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About to start my disc conversion: help


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23 replies to this topic

#1 Geck512

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Posted 05 May 2004 - 12:50 AM

My chevy mechanic friend says that I might be running into trouble with my disc brake swap. I got the rear disks from an 86 turbo 2 door? Sedan? two wheel drive. I am going to be putting them into my 83 gl 2 wheel drive. Does the Master cylinder have a different outlet for the rear discs and the rear drums? Will the flow be enough? Too much? I dont really understand the problems that could arise but he felt that it might be trouble installing them. But then again he told me not to buy the car! :rolleyes:

So anyways I know lots of you folks have done swaps and it works well. But this is an ea82 rear disc going into an ea81 car. I practiced the swap in the boneyard and it looked like it would work (plumbing is a little off and I did grab the hard hose from the original disc-having car) I think I might have to drill a hole through the a arm? the suspension swinging thing =P to get the line from the caliper to the hose running up the car. Or I need to bend it but I dont want to do that I dont think. ::shrug::

Advice beyond the directions already in the subaru manual on the board?

Thanks
Joshua

#2 calebz

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Posted 05 May 2004 - 12:54 AM

Best advice.. tell your chevy friend to stick with chevies.


Sounds like you are good to go.. just bolt 'em
No need to worry about the master cylinder or proportioning valve.

#3 Geck512

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Posted 05 May 2004 - 01:03 AM

Any worries with drilling the a arm thingy so I can slide the hard hose more directly to the next link in my brake system? Is there any easier route? Can I use plyable hose?


Joshua

#4 calebz

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Posted 05 May 2004 - 01:51 AM

I have only seen it done on 4WD vehicles.. and it was a straight bolt on process.. no drilling required.

#5 TheSubaruJunkie

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Posted 05 May 2004 - 02:01 AM

Ive done it on 3 of my 4WD Subaru's. All of them were EA81 body styles. It is a direct bolt on. There is nothing special that needs to be modified or removed.

I also say tell your friend to stick with Chevy's. :)

Oh yeah... here's a page I put together the 1st time I did the swap:
http://www.subaru4wd...s/reardisk.html

Pretty cut and chase.
-Brian

#6 Hondasucks

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Posted 05 May 2004 - 02:58 AM

Josh -- if ya wait until next weekend or your next night off or whatever, I can give you a hand wiht it prolly, if ya wanted to do it in my driveway.

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Posted 05 May 2004 - 04:31 PM

You know, almost every automobile out there where somebody has switched to rear disks on a factory drum brake system has had to modify/change the master cylinder and or proportioning valve. It is very common to have dangerous braking when rear disks are swapped in with no other changes.

I understand that many guys/gals on this board have completed the swap with no problems but just don't discount somebodys concern who is not hip to Subaru's.

Didn't Adam from Rogue River make a comment recently about his brat being able to put flat spots on the rear tires because they had more stopping power than the front's? Could a proportioning valve would solve that problem? Imagine what would happen if that was on a wet/icy road. He would likely be in the ditch (no disrespect Adam).

Anyway the point is....when it comes to safety you can't be too careful. Every modification effects the car in someway good or bad. Mods have to be thought out, even if they've been done 1000 times before on somebody else's car.

#8 TheSubaruJunkie

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Posted 05 May 2004 - 06:46 PM

None of the cars ive had with rear disc brakes have ever had a braking problem. its possible to hold the brake and drag your rear tires with the car in FWD, but on ice and snow... anyone who brakes hard will loose control, regardless of how well their brakes work.

If EA82T's have some sort of valve, or special master cyl, then prove me wrong... but as far as I know, there are absolutly no differences between a stock EA81, EA82 and EA82T brakes other than the drum's and disc's.... everything else is straight bolt-on.

-Brian

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Posted 05 May 2004 - 07:11 PM

None of the cars ive had with rear disc brakes have ever had a braking problem. its possible to hold the brake and drag your rear tires with the car in FWD, but on ice and snow... anyone who brakes hard will loose control, regardless of how well their brakes work.

If EA82T's have some sort of valve, or special master cyl, then prove me wrong... but as far as I know, there are absolutly no differences between a stock EA81, EA82 and EA82T brakes other than the drum's and disc's.... everything else is straight bolt-on.

-Brian


Brian, all vehicles have a proportioning valve from the factory. They equalize the bias and weight of the vehicle from front to rear in regards to braking. They are designed and adjusted from the factory to work with the particular vehicle on which they are installed. It would make sense that a wagon would have a different setting due to its heavier weight in back than a Brat with very little weight in the rear. Likewise rear disks have more clamping/braking power than drum brakes and would likely need a proportioning valve to accomadate that difference. Also, calipers and wheel cylinders have different requirements for volume and pressure when it comes to fluid.

I'm not trying to say rear disks don't work on Subs, they obviously do. However, It doesn't work that way on any other vehicle without at least an adjustable proportioning valve from Summit to compensate for the increased braking from the rear.

Bill

#10 Caboobaroo

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Posted 05 May 2004 - 09:33 PM

Best advice.. tell your chevy friend to stick with chevies.


Hey guys, you gotta give me some credit. I'm a hardcore Chevy guy but I'm on my number 2 Subaru right now!!! As for a proportioning valve, I don't really see why you would HAVE to change it. I know on 82-92 Camaros when doing a rear disk brake conversion you need the proportioning valve which is a b**** because its mounted inside the master cylinder. One reason for the proportioning valve is for the simple reason that it takes less pressure to push on the drum brakes then it does for disk brakes. The other reason for proportioning valve is to keep pressure in the lines for the drum brakes so the wheel cylinders stay partially inflated so they don't get moisture in them and rust them. I don't know if this is true for Subarus but I'm not sure. This is a good swap to try because then it gives you the experience so when other people want to try it, you can direct them in the right direction:D

#11 GLCraig

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Posted 05 May 2004 - 10:11 PM

I just check my FSM, it dosn't show a proportioning valve anywhere in the brake system. Another thing that everyone needs to keep in mind is that the brake circuits are not split front and rear. The split is Left front Right rear and Right front left rear.

#12 Geck512

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Posted 05 May 2004 - 10:29 PM

Interesting Craig. Anyone know if there ARE different master cylinders for different cars of the same year? Or of the same car for different years??


On the hunt for truth and non-death-causing-mods

Joshua

#13 Geck512

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Posted 06 May 2004 - 02:23 AM

bump


Calebz? Shawn? Disorder? Any techs? Anyone? Is this going to kill me? Do turbo cars have the same master cylinders as non-turbo counterparts? What about going from Ea82t to ea81?

#14 Geck512

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Posted 06 May 2004 - 10:46 AM

What about the octopus? Is it different?

#15 archemitis

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Posted 06 May 2004 - 10:59 AM

quit worrying and just put them on! they will work a hundred times better(speaking from experience). just do it!

#16 ezapar

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Posted 06 May 2004 - 11:07 AM

Totally. Put them on, try them out, adjust accordingly. Ask Jeeves aka the USMB had to get its answers from somewhere. Someone has to try stuff out to be able to tell others what works and what doesn't.

#17 Guest_taprackready_*

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Posted 06 May 2004 - 11:59 AM

I just called NAPA to help in the quest for safety with rear disks. There is no difference in part numbers for master cylinders for turbo or non-turbo subarus. So hats off to others who have put on rear disks.

My only reason for questioning is for the safety factor and most other auto makers have differences in the braking for disk vs drum brakes in the rear.

Bill

#18 Partsman

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Posted 06 May 2004 - 03:50 PM

If EA82T's have some sort of valve, or special master cyl, then prove me wrong...
-Brian


How about if I prove you right! The master cyl's are the same 85-94 in the NAPA listings, and I checked with my local dealer and the proportioning valve is the same for disc and drum (at least in 1988, the year I asked about). The master cylinder is different 84 and older - both bores are 13/16" versus one 13/16" and one 1" in the later models, so that might cause a problem when you cross years, but obviously it isn't much of a problem with all the case histories on this board!

#19 Guest_taprackready_*

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Posted 06 May 2004 - 05:37 PM

Partsman, that is exactly the kind of info needed to make educated modifications. Not just because others have done it and nothing happened to them. Great job. Confirms my previous post earlier this morning when I called NAPA.


Bill

#20 TheSubaruJunkie

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Posted 06 May 2004 - 09:51 PM

In the Subaru world... modifications are just that, modifications. Most are not educated, but frankenstien'd. Nobody knew 5lug would work on a RX until Corky did it the 1st time. Nobody knew a 5spd would fit behind a EA81 until Ken did it (unless he wasnt the 1st??) nobody knew rear disc's would bolt onto a EA81 until Pat pulled it off.

I'm not saying research is pointless, or useless... but you'll often find that the best way to modify your Subaru is through Trial & Error.

But, im glad to know im not jepordising anyones life by advertising the ease of the rear disc conversion.

-Brian

#21 baccaruda

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Posted 07 May 2004 - 04:25 PM

I think Ken posted about the difference a while ago and said it was no reason to worry.

#22 Geck512

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Posted 09 May 2004 - 12:43 AM

The master cylinder is different 84 and older - both bores are 13/16" versus one 13/16" and one 1" in the later models, so that might cause a problem when you cross years, but obviously it isn't much of a problem with all the case histories on this board!


I have a 1983. I got my discs from an 87. Am I mistaken or could my rear discs end up like hercules clamps?

Joshua

#23 Partsman

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Posted 12 May 2004 - 08:27 PM

I don't think so. Too many case histories on here with good results. Any Subaru experts know why they changed to different size pistons in 85 master cylinders? I mean, since each side of the m/c runs one front and the opposite rear brake, it doesn't make sense!

#24 Guest_taprackready_*

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Posted 13 May 2004 - 10:28 AM

I think this is a dead horse. Info posted somewhere in the middle of this thread has the specs for the master cylinders and they are virtually the same.


Bill




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