Jetaway vs. TH700

[Dave and Deb]

Hi all,

I'm considering doing something with the transmission in my '58 limo.  It's got the stock Jetaway in it but it leaks and I don't like the 2-3 shift.  I like the idea of a TH700 with the overdrive top gear but I'm not sure if it's able to handle the weight of a series 75.  The engine i'm using is a 1959 390.

My '60 Cadillac has the stock Jetaway and it shifts great, barely detactable through all the gears.  I've got a spare 1960 transmission, would it be a good option to get this one reconditioned and stick it in the limo or is a TH700 the way to go?

Opinions please!

Thanks,
Dave

[The Tassie Devil (Bruce Reynolds)]

I think you would be happier with the rebuilt '60 Transmission, as it will have superior gearing for the weight of the Limo than the TH700.

Bruce.

[Gary]

Dave
did you read this ?
http://www.modifiedcadillac.org/articles/Cadillac_700R4/Cadillac700R4.html

Gary

[Dave and Deb]

Thanks Gary,

Yes, I did read this a while ago and it seems to have worked in this application.  My limo is often over 3 tonnes with a load of passengers which makes me worry about the TH700 and weight.  I'm thinking of staying with the Jetaway with its low first gear and then I won't have to modify the drive shaft.

I read somewhere else that the 1960 onwards Jetaways were stronger than the earlier ones.  Is anyone able to confirm this?

Thanks,
Dave

   

[The Tassie Devil (Bruce Reynolds)]

The only thing I know is that the 1960 and onwards Hydro were smaller in actual size, and I wouldn't be surprised if the modifications made them stronger.

Bruce.

[guidematic]

 The THM 700 R4 is actually a pretty stout transmission. It's used in 3/4 ton trucks that push snow plows, and has held up remarkably well in that application.

 However the physical properties may make it quite difficult to bolt up, ie bell housing dimansions.

 Mike

[Dave and Deb]

Will a 1961 Jetaway bolt up to a '58 365 or a '59 390?

Dave

[Misfit]

Will a 1961 Jetaway bolt up to a '58 365 or a '59 390?

Dave

I would say yes, as the bellhousings are the same. A lot was done to the Jetaway from 59 to 60. The internals were made stronger and refinements were made to the valve body for smoother shifting. The case was downsized, that's why the tunnel in a '60 is smaller than a '59, but the internals of the trans are the same and will swap if needed.

I have a 61 engine and trans in my '59 which is out of the car right now. The engine is almost done, and I'll be rebuilding the trans next. Stick with the Jetaway. It was designed to move this heavy car, and give it good fuel economy.

Pics of the Jetaway rebuild, forthcoming. They say it's the hardest to do of all the automatics. GOOD !!! That means all the rest I ever do will be a cakewalk. I ain't scared. Nervous going in? Maybe. I'd hate the thought of pulling it twice, so I'll get it right the first time.

Fins

[Dave and Deb]

Thanks Fins,

I'm leaning towards staying with the Jetaway.  The idea of modifying the drive shaft doesn't excite me.  If I ended up not being happy with a TH700 I'd have to reverse all of the modifications.

Thanks,
Dave

[The Tassie Devil (Bruce Reynolds)]

............ The idea of modifying the drive shaft doesn't excite me.  If I ended up not being happy with a TH700 I'd have to reverse all of the modifications.

Modifying the Tailshaft would be the easiest part of the swap.

Bruce.

[fiftyv8]

I see Speedway Motors have similar kit just released for about 30% cheaper than the cost from Bendtsen's and Wilcap.
I wonder how good they are?
Too late for me as my order has been placed. 

[EZ]

I don't know if it will bolt up but the 700R4 will hold up just fine in your hearse.
The 700R4 also has a very steep first gear which will help get that barge moving as well.
I think the overdrive would help gas mileage on the interstate but if you mostly drive around town
it wouldn't help all that much.

[fiftyv8]

Yes, great 1st gear, but after that you would need to know what you wanted out of the O/D and have a diff ratio to work with it...