I'm considering a differential swap from 2.73 to 3.23 or 3.42. It's looking like it will be more cost effective to simply swap out the diff than get the gears, have them installed, swap the speedo gear.

My questions deals with the issue of finding differentials with disk brakes instead of drums. What are the issues with swapping from drums to disks that I should be aware of? Is this a simple plug and pray operation where I connect the rear drum brake lines to the new disk assembly and all is good or is there more to it than that?

I'm betting it's complicated...

 

Wow. I asked a stumper?

I can't believe no one has done this before. Anybody?

 

You will need a proportion valve, other wise the rear wheels will lock up way too soon. also not sure what the differences are between lines back there.

 

Your best bet is to swap the whole rear. A gear install will be about $300-400 and you can get a whole rear for $250 or so. You'll probably have to swap the prop valve, speedo gear, and e-brake cables.

Ed

 

swaping a complete rear that has disk brakes is really easy. As long as the rear comes with everything. such as brakes lines, e-brake cables etc.. Its pretty much a bolt on deal. you can either keep the porporting valve that you have now or swap it for one that came with a disk brake setup. gm says it depends on what pedal feeling you want (high or low). Of coarse your going to have to change speedo gears unless you know how to program your car differently so it reads correctly.

Also if you are looking for a rear with disk brakes make damn sure you find one that has the alluminum calipers with the 11.5 inch rotors. Instead or the Iron caliper disk rear.

 

I just did this without swapping prop valves. I think the disc/drum prop valve gives less pressure to the rear lines, is this right? The rear was a pbr disc one.

 

Correct the disk drum brake porporting valve is setup to use lower volume in the rear. Thus you have to push the pedal downward more to make the disk rear work.
Drum porporting valve = lower pedal
Disk Disk porporting valve = higher pedal.
Just depends on what you like is what it comes down to.

 

I've been learning more about this and it is getting a tad frustrating. Here's the deal:

I can score a new differential complete with posi, disks and 3.23 gears for around 250. Cool. I cannot install this myself as I simply do not have the facility living in the city and all. My mechanic tells me he will cut me a deal on the labor but the job still comes up as taking around 8 hours to complete and he recommends changing all the hardware and bushings on the assembly to new ones (which I agree with in principle). This brings me to a combined parts and labor cost around 600-700 bucks not counting the cost for the rear differential.

Option 2 is to buy the kit that swaps the spider gears and all the hardware inside the pumpkin and have that installed. The kit can cost as little as 300-350 and then installation will run about the same. Total comes to around 700 bucks.

The issue at this point seems to be a question about whether disk brakes are worth it or not.

Are they?

Also, is anything I've typed above inaccurate with respect to my estimated costs for labor/parts?

I still want this. Posi good. Rear disks, great!, 3.23 or 3.42 gears, awesome!

 

1. My '82 Z originally had a 3.73's ratio open drum brake rear in it...

2. Switched to a '86 rear with 3.42's and drums and liked the ratio changed but the brakes

3. THEN switched to a '91 "1LE" / PBR rear 3.23's ratio POSI and the good disc brakes....

Let just say the last rear end switch made a completely different car of it !

The 3.23's made it live-able on the freeway with a 4 speed (3.42 ratio 1st gear!) AND the rear disc brakes WOW WOW WOW what a stopping difference ! I paid less than $300 for the complete rear end and the misc swap parts and I would have EASILY paid double that for the AWESOME results I got

P.S. The rear I picked up was from a '91 1LE with 42,000 miles that was T-BONED out of commission, so all the parts and the posi are / were pretty fresh just had to buy some new brake pads and stuff...

Maybe this babble helps in your decision ~DaVe

 

If you drive a 4 wheel disc 3rd gen you'll instantly know the difference. It's that snug feeling when you stop, especially in rush hour traffic! 3.42s are ideal.

Your price quote sounds a little high, that is a $500-600 job. I have some shops for you in Antioch and Vacaville that could do that job and are familiar with 3rd gen road race cars to boot. Let me know if you need contact info. The one in Vacaville is my race car sponsor.

 

That's waayyyyy too much for a 2 hour job tops, with all the parts on hand. Look elsewhere or do it yourself. All you need is a set of jackstands and ramps.

Here's an easy how to:

http://pg.photos.yahoo.com/ph/tarami...er72/my_photos

Ed

 

Ya'll rock. I was looking over the shoulder of my mechanic when he was looking at the billable hours for this job so I know he wasn't feeding me a line. He was just doing what every other general mechanic does.

Still, a specialist could likely knock this out in no time but you pay for that. In some cases it makes more sense than in the other case. Mr Miller, very interesting pics and break down the job nicely. I still couldn't do it though... I'm a silicon valley nerd driving a NON-BMW (and proud of it).

Jules... since the differential is in Sacramento, a stop over in Vacaville is not out of the question although the logistics could be crazy. I could work out a day off to see it happen if your contact could work with me. I'll drop you a PM to see about getting their info.

Once again, I am grateful for the folks here at TGO. Thanks you all.

 

No problemo! We'll get ya hooked up with that nice 4 wheel disc soon! My sponsor just did this swap with my '91 Formula street car and used PBR brakes since my rear did not have brakes...I'm sure he has all the part nos handy if needed!

 

Man, I really hate to see ya pay labor for a rear end swap. Mabee drive out to the desert with a buddy and swap em' on the side of the road?

 

wow. Labor rates sure have gone up these days. That is a 1 to 2 hour job. For 700 bucks you could have all tubular control arms adjustable pan hard bar shocks and a adjustable torque arm. Man find a way to do it yourself, it is extremly easy. Please do not pay that type of money.

 

It's all nuts and bolts man, nothing hard. Review my how-to and take notes. You dont' have to remove the shocks, just unbolt the lower bolt. It's essentially like this after you get the rear wheels off the ground:

Unbolt driveshaft, hang it up;
Disconnect e-brake cables in tranny tunnel;
Unbolt the panhard rod at the rearend;
Unbolt the lower LCA bolts and unbolt the lower shock mount;
Lower the rearend a bit, remove the rear springs;
Disconnect brake line at chassis and remove the rearend.

Install is reverse of removal but you will need correct e-brake cables but that's it.

Give it a shot. But let's do some math here:

$250- posi rearend
$115- Tubular LCAs from Spohn (Item 201):http://www.spohn.net/product.cfm?productid=1292
$50- new disc rear e-brake cables, UBP P/N 94264, Napa
$5- brake fluid for bleeding
$60- Rear set of Earls' braided brake lines, me

Total is $480 with upgrades, $305 without. Is it worth the $300 or so extra to you? Add $15 for beer and a friend to help you out.

Good luck!

Ed

 

That and unbolting your sway bar endlinks really is ALL it takes.

 

I think we are not communicating here...we should be talking different labor rates for 1)Just a swap 2) setting up a diff with new gears. Drastically different!

 

I have a crescent wrench. Will that be adequate? I do have the best laptop money can buy however.

'Nuff Said.



Seriously though, I would die to get away with this upgrade under 600 bucks. Given my lacks, I figure to add another 300-400. I'd love to be able to tool down to the Charlotte area and hook up with Ed but it's obviously not that simple.

~sigh~

 

Yep, forgot that part.

Ed

 

Ed (and others),

Sorry to dredge this up again but some folks are saying I need to get a new master cylinder to support the conversion from drums to disks. Something about needing an MC that holds more volume.

Any validity to this claim?

 

I'll start another thread.

 

I am still using the same prop valve and MC when I went from drums to LS1 disc rear and I haven't had any issue stopping.