Cummins PT pump tach drive question

[F18hornetM]

Good morning everyone.
I'm working on a 1979 M813 with a 250 Cummins. I had the PT pump rebuilt due to fuel contamination that made a mess of it. I got the rebuilt pump back from the injection shop, re-installed the pump and the truck runs great. However,The tach does not work. I found the tach drive they installed in the pump is larger "inside diameter" than the tach cable end. I called the pump shop and they claim they only know of one standard tach drive. Obviously this cant be right because the one I sent them fit my tach cable and the one they installed is larger.
I checked the tach drive on another 250 cummins I have and it measures roughly .166" ID, where as the one they installed measures roughly .191" ID.
Was wondering if anyone else has ran into this or had any experience with different tach drives in the PT pumps.
Thanks for any thoughts

 

[162tcat]

Did you send yours in to rebuild or did they send you a rebuilt one and you sent yours as a core?

If you sent yours in for rebuild, they need to make this right on their dime. If yours was sent back as a core, that could be a gray area but any good shop should make it right for you.

I'm sure over the years there have been many different tach drives used for different applications so that part is not surprising. The one they put in is probably the most common.

Sent from my LG-M210 using Tapatalk

 

[lindsey97]

There may be a thin brass adapter/bushing to make different sizes/style of cable compatible. did it fall out, get left out at pump shop, or is it stuck on the end of your cable?

 

[WillWagner]

No, IIRC there are two different sizes. Make them install your old one.

 

[F18hornetM]

They rebuilt mine. That was the first thing I asked as I've had that before with other stuff [alt, starters etc]. They couldn't find any other tach drive for it except the standard one. So, I dug some and found in the TM section here someone posted a NHC 250 cummins parts manual. [The one with the fuel system]. I found the Cummins part number there and called them. Part # 216908 Shaft, tachometer drive. They found it in Cummins obsolete parts warehouse for $70. The Tech I talked to said he had never used another tach drive other than the one that came in the over haul kit. I asked why didnt they use the old one over. He told me because the kit they use comes with a new one and usually the shaft has been grooved some by the seal. So, I get that. They will change out for free, but of course I still have to remove and re-install the pump again and pay for the new shaft. Total cost for rebuilding pump was $616 + $70 for new tach drive. $686. Just to give everyone an idea of rebuilding them cost.
Will, They did look for the old one but had been thrown out already.
I'll let you know how this works out.

 

[F18hornetM]

Update:Finally got around to taking pump back off truck and took to pump shop. They installed the correct tach drive and all is good. In case any one runs into this kinda thing the correct Cummins part number for the M813 PT pump is 3004979. Was $70 for the drive. They didn't charge to replace it. As they shouldn't have.
Of course this will probably never happen again to anyone. I only contract out mechanical work if I have to , like this pump and every time i have to, it seems it never goes easy.

 

[WillWagner]

There is actually a tool to remove the tach drive assy without removing the pump.

 

[dmetalmiki]

That is an interesting fact, Thank you for posting the detail. Glad you have it sorted out and things are now working 'as they should'.

 

[F18hornetM]

There is actually a tool to remove the tach drive assy without removing the pump.

Yes there is, but since they rebuilt the pump and installed the wrong shaft I wanted them to correct it. I could have drove the truck to the dealer but didn't want to leave it. All done now and runs great.

 

[JasonS]

There is actually a tool to remove the tach drive assy without removing the pump.

I am in the same situation and bought the tool to remove the tach drive assembly. Once it is out, do I simply press the old shaft out of the gear and press the new shaft into the gear?

 

[WillWagner]

I am in the same situation and bought the tool to remove the tach drive assembly. Once it is out, do I simply press the old shaft out of the gear and press the new shaft into the gear?

Pretty much. It can be dine in the jaws of a vice. There are some other pieces inside the cartridge, a wavy spacer and seal. Drop the shaft/gear in the hole, turn it slightly while tap tapping on the shaft, install the other components in the order removed then put the threaded connector on.

 

[JasonS]

The proper tach drive was not available. I cut and slit a thin wall brass tube from a hobby shop and inserted this into the original tach drive. Works perfectly.

 

[LCA078]

The proper tach drive was not available. I cut and slit a thin wall brass tube from a hobby shop and inserted this into the original tach drive. Works perfectly.

That's a nice fix- thanks for sharing.

 

[msgjd]

had a similar problem in the late-70s .. So I built up the drive cable end with (tin) solder then shaped it down to size, and greased the heck out of it .. It has lasted but it has not been run much all these years either

 

[WillWagner]

There are two different ones, one is small and the other larger diameter. The military one I think was the large one. What you did will work, until the brass wears out, You most likely aren't driving it 8-10 hrs a day, 6 days a week, so it will last a bit. Keep grease in it, it will last longer.