Transmission Jumps from Drive Into Neutral

[ZJP]

Transmission

I recently bought a mid 70's vintage Big Max II with a new Vanguard 16hp engine and what looks like a T-20 transmission. I've been having problems with my transmission popping into neutral while I'm driving it. It's been suggested that I check the diamonds, linkeage and shift pins first. Well......I started to do that but thought I would check the trans fluid level first. I removed the top fill nut and then I removed the lower nut and dropped it and about 2 quarts of fluid drained out before I could get it back in. I was under the impression that you only pour trans fluid into the transmission untill it starts to come out the lower hole. Is that right or is it supposed to have 2 quarts in it?

[racerone3]

You are correct on the fluid level, however a lot of previous owners don't know that. I doubt that the trans being overfilled would cause the issue that your having. It sounds to me like one or both of the detent springs is broken. Check the diamonds and shift pins first though, as detent springs will require a teardown of the trans to replace

[ZJP]

Thanks,I guess I was hoping that too much fluid would cause excess pressure and subsequently cause it to pop out of drive. I guess I have no choice but to start tearing it appart. I tried to pull out one of the shifters to check if the pins are worn but it won't budge. I don't want to damage them so I'm a little reluctant to put too much force in removing them. Are they normally that hard to pull out. The linkeage on my T-20 is upside down from what I've seen on the How-To photos (linkeage goes thru the top of the diamond not bottom up) and it doesn't have those retainer bars to keep them in place. Is either of those a problem?

[Mike]

That's shouldn't be a problem. I would put some oil in the shifter holes where the diamond shifters go into the T20 and let it sit overnight. Then work them from forward to reverse, over and over while pulling up on them.

[hydromike]

There's only an o-ring and friction holding them in there. Get a pry-bar or a screwdriver between the shifter and the transmission case and pry up on the shifter. It'll come out eventually....

[speedycoop]

On my vintage Big Max it has a snap ring holding the diamond shifters in place. Look before you pry too hard. Good luck.

[racerone3]

yep, on an older T-20 there will be a snap ring inside the shifter bore holding things in place instead of the metal plate on top. use absolutly no care in removing the snap rings. twist, pull. mangle to get them out... they can be a bogger! they are about 35 cents to replace, or you can make/ buy the hold downs and never have to fight with them again

[c9576]

is it only 1 side jumping out if so its your diamond shifter 35$ 2 bolts and 5 min of your time. I would pull the diamond shifter and check it out before you pull the tranny all apart. There is a pin on the bottom of the shfter it has to be smooth, round, not D shaped. really any ding or dent will cause it to jump out of gear.