combatwombat

Whatsup all,

I rebuilt my 42re about 5k ago, and its been running well. However, on its initial 1-2 shift when cold, its seems to studder, like it wants to stay in 1st gear. It doesnt do this any other time, only when its cold and it hasnt been drivin for a few hours (like overnight). Im thinking its a misadjusted front kickdown band, that it needs to be loosened, but Im looking for a second opinion before I make any moves.

If anyone has any ideas or maybe I need to be more descriptive (its kind of a weird problem Im guessing- have done some searching and havnt found anything).

dave1123

Try this; on startup, shift to neutral and wait about 30 seconds or so before putting it in gear. That will allow the pump to circulate fluid throughout the trans before it's called upon to engage. This is something I do in the winter to allow the trans to warm up when it's near freezing. Fluid doesn't circulate in park.

When you say you rebuilt it, do you mean yourself? I'm not familiar with the 42re trans internals, but in the GM THM tranmissions, first gear is a clutch, second is a band, and third is also a clutch. You may have restricted flow to the band engagement piston, or a leaky piston seal. I believe there is also an accumulator in the circuit that might be leaking pressure.

The way I am lead to believe is in the 42re, first and second and mechanically activated and third and O/D are electronically controlled.

There are several trans techs on this site that may back me up or disagree with me. How about it, guys?

combatwombat

I did the rebuild myself, and Its been smooth since. I cant recall which gears were clutches and which were bands- but I do remember that I replaced 2 cluch packs, the front kickdown band, and all the o-rings and seals I could. I also swapped the valve body and the overdrive unit of another 42re.

The reason I did a rebuild was because the cooling line inside the radiator burst and was sending rad fluid into the trans, and vise versa. I capped off the lines on the radiator and installed an auxilary cooling unit so it cant happen again.

If its a leaking accululator/piston, wouldnt it affect more than just the first shift from a cold start? All other shifts are smooth, it kicks down just like it should. Also the fluid level has been consistant.

Thanks
C

dave1123

I've got one criticisim of your aux cooler. What you've done will work fine until it gets cold. The rad cooler actually WARMS the trans as well. A lot of guys with classic hot rods only use a seperate cooler and they work well, BUT they don't drive them in the winter. My brother did the same thing with his 75 Blazer and found when it got cold, the trans didn't want to shift until it warmed up, and that was a long time when it was 30* or so. Most of the heat in a transmission is generated in the torque convertor because the fluid inside is like in a blender, being swirled in different directions by the turbine blades.

I thought just struck me! This might be your shift problem, seeing as how it only happens on cold startup. I know you don't want to buy a radiator, but just keep it in mind. It's something most people don't think about.

combatwombat

I plan on keeping the aux cooler since I do some towing, but Im not thinking thats the problem. It really only happens on the first shift. As soon as it shifts into second gear, I can stop and get going again and it will shift just fine.

You said the second gear on GM's is a band? I know there was two seperate bands in the transmission, a front and a rear band, and Im thinking the rear band might be my second gear.

Is it possible that after it sits for a while, the fluid pressure in the actuating piston drops, and needs a minute or two to build back up before it can actuaute that band? I replaced all the seals on the pistons so Im pretty sure they arent leaking, but I didnt adjust the bands properly (I didnt have any specs for them, so I just left them as close to what they were when I pulled it apart).

Also did the original cooling lines that went into the radiator have a check valve that didnt allow the fluid to run back into the pan, so it kept pressure in the system while the car was off? If thats the case it makes sense that it would need a minute of oil flow before it can put it into second gear (I usually shift from park to drive, and I know the trans doesnt flow oil in park).

Thanks for the help
C

dave1123

All the accumulators in the trans do is reduce the shock of clutch engagement. They have a piston and spring in them. If there is a check valve in the cooling lines, all that does is keep fluid in the cooler and converter, pressure dies as soon as the pump stops.

All I'm saying is try giving the pump time to bring up pressure before you shift to drive. As far as the bands, I don't know. You should check with a transmission shop about an adjustment.

Haynes makes a technical manual for the GM THM transmissions that's very good and only costs $20. So far I haven't found one for the Jeep 42re or 46re that doesn't cost more than I want to spend unless I really need one.

One of the things we've done for drag racing is to reverse the springs in the accumulators. Then, when it shifts, it will knock mud out from under the fenders!

jnicewan

The front band (intermediate/kickdown) is applied in second gear only. The rear band is only applied in manually shifted 1st gear (low) and Reverse. Since you know the band adjustment is not correct I would start there. It really doesnt seem like a band adj problem so try the above mentioned step and see if letting it idle in "N" for a few seconds helps.
You will need to drop the pan and remove the filter to adj the low/rev band.

Kickdown band adjustment.
1. loosen band adjustment screw lock nut, and back out a few 3-5 turns.
2. tighten band adjustment screw down to 72 in-lbs.
3. then back off the adjustment screw 3-5/8 turns.
4. tighten lock nut to 25 ft-lbs, or just get it tight

Low/Rev band adj.
1. loosen band adjustment screw lock nut, and back out 5-6 turns.
2. tighten band adjustment screw down to 72 in-lbs.
3. then back off adjustment screw 4 turns.
4. tighten lock nut to 25 ft-lbs, or just get it tight

Mdfrdave

Did you ever find the culprit and/or a solution?