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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Dr_Snooz on December 29, 2010, 06:58:52 PM
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This just started the other day. The shift points all moved up to 4,000 rpm. Upshifting is quite violent and downshifts also happen at higher rpms. I've replaced the vacuum modulator and unplugged the kick-down switch and the problem remains. Any thoughts?
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Do you actually have vacuum to the modulator diaphragm? If so check the governor gear
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Checked the governor today. The spindle is scored, but the gear is fine and the weights and springs are all intact. The modulator is getting vacuum. Any other thoughts?
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Is the governor valve moving? Have you adjusted the modulator?
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Is the governor valve moving? Have you adjusted the modulator?
There's a valve? In the governor or the case? Sorry, I don't know domestic stuff so good.
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I hooked up the vacuum modulator to a handheld vacuum pump yesterday. I pumped it down to 22", went for a drive and... no change. Then I wired up the kickdown solenoid to battery voltage and put a handheld switch in the wire. I hit it with battery voltage a few times and went for a drive. I got a clean shift from 1-2 at the right rpms. 2-3 tried hard to shift, but couldn't manage it. Then it returned to shifting at 4,000 rpm. I can hear the solenoid inside the case working, but the kickdown mechanism does not work properly when driving. I was hoping to avoid dropping the pan again, but I'll have to take a look at the kickdown mechanism. If that looks fine, then I guess I'll pull the valve body. Stupid truck.
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Do you actually have vacuum to the modulator diaphragm? If so check the governor gear
One step at a time... You can check the governor without removing the pan.
http://www.dragracingonline.com/technical/vi_9-bm-1.html
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I bought an ATSG book today in anticipation of a valve body rebuild. Reading up on the governor assembly, I finally learned that there is a valve inside the spindle. That didn't move around when I was inspecting the governor, so I'm assuming it's stuck. Is that a safe assumption? How freely should the valve move? Should gravity alone be enough or does it require hydraulic pressure? I'd be very happy if it was an easily accessed $25 part.
I also bought a valve body rebuild kit. I may do that too just to have it done and to get the last of the fluid leaks fixed. I'm tired of keeping stacks of cardboard under it.
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Governor works great. Valve body rebuild is next on the docket. If I don't find the problem in there, then I don't know what happens.
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I pulled the valve body today. The kickdown solenoid looks like this.
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2647.jpg)
The seal is on the left. The screen is in the middle and the solenoid is on the right. I'm assuming the seal failed, opening the circuit at all throttle positions. If it's not that, then I'm completely at a loss. The trans looks really good inside. The valves all move smoothly. There's no scoring or any real signs of wear. Knowing that this truck hasn't had a lot of love, I'm surprised it looks so good inside. The governor screen was completely clean.
Anyone have any suggestions for getting the retaining pins for the shift valves out (below)? They appear to be pressed in and I'm not real sure how to get enough leverage on them to get them out.
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2649.jpg)
Pulling the valve body is giving me a chance to get most of the leaking seals in the trans. The thing makes an unbelievable mess when parked in any one place for more than about 4 minutes. I'm hoping to participate in a volunteer crew building a home next month and I need this thing to pull a trailer full of tools. I hope this fixes the problem. Then I hope it passes smog.
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You can use a pick tool or small screwdriver to push them back or a pair of needle nose or small dykes to work them out.
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Anyone know where this piece goes?
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2671.jpg)
It exploded out of the transmission when I removed the valve body along with a number of other pieces. I've figured out all the rest, but I can't find any diagram showing this one. Any help is greatly appreciated.
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I saw that bushing. it goes at the frame and the shift linkage goes into it. Should go right accross from the linkage on the trans, but at the frame.
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When you say "frame," do you mean the frame rails? Outside the transmission case?
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Yes. there is a rod that comes down from the steering column, then across to the transmission. that is your shift linkage. The rod pivots in that plastic washer.
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I'm glad I asked, because I could have searched for a million years and never realized that it goes here:
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2674.jpg)
I'm not sure how you guys are putting these valve bodies back in, but I had really good luck greasing the checkballs slightly like so:
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2670.jpg)
The grease really held well. I tilted and bumped the valve body as I was lifting it and they stayed put through it all.
I had this spare bracket lying around, so I held the front servo piston in like so while I bolted the valve body.
(http://i441.photobucket.com/albums/qq132/dr_snooz/DSCN2669.jpg)
I also took the opportunity to replace all the little case seals (selector shaft, governor, speedo gear, kickdown switch, etc). I got all of them but the tailshaft seal and the front and rear seals. When I drop the driveline some day, I'll get the tailshaft and rear seal.
The good news is that the truck is running again!!!! Hooray!!
Thank you all for your help!
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FYI
Grease is NOT what you want to use in an automatic transmission. Vaseline/petroleum Jelly or trans gel.
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If that is Lubra-plate engine assy lube He would be fine with just that little bit.
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Using white grease is not an acceptable practice in assembly of automatic transmissions. You need a petroleum based low melting point lube like petroleum jelly or transjel.
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Oh. Good to know. Anyway, the truck passed smog today. It's running great.
Thanks again for all the help.