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Reversing relay info for Jojo


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In a thread a while back you asked about the reversing relay in a superliner you were working on. Rather than sidetrack that thread I wanted to try to help. You may have already sorted what you need . If you did, no problem , this may help others . 

I want to start by saying I'm no expert and most on here know way more than I will ever know. Any info I know came from BMT. It's great. 

I have found through trial and error that the relay valve changes the trucks performance a lot . 

There has been a lot of threads about them in the past . This one is useful , https://www.bigmacktrucks.com/topic/47110-puff-limiter/#comment-347471

Theres different relays for different motors .  They all have a part # that ends with a number followed by an "X"   like "5X" . That number is stamped on the end of the relay valve. The smaller the number the higher the rpm before it fuels . That's to keep the smoke to a minimum . A 5x or 6x will fuel at a lower rpm similar to a good ole 237. I think 237 came with a 5x from factory , but not 100% sure.They go as high as "10x" I think? The 350 your working on would have a 3x I think ? There is a "CX" too. I have tried it on every truck  and decided the best spot for it is on the shelf. Truck has to be at 1700 or so before it kicks in.

I put a 6 x on my 350 4V . It worked really good but smoked more than I liked. I didn't want any trouble from the smoke police, lol .

So my solution was an electric solenoid in the supply line to the relay. I run a 3x. My truck works great and I'm not afraid of a cop behind me, and when I want to have fun or some bottom end power, I flick a switch on the dash. I love it. A lot of the guys used air valves to do the same thing. 

Remember that the relay is only half of it. The number of shims in the rack limiting cylinder on the pump is very important to. Theres info on that in the link provided. 

 

Heres a pic . You can see the new blue line to the relay. It should really be black so it doesn't stand out but that's all I had the day I did it , lol . 

 

IMG_3432.thumb.jpeg.987e60d69d28207ef0016ebad51059b2.jpeg

Hope it helps a little . 

 

Edited by 85snowdog
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Keith 

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Keith, many thanks for detailed and systemized description of that reversing valve operation. I remember many talks on here concerning troubleshooting in the rack limiting setup.

My running R has the system unhoocked and there's black smoke if you try accelerating a bit earlier on revs than you should. I could collect a few relay valves from different engine leftovers to play with but haven't started yet. One thing I did was opening one valve (by grinding off its body) in attempt to fabricate a new housing made of cooper or SS to look bright. But all I got to was a broken rubber diapragm found in the valve. So the quest is to be continued and the info above is going to be of much help.

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Никогда не бывает слишком много грузовиков! leversole 11.2012

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Thank you very much Snowdog...  Excelent info..  The E-6 that I am freshening is still in progress.  it's is part of a complete truck conversion..  The owner calls me in to do Engine, tranny, rear ends, suspension, and some wiring... last week I removed the injection pump and sent it off to be rebuilt.  I will make note of what you posted, and see what the truck does when its running.  Thanks again, Jojo

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On 2/5/2022 at 4:06 PM, Joey Mack said:

Thank you very much Snowdog...  Excelent info..  The E-6 that I am freshening is still in progress.  it's is part of a complete truck conversion..  The owner calls me in to do Engine, tranny, rear ends, suspension, and some wiring... last week I removed the injection pump and sent it off to be rebuilt.  I will make note of what you posted, and see what the truck does when its running.  Thanks again, Jojo

Sounds like a cool project. If the owner is ok with it ? maybe you could share some of the progress. 

Keith 

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Of course after I did all this..... the owner says... pull the injection pump and nozzles and get them rebuilt...  🤣😂🤑

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That looks amazing ! 

I like the colours of the superliner. 

I wish you lived closer,  I have an E6 that could use your professional  :mack1: touch. 

Thanks very much for the pics !!

 

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Keith 

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Im waiting for him to tell me to rebuild it....  It runs great, I supported re-sealing every thing,  the color will be red and black when its done.. He has a crew of talented guys that do these resto's for him. I'm proud to be part of it. I dont know how to paint, and my fab skills are ok, but the guy in the picture is one hell of a welder and fab guy.  jojo

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9 hours ago, 85snowdog said:

I'm sure you know this already Vlad, but if your experimenting with older relay valves. They are designed to leak a small amount of air, out a weep hole on the bottom side of it. I found this out the hard way. Buying a new one to leak the same as the old one did. lol 

The pic below is out of an R model owners manual. 

 

 

IMG_7475.jpeg.861517ce7af555cc7edb56084c1cc3d8.jpeg

 

 

Funny. As the first thought it seems like the bleed from the relay was made to indicate the parking brakes were not applied:)

But actually an interesting point to not worry about the relay's operation.

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Никогда не бывает слишком много грузовиков! leversole 11.2012

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Ok, guys... Forgive me, I understand that a small air leak at the reversing relay is normal, but I'm not clear about when it gets it's pressure. I believe it gets air when the brakes are released... (Yellow Button in)?  jojo

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3 hours ago, Joey Mack said:

Ok, guys... Forgive me, I understand that a small air leak at the reversing relay is normal, but I'm not clear about when it gets it's pressure. I believe it gets air when the brakes are released... (Yellow Button in)?  jojo

Your right Jojo, the relay has no air to it when the parking brakes are applied. When the brakes are released (yellow button in ) it sends air to the relay valve.

Thats why its important to chalk the tires and release the brakes  when you get a smoke test done . I'm sure you know this , but could be very handy info for someone that's new to older Macks. 

 

I love the Superliner dump you posted. Looks too good to use .  

Thanks again for the pics 

 

 

Pic of the small hole that's on the bottom of the reversing relay 

 

IMG_7478.jpeg.55049f223d7816fda600f50ca1d0900d.jpeg

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Keith 

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Thanks Bud... I forget things that I havent dealt with in years, and as far as the air leakoff.. I just learned it, and I will be checking for it when the truck is running..  Jojo

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Single drive with a lift axle saves tire wear.  Setup is just fine for highway/parking lot work where a truck doesn't have to go mudding.  Pulling the tag axle up saves a lot of twisting on the tires, tandem, etc. If I had a truck like that it wouldn't be leaving the blacktop.

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Well its going to go to work when its done.. It will be painted the same way and built the same way as the tri-axle Superliner I posted..  This little truck wil have a Mack 12 speed.. it's been rebuilt and I'm putting it in on Wednesday..  It will be a hell of a truck... jojo

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It's a private shop.. owed by a successful paving company in my area..  heading there tomorrow to stab a 12 speed into a Superliner... oh hell..  My back will be F'd up when i'm done...  :) jojo

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On 2/7/2022 at 6:11 AM, 85snowdog said:

I'm sure you know this already Vlad, but if your experimenting with older relay valves. They are designed to leak a small amount of air, out a weep hole on the bottom side of it. I found this out the hard way. Buying a new one to leak the same as the old one did. lol 

The pic below is out of an R model owners manual. 

 

 

IMG_7475.jpeg.861517ce7af555cc7edb56084c1cc3d8.jpeg

 

 

"but nobody told me " that note was in their operators manual! LOL a number of new trucks came in with complaint of air leak, bring it in SET THE BRAKE : can't find any leak. some of the new save the world  technology was a challenge .old timers didn't know or care about the new stuff, let the new kid figure it out. i was fortunate to have learned from the best mechanics of the older iron. 

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15 minutes ago, Joey Mack said:

It's a private shop.. owed by a successful paving company in my area..  heading there tomorrow to stab a 12 speed into a Superliner... oh hell..  My back will be F'd up when i'm done...  :) jojo

i thought it was your shop. working alone late at night to have clutch job done for am,i had a 12 speed roll off the jack and pin me against side. they are one heavy item trying to move when laying on your side. i have rubber gloves and back brace now just 40 yrs too late

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