Looking for someone who has experience with gm autos before I tear mine out of my truck.
Let me start with my story. I just finished up putting a 4.8 with a small turbo set up in a 1994 c1500. When I was considering transmissions for this I kept coming back to the th400 because they have a reputation for being very stout.
Last Friday the week truck became street legal and a friend and I began street tuning it. This started with putting around and eventually lead to a few short power pulls.
The more we drove the truck the more we realized the transmission wasn’t working quite right. It had been low on fluid at first and we added two quarts which helped. But it still struggled to find 3 gear and seemed to slip a bunch.
By the end of our 5-10 miles of tuning it had developed a whine so we parked it.
Sarturday when I started the truck the whine was back. I added a quart of atf and it calmed down at idle. Took it for a light drive and the whine came back. I dropped the fluid and pan after to have a look and the fluid is clean, doesn’t smell burned but is definitely aerated. It looks like it’s been whipped.
The encouraging news is there was no metal in the pan and while there was a slight film of dark sediment on the bottom there didn’t seem to be anything in the pan that scared me.
I also found the filter flopping around, which apparently is how gm built these things.
I also found the kick down solenoid was not connected. Could this lead to erratic shifting?
My plan as of today is grab some fresh atf and a new filter and new o rings for the pick up and try that. If that doesn’t remedy it what should I do next?
I'll admit I don't know much, but there's a TH400 in my '85 C30 Dooley. Never have touched it, but I do check it once a year or so for fluid level. Like everything else on the truck, it seems robust. Even if floored, it's in 3rd by 25 mph, but it works.
The thing that strikes me about your post is that you seem to have added a total of 3 quarts to the thing after you had run it a while and noticed something wasn't right. Is it leaking somewhere?
I'd start with a complete fluid change. Verify correct level.
After that, I'd take it to a local guy that runs a transmission shop with a good reputation. Should be plenty of old-timers who know their way around these things.
All I know personally, is that the one I had in my 73 454 Cheyenne got the everloving E36 M3 beat out of it, and ignored the rest of the time. It was fine with it.
A pro drag racer I know had one behind the big Windsor in his 9 second nitrous Fox body.
That looks like it has water/coolant mixed in with the ATF, are you running it through your radiator or a transmission cooler?
dclafleur said:
That looks like it has water/coolant mixed in with the ATF, are you running it through your radiator or a transmission cooler?
I think this might be it. ATF cooling lines in the radiator.
It’s in a separate trans cooler, radiator is bypassed.
1SlowVW said:
It’s in a separate trans cooler, radiator is bypassed.
Be sure to trace the lines. Some use both.
Sure looks like coolant (or water). Google "coolant in transmission fluid" and you get pics like yours.
In reply to 1988RedT2 :
I can guarantee 100% that the trans fluid does not go through the radiator. But that doesn’t rule out the possibility that the transmission somehow got water in it.
That is Not what clean OR Burnt ATF looks Like.That Has Water or something in it. DRAIN ALL That you Can Please replace the filter with a New one and NO they DO Not Flop around( Filter) you my also need to change the fluid again so Check Again after Some miles are put on it, just to flush it use Some Dollar Store crap, 400 don't care, but The Fluid should be the same color after Thousands of miles Dark Red but Still See through.
In reply to GTXVette :
Replaced fluid and filter tonight, took it for a drive. Works better but still seems to slip in second at light throttle.
When I get on it it seems to work fine. It just seems confused at low loads around 30mph.
In reply to 1SlowVW :
Not slipping but if your vacuum modulator isn't hooked up or is bad it won't shift out of first until 30.
In reply to 1SlowVW :
Good question. Everytime I've had that I make sure the vacuum line is good and hooked up to the modulator (front right side of the trans) and the carb. That's been the fix for me but I know the modulator can go bad also.
check to see if any Fluid is coming out of the Modulater, as in put a short hose on it and see if there is any vacuum when you draw a breath( suck on it). and there is one that has a screw inside that can be turned to regulate shifting but right this second it's not coming to my Brain but they are cheap.
edit There are different color stripes around them indicating what Vacuum they make the shift, Vacuum equates to load and/or RPM.
I wonder if the old diaphragm didn’t just screw off when it saw positive pressure for the first time in 30 years....you know if I didn’t have a check valve in the vacuum line .
In reply to 1SlowVW :
You don't check valve that line otherwise it sees the same engine load all the time.
Stampie said:
In reply to 1SlowVW :
You don't check valve that line otherwise it sees the same engine load all the time.
I though I read that people put a check valve so it can see vacuum but not positive pressure, I’ll have to do some more reading.
I'll go with the Modulater being the check valve, also a GM hardline ( tube) that goes to the carb/ modulater is Necked down at the carb end and is likely a Restriction/check valve? it's almost too easy to put a Shift kit in one and I do it to all mine, Matter of Fact Stampie is bringing me one in a Week or so, time to clear off that table.
In reply to GTXVette :
My tube was not included with the transmission when I bought it so I just bent a piece of brake line to fit.
I will buy a new modulator today, for 20$ it’s worth trying.
The filter should not "flop around", there should be a kind of rubber coated sleeve that it presses into. If you have any air leaks on the inlet side of the pump you are going to have problems.
I have heard of people covering the seam of plastic/steel filters with silicone, because they could suck air when the front of the filter gets uncovered on hard lauches.
In reply to Knurled. :
Flop around may be a poor choice if words. The filter tube which goes from case to filter fits tightly and I replaced the o ring in it while I had it out. Filter also fits very tightly to the tube. The rear of the filter however is able to move up and down about an inch. The bolt that holds the filter in place allows some movement. I read up on this and apparently it is correct for th400’s.
In reply to 1SlowVW :
i see what you mean. When the pan is in place the filter cannot move.
You do need to make sure you have the correct filter for your pan, though!
Update, new modulator improved performance Took my drag racing neighbour for a drive. He said (your linkage is binding and holding it between gears). He told me not to pull the trans. But instead figure out why I’m having trouble manually selecting drive. I really hadn’t notice the issue but it’s hit and miss as to whether the trans slides down smoothly to d or second.
The saga continues...
Oh Tay, get it off the ground, put it in 1st, crawl under and remove the linkage at the trans, did the gear selector move any farther? was it fully in 1st ?
Crawl out and put the selector in 2nd, go back under move the gear shift mech. to 2nd ,will the arm(rod) fit right back in, no fuss? Should be a very positive Click into each gear you move it to Rotate through all gears to FEEL this, it should allow the rod to be returned to the shift mech. in each position, of course any binding will indicate the rod isn't acting right it can be just a bushing
, Is it colum shift or floor mount? all this is about a colum shift. your buddy is right about not taking the trans out,you can acess everything through the pan, Unless it is a pump (not Likely) or clutch disks (Same answer)
PS it Takes a good bit of effort to rotate the selector at the trans by hand,
