11" drum scraping backing plate after conversion; axle sits deeper after diff swap. What's up?

[cudak888]

The first pic in post #5 is a shot of what an open (non Sure Grip) diff looks like....but that shot is not of an 8 3/4 even though it's very similar.

I know. It was the only picture I could find anywhere of anything illustrative of what I was trying to describe. You'd think open rears would be dirt cheap from the way anyone talks about them online (alas, not so - and finding one locally via C-list is next to impossible).

I still think you need to pull the 3rd member and check the block. Its the only thing that would change right side axle depth. The preload should be close to the original setting if the parts are right. After all the left side is working the right side should also.

I'll probably do that. I'm thinking of grinding a little off the backing plate for now so I can at least enjoy the car until March, then pick up another center section at the Florida Nationals for a complete tear down and service.

-Kurt

 

[mopar 3 B]

The thrust spacer is a three piece part left, right and pin that holdes them together. If missing one side it would create the problem you are having. A $30 part at most. Why destroy what you have over an hours work.

 

[Garys1969RR]

We had the same problem after swapping a 3.23 to a 3.91 3rd member. Since the brake drum was just barely scraping the backing plate, we used a disc grinder to take a little metal off the edge of the drum, and/or backing plate. That solved the problem, and it's been working fine ever since!

 

[oldbee]

Doesn't sound good that the adjuster is so far "down in the hole" though. Thrust block problem I'm thinking. 'Cudak' you do know ur supposed to smack the left axle shaft a couple times before adjusting rt. side? just checking.

 

[Cranky]

The thrust spacer is a three piece part left, right and pin that holdes them together. If missing one side it would create the problem you are having. A $30 part at most. Why destroy what you have over an hours work.

The OP stated that he's using an open diff in post #1 which uses the same style thrust spacer as the cone unit uses. Only the clutch type uses the three piece thrust spacer.....

 

[mopar 3 B]

The OP stated that he's using an open diff in post #1 which uses the same style thrust spacer as the cone unit uses. Only the clutch type uses the three piece thrust spacer.....

Ok so it a open carrier that does not change the housing length or make the axles shorter and as stated in post #5 the adjuster had to almost screwed threw the retainer to get proper end play. That only leaves the thruster. Installing the original should solve the problem.

 

[cudak888]

Just came back in from a whirlwind of last-minute work on the car* and about ready to sit down to dinner, so I'm going to make this quick:

1. Since I can't stuff the car up on jackstands for more than a day (it's parking spot is not in the driveway, and I can't leave it there over the week, only the weekend), I'll need a third, third member (horrors!) to play with before I can drop the 3.23. Putting the 2.76:1 back in was a thought, but I've yet to find a source for the thrust block, and I figure the 2.76:1 is a good and free place to get a known good one from. Also, since I've never had a diff apart before (might have played with one at 6 years old, but never professionally), I figure I might as well learn on one without time pressure too.
2. I went ahead and ground 2mm off the backing plate for now so I can drive the thing next month to the Florida Nats, where I'll probably pick up a replacement center section to build up...because this will probably be my only chance to get one locally. Please wish me luck for a good one, and I'll send cookies if your prayers bring me a Sure Grip.
3. I took some photos (will post them) of the adjuster's present position (for reference). I'll post them shortly.
4. I looked at the thrust block when I took the right side apart today. Seems shiner than usual. Perhaps this is where it got worn off?
5. Yep, I do the dial indicator + whacking the left side and right side as the factory manual says for every adjustment. Even if I didn't, the only thing too much play could cause would be rubbing on the LEFT side (correct me if I'm wrong, but, since the adjuster is on the right side, all slop winds up causing the left side to run farther inboard and the right outboard).

-Kurt

*Unrelated, but a HUGE thanks to bigmanjbmopar for ousting the fact that Spectra REVERSES the orientation of the vent tubes on the '68 gas tanks from the factory manuals. If it weren't for him, I'd be still suffocating of fuel and trying to figure out why the tank would occasionally dump fuel out the J-tube vent. Extremely dangerous issue if one isn't aware of Spectra's screwup: http://www.forbbodiesonly.com/mopar...ting-system-on-my-70-rr.98557/#post-910316182

 

[cudak888]

Just for the record, here is the adjuster position - easy to spot that it's backed in quite a bit:

And here are the cast marks on the center section. Haven't decoded them myself for lack of time:

Ok so it a open carrier that does not change the housing length or make the axles shorter and as stated in post #5 the adjuster had to almost screwed threw the retainer to get proper end play. That only leaves the thruster. Installing the original should solve the problem.

It's got an original. The only remaining question at this point is what happened to it to cause it to get shaved down so much.

-Kurt

 

[cudak888]

P.S.: Doesn't mean diddly at this point, but seeing as all my previous pictures had shown the 10" drums lying on the floor, here is a photo of the actual 11" finned Budd replacement:

-Kurt

 

[mopar 3 B]

Just for the record, here is the adjuster position - easy to spot that it's backed in quite a bit:

And here are the cast marks on the center section. Haven't decoded them myself for lack of time:

It's got an original. The only remaining question at this point is what happened to it to cause it to get shaved down so much.

-Kurt

It may will be the original to the diff but not the housing or axles that it is now being tried to use with. Going back with the original thrust to the housing and axles should solve the problem with the adjuster and drum clearence.

 

[cudak888]

It may will be the original to the diff but not the housing or axles that it is now being tried to use with. Going back with the original thrust to the housing and axles should solve the problem with the adjuster and drum clearence.

Agreed - but I'm really curious now where the specification difference comes from. I've scoured all the online resources which claim that the only variance in the thrust block is pre-'64 on open diffs, and according to the Chrysler parts books, the thrust block was the same from '68 through '74, P/N #2467268. I still need to check '67 and earlier.

Should be interesting to see what's up with the PN and size of the part when I finally get it out.

-Kurt

 

[Cranky]

Didn't have any problem when I swapped out the 2.94 for a 3.91 in my first car....a 66 Belvedere back in the day. Then after making a 200 mile trek when I got into the military, I decided the 3.91 was just a bit too much to be trying to cruise at 70 mph and went to a local wrecking yard and found another 2.94 from a 68 and stuck it in. I've also pulled a lot of chunks out of older pickups from the pick and pull yards around Houston during the 80's. Don't remember the years but there were a couple here and there that were older than 67. I usually avoided the cars that had the bolt on rear drums just because they were usually a rpita to get the axles out of the way....

 

[BCBOUND]

......you may have backing plates for 2" shoes and 2 1/2" drums. Measure carefully. This same thing occurred when l installed finned drums on a 66 Charger without swapping backing plates also.
Problem went away when l went back to original drums.

 

[cudak888]

......you may have backing plates for 2" shoes and 2 1/2" drums. Measure carefully. This same thing occurred when l installed finned drums on a 66 Charger without swapping backing plates also.
Problem went away when l went back to original drums.

How would I go about identifying one from the other?

Haven't really found a source that says which vehicle came with what either, much less tell them apart visually.

EDIT: Just learned there's a 11x3" police variant for the rears too.

-Kurt

 

[dieseldazzle]

I thought all b body mopars with 11 inch drums were 11x3 ??

 

[cudak888]

I thought all b body mopars with 11 inch drums were 11x3 ??

I found this huge thing over at the C-body forum claimed to be an 11x3", but it's a front. Nothing more than interesting for the purposes of what I'm up to...

...unless there's a school of thought that calls the 11x2" Budd brakes 11x3"'s.

-Kurt

 

[cudak888]

FYI: Source of the 11x3" rear drum talk:

http://www.forbbodiesonly.com/moparforum/threads/11-inch-drum-brake-id.119524/

-Kurt

 

[miller]

Only kinda remember, since it's been years since I mounted mine. Looks like the same finned rear drums, in the one photo. 11" drums, but pretty sure there's two different widths, 2 1/2", and the police 3" wide (what I have).
Between the two widths, takes different backing plates, the 3" sets deeper, than the 2 1/2". All simply because on a normal 8 3/4" rear, the axle flanges set the same distance from the housing flanges...if that makes any sense.

 

[cudak888]

Only kinda remember, since it's been years since I mounted mine. Looks like the same finned rear drums, in the one photo. 11" drums, but pretty sure there's two different widths, 2 1/2", and the police 3" wide (what I have).
Between the two widths, takes different backing plates, the 3" sets deeper, than the 2 1/2". All simply because on a normal 8 3/4" rear, the axle flanges set the same distance from the housing flanges...if that makes any sense.

Makes sense. Any place you'd recommend for measurements for each?

-Kurt

 

[miller]

For the brake backing plates, how about the measurement from the axle mounting pad, to the outer part of the plate. One will be deeper, than the other.

Brake drum? Measure from inside at the mounting surface, to the backside outer edge.
You will not get 2 1/2", or 3", trying to just measure the 'width' of the shoe surface of the drums, since they are always wider than the shoes themselves.