Mav’s M1088A1 Conversion

[Mavcaster]

Hmmmm

I know that there is a procedure to delete the front towing air connections. And if down wrong....park brake won't release.

Make me wonder if it's a similar problem.

@Ronmar would know.

And that makes sense since those would be applying air to the truck brakes themselves. Hopefully someone here has deleted the 5th wheel connection before and can point me in the right direction. That's the only brake components I have messed with since they were last working so seems like a smoking gun not sure.

 

[Third From Texas]

And that makes sense since those would be applying air to the truck brakes themselves. Hopefully someone here has deleted the 5th wheel connection before and can point me in the right direction. That's the only brake components I have messed with since they were last working so seems like a smoking gun not sure.

I thought I had saved the front delete instructions, but I can't locate them. Was hoping they might show some insight into your issue.

 

[Ronmar]

Park brake button popping right back out indicates no air is reaching the park control valve. Or the valve itself has an issue.

It requires air to hold the control in the in/on/air applied/park brakes released position. If all the air bleeds away, the control will pop out under spring pressure and return the control knob to the air off/park brake applied position.

 

[Ronmar]

Will have to look into the 5th wheel plumbing as I am not specifically familliar with it. It should be basically paralleled off the normal rear gladhand fittings as it serves the same purpose to feed trailer with red and blue(park/emer and service air) brake air. Maybe you didnt cap something and you are venting away all your park air?

 

[Mavcaster]

Will have to look into the 5th wheel plumbing as I am not specifically familliar with it. It should be basically paralleled off the normal rear gladhand fittings as it serves the same purpose to feed trailer with red and blue(park/emer and service air) brake air. Maybe you didnt cap something and you are venting away all your park air?

That’s what I initially thought and maybe off the mark here but tried holding down the button (not sure that matters at all) but that did not drop air pressure at all.

 

[chucky]

Unless i missed it above doesnt the brake button valves keep popping back out til you have a min of 60 psi in your tanks and wont release the shoes till over 60 psi

 

[Ronmar]

Unless i missed it above doesnt the brake button valves keep popping back out til you have a min of 60 psi in your tanks and wont release the shoes till over 60 psi

Not sure how much prwssure is required to hold in the knob, but basically yes. The park springs need about 60 PSI to fully compress and release the brakes.

 

[Mavcaster]

Valve must not be getting air then or possibly faulty, just seems like a coincidence and if by removing the 5th wheel hookups somehow caused this, how am I not losing air in the tanks?

 

[Ronmar]

Park air comes from a 2way checkvalve between primary and secindary air feeding tge pedal. It is located to the left of thebrake pedal. If the service brakes apply air, then air is reaching the 2way. You can loosen tge middle 2way fitting if air comes out then it ismaking it thru the 2way. Next lift the dash panel and find the other end of the supply airline at tge park valve and loosen it. If you get air then air is reaching tge park valve and it most likley has a problem...

 

[Mavcaster]

Ok I will check that along with some diagrams tonight. I was about to say service brakes are working properly and holding pressure fine.

 

[RRaulston]

Mine did this once... I forgot to close the air tank petcocks.....

 

[Mullaney]

Ok I will check that along with some diagrams tonight. I was about to say service brakes are working properly and holding pressure fine.

.
Making sure that the only valve you are trying to push is the YELLOW one - Right?

 

[Mavcaster]

.
Making sure that the only valve you are trying to push is the YELLOW one - Right?

Oh yeah that’s the one and only.

 

[Mavcaster]

So one other thing I was thinking was back when the truck wasn’t running I had tried charging the tanks through the emergency front gladhand but it didn’t work so I assumed the check valve was bad. Could I have possibly lodged something in there not allowing it to breath like it’s supposed to? Could that possibly cause the parking brake not to release?

 

[Ronmar]

So one other thing I was thinking was back when the truck wasn’t running I had tried charging the tanks through the emergency front gladhand but it didn’t work so I assumed the check valve was bad. Could I have possibly lodged something in there not allowing it to breath like it’s supposed to? Could that possibly cause the parking brake not to release?

Applying air at the front red/emer gladhand should fill the tanks, and it should also release the park brake, just like when you tow the vehicle. It should not effect the park valve operation, if it is getting supply air it should stay in when pushed.

 

[Mavcaster]

RIP oil pump…

 

[serpico760]

.
If it is anything like mine - if you have been getting rain - a drum might be seized to the brake shoes. Seems that several others here have had the same problem. If mine sits around in the rain for more than a week, it requires a "love tap" on the steel part of the brake shoe.

If you have re-plumbed air lines, all bets are off though.

Yeah after just a couple weeks of rain I went to drive mine and it wouldn't move! Went around the truck with a hammer smacking on the brakes giving love taps around the rim of each drum. Got inside and gave it a bit more gas and then a couple popping sounds and then it went. Everything has been fine since then.

 

[RRaulston]

RIP oil pump…

This is interesting. First off, I watched a video of a guy who owns a motor home with a cat engine. 3116 or 3126. He had low oil pressure at 90k miles and put in a new oil pump and bearings. That fixed everything. My truck idles cold at 40 psi. Cruising cold at 60 psi. Warm idle at 17 psi. All within spec. My neighbor has a c7 in his lmtv and has 80 at cold idle and like 60 cruising warm and 40 at warm idle. In other words, more oil pressure than me. So I went to Empire Cat in Tucson to inquire about a new oil pump. She required my engine serial number which I had. If I recall correctly, the original oil pump part has been superseded like 4 times. The latest iteration is a Gerotor type. (is the original not a Gerotor?) She acted like they knew there was premature pump wear and changed the style of pump. I dont know this to be fact, but she was knowledgeable. There are two pumps for a 3116. A new and a reman. Both are like $1800 but the reman returns $1100 with your core making it $700 and change in the end. So, I would be curious to know how difficult changing the pump is and which pump you go with? I may be doing the same someday.... is this the pump you are getting? Thanks, and would love to see more pics!

20R-7247: PUMP GP-GRTR | Cat® Parts Store

 

[GeneralDisorder]

WOOF! The oil pump drive gear teeth! That's not nice of it.

I would be tempted to just run it (the drive gear, not the shattered pump) but it would probably bother me forever and it could happen again and break another pump.

That looks like a sack of buttholes to replace too.

 

[Mavcaster]

WOOF! The oil pump drive gear teeth! That's not nice of it.

I would be tempted to just run it but it would probably bother me forever.

That looks like a sack of buttholes to replace too.

I would have probably run it too if it wasn’t for the crack almost clean across the pump arm.