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  #1  
Old 15-07-19, 23:08
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Default CMP brake question

CMP brake question about both Ford & Chevy C30, C60, and C-GT and their Ford equivalents.

The issue is the, minor or upper adjustment, interval how many miles between adjustment are people getting? My C60S Radio body truck with the 261 engine, curb weight 12,000LBS, gets between 1000 & 2000 miles a year. My routine has been to adjust or check the adjustment each spring when do the general servicing. With the truck up on jack stands it is just makes the whole servicing easier.


Now normally over the years it has taken only the most minor adjustment of cams A & B (Fig. 6 - Adjusting Cams) maybe a few degrees. Once this is done the brake peddle is right back up at the top of the stroke.


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The last three times I have done this three wheels RF, LF, LR all needed almost any nothing, but the Right Rear both A & B have needed much more. What I also noticed was that they turned much easier than all the others.

Has anybody else noticed a similar problem?

I had adjusted the brakes 3 months ago, recently I was not happy with the brake performance, peddle goes down about halfway and with a quick pump brings the peddle right back to the normal top point. So put the truck on jack stands and checked the adjustment and again the Right Rear was out of adjustment again.

Cheers Phil
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  #2  
Old 16-07-19, 01:31
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Phil.

Is there anything significantly different about the brake assembly components on that wheel from the other three, even if just different in maker?

Can the adjusting cam assemblies themselves wear out and require replacing for any reason? Seems a bit odd that set are easier to deal with than the other three.

David
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  #3  
Old 16-07-19, 01:32
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The same bendix system was used on the M35 2-1/2 ton trucks, the 5 ton trucks, the 3/4 ton Dodge, right down to the M38 Jeep. I always did a major adjustment when the brake job was first done, followed by a couple of minor adjustments. At the end of the day, you need the contact to be in the center of the shoe's arc. Repeated minor adjustments won't achieve that once appreciable wear has occured. I never had to do them as often as you are doing. Some variables are the condition of the drums (smooth/scored), the composition of the linings, the type of driving, and possibly the over adjustment of the shoes in the first place.



I would suggest you try a major adjustment again. Turn the lower anchors in the same "waterfall" type direction as the upper adjusters. Some of the bendix drums will let you get a feeler gauge into the drum so you can properly set them up. What you are after is contact in the center of the shoes.....not top or bottom.



If the shoes are correct, and you are still findng the need to pump the pedal, then perhaps a good bleeding is in order. Fresh fluid in the system is a good thing, and a preventative maintenance item that is often overlooked.

Last edited by rob love; 15-08-19 at 02:44.
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  #4  
Old 17-07-19, 21:59
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Default C60S Brake Adjustment Round 2

Hi All

First thanks to Rob and David for responding.

First to David's comments/questions:
I don't think there is any significant differences in the pairs of backing plates. But David your comment made me check the position of all eight of the lower/major adjusters. The 4 rear ones were dots pointing toward each other. While the 4 front ones are at the 2 and 10 o:clock positions.
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Second Rob's comments- "I would suggest you try a major adjustment again" Well I did a careful major adjustment per the manual:

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10. Was getting a stead 30 lbs. pressure on the peddle.

Getting just 30lbs peddle pressure is a touchy thing, wish the manual explained the logic. You can see from the photo how this was done with a 30lbs with hanging pulley so as to put just that pressure on the peddle. This pressure seems to just take up the play in the wheel cylinders, without applying the brakes to drag. If you push down on the peddle just a little more and release the brakes apply and the wheels don't turn. So I went with just 30 lbs pressure.
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11. With a short (3")wrench turned the two lower pins on each wheel just the smallest amount to just cause brake drag/sound. Repeated this on all the wheels carefully re-tightening the locking nuts. When the pressure was removed the wheels turned smoothly with no drag.



Robs last point is well taken "If the shoes are correct, and you are still finding the need to pump the pedal, then perhaps a good bleeding is in order. Fresh fluid in the system is a good thing, and a preventative maintenance item that is often overlooked." Because all CMPs have single brake systems I take preventative maintenance seriously. Any sign of leakage means full brake job. No leakage every 9-10 years replace all the rubber parts in the brake system, cups, boots, lines and of course flush the brake system. Last done on this truck 2015.


Ok after very carefully doing the FULL brake adjustment procedures tool the truck out for test drive, following observations:


1. Peddle right at the top of the stroke
2. Brakes apply very briskly
3. Did several full hard stops from 30-40 MPH nice and straight with good braking. Could not lock the wheels but, but close. Now stops nicely on 9% down grade, which was one of my prior concerns, it just didn't feel like it wanted to, now it stops nicely.
4. After 6-10 hard stops checked the brake drum temperatures LF 136, RF 122, LR 130, RR 129 Degrees Fahrenheit with IR Gun.


Only time will tell if the Right Rear goes out of adjustment, but I have added witness lines to all of upper adjustment so will be able to tell if its shoe wear or the adjuster moving.


Cheers Phil
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  #5  
Old 18-07-19, 01:06
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The 10 and 2 sound more correct. Both dots facing each other would be maximum retraction of the shoes. The shoes are likely wearing more at the top in that case.



Using the weight is interesting. Never seen that done before.



One more thing to consider is if there is a long lining shoe and a short lining shoe, and that they are in the correct positions according to the manual. That could lead to excessive wear on a shoe if it is in the wrong spot.
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Old 18-07-19, 04:00
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Regarding the "Major" adjusting bolts, the manual says there is a special tool (a long oval-shaped hole in a flat bar) that fits the head of those bolts. It wasn't a military tool, it was a regular truck part, but i have never encountered one for sale. I have just used an adjustable spanner on the flat sides, but I don't think that is the best option.

Do any modern US tool makers like Snap-on, Proto or others make the flat-bar tool or a special shaped ring spanner for these bolts, seeing as it is a regular truck adjustment?
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Old 18-07-19, 05:09
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I have never found a modern version of the tool, but have picked up originals at various military shows as well as various military surplus dealers.
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  #8  
Old 18-07-19, 14:18
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Default Pictures Please

Quote:
Originally Posted by rob love View Post
I have never found a modern version of the tool, but have picked up originals at various military shows as well as various military surplus dealers.
Hi Rob

If you happen to have one could you take a couple of photos of the wrench. Are you speaking of the tool for the actual adjustment end or the locking nut? I used a couple different open end wrenches for the locking nuts.. Have one short 3 inch for the adjustment end. I was hoping there is special shaped one for the locking nuts particularly for the front which are hard to get at because of the drive ball units.

Cheers Phil
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  #9  
Old 18-07-19, 14:49
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The tool is for the adjuster. I have always found an appropriate size offset box wrench works best for the locknuts.
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  #10  
Old 14-08-19, 22:22
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Default Problem tracked down- But whats the solution

Hi All


As you may remember a month ago I posted a question about Major/Minor brake adjustments on the larger CMPs at that time I wrote;


"The last three times I have done this three wheels RF, LF, LR all needed almost any nothing, but the Right Rear both A & B have needed much more. What I also noticed was that they turned much easier than all the others."


Here is the Right Rear B Adjuster as it was after adjustment


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Here is the Right Rear B Adjuster 62 miles later as it is today.


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None of the other A or B adjusters have moved, so I think the problem is clear one adjuster is no longer staying put but is rotating back from the force of the return spring. Obviously this is not a state of affairs that can be left uncorrected.


Cheers Phil



So the question is do what do I do and in what order.
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  #11  
Old 15-08-19, 04:11
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Hi Phil, Can you change out the backing plate?
If not, is the offending adjuster working its way off the (adjuster) bolt.
The bolt is usually staked on the outside of the snail. Try compressing the snail back further onto the bolt, with something like a valve spring compressor. If it moves back, peen the bolt?
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Old 15-08-19, 13:18
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Is it possible that the spring for the offending adjuster has either partially or fully cracked? This would cause loss of tension and also create blunt ends at the crack site instead of the ground flat ends of the spring. Possibly leading both to reduced tension and angled application of pressure. I've only seen one such cracked spring (that I recognized, maybe there were others) and it wasn't very obvious.
Just curious, do you notice any difference in force to rotate the two directions on that spring and compared to the other spring on the same wheel? You might have to take out the brake shoes to get enough rotation to notice and remove the effects of all parts other than the specific spring but you are probably getting close to doing that as you investigate.....
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Old 15-08-19, 15:10
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Could it just be the wind up of the spring caused the adjuster to back off? Solution would be to sparingly put a little oil between the backing plate and spring, and the spring and the adjuster cam.



The original was, as Lynn says, likely peened at the cam. The peen could be ground off (in situ...no need to remove the backing plate), the "snail" removed, and a suitable spring put in place. A cut open socket or piece of tubing could be C clamped into place to hold the cam in place, and a spot of mig weld put on to secure the cam. The heat would have to be kept to a minimum in order to not destroy the tensility of the spring.



The proper way would be t have the backing plate on the bench, and the cam would be put in place with a staking tool. We had a C-clamp for that purpose with the Iltis series of vehicles.
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  #14  
Old 15-08-19, 18:43
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Default Nw parts

If you don't have a different backing plate, grant Hopkins has NOS studs and springs.
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  #15  
Old 15-08-19, 18:52
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Default Tapping in to the collective wisdom

Hi Lynn. Grant, Rob


Thanks for the input, you've added to the list of things I want to check.



1. The idea of the spring having lost tension, fits in with the earlier observation that this adjuster turns easier than the others. Next step will be to put a torque wrench on it and see if it really is turning easier.


2. The thought that the spring itself might be winding up as the adjustment is being made, had not occurred to me.



3. Confirming that the adjustment cam is not loose on the bolt is a big thing to rule out. If it is I can not think of the damage that it could do if it dropped off in side the drum. So I suspect that pulling the drum will be a necessity.


4. A broken or weaken spring from crack, rust, age, is I suspect the most likely cause. But what is the fix? Replace spring, or put a spacer under it to increase tension?


5. Replacing the backing plate is probably the hardest, as I have no spare and a used one is just as likely to have the same problem.


This is one of those brain teasers problems that not only do I want to fix but as important I want to understand the cause. Now that I have seen this happen on one adjuster where marking it has shown that it is actually moving. I will be marking all brake adjusters major and minor on the other trucks. Being able to look at a line on the part and know it changed is really nailed down this brake issue.


I'm looking at doing a couple of hundred mile convoy trip with the club in early September so nailing this down a being sure of the fix is important. Either than or carry a wrench and every time we stop slide under the truck and put the line back horizontal.



Will report back with more details and photos of what I find.


Cheers Phil


PS - While I was typing Harry provided a source for NOS replace part. Thanks Harry will follow up if that is the cause.
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  #16  
Old 15-08-19, 20:29
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Never be afraid of pulling a wheel, or in the case of tracked vehicles, breaking track. In the long run, it's better to be thorough. If the problem is buried in the drum, you are just treading water trying to avoid the drum removal.
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  #17  
Old 15-08-19, 23:41
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Default The next diagnostic step

Hi All


Well after responding this morning, went out to the shop rolled under the truck and reset the adjustment this time using a torque wrench to see how much force was needed to adjust or back off. On this particular adjuster less than 2 ft.lbs. the adjuster on the other side was between 10-15 lbs depending on rotation direction. Something is up.


With that adjuster back at the correct point the brake peddle is right back up at the top of the stroke 1/2-1 inch of travel.


Drove the truck around the loop to the post office and back distance 7 miles pulled back into the shop and the marker line had again moved in the counter clockwise direction a visible amount.


Got my roll around drum puller down from the loft and put the truck up on jack stands. Tomorrow I'll pull the drum. As Rob suggest pulling the drum is the best way to be sure of what your dealing with. That is why I built a unit for pulling the drums on these rigs. That has a bolt plate that matches the studs and a lifting arm that is hydraulic so I can just roll the unit the truck level everything and undo the axle nuts and just roll the drum straight out. No damage to seal and more important do damage to me. Just can not man handle the heavy parts like I did years ago.


Cheers Phil
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  #18  
Old 16-08-19, 00:41
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Default CMP brake adjuster cams

Quote:
Originally Posted by Phil Waterman View Post
Hi Lynn. Grant, Rob

Thanks for the input, you've added to the list of things I want to check.

1. The idea of the spring having lost tension, fits in with the earlier observation that this adjuster turns easier than the others. Next step will be to put a torque wrench on it and see if it really is turning easier.

2. The thought that the spring itself might be winding up as the adjustment is being made, had not occurred to me.

3. Confirming that the adjustment cam is not loose on the bolt is a big thing to rule out. If it is I can not think of the damage that it could do if it dropped off in side the drum. So I suspect that pulling the drum will be a necessity.

4. A broken or weaken spring from crack, rust, age, is I suspect the most likely cause. But what is the fix? Replace spring, or put a spacer under it to increase tension?

5. Replacing the backing plate is probably the hardest, as I have no spare and a used one is just as likely to have the same problem.

Cheers Phil

PS - While I was typing Harry provided a source for NOS replace part. Thanks Harry will follow up if that is the cause.
Hi Phil,

Just looking at a brake adjuster cam that I removed a long time ago from a F15-A rear backing plate. I doubt if the cam is turning on the bolt as the elongated hole on the cam would prevent that.

A broken spring could well be the problem as that is the reason I removed this adjuster cam. The spring in the picture is a new one I had made up. In the end I found two NOS rear backing plates and never proceeded with replacing this cam's spring and another cam than had a broken spring.

If the spring is not broken then the thought occurred to me, what if the cam is resting on the shoe just past the highest point, and the return spring is enough force to rotate the cam back towards the low point on the cam that has a weakened spring?

If the linings have substantial wear it is possible the cam would be close to the top of the cam at the contact point with the shoe.

If you have to remove the cam to replace a spring a method that worked for me was to carefully grind down the side of the flat on the bolt where it is splayed to hold it to the cam. I used a Dremel cut off disk to do it. Was going to then weld the cam back on to the top of the bolt but never had to do it thanks to finding the NOS plates.

Will look forward to hearing the solution to the problem.

Cheers,
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  #19  
Old 16-08-19, 02:15
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Or you could get a bit fancy?:

https://www.ebay.com/itm/39-48-FORD-...sAAOSwKIpWEWN1
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Old 16-08-19, 09:00
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Default S/S brake adjuster cams, studs, and springs

Real purdy!!!

Checking the F15-A parts list, the studs, cams, and springs are not unique to CMP vehicles so these stainless steel ones should fit properly. Parts do not have an asterisk in front of their number so they should be generic to all Fords of that era.

92Y 2038 Stud- adjusting cam
92Y 2041 Cam- shoe adjusting
92Y 2049 Spring- brake adjusting cam

Makes part finding a little easier when the * is not there.

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  #21  
Old 19-08-19, 22:00
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Default What I found

Hi All


Well as I think everybody suspected the problem is in the tension spring on the adjusters. So I will be ordering some replacement springs.
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The rear most or trailing adjuster once the brake shoe was pulled back could be turned by hand with almost no resistance. Once the end was ground off so the adjuster could be remove revealed the spring was broken.
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While the forward or leading adjuster required 25-30 ft.lbs of torque to turn, but on close examination it was discovered was broken into 3 segments.

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Take a look at the brake shoes, these are the original shoes mileage 24844.
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Old 19-08-19, 22:10
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Default What I found part 2

Continued

Here is the trailing shoe
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This is the unit I made up for pulling drum and hub assemblies. Some of you might recognize as the parallel lift platform I use for holding to drill press when drilling frame rails.


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Will report back as I get replacement springs and reassemble.


Cheers Phil
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Old 21-08-19, 21:54
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Default Not the part we need




Hi Tony


Thanks for the lead, but it turns out that these are for the adjusters for the pickup truck and use a 7/16 bolt. I contacted the seller above and he responded very quickly saying they are 7/16 inch.


The search goes on.


Cheers Phil
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Old 21-08-19, 22:59
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Hi Phil, I could supply the bolt and snail, but unfortunately I don't have the spring as nos.
I could strip them from a back plate but they are rusty.
Surely someone closer can help, but if no one steps up, send you address.
Lynn.
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Old 21-08-19, 23:24
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Default May have found the source for the springs

Hi Lynn


Thanks for the offer, but I think I have a sources for a replacement springs that I can cut to length. Comes in 36 inch lengths. Another supplier looks to have ones which will work but has a $40 minimum order.



So I got to do a little more measuring, in particular is the spring force to compress the spring one inch.


Cheers Phil
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Old 21-08-19, 23:58
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I suggest caution cutting a spring for this application from a longer coil as the springs I have seen for the snail adjusters have flat, closed and ground ends. I believe most springs of similar dimensions (free length, wire diameter and number of turns) will behave similarly unless there is a large difference in the material properties. I have found several springs wanted for CMP projects at https://www.centuryspring.com/ You can search their catalog online by inputting whatever information you have about the spring you are trying to match.
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Old 22-08-19, 02:11
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Default Century is one of the sources

Hi Grant



Century is one of the sources I was looking at this afternoon, spring compression strength I will try measure tomorrow.


Cheers Phil
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  #28  
Old 06-09-19, 23:42
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Phil Waterman Phil Waterman is offline
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Default Ok finished replacing the Brake Adjustment Cam Tensioner Springs.

Ok finished replacing the Brake Adjustment Cam Tensioner Springs.

Found two sources of springs that looked like the right size and spring tension, more on that later.

First step was cutting new adjuster bolts with the squared of area for the cam plate to lock into.

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I cut the flats by chucking the bolts up in lath head, and cutting the flats with High Speed Grinder attached to the tool head. This could be done with a flat file and vice. Either way you want to get as tight a fit as possible.
The bolts are Grade 8 1/2 bolts, found that course thread work better than fine thread.

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Once the bolts are notched down the correct length for the spring with a spring washer and cam plate you can check the torque required to turn the bolt head

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Old 06-09-19, 23:46
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Phil Waterman Phil Waterman is offline
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Default Part 2 Replacing the Brake Adjustment Cam Tensioner Springs

One of the things discovered was that only one washer should be used as using more than one spring reduces the torque needed to turn the adjuster.

I tested two different types of spring from two different suppliers and found that they both yielded about the same results with the adjuster bolts when installed and the springs compressed short of being coil bound or totally tight of 10-15 Ft.LBs. of turning torque (initial torque to get the adjuster moving was around 20 Ft.LBs)

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Do not paint or grease the contact sides of the cam plate or backing plate as this greatly reduces the force to turn the adjuster. Which was the problem with the broken springs.

Now how to attach new bolt to cam plate while holding tension on the spring, I when simple put a nut on the bolt thread tighten it down, but with a spacer that would allow me to weld the bolt to the cam plate. Then with Mig welder turned up welded one side of the bolt and then the other.

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Then just cut off the excess to make clearance on the back side of the brake shoe and it is done.

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The adjustments now take a nice steady force to turn so I expect that the backing off of the adjusters will be a thing of the past. Yes, Iím going to give both adjuster a horizontal witness line so that any movement will be easy to spot.

There is only one bad thing about crawling around under the truck and having the wheels off the ground, you spot other things that need attention. See Loose Universal Ends.


Loose Universal Ends
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