S-Cam question

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by PSM379, Jan 18, 2024.

  1. PSM379

    PSM379 Heavy Load Member

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    41F7AF31-353C-4886-96E3-05742C49DEE1.jpeg Doing a full brake job, noticed play at the s cam thought bushings were worn, pulled S cam shaft, signs of wear, bushing seemed ok, ordered S cam bushings replaced, put old S cam in seemed like excessive play, said know what may as well do all 4 S cam shafts as I don’t want to have this apart again hopefully for a while. New S cam shafts, new bushings and seals, still up and down play 1.5” shaft, 1.5” bushings. I’d post a video not sure how, here is a picture of the new cam in the new bushing though. Me and a good friend of mine agree the play is excessive. Not sure what I’m missing here, or maybe I am wrong. Anybody with more experience want to chime in I’m all ears. Thank you.
     
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  3. JB7

    JB7 Medium Load Member

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    Bendix recommends keeping radial play below 0.010 of an inch by replacing cam bushings as needed. That is up and down play checked with a dial indicator with the cam installed. End play is adjusted with washers at the slack adjuster.
    S-Cam Foundation Brakes: Preventive Maintenance | Bendix (cbsparts.ca) Info is same on the Bendix site.
    Be careful on installing the cam seals. The one on the brake shoe side has the rubber part/lip facing out, the one at the slack should be facing in. Another way to visualize it is that both seals face the same way if you are looking from the axle end/brake shoes.This is so that when greasing, grease only comes out by the slack and not into the shoes and drum area.
    I'm thinking the bushing is going to slightly compress/collapse once installed. Check the play with the cam and bushings installed though it sounds as if you may have done that. What brand parts did you buy?
    Bendix has free training videos on their website, you just need to register. There is one specifically for checking and replacing s-cam bushings.
     
    Last edited: Jan 18, 2024
    Goodysnap Thanks this.
  4. Goodysnap

    Goodysnap Road Train Member

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    Push the bushings in the bore and install the camshaft. The nylon should compress slightly when installed.

    I prefer the bronze vs nylon, more durable and resists wear.
     
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  5. PSM379

    PSM379 Heavy Load Member

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    Thank you guys for the replies, this is happening inside s cam tube, I just posted this picture for reference. It still has up and down play. New bushing in tube, new s cam shaft.
     
  6. Goodysnap

    Goodysnap Road Train Member

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    The bushings have no reliefs in them for the grease to travel. My guess is the bushing design is for grease tolerance to take up the gap between the bushing and the cam.
     
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  7. JB7

    JB7 Medium Load Member

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    I was thinking the same thing Goodysnap stated. Also there are many different S-cams so you may have the wrong parts. The diameter at the bushing can be 1.25, 1.5, 1.625.... and the S can be different. Difference between 1.5 and 1 5/8 is 1/8. If the cam is centered on the bushing then that would be 1/16 gap on top and bottom. That could be about what you have in the pic.
    Hard to tell how much gap/play you have without a measurement or video.
     
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  8. PSM379

    PSM379 Heavy Load Member

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    I truly appreciate the replies, according to my measurements and the bushing kits I have the correct parts. 1.5” Diameter were the bushing rides 1.5” diameter bushing kit. I wish I knew how to upload the video. I’m sorry if I’m explaining it wrong. Will double check everything again though.
     
  9. PSM379

    PSM379 Heavy Load Member

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  10. JB7

    JB7 Medium Load Member

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    Still say the bushing is wrong. As I asked in post #2 what brand parts did you buy?
    Your indicator reads in 64ths of an inch or hundreds. 2/64= .03125 or 3 hundreds or 31 thousands past the 1.5 for a total of 1.53125. This is 31 thousands over 1.5 and the cam is .01 or 10 thousands under so that is a total of 41 thousands clearance. The radial (up and down) play spec is .030 max. So with new parts you are out of spec.
    Watch the Bendix video. In that video the cam play is .010 and you can see/watch how much movement there is for 10 thousands on the indicator.
     
  11. PSM379

    PSM379 Heavy Load Member

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    I agree with you parts guy doesn’t with me. The bushing kit sold to me was OTR399b3 which crosses to meritors brass bushing kit for this cam. I just did this same job on my western star and there was no shaft play yo be concerned with. I wish I can explain better, I’m a parts charger and work on my own stuff, and know when something doesn’t look or feel right. Thank you for the reply, just wanted to see if anyone else had ever dealt with this
     
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