need to move or reshape the axle hard lines, and if going from drum to disc, you'd be better off getting new ones from Fine Lines, Inline Tube, or Classic Tube. The rest will bolt on..


Ed

 

Ok, I kinda figured that, but I was hoping maybe I'd be wrong The rear is going to need new hardlines anyway since it was stripped of all that stuff, I figured I'd grab a set from Fine Lines, I've had very good luck with other stuff from them so far. Just out of curiosity, how different are the 10 bolt backing plates from the 9 bolt ones? In that pic I posted the link to from JamesC's thread they look really really close, just a slightly different bolt pattern. I'm assuming the difference comes from having to deal with the bolt in axles in conjunction with the backing plates, but I'm a 9 bolt newbie so I'm learning as I go

 

Mainly the bolt pattern.

Ed

 

you forgot part availability Ed replacement parts for a 9bolt are a pain, but supposedly they don't break as often.

 

You can use those backing plates by switching sides and redrilling them to the 9-bolt pattern.
I have done this a couple of times, so I know it works.

 

Good to know Don. Now if I can't find any 9 bolt plates at least I know I can make the 10 bolt ones that I'm getting work for what I need

87CIZ: Yeah, it's too bad that parts are so pricey for them, but I'm hoping I won't need parts all that often lol. I already bought a spare 3 series posi unit with 75k miles on it off ebay, so I'm working on getting a collection of spare parts as I go, in case I need them

Everything looks pretty good inside the rear though. I'll probably put new axle bearings and seals in, but other than that I'm going to set it up and use it as is and see how it goes. Somewhere along the way it's even been cleaned up and painted. There aren't huge chunks of rust all over it like there are on my current 10 bolt


-Paul

Pic of the inside of the rear:

 

what's the gear ratio you have? my 9 bolt is a 3.70 and it's to much for my car. well not really but i miss the gas mileage alot. i went from a 2.73 to a 3.70 then the gas prices jumped. Know where i can get a spare ring and pinion for ridiculously cheap? lol

 

Those gears are 3.27's. The 10 bolt in my car now is a 3.73 and even with the 6 speed ('93 unit with .62 overdrive) it turns somewhere on the order of 2000 rpm at 70 mph so I think the 3.27's will be a nice change of pace. I almost had a 2nd set of 3.27's that I would have sold you cheap. The posi I got off ebay has a 3.27 ring gear on it and the guy was going to include the pinion for an extra $5 also, but he emailed me and told me he couldn't get it out of the rear, so all I'm going to have is the ring gear There was someone in the classifieds selling a 3.27 gear set for $30 last week or so. The ad is still up if you search for it. Don't know if he still has them or not though lol. Also over at www.9bolt.com he lists 3.27 gear sets (used) for $60. I'm pretty excited to get this thing installed in my car, it's killing me being at school and not being able to work on it! I can't wait to have posi and actually be able to put some power to the ground lol. Now I've gotta decide on control arms, panhard bar, and possibly a torque arm and whether or not I want all of them adjustable or not...decisions decisions :lala:

 

mine turns 70 at 2500 rpms with a 700r4 they said that it would jump 1000 rpms when you jump one whole point in a gear ratio. eh im gonna look up those gears cause it's to steep.

about going adjustable it depends if your going to lower the car or drag race it