1979 Dump Truck Clutch Parts

[Gunny65]

I have a 1979 DM685sx T/A Dump Truck.  The clutch is worn to the point it can no longer be adjusted and it is slipping. I believe I have the MaxiTorque Transmission (TRL107) with MACK clutch. The ID plate says: (REGU.S. MACK Maxitorque Transmission PAT.OFF) There are no other numbers or markings on the plate (top left side rear of trans housing).

Where should I go to buy clutch parts for this year and model?  

I found a service manual that will help me remove and install the clutch. Any pointers would help as well.

Thanks!

[Joey Mack]

I believe you have a 14'' dog dish clutch..  I have replaced that setup with a 15 1/2'' clutch on an E-7 flywheel...  I wish I knew the part number for the flywheel..  I have seen posts that say you can still get the clutch and flywheel that you have. 

I lean towards the larger one because it is readily available and you can get a 9 spring HD clutch whether you need it or not and you can get an Eaton ''Easy pedal''  clutch that is.... easy on your left leg..  take a minute to search out these posts here...  Jojo

[JoeH]

https://maps.app.goo.gl/ea5bGe6WJHoKPRKL6

A&R industrial is near you, no idea what their reputation is.

If you're confident you can do the repair yourself then get it apart, take your old clutch to them and they can order you a new one based on the parts you show them. Assuming they're the friendly and knowledgeable type.

If you aren't confident then you could just have them do the repair.

[Gunny65]

Joey, I like the idea of changing to more readily available parts that fit. I need to take it apart anyway so why not?  I will look around the posts here and see if I can find more info on what you are describing. Thanks.

JoeH, I am pretty sure I can do the repairs. I did rebuild a 700R4 once. The weight of this trans is the biggest issue.  I can do the work, it is the crashing down weight thing that worries me. LOL. I will need to invest in some tools specific to this operation though.  I have no clutch tools at all. I have Lots of tools, just never worked on clutches before. It has always been: how much does the repair cost, can I buy the tools needed and so it myself cheaper than it would cost to pay someone?  Then I do it myself and end up with more tools. Win, win for me.

[Joey Mack]

assuming you have a Mack transmission,  it is very heavy,  I think around 700 pounds..  I have a transmission jack from harbor frieght that is decent and strong enough.  it is the biggest one they offer in the store, around $300.00  (4 years ago), dont know the prices in your area..  

I have a few suggestions...   when i do a clutch in a DM, i remove the right side door..  it may take a half hour or so but you will gain a ton of room to get it there and pull the seat and floor pan..,  also, when you have the floor out, this is the time to decide whether you want to replace the treadle valve and brake pedal base.  next, there are no rear engine mounts, so the engine will need to be supported before pulling the transmission back. now on the plus side, you can pull the doghouse and get even more room.   next,,,  if you have to do any work on or under the rear valve cover this is a great time to do that as well, because you will have room and you can lower the engine after the transmission is out, and easily remove the valve cover..  

I am adding work to this job, but trust me, if you do it during the clutch job, you will thank me later.. Just imagine having to do those other repairs individually, and the work to get in there to fix it. You may want to inspect the throttle pedal base too.  they corrode the heel plate and nutserts (for the brake pedal) are still available.  

 the rest is just 'good ole' hard work..  Jojo

[Joey Mack]

If you have to replace the rear main seal, I have a tool that is still available and it works great. I can post pictures and part numbers for the tool..  Jojo

[mechohaulic]

never gave thought to door removal , guess when your younger the body has more flex to it . that's where the phrase "do now pay later "comes in .  I made up a cradle bracket to mount  on the transmission jack . made life safer when removing the top heavy tri shaft  units.  1 1/2 channel iron welded together went 1/2 way up sides . sure hope first time ever the jobs NOT being done alone; there is a helper. that's a lot of very heavy parts  to man handle. like a brake job when younger ++ "heck I can lift those drums " ! that flywheel isn't "heavy" when it's the first one . 50 yrs  and many flywheels later. ????  unless the plan is to do many clutches ; I would attempt to borrow/ rent needed tools . rear seal installer can't be cheap nor a GOOD jack. doing a Mack first is also a challenge ; unlike "other brands" having rear mounts on the bell housing  making life easier .

[mechohaulic]

"79 DM with Mack clutch : brain cells trying to focus = that would be a push clutch ; not pull (Spicer/Eaton) ??  cable linkage replaced mechanical rod linkage by '79 ?? clutch brake ? lower counter shaft not on pilot shaft . ??

[Joey Mack]

https://www.freedomracing.com/am-j-37716-b-mack-rear-crankshaft-seal-wear-sleeve-installer.html?___store=default&msclkid=de7f924d905d15df57b8f726bde0e1c4&utm_source=bing&utm_medium=cpc&utm_campaign=**LP - Shop - Specialty Tools > Big Truck Tools %26 Parts&utm_term=4578710021033717&utm_content=AM-J-37716-B | AM-J-37716-B Mack Rear Crankshaft Seal%2FWear Sleeve Installer | 27 | %24534.55#:~:text=Call Us 641,%2441.00

[JoeH]

The Mack triple shaft transmissions sit like a V , it will want to fall over on a trans jack, so a cradle is a must have! 

Do yourself a favor and replace the rear cab mount bushings, we just did on our '79 R model and gained more than an inch of height back. Makes a lot of difference when you're working in tight spaces.

Access to a helper is strongly recommended, there's a number of things that really need 2 people.

[JoeH]

We usually take a fuel tank off the truck so we can get the transmission out from underneath, but if all you're doing is a clutch then you may not need to.

[Joey Mack]

I know one thing....  if this is his first big truck clutch job,,,   He picked a 'Doozy'    

[JoeH]

Usually takes us a day or two to get it out, and another 3 days of rocking the transmission back and forth and up and down to finally get the input shaft into the pilot bearing. 😱

When we pulled the allison transmission out of our MR688 2 years ago we had the whole thing out and back in in one day! That MR is the easiest thing to work on. Our 1980 DM is about the hardest thing to work on. Don't recall how hard the clutch was on our DM, but it might not be too bad.

Our R models we usually stick a heavy wall pipe through the windows and hang the pipe from the roof with a rope going back and forth a bunch of times.  Gives us a beam crane for our chain hoist inside the cab to hang the transmission from.

[mechohaulic]

topic heading calls it a T/A dump. another one where pictures help make accurate assessment. could be short wheel base tractor converted to dump having a T/A shoved under it , or number of other configurations. unless it's a fairly long unit , might not have room to move transmission out of the way. hey day way back when tag axles were installed on ten-wheeler for new weight laws. did a clutch job on a converted ten to tri ;took 8 hrs to completely remove tag axle for transmission access and removal. 

[JoeH]

He's working on this dog.

Its a short wheelbase, the driveshaft will definitely need to be out of the way.

 

[mechohaulic]

On 12/2/2023 at 8:27 AM, Joey Mack said:

I know one thing....  if this is his first big truck clutch job,,,   He picked a 'Doozy'    

for safety sake ; first one ==I would find a mechanic knowing the job put up some $$$; then pay very close attention to how it's done while being an assistant. too many things can go wrong by your self doing first time project. It was  middle of night doing clutch on R with twelve speed ; start to rock and sway transmission to install= transmission slipped off jack ( a real truck jack ) and pinned me between air tanks and transmission. no one else there and NOT my first clutch job. the 12 is very heavy when trying to lift/ move it. 

[mechohaulic]

2 minutes ago, JoeH said:

He's working on this dog.

Its a short wheelbase, the driveshaft will definitely need to be out of the way.

 

thanks, I remember seeing that unit  earlier post. that's the R/R truck used on tracks or something. swivel dump.

[Gunny65]

Yep, it is the swivle, Ex-railroad dump truck.  I thought T/A meant Tandem Axel?  Is that correct? At one time I was thinking triple axle but later reading led me to believe it is tandem. Correct me if I am wrong.  Thanks.

The transmission is connected via linkage rather than cables. External linkage anyway.  Not sure inside but it looks like the triple shaft "V" shape that JoeH described.

I did have a helper but he had to move for job purposes.  Now I do things alone but with a lot of safety/self-preservation planning. I will buy a trans jack and modify as noted above. Make a cradle on the jack so to speak. I MAY have a diesel engine mechanic that could help but he is pretty busy. We will see. I didn't see to much oil leakage around the rear main but thanks for the heads up.  Good ideas on what to accomplish while I have the engine more accessible.

The good thing is this truck model does not have a passenger seat so I don't need to remove that.  I need to clean the cab out any way to access the panel you are referring to. That would not have crossed my mind, I doubt. Thanks.

I planned on removing the prop shaft, lowering the trans, securing it, and then doing the clutch work in between the open space if possible.  I think it is possible based on looks under the truck.

I believe I found the proper E7 flywheel.  Not as expensive as I had expected. That was nice. Still have not found a clutch plate, springs, etc. I need to do more reading.

Thanks everyone for the input/help. All of it helps.

BTW, this operation isn't going to happen till spring but I need to research and buy in preparation for the job.

Edited December 4, 2023 by Gunny65

[Joey Mack]

Look at Eaton 9 spring ''Easy Pedal''  clutch for Mack E-7...  Problem solved,, the whole clutch kit is in one box. just have to buy a pilot bearing and a clutch brake..  if you have to replace the cross shaft bushings and shaft and fork, they are available, and keep up with us and we will guide you along. 

[terry]

Don’t know what kind of clearance you have there, but sometimes you can just slide trans. Back and do your clutch work.   Terry

[JoeH]

Personally I would just get the right clutch for your existing truck.  Chances are that'll be the last clutch that truck ever needs, unless you're going to be putting 1,000 hours or more on it per year.

[JoeH]

Remembered I have a 237hp motor from a 1976 U685T sitting here with the transmission off. Has a Dana Spicer clutch on the flywheel. Here you go:

[JoeH]

Looks to me like 4034836, but idk. Probably a 30 or more year old clutch, don't think my dad ever put a clutch in it, and we've had the truck since I was a boy 25+ years ago.

[JoeH]

IIRC on this style clutch you take out the lock tab, push the clutch pedal in, then spin the flywheel to thread the clutch tighter? Then reinstall the lock tab and you're good to go...

I may be a weee bit off though...

Edited December 6, 2023 by JoeH

[Joey Mack]

no sh!t...  thats a new one for me..  I never tried that..  I have a crank handle that bolts in where the locking tab bolt goes..  I have even used a large screwdriver and pointy bar to make adjustments..  

so do you turn the flywheel 360, then check free play? and keep doing it till its set?  

[terry]

31 minutes ago, JoeH said:

IIRC on this style clutch you take out the lock tab, push the clutch pedal in, then spin the flywheel to thread the clutch tighter? Then reinstall the lock tab and you're good to go...

I may be a weee bit off though...

This is a new one on me to adjust.    terry