I'm trying to gain some knowledge before the diff repair shop calls me. The diff first gave me trouble when I made a hard right turn at idle and I heard some hard clunking back there, but straight line driving was no issue, however, tight turns ...usually ...produced some clunking. I changed the fluid and added 2 bottles of GM additive but while spinning the diff by hand to check both sides for rotor runout, at first the wheels went around. Then I needed to rock the one wheel backward a little to get it to roll ahead by hand to continue checking the runout on the opposite wheel. Finished my leaky caliper brake job and buttoned everything up to go for my first drive and the rearend locked up couldn't even move on my hoist?

History is 1969 engine 350/350hp built by Dave's Engine and Machine in California started in 2003. The car owner had a stroke sold the car to his best friend the guy I got it from is 67 years old. I doubt any of us has beat on this car since the engine build of a good honest 450hp.

I don't race nor unnecessarily beat on the car, I use it almost daily to go for coffee in the morning and whenever suitable to just run up town. Once a week a guy just has to stick his foot in there and it lights up 235/60/15s from 20-25mph no sweat and of course this makes my heart flutter.

My question is this ...I love the car and will keep it maybe 10 years. I didn't really want to go overkill throwing money around but it still needs to suit my needs. First thing....is the stock diff even a good one to put any money into? What are the must haves ... etc ...

 

Is it the original 69 diff? If it locked up then you might have a backed out RG bolt or issue with the posi spiders or case. You won't know until you open it up for inspection. 69 diff's weren't bad, they had 10-18 spiders which are not as good as the later 10-17's. It was the first year for the 2nd design Eaton posi which was better then the 65-68 Eaton posi but not as good as the later 72-79's..

So it is hard to answer your question, you need to get a little more detailed.

1- What power level= 450?
2- Trans= Muncie= not going to hold up to abuse with 450 hp
3- Diff- what condition it's in, was it ever rebuilt, what is broken inside
4- traction- tires that slip or bite in?
5- Use- how heavy is your right foot?

Shock loading a stock drivetrain with 450 hp will turn parts into instant junk in no time.

 

Ok...I'll try to clarify as much as I can

1- What power level= 450?
I doubt the car has had a tune-up since the build and near as I can figure was maybe 3000mi ago at most. It runs fine on all 8 with an Isky cam 5.65 lift and GM aluminum 2.02 heads. All good name brand parts Weiand tunnel ram, open side pipes etc... It won't put out 450hp today but my butt dyno says 420 and I'm not looking for more until it needs something to keep it going

2- Trans= Muncie= not going to hold up to abuse with 450 hp
It is a muncie and not the rock-crusher model. It shifts really nice, it's quiet and no leaks, very clean looking so I suppose somebody went through it not real long ago, and I'm not looking to blow it up

3- Diff- what condition it's in, was it ever rebuilt, what is broken inside
diff looks pretty much original 69. Lots of surface rust under the car but everything including birdcage has solid mounts still. The funny thing is that I dropped the whole assembly trailing arms and crossmember, the crossmember had anti-seize on the two bolts but the diff cover bolts looked never been out. The crossmember was a little tough so it's been there awhile. The only other thing he done was a TRW fiberglass monoleaf, so no, I don't think the diff had a previous rebuild. I should be finding out this week when the shop has time to open it and see what they say....I'm guessing a bolt or two is backing out is my problem...how much money do I throw in there? At 50 years old should I turf it and do what ??

4- traction- tires that slip or bite in?
must have been a sale on Yokohamas 245/60/15 cause they are not an attractive tire, they do not have a lot of bite, I don't mind burning them up but the little bit I do they will probably last 2 or 3 summers yet. I love BFG's and when I get them I'll be back to the coolest idle at red lights around town ... no smoking those BFG's

5- Use- how heavy is your right foot?
All of the above is meant to say I don't really have a heavy foot.

Shock loading a stock drivetrain with 450 hp will turn parts into instant junk in no time
I don't do any (none) holeshots ... worst I do is getting it rolling at 20mph, let off and punch it the tires break loose pretty quick. No speed shifting 2nd or 3rd

Appreciate any and all thoughts ...

 

Well the fact you are not going to hammer the car the drivetrain should hold up.

In respect to the diff, you have to see what the deal is inside. There was/is an issue with it so you can't move forward with it until you know. Will you need new gears, new posi, etc?

I can tell you how I would build it for my own 69 with up to 450 hp and street, not hard drag racing use. This is how I built mine, they are in the cars and run great.

1- Fully prep the housing cover- blast, etch, POR15, top coat
2- Tap drain hole in the housing- not the cover, use a magnetic plug
3- Fit the bearing caps to 001" rock, bottom tape, countersink, and install shcs in place of the hex heads
4- Use only Timken bearings
5- If you need or change the gears use only Tom's gears
6- ARP ring gear bolts
7- Fully polish the posi, no crappy partial grinding calling it polished. Take the time to radius the windows, blend and polish the OD and ID
8- Mill the posi pad for better support
9- Use only solid steel clutches
10 Use 10-17 spiders, 18 will work but the 17's are better
11- Tune the posi and balance it. This means no springs or plates are used. A tuned posi will not have them.
12- Dial in your pattern and lash rechecking after final total preload is made so nothing has changed
13- Set up axle endplay between 005-007" make sure they are hardened.

There are other options to build these but if you build it like this it will hold fine for your application. This is not meant to be an in depth "how- to" procedure on all those steps - just to answer your question and how I would build it if I was putting one in my 69,4 speed vette. For our 75 which has a lot more power this would not work for long, that application required a completely different setup.

Good luck, talk with your builder on what he would do. Ask him if he knows how to polish and tune a posi. A stock spring type will work here but I wouldn't use one. I have boxes of posi springs and plates sitting on my shelf and more I threw out.

 

Check out Summit Racing. They sell an Eaton center section, Same as OEM, when I purchased mine it was about 500 bucks. It's duty is behind a S/C 355 and sees track duty, no problems at all. I also don't do hard launches. T

 

I appreciate what you say and the time it took for you to say it...Thank you.
The next post for a drop-in from Summit is more the way I think I will go depending upon what the shop says. The abuse I will give it will be a lot less than other buddy at track days, and 500 worst case scenario is enough money to throw at it for results I'm after.

Thanks again !!

 

Great idea. Worst case 500.00
That's what I have, 355 10.3 compression very streetable, great car for a showoff without the hard launches. I also have a 71 in close to pristine condition like a wife, but I tripped over this green 69 and like a girl friend it needs money

What is S/C ?

 

Good luck, let us know what they find. Maybe your posi case is fine? The new loaded Eatons come with fiber coated clutches, less per side, huge yellow preload springs, different spiders and cost about $550 from any Eaton Dealer. They would work in your application but wouldn't be my first choice. I would take a NOS or good used Eaton over the new imported ones but again it all depends on what you want and expect. Post some pictures if you can, I would be interested in what it looks like.

 

It's a pretty reputable shop and they are really busy so yes, soon as he text me some pics I'll get them to you and see what you say. Hopefully this week. I'm not above spending a little more for better just not real interested in the costs if I can stay off the go pedal. By the time I do a few things hardware wise it already looks like 2000.00. Trailing arms rebuild, stabilizer bushings, u joints, sandblast, paint etc ...My buddy check all over the net for me for NOS and came up empty

 

Vortec super charger. T

 

Oh nice !! ...and now I know what S/C is

 

found out this much....add 35% to USA prices to get cad equivalent
my case is fine and I asked about 10-17 spiders... these are included
Differential
Eaton Posi New $850.00
Motive Performance ring & pinion 3.70:1 New $350.00
Timken bearing kit $195.00
Small parts kits $110.00
Labour $395.00
Total $1900.00 + tax

Trailing arms:
Inner seal $22.16 x2
Outer Seal $24.58 x2
M86610 $14.72 x2
M86649 $24.78 x2
A5 $25.38 x2
Labour $250.00 per side
Total $723.24 + tax

so much for 500.00
It's all I know right now

 

got a price and replied to buddy above

 

Well not to get in the middle of your quote but you did ask for opinions. The diff prices are high, even with dollar exchange rate, the gears are imported you are closer to Tom's to get the good USA made ones, it is unknown what the small parts they are speaking of, and the labor is low. You end up with a price range for a custom built diff but what will you get? I don't know your shop so I can't say but I have seen quotes like this here for many years and know exactly how they are built.

The TA quote is showing seals and bearings only, labor is ok per arm if they take the time to fit the bearings correctly. There are other parts that would be replaced not listed so I would be concerned on just what is going to be done. Reminds me of the TA invoice I got with the 75 coupe I bought 15 years ago. The owner used his trusted garage for all the work, while they may have been excellent with passenger cars they didn't know old vettes. The invoice was for $1100 usd, for one TA rebuild! When I took the arm apart it was total junk, I had to replace the arm, bearings, axles and parking brakes - all damaged by the local expert. Point is if you don't do your homework you may be in for a big surprise.

Good luck with it.

 

Just checked Summit. Eaton posi limited slip differential carrier part number ETN19670010 prices for $559.99. Sorry for saying 500 there has been a price increase since my purchase 7 years ago. T

 

yeah I get that part, stuff goes up faster than I can buy some of it. The carrier from my guys at 850 equates to 560x35%=756 plus the border so they definitely are getting me a little on that one but 400 labor is reasonable I'm thinking so they pick up some on parts which I guess I'm ok with. Where I have trouble is from 500 to 1900...and then TA's...crap !!

Appreciate your input to help me make an informed decision ..

 

yes, clearly understand what your saying. I'm using IWE Rear Ends Only in Vancouver. Been around forever even the staff, highly recommended shop here. Motive gears are made in Italy is what they get a deal on I suppose. My 71 has 36,000 in receipts from a shop like you mention, not exactly butchered but for instance a rebuilt steering box exactly what is that ?... a new "O" ring for 400.00 ?...the car does not steer it's like the box is wore out. Certainly there is value in a lot of stuff they did do but not even a wheel alignment was done...they just threw parts at it. On the other hand the guy who spent the money gave the car to his son who sold it to me and neither of those two knew what they had.

I appreciate your effort here to help keep me out of trouble, I do have a couple friends that race here and Western USA on the same page as you to help me as well, the consensus is such that this shop is not a bad choice for my requirements and if it does go south I'll be back whining...

Thanks for make me look at my TA rebuild, your right, no cost for bushings ? I have a call into them now

 

they just now sent me a little more complete list as follows...
Eaton Posi New $850.00 Has a high strength nodular case, carbon fiber friction discs, precision-forged gears. Motive Performance ring & pinion 3.70:1 New - $350.00Timken bearing kit. This includes the stub axle torrington bearings, diff bearing & races - $195.00Small parts kit includes shop supplies, oil, additive seals, crush sleeve, pinion nut & shims. - $110.00 Labour $395.00

as you predicted not much info there in the way of heavy duty stuff so I'm guessing I should bend over for the amount charged

 

I am going to sign off of this thread now, I covered my points so you can use them if you like to discuss with your rebuilder. I would not expect they will agree with anything I listed though. Clear enough why.

Here is the posi case
https://www.jegs.com/i/Eaton/362/19670-010/10002/-1

 

well I appreciate your thoughts...I'm stuck between a rock and a hard place just to get the job done. It's above my head without 2 months to study