Transmission not selecting drive intermittantly

[Westerly147]

Hello there,

I have a 4x4 Bongo tin top year 2000 which has given a lot of trouble free motoring. Over the last year or so selecting drive has involved giving the engine a rev to get it to jump into gear, sometimes with a bit of a lurch. I also note that if I kick down when pulling up a steep incline to low, the transmission occasionally fails to engage and revs before engaging. While a bit of a nuisance, the van is still driving well, the fluid has been changed and checked to eliminate anything odd there, but I guessed it was a matter of time before one day it would not select drive at all and I would be stuck. That day arrived a while back and I have had to be recovered twice this summer.

I suspect a solenoid problem and have the sump dropped from the transmission to expose the array of devices. I usually check solenoids for coil resistance before condemning them, but the set in the gearbox is fitted with very fine pins on each plug that would be easily damaged. I also suspect they need to be changed as a complete set.

Can anyone give me some insight as to whether this fault is likely to be the solenoids, how I should confirm this or check for a different root cause. The Bongo is in a garage with my mechanic, and I am an engineer, but neither of us have a lot of experience with automatic transmission in general and this is the only Bongo around here to have presented with this fault. (I am based in the NE of Ireland).

Any suggestions would be appreciated.

[cutlass]

If need - I have manual AT RA4AX-EL - PDF-file, volume - 12.5MB...
PS- do you run self diagnostic? what lamp "hold say"?

[Westerly147]

I have a manual, but it has limited information. Can you point me to somewhere I could download this manual.

There are no indicating lights or error messages. I have in the past repaired a faulty solenoid in the EGR system that was giving rise to a flashing glow plug lamp. When put into diagnostic mode (by linking two terminals in the test block connector in the passenger seat well) the lamp flashed specific codes, which were of limited help in getting to the bottom of the problem. This time however, no lights are flashing. I have read about a separate gearbox controller somewhere. Is there a separate controller with separate diagnostics I could check out?

[cutlass]

sorry! I may only sent e-mail....write e-mail into privat... on my bongo for start self diagnostic AT- i connect "ground" and TAT - than look "hold"....from "glow plug" i look error in engine, when i connect "ground" and TEN

[Alacrity]

I am assuming the oil level is being checked correctly - engine running in Park? If OK I would be surprised if it were a solenoid issue causing this issue, is the same in D & R? If only in D then it isn't a oil level issue. It's an unusual fault but solenoid issues tend (but not exclusively) to be either when hot or (usually) cold. What colour was the oil that came out on the oil change.

[cutlass]

I find photo, may be help -

[Westerly147]

I am assuming the oil level is being checked correctly - engine running in Park? If OK I would be surprised if it were a solenoid issue causing this issue, is the same in D & R? If only in D then it isn't a oil level issue. It's an unusual fault but solenoid issues tend (but not exclusively) to be either when hot or (usually) cold. What colour was the oil that came out on the oil change.

The oil level has been checked correctly. This was the first thing we suspected. The oil colour was normal, and changing it did not solve the probkem. When the sump was dropped off, there was some sludge, but the filter seems clean enough. The problem is only with drive. Reverse engages without any problem. There is also no problem changing up or kicking down, except into 1st gear. I suspected a solenoid problem because it is so specific, although I would have thought that an electrical problem, such as a high coil resistance, would have given rise to a failure indication of some sort. A sticky or worn rod would not, but I can see why this would be more of an issue either when hot or when cold. I am assuming that the solenoid opens an oil way to actuate a gear or clutch engagement in a sundial gear arrangement above the sump. If not the solenoid, then the clutch or gear is not engaging and I guess this will mean a new transmission.

[cutlass]

I see video - man install LED-lamp at AT-wire connector and look how change gear - how work solenoid...at 1gr - Low clutch - Shift solenoid B,Shift solenoid C,Shift solenoid F - are energized and the oil pressure switches are on

[Westerly147]

Many thanks for the pictures. Do you have a pointer to the video, I am not clear on what the test was and the set up, but it looks like the sort of thing I need to do. I also thought to drop out the solenoids and test them on the bench. Is there anything I should know before starting to unbolt things?

[cutlass]

it is video - do you understand russian? i may ask him how it work... https://youtu.be/KY8qTYuF7Hs

[Westerly147]

My Russian is not too good! The garage owner has returned the Bongo to me after cleaning out the sump and replacing the transmission fluid. It does seem to be engaging drive without any initial slippage, but I think I may remove the solenoids and check to see if there is any sludge on the pins. I have seen other videos on automatic transmission where this was a problem. Thanks for the guidance anyway.

[cutlass]

NOTE- it is wery wrong way - if you want sale car have crushd clutch disk - you use motor oil in AT=more the viscosity= more pressure....

[Westerly147]

Hi Cutlass,

Not sure I understand your last post. The only fluid used in the transmission is Dex III, which I understand to be correct.

Since the last post, I have taken the Bongo back to my own house, propped it on blocks, drained off the ATF and removed the sump. I have tested all of the solenoids. The 4 shift solenoids show a coil resistance of 3.2ohms. The hold and pressure solenoids show 11.9 and 12 ohms respectively. I dropped off the filter and cleaned it with K&N air filter cleaner, which is a strong detergent that rinses off with water which was then dried off. There wasnt a lot of material came out when washing out the filter, so I do not suspect any problem here. I then dropped out all of the solenoids in sequence. There was no visible problem with each, and the pressure solenoid channels were clear.

I have found one issue. The temperature sensor is showing open circuit. I tried a little hot air on it in case it was too cold for it to show anything, but no change. I suspect this component is open circuit. I would have expected something between 320 ohms and 1000 ohms and this to decrease with warm air assuming it is a thermistor device with a negative temperature coefficient. Does anyone in the forum know if a faulty temperature sensor could cause the problem? Better still, does anyone know where I could pick up a replacement or equivalent?

[cutlass]

"Not sure I understand your last post" - if oil pump, the piston in AT is old =you have little pressure - motor oil more viscous=more pressure! use that only for back home!
on may bongo - if I disconnect temp sensor AT - I will dont have 4-st gear and lock TC...
it is info about resistance temp sensor

"3.2ohms. The hold and pressure solenoids show 11.9 and 12 ohms respectively" - i think it normal! on my bongo - 3,8 and 13.4

[Westerly147]

Yes, I screwed up the resistor test referenced on my last post. I did not test the correct pin after tracing the resistor. It is working properly. I have put the sump back on and filled with new dexron III transmission fluid. When cold it is working fairly well, but when warm, it still has a lag when placed into drive, 2nd or 1st. The oil is brand new, and I overfilled slightly and pumped some back out. Oddly the red colour has gone with only a few miles to heat it all up. I am not sure if this is mixed with old oil perhaps in the cooler, but perhaps it indicates something else wrong.

I have run out of options i think. Thanks for keeping up the posts.