NCC-2569

iTrader: (1)

Hi guys,

I seem to be losing reverse on my transmission.
When backing the car up, it sometimes drops out of gear.
My shift lever is in R and remains there, yet reverse does not come back until I shift to P, N or any other gear.
When this happens, there is no specific sound like clicking or anything.
I just feel that there's no more power going to the wheels and I can rev the engine however I want to.
Just like it does in neutral.

Don't know whether this is directly related, but a week ago I started off from a traffic light with medium throttle and the car did not go above second gear until I stopped, went to park and back to overdrive.
My shift lever never went into another position than overdrive at that traffic light.

There were no issues with any forward gear since/before then.

Transmission fluid/filter has been changed a couple of months back, fluid is red/light brown, transparent and at correct level; just checked that properly.

My service manual goes from boost valve to clutch, simple to hard.

Any ideas what the most common failure is for this to happen?

NCC-2569

iTrader: (1)

I'm thinking either the booster valve may be defective OR, more likely, the valve body gaskets have somehow sprung a leak.
I don't see how that valve could break. Seems quite rigid to me.
Since the transmission sometimes stays in reverse and doesn't drop out... it builds up pressure and then loses it, so I guess it's bleeding out internally.
I'm ruling out the clutches, because I have proper grip in those cases where they stay engaged.
Perhaps it's enough to look at the valve body and the oil pump, which would be less trouble than overhauling the entire transmission.

OrangeBird

iTrader: (1)

Hi NCC-2569 ,

I'm sorry I have no direct answer for you , however , this statement leads me to believe there is more going on here then just something affecting reverse . For it to have been stuck in the lower gears and need to be put into park to "fix" really means that something does need fixing beyond reverse . I don't even pretend to be any kinds of 700R4 expert , but I think you should be possibly looking for something that would affect both reverse and forward gear upshifts as these have been your two symptoms ?

NCC-2569

iTrader: (1)

Hi init4fun,

thanks for your reply!
Seeing that quote, I think I need to clarify one thing.
"My shift lever never LEFT the overdrive position at that traffic light".
The original quote seems to suggest I wasn't able to move the shifter. I didn't try to, because I had no reason to do so while standing still at the traffic lights.

Back to business...
Perhaps something tiny has broken loose and floated into one of the responsible forward valves or blocked a passage, whatever part it might have been.
Would explain why I've not experienced any forward gear issues since then.

According to sethirdgen.org's diagram from the service manual, only the reverse clutches are in use while in reverse.
I guess either the 2-4 band was unable to release for that one instance or the 3-4 clutch was unable to engage. Neither RPM nor forward thrust rose or dropped unexpectedly when reaching the usual shift point, which suggests a temporary blockage... kind of like a clot in an artery.


I'm also no transmission expert... VERY far from it
Every hint is appreciated, though, and we can only learn from this, so thanks again init4fun!
Hmm. Looking at that diagram again... when it drops out of reverse, I could watch what happens when I go from R to N and back, from R to (D) and back... and so on and see what happens.