I went to the junkyard today and found a GSL with a complete rear end, and was curious about a few things:

1) Would it be worth swapping that into my '85 GS?

2) Does it have a LSD? If so, is it an independent rear end or solid?

 

I put one into my 85 GS and love it. It does have the limited slip, which is great, and also disc brakes. Installation was a breeze... This swap is well worth it in my opinion.

 

Just make sure it is from an 84 or 85. Otherwise it will not be a direct swap as mazda changed the rear ends for the last two years (bigger axles if I remember correctly)
If its from an 81 to 83 just send it to me as I've been looking for one!
Good luck.

 

A complete rear end is a bolt in. Meaning axle to axle so it would not matter.

 

Make sure to get the emergency brake cables from both sides also.

 

Well that is good to know. Do you have to switch driveshafts or something to make them work? Thanks for the info doc.

 

Only if you have a 81-82 model that you are putting it into. The 83-85 have the larger pinion flange.

 

What about an 80? Sorry for the thread jack. This is my last question I promise!

 

1. definitely worth it... I have one waiting to get swapped into my GS

2. Yes it does(already answered) and it is a solid rearend... they all were far as I know

I'm not sure on this one, but you may need to snag the proportioning valve or whatever contains it as you would be switching from drum to disk brakes...

Can someone answer for sure?

 

Yes you can. It is not really needed, and can be ran without the disc PV. I have a whole rear end ready to swap over including everything braking related. It would be better to swap the PV over to get the brake bias correct.

 

81-82 drum/disc both used the same PV, however, starting in 83, the disc rear had a different PV, while the drum continued to use the same as the older cars. The master cyl, on the other hand, is different between drum and disc.

As for guy asking about an 80 model, you will need a special rear chassis to axle brake hose.

 

I'm sure I'll get a little flaming for this, but I did not change the master cylinder or the proportioning valve when I did my swap. Brakes work great, even while racing. I couldn't be happier with the braking performance just the way it is...

 

I have a complete 82' GSL Rear end and I want to swap it into my 85GS. What all do I need to swap. I have the parking break cables. I also have the master cylinder do I need to switch it as well?

 

No, but make sure you have the 82 driveshaft. The flange is different on the larger axle cars.

 

I didn't change the PV either, but I did swap the master cyl. At first, I left the drum MC on the car, but it started leaking. When I went to replace it, the reman disc MC was actually less, so I went with it.
FWIW, the only "real" difference between drum and disc MC, is the residual pressure valve in the drum unit. It is (normally) located under the large hex head plug that the rear line bolts into (front of MC), and can be removed to convert a known good drum MC to disc.

 

Is there a place to get these, or do I have to come up with something myself? So if I get a rear end from an 81-82 gsl, do I need to get the driveshaft or will mine work? Thanks.

 

There are plenty of places to buy the hose. I believe respeed and mazdatrix both offer it seperately, as well as in a complete DOT braided stainless kit. There's many other places that sell the full kits.
As for the driveshaft, 79-82 used the same, while 83-85 was different.

 

So I should try to find out what year this GSL is first? make sure it's an '84-85 so my differential will match? And if possible get the Proportioning valve?

And is the a Brake Master Cylinder necessary? or was someone saying you can convert a master cylinder for drums over to rear disc.

 

Just to clarify, 83 was the mid year change. So some early 83's had the small flange and axles while later 83's had the larger flange and axles. The rear end with hoses and e-brake cables are all that is necessary(with matching driveshaft if applicable). The Master Cylinder and Proportioning valve are optional

 

Okay, awesome. Thank you. I'll look into getting this then, and will let you guys know how it goes.

 

You have an 85 (according to yje 1st post) so you will need either: A, a GSL diff from an 83-85 to use your current driveshaft, or B, A GSL diff and driveshaft from 81-82, and use the early driveshaft.
A simple wat to see which style driveshaft is needed, look at the flange that the driveshaft bolts to. 4 threaded holes = 81-82. 4 non-threaded holes = 83-85.
I have heard that early 83's had the smaller flange like the 79-82, but the Mazda parts microfiche doesn't support this. Nor does it support the mid-83 axle size change that is often reffered to here. Not sure who is *really* correct, the experts here, or Mazda's parts list.

The brake master cyl is not 100% needed. There is only one internal difference between drum and disc MC. There is a residual pressure valve (often called a check valve) in the rear brake section. It can be removed, if desired. I drove my car for about 3 months with a drum MC and PV without any issues. The MC went bad, so I replaced with disc brake unit.

The proportioning valve, according to the parts microfiche, is the same from 81-82 for drum or disc, but 83-85 did use a different PV for disc. This means the the PV is not 100% required, but if one can be found from a 83-85 GSL, it might be best to use it. I'm not sure if the GSL and GSL-SE used the same PV, but the MC seems to be the same.

 

could i just use the LSD diff from the GSL with my axles? or do i need to do a complete swap?

 

I believe the axles are the same as yours. Other then the durm vs. disk.

Edit, look here backing plates are different. http://mrmazda.no-ip.com/interchange.html#AXLE

 

The axle shafts will interchange between drum and disc, as long as they are both the same diameter. The 79-83 had small axles, while the 84-85 had larger axles.
The axles are totally different between big and small, the entire length is different diameter.
So, as long as you aquired a LSD center from an 84-85 model, yes it could be placed in your current drum brake rearend housing.

 

I did this swap on my 85 GS. Along with NEW discs, pads, bushings, RB springs, RB sway bars, shocks, and SS brained lines.

My rear brakes WILL LOCK UP FIRST under panic braking on the streets.
(don't ask how i know)

While on the track or twisties i'm am better able to modulate with the pedal.

Just a great, great mod to do. No more whimpy one tire peal-outs. Character of the car has changed.

Conclusion - I will get the proportioning valve once I have a chance.