TH350 to Th400 gearbox swap

[uncle albert]

Ok, due to corona virus lock down,i am unable to ride my motorbikes, drive my classic cars,and more importantly go to the pub......so I have decided to re-commission my 68 corvette. Its been laid up for almost 10 years after having a gearbox problem. When I got it, " from a friend" I knew it had the wrong engine fitted,but assumed it had the 400 box in it...{ it didn't} To cut a very long story short.....I bought a s/h 400 box for it years ago and now realise the box in the car is a 350...…….. yep the wife laughed as well. !!!!! So my question is have any of you ,got experience of putting a 400,in where the 350 was. I believe the yoke going into the box is different,but interchangeable...and the tacho set up is different....but is the prop the same..and more impotantly the mounting points.... I have asked a couple of people who I thought should know...……..but...well.... you can quess… So answers on a post card please...….

 

[Oneball]

The out put yokes are different and not interchangeable as the TH400 is bigger with more splines 32 v 27). I’ve no experience of doing the swap but the TH400 is longer so I’d imagine you’ll need a new propshaft and rear mounting.

 

[uncle albert]

Hi,thanks for the reply. I've been told the 400 yoke will bolt up to my prop.?? I knew about the different amount of splines, but was told just to use the 400 yoke... I've also been told the boxes are the same length !!!!!!! I will try measuring them later..... So conflicting views.. Who I really need to hear from,is someone who has actually done this job....there must be someone on here..……..cheers again..

 

[Oneball]

I think they both use 1310 Spicer UJs so will bolt up to the prop, I think, that’s an easy width to measure. As is the length. Both boxes were fitted to C3s in the same period so it’d make sense if they were the same length.

Is yours a big block car?

 

[uncle albert]

Hi, no..it started life as a 327,and would have had the 400 box behind it. Which is what I thought it still had...….it now has a 350 clk engine fitted. with a 350 box....which relates to a Z28 camaro….BUT it has just occurred to me, {light bulb moment} !!!!!!!!! If it originally had the 400 box...it must be possible to refit it with a 400 box and reverse any of the mods...….!!!! Watch this space.

 

[uncle albert]

I think they both use 1310 Spicer UJs so will bolt up to the prop, I think, that’s an easy width to measure. As is the length. Both boxes were fitted to C3s in the same period so it’d make sense if they were the same length.

Is yours a big block car?

I think they both use 1310 Spicer UJs so will bolt up to the prop, I think, that’s an easy width to measure. As is the length. Both boxes were fitted to C3s in the same period so it’d make sense if they were the same length.

Is yours a big block car?

Funny story for you....just looked at car to see about taking box out....crossmember is welded in...…...So was originally a manual car....which i've been told means the engine has to come out as well or at least moved forward. !!!!!!!!! Any ideas.???

 

[Oneball]

I guess it’s engine out time then.

 

[uncle albert]

I guess it’s engine out time then.

Well,...….i'm not keen on the idea.....do you know if its possible to separate the engine /gearbox,then raise the engine a little and move it forward,and then drop the gearbox down ???? I think its clutching at straws time...might even be sell the car time.....

 

[Oneball]

I’ve been told it’s possible to remove a manual gearbox by itself but not sure about auto with a fixed crossmember.

If you’ve not got a four post lift I reckon it’s easier to pull the engine and box as a whole than struggle under the car trying to get the box out by itself.

 

[uncle albert]

I've now spoken to several corvette specialists...the common theme is ...if my crossmember is welded in,the only way to get the auto box out is to lift the engine...as well. One suggested splitting the gearbox first,but still the engine has to come out.........One said I could cut the crossmember and weld it back on...……….
I don't have a four post lift....or a large garage.....but I can borrow an engine hoist and do the job in my front garden...not keen though....but thanks for your input. I'll have a long think about it this weekend....