Hey,

This spring I will be draining my rear end and adding synthetic gear oil, posi additive...

I called my local GM Dealer and asked for a rear end gasket...his question to me was:

What size? 7.75" or 7.625" ??

I told him I had the 3.27 9-Bolt Borg & Warner rear but that never helped him... he said he showed two part numbers.. the 7.75" and the 7.625"

How am I going to find out what size mine is?

 

Buy one of each gasket and after you've done the work return the one that doesn't fit. I do this often when I am not sure 'which size fits'. GM and 99% of the majority of other shops never charge a re-stocking fee.

RP.

 

I'm 99.9% sure that it's the 7.75". I would order that one and when you pick it up just count the bolt holes.

 

IROCKER is right. It is 7.75". I am 110% sure because I went through three last summer because I couldn't get the damn thing to seal.

 

I checked it out last weekend.... GM dealer don't have any in stock and it costs $12.05 ... little too much for a piece of cork .. so I am going to re-seal it with RTV silicone sealant!

 

Not a good idea! You're gonna want the gasket...Trust me. This will probably be the last time you ever need to change it so you might as well do it good the first time round. With just the RTV it's guaranteed to leak. I just don't want to see you waste your time.

 

Hey Chris,

I am taking your advice! I dropped into my local Chev Dealer and ordered the 7.75" rear end gasket. I should have it tomorrow, and when I pick it up I am getting a bottle of Posi-Addititive as well... my rear end is going to be one of first things I do when I take my car out.

The list in order is:

1. New tires, wheel balance, and 4 wheel alignment
2. Rear posi fluid removal and replacement
3. SFC's installed.
4. Paint job - 2nd week of June
5. repair the headliner and put it back in.
6. Look at the t-top seals and re-seal with silicone sealant
7. Window tinting
7. General tune-up (plugs, wires, cap, rotor)
8. The small mods (K&N's, air foil, modded airbox)
9. The experiemental mods (custom chip) ..
10. Hand my younger brother *** over to him at the track!

That's about it I guess for this summer.

 

Sounds like a plan! So when ya coming to Ontario? I think you need to make a road trip.

 

Hey Chris,

A long road trip may not be completely out of the question. I have family/friends in Toronto, Maple, and Brampton.

If you see a real kick-*** Artic White Iroc in your rear-view it may just be me!! hahahaha

By the way...I picked up my gasket today, it is a 9 bolt one and the guy at the counter said " Geeze I didn't think GM made 9 bolt rear ends"... I looked at him and sorted laughed.. I said " Yup, they do, got a kick-*** 9 bolt in the rear of my '87 IROC, 3.27 Posi to be extact".... he was like " Ahhh cool!! That makes sense!!"

HAHHAHAHA.... he must have been a new guy

 

One thing you might want to consider and it is a REAL pain in the butt, how old are your injectors and when is the last time you had them out and backflushed, balanced for flow, etc ???

I was very surprised at the difference it (getting a balanced set) made with mine. With 8 injectors one or two with poor flow or low impedance can really effect the performance in a negative way and if it was like that when you bought it you would never know you were down on power.

Also, don't mind me if I shed some grief over number 4 on your list. Don't get me wrong I love the IROC in arctic white, but your medium blue is a beauty in the eyes of this beholder.

have a nice day,
RP.

 

I'll be watching for ya...of course my rearview mirror is as far as you're gonna get too!

 

Sure sure Chris.... ... until I pass ya like you were tied on to a post!!

Well maybe not...

Why don't you come down to Nfld. I am sure you must know at least 1 Newfoundlander up there!! Sure they make up 50% of the population of Ontario!! hehehe

 

I have family in NS, but I was just there a couple years ago...probably won't be going back for a couple more.

 

Before you put posi additive in your 9-bolt, you may want to read this thread (and the links to other threads).

https://www.thirdgen.org/techbb2/sho...threadid=77011

 

Seems like there is a lot of conflicting data! Should it be used or not? I was told it should be used as it helps friction in the cones, now I am not so sure!!

 

The additive is really your call. I personally added it to mine last year when I switched to synthetic. Perhaps try it out with out the additive first. If you notice any ill effects like one-sided traction or a lot of noise coming from the rear then put it in.

 

I honestly don't know what to believe. I can say that I am not putting the additive in my car when I change the oil in the coming weeks, but this is because my posi is already weak. In rain or snow, the posi works fine. On dry with my sticky tires, I sometimes have a one-legged monster.

I have been told two things about the additive:
1) It is a "friction modifier" for clutches (9-bolts are cone-type posi's)
2) It is only to reduce noise (shouldn't matter what kind of rear you have)

Who to believe?

I have some Red Line Oil that I plan to put in there. The label specifically says that it does NOT have the friction modifier and claims to allows the posi action to be more pronounced (like shimming, I suppose). Since my cones are worn out, I figure why not.

It's up to you, I suppose. I've seen no compelling argument either way. In my case, I am hoping that leaving it out will help my posi work better.

 

What weight of lube did you use in the synthetic? Did you find any difference? I have 1 litre of 75W90 Synthetic Blend and I need another ( I think it takes 2 litres of fluid)

 

To be honest I can remember the weight off hand. I used the full synthetic and I know the weight was slightly different than the conventional. I used a little under 2L...but yeah you'll need two bottles. I got the stuff from Canadian Tire.

 

That is what I thought.....the stuff from Canadian Tire in the gold bottle right? If so it's 75W90... I think the spec is 80W90 so it isn't that far off..

I can't remember but what gears are you running out back? 3.27's? 3.45's? It's a 9 bolt B/W posi right?

Any bad effects of going with the Synthetic Lube and additive? Notice any problems with your posi since the switch?

 

Chris,

Did you change your gear oil yourself? Was it hard to do? Seems to me a simple job,

- raise car and support on jackstands (to let the rear axle drop naturally giving you more room to work)

- loosen all 9 bolts (don't completely remove the top ones)

- gently pry around the cover and let the bulk of the gear oil drain

- remove all 9 bolts and remove inspection cover.

- scrape/remove all of the old gasket material from axle and cover

- inspect the gears (check for metal filings and general wear)

(optional) - clean the gears with brake cleaner spray...I am not sure if this is right or not but I thought I heard it somewhere.

- install the proper 9 bolt gasket (you can use a bit of axle grease to keep it in place)

- put the cover back on and replace the bolts (tighten in a cris-cross pattern), do not over tighten

- remove the filler plug (should be on the passenger side on top)

- add 1 L of your favorite gear oil first

- add 4 ounces of limited slip additive

- crack open your second bottle of gear oil and slowly pour in until full.


That should be right as far as I know... if there are any points that I have missed please let me know!!!

 

Yup the stuff in the gold bottle. I've had no ill effects so far. I think my posi is on the way out anyway so if any there were to be any troubles it would be because of age and not because of the oil.

And yup, did it myself. Couple tips...

1) Loosen all nine bolts but don't take any out. With a huge oil pan underneath, very very slowly start to pry the bottom of the lid off and let it drain slow. The stuff is messy!

2) I clean everything pretty good with the brake cleaner. It's not easy with the angle, but definately possible.

Otherwise you got every on the list that's needed I believe. Have fun!