Mechanical Booster Pump "making oil"

After going through all of the possible areas on my multifuel M35A2 trying to figure out where the truck was leaking fuel into the crankcase, I finally figured it out. I had done the FDC bypass, replaced the 3 seals in the hydraulic head and shut down lever, didn't have the flame heater on the intake side and the truck ran too perfect to have any issues with holes in the pistons or injectors that weren't working. Since the issue had to be with the booster pump, I decided to rig up a simple bench check to determine that this was in fact the culprit.
By removing the 2 front motor mounts and the rear drivers side mount, I was able to jack the motor up and to the passengers side enough to clear the steering box to free the pump. I then picked up the two fittings at the hardware store to enable me to plug the output hole and pressurize the inlet hole on the pump. I then filled the pump up with mineral spirits, attached my new fittings accordingly and used my old bicycle pump to apply pressure. As you can see in the video, the seal on the drive shaft leaked immediately with next to no pressure on it. I did switch out the fittings to see if there was any difference in the amount of leakage and they both were the same under the same amount of pressure. Sorry about the video being sub Steven Spielberg quality, but it gets the point across I hope.



Bench check of M35A2 Mechanical Booster fuel pump - YouTube


Also, if anyone knows exactly where to get the correct seal and you know for a fact that it's the correct seal because it was tested and known to work...please post up your info. I've cross referenced the TM some, but I'm not finding an EXACT match still readily available??

Dylan

fordgasmz said:

.................................... I've cross referenced the TM some, but I'm not finding an EXACT match still readily available??
.........

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Glad you found the cause, at least!

As I had posted here, bore diameter is an odd one (21.3mm); besides that the OEM seal prob. was designed on a Friday, last minute... (IMHO)

So you will not find any std. oil seal to fit in there and either need to get the original AMBAC part, or...
follow my suggestion, ordering a seal# 472810 (Timken or any equivalent), then take pump and seal to a machine shop and let them do what the drawing shows...


G.

Well...after some searching, I now have a new seal assembly in the mail. We'll see how well my pump does with some new seals...hopefully this fixes the leak!!

Did you get the #472810 or a different one?

I actually picked up some oem nsn seals. The rotating gear wasn't scored so a pliable new seal should work great. I'll update when I get it and I can do a new bench check!

And the new O-ring kit has arrived for the mechanical booster pump...bench checked good following the same procedures as above and tomorrow it will be installed! I do have a video of the "good" bench check, but of course no leaking fluid is the bottom line right?! My source for the seal kit was Southeastern Equipment Company out of Ga. It is the same kit that the TM references NSN 2910-00-489-5994 The kit was around $22 shipped for all three seals inside the pump and the lockring for the gear. I'll post up the video tomorrow, but for those of you that have been trying to figure out where that final leak could be coming from ....I hope this helps!!

Good to know that there is a source for good OEM shaft seals!
Thanks for posting!

G.

fordgasmz said:

I had done the FDC bypass, replaced the 3 seals in the hydraulic head and shut down lever, didn't have the flame heater on the intake side and the truck ran too perfect to have any issues with holes in the pistons or injectors that weren't working.

Click to expand...

What is the FDC stand for? Thanks. Great post by the way.

fuel density compensator

Fordgasmz,
Do you have a phone number or website for Southeastern Equipment Company where you ordered the seal kit? Thank you!

A quick Google search... SECO Reconditioned Army Military Trucks 2 1/2 Ton 5 Ton M35 M54 Cargo Fuel Water Dump Wrecker M123A1

doghead said:

A quick Google search... SECO Reconditioned Army Military Trucks 2 1/2 Ton 5 Ton M35 M54 Cargo Fuel Water Dump Wrecker M123A1

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Yip, this is the place...don't use their search feature because it's not up to date. I called them and they were extremely helpful. They did say that they MIGHT even be able to just sell the double lip oil seal, but most likely you're going to need the lock ring that comes in the kit as mine was bent up pretty bad by the time I got it off. Also my internal seal that goes on the regulator was pretty dry and distorted as well...so all in all...just get the kit unless you already have everything else just sitting around.

fordgasmz said:

Yip, this is the place...don't use their search feature because it's not up to date.......

Click to expand...

Don't know, works for me.... put the NSN 2910-00-489-5994 in there and it pops right up. And it says they have 1754 of these kits in stock...!!

G.

is the booster pump hard to change in the truck ?
is there any difference from IP on a turbo and a IP from a non turbo ?

Thanks for the lead on the parts. I just ordered a kit from them, $19 + the ride = cheap peace of mind!

great info for the diesel fuel in oil problem.

thank you

fordgasmz said:

I decided to rig up a simple bench check to determine that this was in fact the culprit.

By removing the 2 front motor mounts and the rear drivers side mount, I was able to jack the motor up and to the passengers side enough to clear the steering box to free the pump.

Click to expand...

I want to thank Dylan for taking the time to post up this most excellent thread. It was an immense help to me and I appreciate it.

THIS is exactly what this site is for: To assist in ways the TM doesn't. The TM doesn't show any "tricks" to moving the engine over to access the booster pump. I looked in the IP TM and didn't see a bench test method either, but since I'd already found this thread, I admit to only glossing over the TM.

My truck started making oil recently (not exactly sure how recently, I have not checked the oil in about a month-I totally admit to slacking on pre-flight procedures. That's on me) and by doing a quick search, I found this and several other threads that covered the topic pretty exhaustively.

Drained the oil and had had about 7.5-8 gallons. Knew it couldn't be the FDC since it was bypassed and people say it's either the hydraulic head shaft or flame heater. Checked the flame heater that wasn't it, ran good so I thought it had to be the booster pump. Pulled it off and bench tested it and it leaked at about 30 psi. Not as bad as Dylan's but plenty.

digitaldust said:

is the booster pump hard to change in the truck ?
is there any difference from IP on a turbo and a IP from a non turbo ?

Click to expand...

With Dylan's advice, I was able to get the engine moved far enough away from the steering box that I was able to remove the booster pump. Remove your heater box (if equipped), unhook fuel lines on booster pump, then unhook the front mounts and drivers rear mount. I lift the front of the engine, then pulled it towards the passenger side and that was enough to get the booster pump out. You may have to rotate the pump as it comes out to clear the box.

I think the IP's are the same turbo and non turbo. I've only had one non-turbo truck and I didn't have to do any IP work.

Enjoy the pics!

This photo editor hates me.

The other 3.

Good job of documenting these issues and fixes guys. Just might come in handy one day! Thanks!

Looks like I may be doing this to my truck very soon. Its almost tempting to just stick a whole new IP on and call it a day.