11" drums on an 83 CJ?? - JeepForum.com
 
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post #1 of 12 Old 03-17-2020, 02:50 AM Thread Starter
MomoJeep
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11" drums on an 83 CJ??

is it possible to swap in the 11" drum that came on late 70's Cj's to a 1983 CJ8. I have a hardtop, rear seat, roof rack, tow a boat, etc, and have done other upgrades to the brake system, and need every bit of increased braking I can get! I've heard it's very hard to do this swap only because the 11" backing plates are almost impossible to find? (It's an AMC 20, solid axle).

Also, correct me if I'm wrong but I've heard doing a rear disc conversion means I'd end up with a crappy emergency brake?

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post #2 of 12 Old 03-17-2020, 06:54 AM
jsal
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I swapped my 1978 11" drums to a 1984 wide track axle with no issues. Its a straight up swap.

1978 Jeep CJ-5
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post #3 of 12 Old 03-17-2020, 07:54 AM
schardein
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I have a 77 AMC20 axle that has the 11" drum brakes (not for sale, sorry). I think you are on the right track for a good upgrade. Everyone wants to do a disc conversion, but often end up with less than ideal parking brake performance. 11" drums used to be the "end all" of brake upgrades before discs, AND you get a great parking brake. As you stated, finding the plates may be difficult. I think they were used 76-78. One way you may be able to tell a difference (visually, besides measuring)- on my axle, the parking brake cable attaches to the backing plate using two bolts, versus the later 10" brake cables inserting in the hole and using expanding fingers for retention (more common setup). Finding new parking brake cables may be difficult also, I would research that before committing to a pair of backing plates missing the cables. Others with the 11" drums may be able to back up these details.

Also, if you are looking to improve brake performance, do you have power brakes? If yes, it is the factory setup? If yes, the power booster is a single diaphragm. Upgrading to a dual diaphragm, either aftermarket, or adapting a 1995 (4.0 engine only) YJ dual diaphragm unit would be possible upgrades. Or, convert to a hydroboost brake booster.

1983 CJ7, 5.3, NV3550, D300 4:1, Fr D44 Detroit, Rr D44 OX, 4.56, 35" Falken A/T3W on beadlocks
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post #4 of 12 Old 03-17-2020, 12:15 PM Thread Starter
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Good to know!

Quote:
Originally Posted by jsal View Post
I swapped my 1978 11" drums to a 1984 wide track axle with no issues. Its a straight up swap.
Good to know! Thanks!
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post #5 of 12 Old 03-17-2020, 12:21 PM
bob4703
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Contact David

Ironman Restoration LLC
1599 Midway Rd, Pickens, SC 29671
(864) 878-2903

He will have them and ships. He can also tell you what else you'll need for the conversion. This an old school family business. No website and won't take credit cards. Another member ordered a backing plate for an intermediate Jeep and said David shipped it before he received the check. He also won't sell junk!

-----

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post #6 of 12 Old 03-17-2020, 12:27 PM Thread Starter
MomoJeep
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Thank you, whee to find?

Quote:
Originally Posted by schardein View Post
I have a 77 AMC20 axle that has the 11" drum brakes (not for sale, sorry). I think you are on the right track for a good upgrade. Everyone wants to do a disc conversion, but often end up with less than ideal parking brake performance. 11" drums used to be the "end all" of brake upgrades before discs, AND you get a great parking brake. As you stated, finding the plates may be difficult. I think they were used 76-78. One way you may be able to tell a difference (visually, besides measuring)- on my axle, the parking brake cable attaches to the backing plate using two bolts, versus the later 10" brake cables inserting in the hole and using expanding fingers for retention (more common setup). Finding new parking brake cables may be difficult also, I would research that before committing to a pair of backing plates missing the cables. Others with the 11" drums may be able to back up these details.

Also, if you are looking to improve brake performance, do you have power brakes? If yes, it is the factory setup? If yes, the power booster is a single diaphragm. Upgrading to a dual diaphragm, either aftermarket, or adapting a 1995 (4.0 engine only) YJ dual diaphragm unit would be possible upgrades. Or, convert to a hydroboost brake booster.
I did put in the dual-diaphragm, and honestly I was disappointed to not notice any difference. I was under the misconception that a dual-diaphragm offers "double" the power. But I still didn't notice any difference. I'm not sure what the advantage is, other than maybe saving space or reliability?

Do you know a source for 11" backing plates? Would that be new or used? For the parking brake cable, couldn't I just buy a new one that fits the 11" brakes? If so, would this cable also fit on the pedal end?
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post #7 of 12 Old 03-17-2020, 01:31 PM
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My 80 CJ-5 has manual discs and the brakes leave something to be desired. I obtained 11" backing plates and drums but haven't installed them yet. I need the parking brake cable (and some motivation). My question is, will the larger rear brakes lock up prematurely? Does anything need to be done to the proportioning valve? I've also thought about keeping the stock rear drums and coverting to power brakes but the thing I don't like about power brakes is the loss of braking power when the engine dies on a hill.
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post #8 of 12 Old 03-17-2020, 01:41 PM
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Quote:
Originally Posted by MomoJeep View Post
I did put in the dual-diaphragm, and honestly I was disappointed to not notice any difference. I was under the misconception that a dual-diaphragm offers "double" the power. But I still didn't notice any difference. I'm not sure what the advantage is, other than maybe saving space or reliability?

Do you know a source for 11" backing plates? Would that be new or used? For the parking brake cable, couldn't I just buy a new one that fits the 11" brakes? If so, would this cable also fit on the pedal end?
Dual diaphragm boosters do offer more "boost"- less perceived pedal effort for the same braking effect. Many of the aftermarket dd boosters are a smaller diameter than the stock unit, so it wouldn't be exactly doubled. I suspect a math expert could figure out surface area of each diaphragm to make a comparison... If you were disappointed, assuming the brake system is otherwise good to go, a hydroboost conversion might be worth considering.

My experience was similar to yours- I had the stock CJ booster, went to a YJ dual unit. Noticed some/minor improvement. Later, went to HB- now I can lock up my 35s with moderate pedal pressure and it is very controllable.

Keep in mind that during normal driving (braking), most of the work is done by the front brakes. Swapping to larger drums in the rear may have little effect in normal driving. But, with the increased surface area, you should get a stronger parking brake, and more resistance to brake fade (due to heat) under heavy use. That could come into play if you are towing and driving on hills. Proper technique of course comes into play, downshifting to maintain a safe speed rather than riding the brakes all the way down... nonetheless, larger brakes should be able to shed more heat before fade sets in.

I don't know of a source for AMC20 11" backing plates. 11" drum conversions were very popular on early CJs as well (talking 40s-50s-60s here). They were swapped on the rear D44s and front D25s, D27s & D30s. I don't believe those same plates work on an AMC20. But, that's just an educated guess. The only source I know of for sure is used AMC20 backing plates, which will be 76-78 CJs. Another source might be from full size Jeeps (Wagoneers & Pickups) or even AMC cars, if they used the same axle (I have no idea on the cars).

For the cables, yes it should be simply a matter of buying new ones. But, I checked Rockauto, and they don't list them... they do list the later ones... that tells me they "may" not be available. I didn't check any other sources.

Good luck and keep us posted!

1983 CJ7, 5.3, NV3550, D300 4:1, Fr D44 Detroit, Rr D44 OX, 4.56, 35" Falken A/T3W on beadlocks
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post #9 of 12 Old 03-17-2020, 08:12 PM
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I did an 11" swap on my CJ using stock Wagoneer brakes. Rears were a direct bolt in (D44). I'm not sure if the D44's will swap over to the 20. If they do, then that may be an added option to source your brakes.



Any 5 bolt Waggy should work. Insure the brakes you get are self adjusters.



I too would be worried about the added braking in the rear. If you get them installed, be sure to test them out to insure the rears don't lock up before the fronts. If you have issues, you can purchase an adjustable proportioning valve and dial to dial them in.

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post #10 of 12 Old 03-17-2020, 08:54 PM
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Here are some pics of the 11" drums on my axle. Ring gear is dated 1977.
Attached Thumbnails
IMG_7601.jpg   IMG_7602.jpg  

1983 CJ7, 5.3, NV3550, D300 4:1, Fr D44 Detroit, Rr D44 OX, 4.56, 35" Falken A/T3W on beadlocks
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post #11 of 12 Old 03-21-2020, 09:50 PM Thread Starter
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Your Drum sizes

Quote:
Originally Posted by 80cj View Post
My 80 CJ-5 has manual discs and the brakes leave something to be desired. I obtained 11" backing plates and drums but haven't installed them yet. I need the parking brake cable (and some motivation). My question is, will the larger rear brakes lock up prematurely? Does anything need to be done to the proportioning valve? I've also thought about keeping the stock rear drums and coverting to power brakes but the thing I don't like about power brakes is the loss of braking power when the engine dies on a hill.
Where did you get your 11" backing plates?

When talking about Brakes, I want to be safe and not spread any inaccurate information. With that said, the impression I get is that 11" brakes won't be that big of a jump in braking from the 10". However, I haven't tried it yet. You could just try and see. Adjustable proportioning valve could be an option. The reason I want 11" is that I've got a Scrambler, Hardtop, backseat, gear, roofrack and I sometimes tow a boat. All of this means somewhat less weight transfer to the front, and less likely that larger rear brakes would lock up.

Another solution would be simply getting "Stickier" Aftermarket linings. I can find them for my front Discs, and they claim around 20% more stopping power, but so far I can't find anyone making them for the rear. Anyone know a source?

And if you end up not using your 11" backing plates and drums, please let me know!
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post #12 of 12 Old 03-22-2020, 12:24 AM
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Quote:
Originally Posted by MomoJeep View Post
Where did you get your 11" backing plates?

When talking about Brakes, I want to be safe and not spread any inaccurate information. With that said, the impression I get is that 11" brakes won't be that big of a jump in braking from the 10". However, I haven't tried it yet. You could just try and see. Adjustable proportioning valve could be an option. The reason I want 11" is that I've got a Scrambler, Hardtop, backseat, gear, roofrack and I sometimes tow a boat. All of this means somewhat less weight transfer to the front, and less likely that larger rear brakes would lock up.

Another solution would be simply getting "Stickier" Aftermarket linings. I can find them for my front Discs, and they claim around 20% more stopping power, but so far I can't find anyone making them for the rear. Anyone know a source?

And if you end up not using your 11" backing plates and drums, please let me know!
Got the backing plates from a friend who was parting out a 76 CJ-5. They're hard to find.
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