| Transmission Noise - Higher RPM "Thump" when Shifting Up. [message #251920] |
Tue, 10 June 2014 22:55  |
Clark76
Messages: 62
Registered: February 2010
Karma: -2
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Should I be concerned about my hard shifting "Thump" and what actions should I take to fix it?
After an event free smooth shifting 1,600 mile journey two months ago, I started my coach for the first time today since trip. My routine, Start, Idle in Park about 3-5 minutes to allow airbags to pump up then back out of the Storage Shed. This time I noticed a new fresh small 5" diameter puddle of transmission fluid on the concrete where the overflow line from the transmission sits. None has been there before.
(I have since learned that after sitting for lengthy time, it is best to engage the transmission into drive, with foot on brake, to allow transmission to circulate better through the system while the engine warms up vs. just keeping it in park which tends to "Burp" out transmission fluid as mine did.- true?)
I drove 6 miles on the streets and noticed a little higher RPM noise(no gauge) before the transmission would shift from 1st to 2nd gear at around 25-28 mph on flat surface. The shift was HARD - a noticeable "Thump". This happened after each stop/go on my six mile journey. This is a new sound/feel while driving. At the end of the 6 miles, the Trans Temp was 150 degrees. A check of the fluid level indicated it was about 1/8" to 1/4" below the lower mark on the Transmission dip stick. About ~12 OZ of Transmission fluid was added to bring the level up to mid-to high mark.
Now, After 1 hour of smooth driving at highway speeds and 180 degree Trans Temp, Trans fluid level still shows full on the dip tube (assume it is calibrated correctly). Yet, after the hour drive and now driving on local streets in stop/go traffic, the higher RPM/HARD shift is still noticeable from 1st to 2nd and 2nd to Third.
Additional background: The transmission was rebuilt 2 years ago by a GMC tranny guru. To my knowledge the transmission has not been above ~200 degrees and less than about ~8,000 miles on the new re-build. The fluid is clean and pink using Mobil 1 synthetic transmission fluid.
Should I be concerned about my hard shifting "Thump" and what actions should I take to fix it or diagnose it better and keep it from doing this again?"
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| Re: Transmission Noise - Higher RPM "Thump" when Shifting Up. [message #251921 is a reply to message #251920] |
Tue, 10 June 2014 23:05  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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I think I'd be looking for a vacuum line issue. If you have a cracked or split line going to the modulator you could have a shift problem. Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: Transmission Noise - Higher RPM "Thump" when Shifting Up. [message #251922 is a reply to message #251921] |
Tue, 10 June 2014 23:31 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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Hal StClair wrote on Tue, 10 June 2014 21:05I think I'd be looking for a vacuum line issue. If you have a cracked or split line going to the modulator you could have a shift problem. Hal
That would be my guess or the modulator
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Transmission Noise - Higher RPM "Thump" when Shifting Up. [message #251978 is a reply to message #251924] |
Wed, 11 June 2014 16:27 |
Clark76
Messages: 62
Registered: February 2010
Karma: -2
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Wow! What a difference a 4" vaccum line makes. Upon closer inspection, I found a crack in the vaccum hose that transitions from the diaphragm on the passenger side of the transmission to the steel line that runs up to the top of the engine. Now I have smooth transitin from first to second at about 20 mph and 2nd to third around 40-45 mph. The latest test drive trams temp 195. Water temp 208 ambient temp 80 flat terrain.
All seems back to normal. I will continue to watch it. Thanks.
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