I just finished installing my TH400 transmission to engine and was about ready to start lifting the assembly for installation into my '74 coupe when I decided to lubricate the engine one more time since it hasn't been fired up since being rebuilt. But I can't turn the engine over using a breaker bar on the front of the crank. Prior to bolting the transmission to the engine it turned over just fine.

Any ideas before I un-bolt & remove tranny it to check things out?

Should I be able to turn it over with TH400 mated with it?

 

yes the engine should be able to be turned over from the crankshaft with the transmission bolted on. Turning it should just cause the torque convertor input shaft to turn. I assume there are no spark plugs installed. I have done the same process to adjust valves many times and the engine turns freely.

 

Thanks MelWff for quick reply.

The engine tuned over when I was intalling the torque converter, cause I had to rotate it to be able to tighten the bolts so it must be something related to just the TH400.

Do you know is there anything special that needs to be done when mating the TH400 to the engine? I did have some trouble getting it to slide together and needed to use the tranny mounting bolts to pull it together.

Additional info.: I unbolted the transmission and engine turns over. It looks like Torque Converter is keyed to the input of transmission and this time I made sure the key was aligned. I got transmission lined up and started input shaft into TQ, hit some resistance so I wiggled tranny i.e. rocking is left and right and tranny appeared to slip in. I checked rotating the engine and it rotated but there was more resistance. I started to bolt the tranny up to engine and even before I got the housings to touch, the engine won't rotate. Backed out the tranny bolts some and engine frees up. I can't imagine what's going on. Tranny was fine when it was originally removed.

 

Check the convertor is fully seated into the trans. It's possible to install the drive gear in the pump backwards too. The drive lugs are offset to the rear- if the gear is backwards, it moves the drive lugs forward and the convertor won't go back far enough to clear the flexplate.

If you use the bellhousing bolts to pull the trans up to the engine, you stand a good chance of breaking the trans case. Use the bolts as a guide but until you get the trans and engine to seat together don't tighten any of them.
You should be able to lay a straight edge across the front of the trans with the convertor installed and have clearance between the convertor and the bar. The center hub on the convertor might stick out a little, maybe 1/8, but it should slip freely into the rear of the crank.
I have seen some convertors that had been rebuilt, and the OD of the hub was not machined so it would fit in the rear of the crank. Slightly oversize.

 

Did you seat the torque converter to the trans when you replaced it?
As you slowly turn the TQ, push towards the trans and when it seats
you should feel it engage.


Donnie

 

Thanks everyone for your input. No I didn't seat the TQ to the transmission first. Error on my part and I'm on my way with tranny to transmission shop. The guy said they've seen this before and there's a good chance I crushed the pump gears. Definitely inexperience on my part and looks like I'll pay for it. I'll update you with how this all turns out but it's definitely better to find out now and fix rather than after I got engine/tranny back in the car. http://forums.corvetteforum.com/imag...ies/salute.gif

 

Tranny shop called today and said the pump & gears at front of tranny were OK. Said they couldn't find any problems. I asked if they also checked the Torque Converter and they said it appeared fine.

Sorry for not responding to TimAT's post ... nothing had been touched inside the transmission as it had been running just fine when removed from the car so pump gears hadn't been changed. I did try the straight edge across the front of tranny with TQ seated and everything clears.

It's hard for me to imagine that nothing was damaged and that I didn't break anything on the tranny case but I don't know what else to do except re-install it correctly and try it.

Right now I feel like I dodged a bullet but probably won't stop worrying about it until I actually try it.

Thanks for input everyone.

 

When bolting the trans to the back of the engine, make sure that the torque converter spins freely as the gap between the two is closed up. If it doesn't, the converter is misaligned with the crankshaft - don't run it this way as it will ruin the TC bushing and/or the engine bearings.

I had one like this and had to use offset engine-trans dowels to get an alignment. I'll try to post pictures and the checking process tonight.

 

It sounds as if you bolted the torque converter to the engine and then installed the trans to the engine. If so, that's not the right way. Install the T/C to the trans first and spin it to make sure it's in all the way. There should still be a small gap between the flexplate and t/c when the trans is tightened up to the engine. Then install the t/c bolts last.

 

larrywalk ... yep TQ spun freely so I could line up bolts. Engine turned over nicely too as I rotated things to get to other bolts.

'75 ... yep I screwed up big time ... guy at tranny shop told me that even some of their new recruits make that mistake. I never had a Vette with an automatic before and without knowing that TQ drives that front tranny pump ... just wasn't thinking. Believe me I'm really embarrased about this but maybe this thread will keep someone else from this mistake.

 

No reason to be embarrassed, now if you knew the right way and still did it wrong, that's another thing!!

 

I'll drink to that!

 

And on top, you had the sense to stop when you had a feeling something was not right. I've seen more than one pump and convertor totally destroyed by someone not stopping or even thinking that there "might" be something wrong.
Overall, GOOD JOB!!

 

Thanks TimAT.

Last night I agonized over this. Everything seemed to go together just fine after following proper procedures, but in the back of my mind there was this nagging feeling that something had to give to enable me to do what I originally did wrong. If the pump and gears in the front pump of the tranny didn’t give and the torque converter didn’t give and the case of the tranny didn’t give … then what gave … something had to. Then I thought of the flexplate. Today I unbolted it again and to me the flexplate looks bowed. Looking at it as installed on the crank it’s convex. I don’t know if they’re supposed to be convex but that is the direction that force would have been put on it if TQ and Tranny didn’t give any.

Is it easier to replace the flexplate with everything out of of Vette or after it’s in? No brainer … I ordered a new flex plate. Even if the new one is convex, the other one had to be stressed and with a freshly rebuilt LT-1 supplying power … I just don’t want to take the chance.

Wish me luck on installation!

 

Shoot some pictures of the flexplate and post 'em up..

 

OK ... I tried taking some pics but it was hard to get this to show up. Here's the best one. This was taken with the transmission side of Flex Plate facing up. I put a level on top of the hub. I don't know if you can see this but the distance at the two red arrows (bottom of level to FP surface), gets greater as it goes towards outer diameter. Also the distance between one side is greater than the other side. It's not a lot but I didn't think I wanted to chance reusing this Flex Plate.

 

Did you be sure that the torque converter was on the shaft on the lugs as it would be when installed? if it wasn't on the lugs, You can bolt every thing up, but it will put the torque converter in a bind on the shaft and probably won't spin. It would be worth unbolting everything and double checking if your not sure. You can destroy the pump if things arn't line up properly. Good luck on your project. Blue

 

Blue ... actually everything is apart right now. The pic of everything together was before I decided to pull it apart and check Flex Plate. I'm heading out to pick-up new FP this morning and will TRIPLE check everything as it goes back together unless someone else can think of anything else to check. Thanks everyone for tips and encouragement!

 

Good luck.

 

To the naked eye the new Flex Plate doesn't look a whole lot different ... to me the old one looked worse but again just looking didn't make me feel real confident. I decided to measure both. Same as in picture with a level across the top with both oriented exactly the same way in same spot.

The best measurement tool I had available is a feeler gauge. The distance between the bottom of my level and the ring gear was:

Old FP: 0.07" (right side), 0.105" (left side)
New FP: 0.05" on both sides

It does look like the old one was deformed some. If anyone thinks the old one is just fine and you want it ... just send me the postage for mailing it and it yours. Cheers