Hi All,

I am doing a rear disc brake conversion on my 68 Charger using a kit from Summit. The previous owner already had a conversion done, and it was using calipers and pads from a mid 70s Lincoln Mark IV, so there are already some Ford parts on there. You can see from the picture the part that the Calipers bolted into. I cut part of that off with an angle grinder, as it got in the way of the parts that came with the Summit kit.

I was able to install new inner axle seals and the disc brake conversion kit, however the passenger side axle has about a quarter inch of play, which is causing a lot of problems when I try to drive it.

I tried doing the adjustment as described in the service manual, but wasn't having much success. As some work on the axle has already taken place, I'm not sure I even have the necessary parts to do the adjustment.

If anyone has any tips I would very much appreciate it, or if you can tell from my pictures if I'm missing anything. I'm having a hard time since there was already work done on it, and I don't know if I have all the parts I need. If I can't adjust the axle play correctly, I think I may just remove the tapered bearings and put on green bearings.

Here's a pic of the part I had to cut part of off.

Thanks for the reply.

I haven't dug into the differential yet, but in the paperwork I have from the previous owner, I see a receipt for a Detroit locker, and the wheels definitely chirp when I go around corners while giving just a little gas.

The previous owner kept all his paperwork, and there is no mention of machine work on the axles so I'd be surprised if the axles were shortened. All I see in the paperwork for the disc brake conversion is that the customer supplied spindles, rotors, calipers, and bearings. I will definitely measure the axles though. Just gotta unbolt everything first.

Your welded on bracket doesn't look to be an issue. From the look of the bearing collar it almost looks like the bearing isn't pressed all the way down. Make sure of that before going farther. The green bearings are not ideal. If you are going to replace bearing just use another tapered bearing.

The stock tapered Timken wheel bearings need very little(.003 to .008 or so), if any, end play. Think of the same type and brand bearings in the third member They have a ton of preload on them and live for ever. My message is to reduce the end play one way or the other As already mentioned the original clutch typ posi and the later cup and cone posi in the 8 3/4 used a set of floating pins or a floating block to set the axle end play How is the left side end play, the axle with no adjuster on it? Both sides need to be checked for total end play. Have you tried adjusting the end play with the stock adjuster yet? If not now is the time to try it Scerw it in to reduce the end play Don't we love after market parts BTW, the Green axle bearing kits that Dr Diff sells work good on the street, that may be your only viable option if you can't make the end play adjust like you want it I use them on my cars with spools in them on the street

The drivers side has zero end play, and I assume everything is working fine because I can't hear any noise on that side. It's all coming from the passenger side.

I'll try the adjuster again. Ballpark how many revolutions are needed to get rid of 1/4" of end play?

Also assuming there is a Detroit locker in the diff, can the thrust buttons still be an issue?

Thanks!

Take a flashlight and look inside the axle tube towards the center of the locker to see if their is a passage for the thrust buttons in the middle like the stock early ones had I've seen half of the button stick onto the end of the axle and then drop off inside the axle tube The stock axle bearings like yours have to have some way to set the axle end play, as far as how many turns it will take is anyones guess Start adjusting and quit when it is right(.002 to .008 end play on that one side ) or the adjuster comes apart Good luck, let us know how it works out

I was able to work on my problem a bit today. I pulled the axle out and shined a flashlight down the tube and saw what appeared to be a thrust button. I tried fishing it out, but it just dropped down inside the differential housing.

I adjusted the end play as much as possible, but still ended up with 1/4". Because of this, and like someone mentioned, I'm wondering if the bearings aren't pressed on all the way. I measured 25.25" from the end of the spline to the start of the bearings. I'm not sure if there is a spec for this.

I was able to find a spec for the axle shaft length (end of spline to outside flange) of 29 3/16", and this measured fine on mine.

Thanks a lot for the help and bearing with me!

Also, the axle is out so I'm happy to measure or take pictures of anything.

You would need to reinstall the thrust buttons but you had the problem before you took em out. Likely you could fish em up & out with a magnet on a pole and some string but I think you'd need the pig out to reinstall em. If the housing/axle length is unaltered & the thrust button(s) were in place then as you said I would take a somewhat closeup pic of the shaft/bearing area behind the flange at just the right distance & see if the dimentions/distances tells one of us something

I read this again and thought, have you eliminated the usual drum backing plates? Is there anything taking their place? If not, this needs to be addressed as adjustments are taking the plates into account as these axles mount onto the housing with backing plates mounted first.

Yeah, the drum backing plates are long gone... I assume when the previous owner did the original disc brake conversion. This pic I'm attaching of what the calipers bolt to measures .38".

With the adjuster completely screwed in, I still have .25" of play. With a Detroit locker, and original tapered bearings, are the thrust buttons necessary? I read a lot of threads where people didn't worry about broken ones.

Since mine fell out, I assume the retaining pin is broken and I'll need to get a new one if I need to use the thrust buttons? Any idea where to get one?

There are three pieces that make up the center floating axle end play adjuster, the two side peices and soft center piece that needs to be flattened or centered punch, swollen into place after the other two pieces are in the hole where they go Dr Diff on here sells that assembly new I use to use thick axle grease, wheel bearing grease, to hold the two center peices in before I knew where to get the soft center retaining piece The only bad thing about using the grease is the two center peices can stick to the axle ends when you pull the axles out the next time BTW, I use a long, powerful stick magnet now to remove those center pieces to avoid dropping them into the axle housing, like you had happened IHTHs My message is your not the first person to have them DANG center shoulder ends fall into the center section IHTHs

The 5-hole wheel bearing adjuster/retainer must mount 1/8" from the housing end. If the bracket or spacer under the 5-hole retainer is thicker (or thinner) than 1/8", the axles will not fit correctly and the wheel bearings will never adjust.

Thanks a lot for the replies.

Tomorrow I'll pull the carrier, go fishing for thrust buttons and see if I learn anything new.

Here is a close up pic of my bearings in case anyone sees anything noticeably wrong.

Alright... The differential is out (that thing is heavy! I do not look forward to putting it back in!). I found two thrust buttons and a pin in the bottom of the housing. The buttons fit together very loosely. There was a notch in the ion that I opened up a bit with a screwdriver, and now there is much more tension when I put the buttons backs together.

My next step is to out it all back together and try the adjustment with the thrust buttons firmly in place.

A few questions: is there a link to the exact procedure on how to do the adjustment?

What do you guys use for the 8 3/4 gasket? Something from summit, then some RTV or form a gasket?

I installed new axle seals from the local parts store ($15 each, so not cheap ones), and one side already started leaking when I jacked the other side up. Is there a certain brand or website you guys can recommend for axle seals?

In regards to Dr. Diff's comment about the 5 hole adjuster needing to mount 1/8" from housing end... I'll defer to those who know more about this than me (everyone), but I find it hard to believe that Summit would sell a disc brake conversion kit that doesn't work.

Thanks again for the help!

I use a tailor made parts house 8&3/4 ring gasket as opposed to RTV (too messy on the next pig change). yes you need to change the new inner seal that is leaking. I pack the spring with grease to hold the spring in place and drive it in with a circular piece of round THICK stock/drift/BFH with as few strokes as possible as each stroke increases the chance of distorting the seal. As you drive it in if it starts to tilt then move the drift over to the high side & hit it a time or two to get it back even then move the drift back to center & continue. You want your piece of round stock the OD to be slightly less than the OD of the seal so it contacts it very near the perimeter (where it is strongest). If I plan on some pig changes I slightly oil the gasket and if not then I spray it with Permatex 99MA "high tack" the red thin spray gasket/glue. EDIT You're 1/4" off & from what I gather from Doc, backing plates are 1/8" & I'd mockup some 1/8 spacers under several of the bolts on each side to space the 5 hole retainer out 1/8 from the housing flange & see if you're good

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but I find it hard to believe that Summit would sell a disc brake conversion kit that doesn't work.

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Is it possible it was set up before with the green/ford ball bearing wheel bearings?