Hello to all: I have a unusual conversion that uses a TH 425 transmission. This unit sits behind a highly modifed 350 motor that is mounted mid way in a old(1969) Porsche 911. In keeping with a long family history of Oldsmobile's and my first 'hot rod' a 1956- 88 , my current license tag on this ride is ROCKET. Is there anyone who can help me solve a problem with the TH 425 ? Thanks, Ken N.

 

If you are having difficulty with your TH 425 you should be able to get any decent transmission shop to repair it for you. A TH 425 is a variant of the TH 400. These transmissions are about the best automatic transmission built. If you have specific questions let us know and we will try to help; however, unless you have specialty tools and a garage that is CLEAN, you will probably have to have it diagnosed and repaired by a professional.

 

Appreciate your suggestion. Here's whats going on. Anytime that it's driven, transmission fluid leaks from the vent valve, initial I thought it had been overfilled. After draining it and measuring what was left, about 4 quarts, I ruled out the overfilling. If there is anything that I can do to check things out please let me know. Thanks, Ken N.

 

It is a vent tube. There is no valve on it.

Here are 3 possible causes: To much ATF, loose or defective filter, and turning it at higher than normal RPM.

Norm

 

When you drained it did you change the filter?

 

Thanks to all for replies. I will change the filter. The vent is moving freely. Do you have any recommendations as to the ATF? Thanks, Ken

 

Very cool. This has always been one of my favorite swaps. Back when I was a kid (before the glaciers melted) I had a copy of the Petersen's Engine Swaps book (Issue 3, I think). I about wore out the pages that described the swap of a Toro drivetrain into a Porsche 912 (the low-rent 911 with a four cyl engine). The best part was how he covered the engine in the back seat. He bought a bunch of old, square-cornered suitcases, bolted them together, then cut out the bottom to make an engine cover. Very cool.

That same issue also had the swap of a Corvair drivetrain into a BMW Isetta, but that's the topic of a different thread.

Welcome.

 

You should use Dexron, Mercon Type III or better. If you were rebuilding the transmission completely you could put type F into it for more positive shifts, but it is best to keep the stock fluid in there since you will only be changing the filter.

 

cliffdweller, post some pictures. I for one would like to see this conversion

 

I think as a 'Newbie' I can only write text messages and not add photo's. That other Porsche/GM TH 425 conversion has a 500 CI Cad motor and is more of a show car than mine.
Your 57' Super 88/455 is one of my favorite years for Old's. Maybe it's my age but from 55 to 57 are the three years I relate to best. Ken

 

One more post and your in and can post pictures. Can't wait to see the conversion

 

Welcome to our site and I second the request for pictures.

 

Thanks for making me feel welcome. I need a little warmer weather to open up the garage and get some photo's from under the car so you can see the hookup. But here are a few that I have saved.

 

Wow! like the second shot. Those tailpipes tell a secret for anyone observant enough.

 

Cool looking, can we see a shot of the engine bay. I agree with Dan those tail pips are a tad larger then the flat four had

 

Very cool.

 

Interesting that your from Massachusetts and have a Porche with a licence plate "Rocket". Didn't the Rocket (aka Roger Clemence) sp? have a porche too in his Red Sox days? I believe his licence plate said something like 3SIyoung. He would have wanted your plate.

 

Who'd a thought That's cool

 

It is taking me longer to resize the image than I expected. Hope this works. Under all the chrome is a 350 out to 383 with all the good stuff. Ken

 

 

The local minor league team in this area are the Brockton Rox, they ran a promotion a couple of years ago that offered the real Rocket my car for a day. He didn't bite but I did score a dozen tickets to opening day. Ken

 

That cooling system modification is interesting. I see you have modified the thermostat housing to fit a radiator cap on it. I guess you add coolant there? Where is the radiator and how is the rest of the system plumbed?

 

If you look at the earlier post of the front of the car you will see there is a radiator in/below the bumper. This is backed by the transmission cooler and both have fans to draw the air. The hood is modifed so that the radiators are actually open on the backside to keep air flowing. The plumbing runs thru the center hump, radiator and transmission lines. The raditor connects to the std. water pump. In addition to this I have built a bulkhead into the 'trunk' with two 9" electric fans that vent thru the 'whale tale'. The small scoops behind the doors in the rear fenders are also vented directly into the engine compartment.
All this is seperated from the cockpit with a full firewall with a window.

 

Very cteative design. Must have been fun and hair pulling to work all of the details out and still come out with a nice looking uncluttered install. Good work

 

Chev in a Porsche is nothing new. I've probably seen 15 or 20 since the early eighties. Not much different than a Chev in a VW, which was relatively common.

Norm

 

Norm: Your in the orginal 'hotbed' of Porsche/Chevy conversions. Initally , they started with the 914's. I have one of these that at one time was 'the world's(probably not a big world') fastest Porsche. I ran a 383 stroker with at T-04E stage one turbo. This car turned an 8.68 at 168 at NE Dragway in N.H. The turbo is gone, so is the sroker. It now has a 355 and NOS so it still quick but I am getting older. The 911 is usually a rear mounted V6/V8/Subaru. There maybe others but I only know of 2 mid- engine set ups. One is in your area with a 500 C.I. Caddy and the other is mine.
The great thing about the TH 425 is that it is really rugged and handles the increased load with ease. Ken

 

with a plate like that on a Porsche most people probably think it's a football player driving it....but a motorhead could tell pretty easily that there's not a flat 6 breathing under that decklid...after the tire smoke cleared out.....

 

Where I am, has nothing to do with Oldsmobiles.

Yes: A Chev engine that has nothing to do with Oldsmobiles.

On an Oldsmobile site, a 355 is an Olds engine.

On a Buick site, a 355 is a Buick engine.

On a Pontiac site, a 355 is a Pontiac engine.

Now comes the important part: On a Chev site, a 355 is a Chev engine. On any of the above sites, it is always identified as a Chev engine. Your attempt to pass your Chev engine off as an Oldsmobile, is an insult to the Olds community.

Having said that: We are eager to hear about your Oldsmobiles(s).

Norm