Hydramaster 4.6 CDS RPM's Drop then go back up | TruckMount Forums #1 Carpet Cleaning Forums

Hydramaster 4.6 CDS RPM's Drop then go back up

brian3180

Well-Known Member
Mar 7, 2010
1,810
303
83
Texas
Real Name
brian l
Business Location
United States
The clutch would essentially stop and start rotating again. Seemed like when vacuum was under load RPMs would drop. High pitch noise coming from the motor. Didn't sound good when rpms would drop. RPms would drop for a few seconds then full power would be restored. What could be the problem? This has never happened on this machine.
 

Todd the Cleaner

Todd Cottino
Staff member
Administrator
Moderator
Premium VIP
Sep 4, 2011
22,936
15,068
113
49
Pahrump, Nevada, United States
www.toddscleaningservice.com
Real Name
Todd Cottino
Business Location
United States
The clutch would essentially stop and start rotating again. Seemed like when vacuum was under load RPMs would drop. High pitch noise coming from the motor. Didn't sound good when rpms would drop. RPms would drop for a few seconds then full power would be restored. What could be the problem? This has never happened on this machine.
You mention a high pitched noise, is it possibly a belt slipping? Check the blower belt tension and possibly replace it.
 

Jim Davisson

Well-Known Member
Aug 23, 2016
4,310
5,167
113
Serving the greater Charlotte area
Real Name
James Davisson
Business Location
United States
Definitely watch your vacuum pods when you put a load on the motor. Sounds like you have a vacuum leak. One pod always has vacuum and essentially keeps the machine at the right RPM, the other vacuum pod is connected to the blower and maintains RPM under a load. That's probably the vacuum pod I would look at first.
 

brian3180

Well-Known Member
Mar 7, 2010
1,810
303
83
Texas
Real Name
brian l
Business Location
United States
Definitely watch your vacuum pods when you put a load on the motor. Sounds like you have a vacuum leak. One pod always has vacuum and essentially keeps the machine at the right RPM, the other vacuum pod is connected to the blower and maintains RPM under a load. That's probably the vacuum pod I would look at first.
How do I check pods? Thanks for response
 
  • Like
Reactions: Jim Davisson

Jim Davisson

Well-Known Member
Aug 23, 2016
4,310
5,167
113
Serving the greater Charlotte area
Real Name
James Davisson
Business Location
United States
Hook up a vacuum hose and open the hood. While running at normal RPM and watching both vacuum pods block off the hose and watch the cables running out the back that control the vehicles throttle. One probably goes limp under a load, that is the secondary pod from the blower. It's probably either a cracked vacuum hose or a worn out pod. Check hoses first, it usually the simple things that get us.
 

brian3180

Well-Known Member
Mar 7, 2010
1,810
303
83
Texas
Real Name
brian l
Business Location
United States
Hook up a vacuum hose and open the hood. While running at normal RPM and watching both vacuum pods block off the hose and watch the cables running out the back that control the vehicles throttle. One probably goes limp under a load, that is the secondary pod from the blower. It's probably either a cracked vacuum hose or a worn out pod. Check hoses first, it usually the simple things that get us.
I checked and didn't notice anything unusual. So I had this problem yesterday. I was cleaning my own home. I set up hoses and started van up then machine. Do you suppose I should have let van warm up? After I rushed through the cleaning yesterday I couldn't get the machine to act up. This afternoon I started van and let it warm up before I re cleaned a room today with no issues. What do you think?
 

PROSTEAM22

Member
Aug 2, 2009
84
4
8
Panama City, FL
Real Name
Scott Medlock
Business Location
United States
Hmmmm. I was just searching and seem to have about the same problem. Just noticed last night so I haven’t had time to see if the van rpms are dropping but when I put the blower under a load it sounds like the machine quickly loses rpms and is about to completely shut down until I release the vacuum. Then it comes back up. Does this sound like the same issue? And are those vacuum lines the hoses that run right above the pulleys and most likely to bounce off the pulleys and wear a hole?
 

JDARNOLD

Active Member
Jul 31, 2012
327
129
43
58
Real Name
Edward Arnold
Business Location
United States
What year model is the van and unit
 

brian3180

Well-Known Member
Mar 7, 2010
1,810
303
83
Texas
Real Name
brian l
Business Location
United States
2002 GMC Sierra 4.6 CDS - There were some wiring issues going on. I cost about $2000 to get it straightened out at the dealership.
 

JDARNOLD

Active Member
Jul 31, 2012
327
129
43
58
Real Name
Edward Arnold
Business Location
United States
The reason I asked is because right around that time is when vehicles went to fly by wire for throttle control. thus no vacuum pods. It is controlled by a unit that is plugged into the vehicle diagnostics port under the dash. also make sure that your A/C or defroster is turned off when running the unit.