[GMCnet] A Modification not recommend for GMC Motorhomes

[Matt Colie]

A Modification not recommend for GMC Motorhomes

Like many others, I have had trouble with fuel sending units. As I don’t have holes in the floor, this requires defueling and dropping the fuel tanks to attempt any service at all. I have been around this course three times and was not looking forward to a fourth.

An attempt to replace the sending units on the fuel pickup with an after market part by Equus though outwardly successful was time consuming, problematic and required efforts beyond the reasonable for a parts change. Though my tank level gages now do respond to the fuel level. There are inconsistencies and calibration issues that make this only qualify as a “Better Than Nothing” repair.

The failures of the existing senders were all instigated by connection failures in the actual sending unit inside of the fuel tank. These failures were most likely the result of corrosion allowed by alcohol now in motorfuel. Please note that the inside of my fuel tanks are very clean, and there was no visible corrosion. But, electrical connections that looked as if they should have been good often tested bad in an actual test that required them to pass current. GM sending units are a nominal 0 (empty) to 90 (full) ohms. This means that any error of increased resistance makes the gage report more fuel than is present. (Personally, I think this it really stupid on GM’s part, but it is far from the stupidest they have been.)

The Equus sending unit though it says it is good for tanks from 5 to 30 inches deep in actual fact cannot report effectively on very shallow tanks because the included float it too large and much of the travel will be lost. I had to salvage and reuse the OE float to get near the resolution needed for a vehicle gage to make sense. (If the top and bottom 1/4 are not included in the gage travel??)

It has also been noticed that the wipers have very high drag and frequently I have noticed the indicator reporting low when I restart after fueling. But, as soon as we get on the road they come along. This would concern me greatly if I was counting on them to report how much fuel I had available for the APU.....

Also, to get the float away from the pickup, the direction of the sending unit had to be reversed. This meant it couldn’t mount where the original was in the same direction, but had to be in the same place, but backwards. I hope to put pictures up in the next day or so. That may allow any people that are interested to make some sense of this whole circus.

So, if you have been considering this as opposed to buying replacement senders, think long and hard about your own time and effort.

Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumière (say show-me-air)
Now with 4 working Rear Brakes
SE Michigan - Twixt A2 and Detroit
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[Emery Stora]

Another good reason to buy from our known GMC vendors. Jim Kanamoto at Applied GMC has exact replacement sending units.

Emery Stora
77 Kingsley
Frederick, CO

[Johnny Bridges]

I've not done GMC motorhome pickups, but from many pickup repairs on old cars I find, as long as the winding is solid, usually replacing the fasteners (normally rivets) with screws and star locks   On my last F150, I soldered the wiper back together using a bit of relay leaf to bridge the broken part.  The PIA is getting the thing out and then back, so considerable testing for proper operation, no biinding or dead spots, etc. is in order.
 
--johnny
'76 q23' transmode norris
'76 palm beach

From: Matt Colie <matt7...@gmail.com>
To: gmc...@temp.gmcnet.org
Sent: Wednesday, May 29, 2013 5:19 PM
Subject: [GMCnet] A Modification not recommend for GMC Motorhomes

A Modification not recommend for GMC Motorhomes

Like many others, I have had trouble with fuel sending units.  As I don’t have holes in the floor, this requires defueling and dropping the fuel tanks to attempt any service at all.  I have been around this course three times and was not looking forward to a fourth. 

An attempt to replace the sending units on the fuel pickup with an after market part by Equus though outwardly successful was time consuming, problematic and required efforts beyond the reasonable for a parts change.  Though my tank level gages now do respond to the fuel level. There are inconsistencies and calibration issues that make this only qualify as a “Better Than Nothing” repair.

The failures of the existing senders were all instigated by connection failures in the actual sending unit inside of the fuel tank.  These failures were most likely the result of corrosion allowed by alcohol now in motorfuel.  Please note that the inside of my fuel tanks are very clean, and there was no visible corrosion. But, electrical connections that looked as if they should have been good often tested bad in an actual test that required them to pass current.  GM sending units are a nominal 0 (empty) to 90 (full) ohms.  This means that any error of increased resistance makes the gage report more fuel than is present.  (Personally, I think this it really stupid on GM’s part, but it is far from the stupidest they have been.)

The Equus sending unit though it says it is good for tanks from 5 to 30 inches deep in actual fact cannot report effectively on very shallow tanks because the included float it too large and much of the travel will be lost.  I had to salvage and reuse the OE float to get near the resolution needed for a vehicle gage to make sense.  (If the top and bottom 1/4 are not included in the gage travel??)

It has also been noticed that the wipers have very high drag and frequently I have noticed the indicator reporting low when I restart after fueling.  But, as soon as we get on the road they come along.  This would concern me greatly if I was counting on them to report how much fuel I had available for the APU.....

Also, to get the float away from the pickup, the direction of the sending unit had to be reversed.  This meant it couldn’t mount where the original was in the same direction, but had to be in the same place, but backwards.  I hope to put pictures up in the next day or so.  That may allow any people that are interested to make some sense of this whole circus.

[Todd Sullivan]

I've spent thousands at Applied and never had a bad experience. Jim is typically competitive and always has the correct parts. I shopped his front suspension wear parts and found no better deal than his ball joint prices( body shop cost even)

Sully
77 royale
Seattle

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