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1980 300 plus looping on start up


Jpri
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  • 2 weeks later...

Every old Mack that I have operated has done a little bit of this after a cold start.  It's always subtle, but they do it.  ALSO, many seem to do the same when accelerating lightly (apparently this is due to worn governer springs in the American Bosch pumps).  I do have 2 trucks that do this but run 100% otherwise.  I do plan on sending the pumps out at some point to have the governor springs done to see if this corrects the issue.  As time goes on and these trucks get older, it may become a more common problem that needs to get dealt with.  

If I had more time, getting that issue sorted would be much higher on my priority list.

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  • 2 weeks later...

Not sure if they even offer it any longer, but there used to be a patch kit that was a light spring that held the rack against the slack in the pump. I did this on my R-Model years ago and it still runs great. 

 Check with a Mack dealer that knows the older trucks or a reputable pump shop.

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1971 Mack R600 Toterhome "Superdawg"

living the life of leisure pulling

1999 NuWa Snowbird 34+2 SE102 "Dawghouse"

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4 hours ago, mechmagcn said:

Not sure if they even offer it any longer, but there used to be a patch kit that was a light spring that held the rack against the slack in the pump. I did this on my R-Model years ago and it still runs great. 

 Check with a Mack dealer that knows the older trucks or a reputable pump shop.

Oh that's great to know about.   Did you install it with the pump still on the engine?

Im sure MANY a old Mack could use that kit to buy them several more years out of some tires governor spring.   Mine sure could

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1 hour ago, Full Floater said:

Oh that's great to know about.   Did you install it with the pump still on the engine?

Im sure MANY a old Mack could use that kit to buy them several more years out of some tires governor spring.   Mine sure could

Yes, install is done with pump on the engine. Years ago I worked on a lot of older R-Models that were bad about loping, even when going down the road, this would stop most of that.

If I remember correctly the kit consisted of a lightweight spring, a washer and a roll pin. It goes on the rack at the front end of the pump. I seem to remember that you have to drill a hole in the rack for the roll pin.

  • Like 1

1971 Mack R600 Toterhome "Superdawg"

living the life of leisure pulling

1999 NuWa Snowbird 34+2 SE102 "Dawghouse"

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14 hours ago, mechmagcn said:

Yes, install is done with pump on the engine. Years ago I worked on a lot of older R-Models that were bad about loping, even when going down the road, this would stop most of that.

If I remember correctly the kit consisted of a lightweight spring, a washer and a roll pin. It goes on the rack at the front end of the pump. I seem to remember that you have to drill a hole in the rack for the roll pin.

I will soon attempt to contact Mack to see if this kit can still be had, if I find it; I will report back with a part number.

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