Tach part (generator) needed for PD4106

richard5933 · June 30, 2017, 09:20:54 AM

Our coach is just about wrapped up at the shop after the throttle cable repair. Seems the last part that's holding up the works is a failed tachometer generator.

We've got a 1964 PD4106 with a DD 8V71. The tach is driven off the engine through a little cylindrical generator. They were going to go with an aftermarket piece, but apparently there is not enough clearance for the larger diameter of the aftermarket part.

Anyone out there know of a source for one of these or happen to have one laying around unused they wouldn't mind selling?

Thanks!

lostagain · June 30, 2017, 08:06:10 PM

Start by asking Luke at US Coach.

JC

richard5933 · June 30, 2017, 08:10:29 PM

Thanks JC.

Luke was at the top of the list I gave to the tech at Interstate. Didn't seem that he had the necessary part.

TomC · July 01, 2017, 07:32:00 AM

Where specifically on the engine is the tach generator driven off of? Mine is at the end of the blower. Good Luck, TomC

richard5933 · July 01, 2017, 07:58:24 AM

When looking at the engine from the rear of the coach, the tach generator is located roughly at the bottom of the fuel filters. The shaft driving it seems to come from the right side of the blower casing (I think). There is a square-headed drive inside a pipe, and the generator connects to that and matches up with the square drive.

The original was about the size and shape of an old plastic 35mm film case, but a bit longer. There are aftermarket ones available, but the problem is they are all wider. The old one snookered into one of the curves of the flywheel housing neatly. The aftermarket pieces are too wide and won't fit without hitting the flywheel housing. I've seen photos of aftermarket ones in place with an extension to help them clear the flywheel, but I have not seen the extensions available anywhere. Maybe it was shop made?

I'll be talking with the shop again on Wednesday to see what they've been able to figure out. Until then I'll keep searching online. At least it makes me feel like I'm doing something to help.

richard5933 · July 10, 2017, 01:47:58 PM

Latest chapter to the saga of the tachometer...

Tech thinks that they've got the sending unit working properly. When fired up however, it's reading somewhat higher than it should be. Even at that, it's somewhat erratic. Tech now thinks that the tach itself might be bad.

Now the search is on for a replacement tach. Anyone know if replacements are out there anywhere? US Coach was not able to help. I've seen other tachs on a site listed as working on the 8V71, but I don't have confidence that it will be able to read the current generator properly. Seems this one is intended to either pick up an ignition coil on a gas engine OR a connection to the alternator on a diesel. I asked if it would work on the existing sending unit, and the guy said it was adjustable and should work.

Not having any experience, I'm asking for the experts out there to point me in the right direction.

Anyone else have success installing a new tach on a PD 4106?

Geoff · July 10, 2017, 04:25:20 PM

I used an Isspro tachometer that was adjustible.

--Geoff

luvrbus · July 10, 2017, 04:50:46 PM

Most impulse generator driven tachometers require twisted wire from the impulse generator to the head or do weird things

richard5933 · July 10, 2017, 04:59:35 PM

Geoff - Which tach did you get from them? I just looked through their website and there are a lot of options.

3K or 4K?

Are you using the original sending unit (pulse generator) which is shaft driven? If so, which of the options for tach (MPU, etc)?

Any info would be greatly appreciated, as I'm in over my head trying to understand all this.

Richard

richard5933 · July 10, 2017, 05:01:44 PM

Also - what is the pulse rate of the shaft driven pulse generator? Looks like I'll need to know that before selecting a tach.

chessie4905 · July 10, 2017, 05:05:25 PM

You can check these out at Summit performance. Of course, you'll have to purchase the appropriate head. 0-3500 or less. You could remove tach from dash and wire it up by engine in case of wiring issues.

https://m.summitracing.com/search?keyword=Tachometer%20sending%20unit&ibanner=MobileSwitchYes

richard5933 · July 10, 2017, 06:51:42 PM

Thanks for the Summit suggestions.

I'm trying to keep the existing sending unit, since it appears to function. Since it uses the large square drive shaft I don't think that these others would fit anyhow. I'll get a few photos of the existing generator to post, and hopefully someone will have information regarding the pulse rate, etc. so I can match it to a new tach. I've checked the tachs at ISSpro and Speedhut. They both have units that would appear to work. The Speedhut tach is much easier to adjust, but the smaller range they carry is 0-4k rpm. The ISSpro tach is easier to read being only 0-3k, but the adjustments seem a bit more manual.

Geoff · July 11, 2017, 01:59:48 PM

Quote from: richard5933 on July 10, 2017, 04:59:35 PM
Geoff - Which tach did you get from them? I just looked through their website and there are a lot of options.

3K or 4K?

Are you using the original sending unit (pulse generator) which is shaft driven? If so, which of the options for tach (MPU, etc)?

Any info would be greatly appreciated, as I'm in over my head trying to understand all this.

Richard

The people who can help you are instrument Sales and Service in Portland,OR
The know their stuff and can get you a tachometer. 503-239-0754

--Geoff

richard5933 · July 11, 2017, 02:16:46 PM

Thanks! Called and have the part number I need.