Transmission dipsticks?

[crashz]

I was always under the impression that TH400s were TH400s and the dipsticks would all be the same. I proved that to be false Friday. In preparation of its maiden voyage with a load on, I changed the squishy transmission mount, changed the fluid and filter in the tranny, greased it, did some underbody cleaning and painting, changed the belts and topped off all the fluids.

One thing that needed attention (PO was a farmer who like to repair on the cheap) was the transmission dipstick needed replacement. The cap at the handle was missing, so it was a point of entry for dirt and grime. So I bought a parts store cheapo replacement (chrome) and when side by side, they are about 4 inches different, with the new one at 27 inches long and the old one at 31". For reference I pulled the one in in my 83 and its 29 inches long! These are all TH400 transmissions, but the trucks are used and have both had replacement transmissions done by previous owners, and who can trust those cheapo chrome parts?

So not knowing which to trust, I split the difference and popped in the 29" stick, filled six quarts, and drove the truck. Still shifts late (the tranny was replaced, so i'm assuming the governor and TC have not bee changed to match), but it shifts with less of a bang, but more positive & consistent feeling in each gear including reverse (if that makes any sense). The fluid removed was still clean, but a little burt smelling and there was a moderate amount of wear material in the pan, but nothing alarming.

So does anyone know what length of a dipstick to put in there?

BTW - took her out on Sat. for a 50 mile round trip with a load (about 1.5 cy of clean gravel) and she ran beautiful.

[DmaxMaverick]

As a general rule, unless you can see and compare one with another, I recommend (and practice) always replacing the dipstick and tube as a set. The tube is unique to the tranny and powertrain (chassis, engine, outfitting, etc.), but the length of the stick in relation to the tube is always consistent (the protrusion or fill marks extending out the bottom of the tube). Even when the dipstick lengths are identical, the fill marks may be different. The aftermarket makes this even more difficult, as none of them seem to follow a set standard. Otherwise, you'll have to use the original stick to locate the correct fill level, then mark the new stick at the proper level (I drill pinholes). Much the same applies to oil level dipsticks in many cases.

[crashz]

Thanks Dmax!

I'm going to make the assumption that the original dipstick is the proper one and install the cap on that one. When I had the pan down, the original dipstick seemed correct as it protruded the the tube by about 1/2". Looks the most correct anyway. This is temporary as I'd like to have a freshly rebuilt TH400 with the correct TC, governor and stronger friction materials built for the truck within the next few years.

I find it funny that so many parts are similar along the lines of GM vehicles, yet something that simple would vary. It does makes sense though, as different tube heights are needed to clear small block gas engines, big block gas engines and diesels all using the same transmission. Never thought of that. ;)

As always - TDP is a vast wealth of knowledge.

[4x4toys]

I replaced the transmission dipstick in my 1985 Chevy C20 with 350 gas and 400 trans. I had a dip stick from a 4L80E lying around and it was the exact same length. The only difference was the stick from the 4L80E had the flip over handle that locks in the tube. I kinda like that better. I think the price from GM was around 10 bucks. Hope that helps with your with your vehicle. If you use a stick with the locking handle lube the rubber gasket on the stick with ATF so it will release easier next time you check fluid.

[Robyn]

OK

The best way to do the fill is to do these is to fill up plenty then having it warm loosen the pan enough that it will allow oil to flow out over the pan rail.

(truck must be level)

Once the fluid is flush with the top of the pan rail, mark the stick you have with a FULL MARK and go with that.

The hard shifting is likely due to a misadjusted vacuum valve on the IP.

Loosen the two bolts on the vacuum valve ( RH side of IP) rotate the valve slightly clockwise (looking at the valve from the RH side) and try a road test.

probably the valve is just putting a tad too little vacuum to the valve.

High vacuum at the modulator = low throttle pressure and early soft shifts.

Lower vacuum at the modulator = later and harsher shifts.

WARNING

To much vacuum and a real soft shift with major throttle can cause damage.

Make the shift so it is just crisp and not real late and slaming.

The wrong governor will make the shift late (Gasser)


If the fluid smells at all burnt there is a reason for it.

Hope this helps.


Missy

[crashz]

Good to know, 4x4toys. Maybe after I get the correct markings, I can match up a new OEM stick. I like those compression seals too.

Thanks Missy!

Thanks for the dipstick procedure. I'll check/modify the longest stick according to this procedure next time I'm working on the truck. Still got quite a few more chores to do on it.

I read other threads where you had mentioned the vacuum adjustment, but if figured it may not be relavent since the PO told me when I bought the truck that he replaced the transmission with one from a junkyard. Naturally with the way it shifts, I assume it was from a gasser with the gasser TC and governor.

The truck was used to haul a salt spreader around, and I'm sure it spent plenty of time overloaded. So that combined with lack of proper cooling (no additional cooler on the transmission) and maybe the the gasser TC, I can see this getting pretty hot. Probably why the fluid was starting to smell a little. I'll flush it a few more times, as I installed a drain plug. I will eventually bypass the radiator cooler and install the largest transmission cooler (and new lines, they are copper now!) I can find.

Now on deck for repair:

-Right side exhaust (from manifold to tip)
-Radiator flush and fill + hoses
-Front shocks+stabilizer
-Front spring bushings (leaves ride on the frame!)
-Replace all fuel feed lines (still getting a little air based on the clear tube test).
- Repack the dump body lift cylinder or replace with a better hoist system
- Repair weak dump body floor

The truck is not driven very much, so this is more a labor of love than anything else. Basically, I like to get my hands dirty and it relaxes me from my day job.

Thanks for all the help guys!