Reverse Slam

[shortstuf212559]

my SSE has a terrible slam when you engage reverse. it doesn't do it as hard when the engine/trans is cold. it gets worse as the vehicle warms up. it slams so hard i think the windshield is gonna crack! the previous owner said it had been doing it since around 160,000 miles. I'm at 212,000 now. my car shifts through all the forward gears PERFECT. i barely feel it shift at all. i have replaced all tranny and engine mounts.

any ideas?

oh btw i have the GX3 tranny, 3.33. original never been touched.

[wjcollier07]

As in original never been touched, I sure as hell hope that excludes normal 20,000 mile fluid and filter replacements! If not, I'd get on it and QUICK. Check your fluid color, level and smell.

[myfirstbonnie]

Check you vacuum modulator also. That is what is used on these trannys to control the line pressure. They are cheap and one bolt and a little tug and its changed. The new ones are usually adjustable with a little screwdriver in the center where the vacuum line connects. Other than that, as wjcollier mentioned, get a fluid and filter change done.

[shortstuf212559]

i have reconds of fluid changes every 30k miles, one was done at 190k. fluid is bright red and smells normal

[wjcollier07]

Oh that is absolutely awesome! Glad to know there's one that has been maintained for sure.

You're up on 20k though for this change...if you want to wait until 30k, be my guest, but I suggest two things. One is that you add a thermostatically controlled air to oil transmission cooler, bypassing the water to oil radiator heat exchanger. And the other is adding seafoam trans tune to the transmission before the next flush. Probably about 100-150k beforehand would be the best time. Regardless of how well its been maintained, it still builds up varnish on the valve body, clutches, etc, so its best to do this every other flush or so.

[shortstuf212559]

i guess i'll get the seafoam transtune. anyone know where its sold?

[myfirstbonnie]

Napa. Did you ever look at the modulator?

[shortstuf212559]

I'm going to pick one up this weekend.

[wjcollier07]

TransTune is sold at almost every parts store under the sun.

And yes, the modulator is probably all dried up and cracked inside, excellent suggestion.

[shortstuf212559]

when i change the modulator, will i lose trans fluid? if so, how much? little, a lot?

[myfirstbonnie]

I didn't loose any when I did mine, but if any it would only be a small ammount. If you have ramps you can put it on those. I did mine while I was doing the filter and pan gasket.

[shortstuf212559]

Okay, Great!

[shortstuf212559]

replaced the modulator today. the old one was full of trans fluid and the big pintle on the end moved just when shaking it real easy unlike the new one i got, i had to use force to move it on the new one. about 70% of the slam is gone now. i picked up trans tune and will put it in tomorrow and change the fluid prolly next weekend. when any of you changed yours, did you adjust the screw of leave it the way it came? i left it the way it is. should i mess with it?

oh and btw in forward gears my trans feels like its a brand new GX3 now, i cant even feel the shifts whatsoever unless im really hard on it. it doesnt even make any feeling when i downshift at all anymore. i just have a feeling all these years with excessive line pressure has done a little damage to the tranny a bit

[clm2112]

I left it the way it is. should i mess with it?

Only if you have a gauge for checking the transmission line pressure. With the engine at idle, transmission in park, and the vac modulator adjusted properly, your line pressure shoud be around 69 psi. You adjust the screw on the modulator until the engine vac signal causes that line pressure. You also want to check your TV cable is adjusted right, so when the pedal is to the floor, the TV cable is pulled to it's limit.

That clunk you heard was the reverse band being applied with over 250psi of line pressure instead of the normal 69psi. It's a little hard on the band, the apply piston, and the spring loaded parking pawl (it may not have had time to get out of the way before the reverse band grabbed and started spinning the output shaft in reverse.) Not much you can do about it now, what's done is done. Your plan of cleaning out the transmission with new filter and fluid is about as good as it is going to get. Until the transmission failed to go into reverse, it isn't worth tearing it apart to zero out the extra wear from the faulty modulator.

[shortstuf212559]

how do i check and adjust the TV cable?

[clm2112]

how do i check and adjust the TV cable?

Up at the throttle, you have three cables attached to the bellcrank. One is the throttle cable coming from the gas pedal. Another cable is from the cruise control, allowing it to move the throttle. The last cable is the Throttle Valve (TV) cable leading down to the transmission.

To adjust it, sqeeze the metal tab (shaped like a letter "D") where it passes through the steel bracket that holds all the cables to the intake manifold. That will release the ratchet and let the cable go slack. Pull the cable all the way back away from the throttle body. Now, press the gas pedal to the floor. The tension from the gas pedal will pull the ratchet mechanism taunt with the throttle opened as far as the pedal commands. So that when you have the pedal to the floor, the cable has pulled the TV cable as far as the valve inside the transmission will allow.

The TV valve and cable tell the transmission what your right foot is doing...it uses that valve to regulate pressure to the slide valves. If the cable is loose, the shifts will be sloppy, even with the correct line pressures inside the transmission. A lot of the cables get mal-adjusted over the years, so it's a good idea to check it regularly when checking other stuff under the hood.

[shortstuf212559]

well i was under the car today while i was doing new front brakes. and low and behold i look at my rear passenger tranny mount, and its all cracked up and falling apart! i just replaced it in march!!!!! and i had it done at a shop too! so im taking it back there on monday and bitch. hah

[shortstuf212559]

oh and another thing i noticed, is this fixed my 2-1 clunk when coming to a stop.... something i've had on every 4T60 i've had...