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th400 help

bigbadchev84

bigbadchev84

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Just got done installing a th400 into a buddys truck. It was a fresh rebuild from the tranny shop, We picked it up new convertor and all.

Pulled his old th400 out and installed the new, Filled up the convertor with around 3/4 of a gallon of atf and installed, did not stack the pump or anything. Filled up with I think around 13 quarts total and is where it needs to be on the dipstick. In let it run for about 15min and ran it through all the gears.

It feels like it puts a slight load on the motor in reverse and D1, when running and putting it back in park it grinds really bad on the park pawl.

Gonna take it to the tranny shop tomorrow evening after I get off work. Just wondering what the hell?
 
no 2 trannys are the same. try adjusting the shift linkage a bit . might be getting almost the amount needed but not full movement . thats all i can say i have seen.
 
It can't grind the park pawl unless the shaft is spinning. Do you have a driveshaft hooked up, or is the transfer case in neutral?

If there is no load on the output of the transmission, the output shaft will spin in all gears including neutral.
When you try to shift into park with the shaft spinning, its trying to force a spinning gear into a locked gear.

Noise, grinding, and possible damage ensues.

And its normal to put a slight load on the engine when you put it in gear. Even if you have no shaft hooked up. You are spinning lots of pieces and pumping fluid.
 
the transfercase is the first thing I checked, it does it no matter what position the transfercase is in, checked the tranny linkage, same thing, even disconected the linkage and put it into d1 and started it.

I know it is from something spinning, but it acts like the transfercase isnt getting any power. Both driveshafts are hooked up. I know the transfercase isnt jacked since I drove it to my house, the only thing that has changed is the new tranny
 
Well, somehow you do not have a connection between the transfer case and the transmission.
The park pawl engages the output shaft pretty close to where it comes out. So its the output shaft of the transmission that is spinning.
Which means it is not seeing a load.

My guess is that the "new" transmission has the wrong output shaft. There are several lengths I think, and it is not reaching the transfer case.

Before I paid someone to look at it, I would drop the transfer case and measure. Probably won't even have to measure. Odds are its going to be obvious.
Either too short, or wrong size.
There are differences between car, two wheel drive, and four wheel drive versions of that tranny.
 
With GM TH400's there are 3 different length output shafts, the longest that is used in 2WD and 4WD applications (only with 205's behind them) and then two shorter output shafts (for 400's that originally had 208's, 203's and 205's after 85).

Could be the wrong output shaft, what transfer case is being attached to the 400? If you take it apart, measure from the end of the trans case to the end of the shaft.
 
Ok here goes. My buddy Eddie originally had the tranny, it is a 4wd and had the tall adaptor with a 208 behind it. It was rebuilt for eddie, but he deceided to go 700r4 instead.

My buddy tony bought it for his 87. We took the short adaptor and 208 tcase off his old th400 and put it on the rebuilt 400.

When I installed the t-case it engaged the shaft and I spun the tcase into posistion and put the bolts in it.
 
I just went out and disconnected the rear driveline, tranny in park and the t-case in gear the rear driveline freespins. I measured the adaptors and the tall one is 2-1/2" thick, the short one I am using is 2-3/4" thick. Guess I will tear it back apart tomorrow and see whats up
 
Ok, just dropped the t-case and it looks like the shafts are different diameters? The rebuilt one is 1-3/16" diameter and the old one is 1-5/16" diameter. Not sure what it originally came out of, but am getting the 208 that was mated to it tomorrow after work.

The old case is a k-case and has the cast aluminum inspection cover. The new one looks to have had the plastic or tin cover, not sure if that makes a difference at all.
 
Strange.
I suggested wrong size, but I just threw that in. I thought all of the 32 splines were the same size.

That shaft is pretty hard, so I doubt it did any damage when it slipped. It shouldn't have had much load on it.
You mentioned that it seemed to engage when you were putting it in. So, there must have been a slight amount of connection, but most of that was probably when the two halves were not quite aligned yet.
 
All GM TH400's are 32 spline and ALL are the same diameter, pitch, etc. The only differences in the GM 400's are length (and the 2WD ones sometimes have the output drilled/tapped for a yoke)
 
I will get a pic tomorrow it is 1/8" smaller, it is a th400 and had a 208 behind it, the shafts look different as well. will get pics tomorrow
 
In the transfer case world, 32 spline is 32 spline.

If it's smaller (you didn't specify if the trans output is smaller or if the t-case input is smaller) then it's likely not 32 spline like you may be assuming, Advance Adapters has several aftermarket output shafts for the TH400.

I would count the splines to be sure of what you have.
 
OK, something about this twinged something back in the deep recesses of my brain....Trust me, you do not want to visit there.

In the early 60s, GM made a TH400 with a smaller shaft.
Which, I think, was 32 spline although it might have been 27.

There was also a TH375 made, not to be confused with a TH375B, which was entirely different.....
The 375, no "B", was a light duty 400. Had the same pan, weaker clutches, and a smaller output shaft.
Most of them had TH375 molded into the bottom of the tranny housing close to where the adapter bolts on.
 
I just went out and looked at it, there was an 11 at the tailshaft area. The rebuilt tranny has a shaft with a bevel on the end with a non threaded hole in the shaft about 3/8" deep.

The old th400 has a blunt end and looks alot beefier than the rebuilt one.

My buddy said he wasnt sure what it came out of but thought maybe a 4wd van? He bought it with the 208 attached
 
Fordum said:
OK, something about this twinged something back in the deep recesses of my brain....Trust me, you do not want to visit there.

In the early 60s, GM made a TH400 with a smaller shaft.
Which, I think, was 32 spline although it might have been 27.

There was also a TH375 made, not to be confused with a TH375B, which was entirely different.....
The 375, no "B", was a light duty 400. Had the same pan, weaker clutches, and a smaller output shaft.
Most of them had TH375 molded into the bottom of the tranny housing close to where the adapter bolts on.
Click to expand...

4WD ones, no, I don't think they did. As per the diagram above, there are a bunch of different, odd variations. Most of the odd stuff is car/2WD/Jeep stuff. In the 4WD's, there were three as previously mentioned (they are covered in the above chart).
 
bigbadchev84 said:
I just went out and looked at it, there was an 11 at the tailshaft area. The rebuilt tranny has a shaft with a bevel on the end with a non threaded hole in the shaft about 3/8" deep.

The old th400 has a blunt end and looks alot beefier than the rebuilt one.

My buddy said he wasnt sure what it came out of but thought maybe a 4wd van? He bought it with the 208 attached
Click to expand...

Have you counted the splines on the output shaft? You never know, there are aftermarket shafts for TH400's that aren't 32 spline.

If it came with a 208 attached it likely had a ~2.5" stickout 32 spline output shaft but again, you should count/measure that.

If you have two TH400 outputs that are different sizes you either have one of the oddball ones (i.e. Jeep, Caddy, Advance Adapters, etc) or there is something else going on.
 
Just went and counted it 3 times, It is a 27 spline shaft:confused:

What the hell is this thing? It definately looks to be a lighter duty case, since the dust cover design is not near as beefy as the old one
 
Sure sounds like a 375. I think they used the 350 shaft. But its late, and I am straining the limits of recall right now.
 
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