I have a '78 D3 II that runs great with lots of power when cold, but after working it for about 40 minutes, the transmission starts to slip progressively until there is no drive at all. When it cools off it runs fine again. I can also hear cavitation in the steering lines when this problem occurs. Any help on this would be appreciated.
-
Thank you for visiting HeavyEquipmentForums.com! Our objective is to provide industry professionals a place to gather to exchange questions, answers and ideas. We welcome you to register using the "Register" icon at the top of the page. We'd appreciate any help you can offer in spreading the word of our new site. The more members that join, the bigger resource for all to enjoy. Thank you!
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
'78 D3 II Transmission Problem
- Thread starter Big D 808
- Start date
I have a '78 D3 II that runs great with lots of power when cold, but after working it for about 40 minutes, the transmission starts to slip progressively until there is no drive at all. When it cools off it runs fine again. I can also hear cavitation in the steering lines when this problem occurs. Any help on this would be appreciated.
What trans do you have? 3F3R or 3F1R. Need to check pump pressure at high and low idle with oil at operating temp.
Later Bob
"78 d3
I don't have a shop manual but the serial# is 79u04818. How do I tell what trans I have?
thanks, D
What trans do you have? 3F3R or 3F1R. Need to check pump pressure at high and low idle with oil at operating temp.
Later Bob
I don't have a shop manual but the serial# is 79u04818. How do I tell what trans I have?
thanks, D
I don't have a shop manual but the serial# is 79u04818. How do I tell what trans I have?
thanks, D
D, I should have said does it have One speed or Three speeds in reverse.
Later Bob
D, I should have said does it have One speed or Three speeds in reverse.
Later Bob
Bob, it has one reverse and 3 fwd
From what you say" works good untill up to temp" I read "a leak someplace"
The trans pump is under the top cover at the front and has a few orings.
Clean the top off good and then remove the cover. Start the engine and watch for oil leaks around the pump and lines.
Also there is a suction screen under a big cover on the RH rear of the trans case, pull it and clean it.
Later Bob
The trans pump is under the top cover at the front and has a few orings.
Clean the top off good and then remove the cover. Start the engine and watch for oil leaks around the pump and lines.
Also there is a suction screen under a big cover on the RH rear of the trans case, pull it and clean it.
Later Bob
From what you say" works good untill up to temp" I read "a leak someplace"
The trans pump is under the top cover at the front and has a few orings.
Clean the top off good and then remove the cover. Start the engine and watch for oil leaks around the pump and lines.
Also there is a suction screen under a big cover on the RH rear of the trans case, pull it and clean it.
Later Bob
Bob, Thanks for the advise, the suction screen you mentioned seems like the first thing we'll try. The trans will go in gear again after shutting it down for a little while even when the oil is hot so it almost seems like a suction restriction that builds up as the machine is running. We will try your suggestions and let you know if we find anything.
Thanks again, D
Seasons Greetings Bob, suction screen was clean, no visible leaks on pump and lines, have decided to pull the pump and replace the o-rings since that seems to be the weakest link for leakage, any tips or things I should be aware of when pulling the pump?
Also, there was a post awhile back where someone had a similar problem and after replacing the pump, control valve, filter screen and o-rings, ended up having to remove and disassemble the trans and apply some JB Weld around the lower suction tube where it fits into the trans case. Crossing my fingers that's not the problem I have. anyway, thanks for all the great info,
D
Also, there was a post awhile back where someone had a similar problem and after replacing the pump, control valve, filter screen and o-rings, ended up having to remove and disassemble the trans and apply some JB Weld around the lower suction tube where it fits into the trans case. Crossing my fingers that's not the problem I have. anyway, thanks for all the great info,
D
Check your pump for wear. Then put a 600PSI gauge into the valve and check the pump pressure at high and low throttle with warm oil. Check in all gears and come on back with results. Thanks for the Christmas greetings, I would like to recipritate and wish you some SNOW to go with it BUT, I did that to a guy in CC Texas a few years back. He came back Christmas morning all excited with pic's of the snow, the down side was it caused them to shut the city down for the night.
Later Bob
Later Bob
Check your pump for wear. Then put a 600PSI gauge into the valve and check the pump pressure at high and low throttle with warm oil. Check in all gears and come on back with results. Thanks for the Christmas greetings, I would like to recipritate and wish you some SNOW to go with it BUT, I did that to a guy in CC Texas a few years back. He came back Christmas morning all excited with pic's of the snow, the down side was it caused them to shut the city down for the night.
Later Bob
I don't think we'll ever need to worry about that happening out here. Hey, have you ever removed one of these pumps before? It doesn't look like there's much involved in getting it out but want to be sure that I don't hear that all too familiar sound of something falling to the bottom of the trans case once I pull it loose.
Thanks, D
Just hold onto the bolts. Then slip it off the tube and lift it out. Or take the valve off first then lift the pump out.
Later Bob
Greetings Bob, Happy New Year, didn't have time to work on the dozer over the holidays so we finally got to it this weekend. Checked the pump and it looks fine, found the pump pressure drops from around 300 down to 80psi when it quits. ran with trans cover off and found oil blows out of a vent hole in the top of the control valve for about a minute after start up then stops. found a cracked plastic check valve inside, replaced it but didn't make any difference. Is that oil supposed to bleed off? I am just stumped at where to look for the source of pressure loss. Also there are 3 test ports on the control valve, not sure if I'm checking the correct one. It does seem to be getting worse, now it quits after about 10 minutes of running. possibly a relief valve I'm overlooking?
I'd appreciate any suggestions.
Thanks, D
D, I have to research the pressure control valve a bit here. Sounds like your trans is going to Initial pressure and staying there. Initial is the pressure when you shift gears and it fills the clutches, then ramps up to full pressure. Like the way you let up on the clutch peddal of your truck as you shift gears.
Later Bob
Later Bob
D, here are the pressure specs. Looking at the trans valve the closest plug of the three to the end is the TC inlet relief pressure 0 to 10Psi at low throttle or 85 +/- 15 Psi at full throttle with brake on and trans in 3rd speed.
The next plug in is the pump pressure and should be 280 Psi at low throttle and 300 +/- 15Psi at full throttle
The next plug in is the clutch pressure and should be the same in third speed with brakes on, check in all gears at low throttle tl check for leaking clutch.
The check pressure at the same plug again at full throttle in neutral with the plug at the far end of the valve removed. This is initial setting and should be 60 Psi
Hope this helps you.
Later Bob
The next plug in is the pump pressure and should be 280 Psi at low throttle and 300 +/- 15Psi at full throttle
The next plug in is the clutch pressure and should be the same in third speed with brakes on, check in all gears at low throttle tl check for leaking clutch.
The check pressure at the same plug again at full throttle in neutral with the plug at the far end of the valve removed. This is initial setting and should be 60 Psi
Hope this helps you.
Later Bob