1972 Blazer 700R4 to SM465 Swap with NP205

[jfoley]

I put this in the Blazer/Jimmy section but only got one response, so I thought I would try here.

Hello, I have three questions before I start buying parts and tearing things apart.

1. I have a 1972 blazer with a 700R4 and NP205. I love the OD, but not a huge fan of autos. The other day I overheated the tranny pulling a hill bad enough it started venting. Not sure why it overheated. It was pretty cool out, the blazer has 3:73 gears with 33" tires. Turns about 2500 rpm at 75 mph. Does not have a external tranny cooler. It is a 1986 model and not wired for lock up. It still shifts through all the gears but kind of slides into gear now not hard shifting like it once was. I set the TV cable using a pressure gauge and shift points were correct. I did change the fluid and it was pretty dark. Does this tranny need to be rebuilt? I have rebuilt 700r4s before, but I'm not an expert. I don't want it to fail in the middle of no where and leave me stranded.

2. I have a SM465 complete with pedals, bellhousing, ZBar etc. out of a '71 blazer. To swap this to the NP205, all I need is the adapter for the SM465 to bolt to the transfer case, the 27 spline to 10 spline coupler, and the tall tranny tunnel?

3. I know the 700R4 is longer that the TH350 the blazer came with. Will my drive shafts be the correct length with the SM465? The transfer case shifter is in its original location.

Thank you

[Wrenchbender Ret]

You will miss that o-drive. The SM465 gear ratios are too far apart. If you have to downshift you are crawling with the engine screaming.

George

['68OrangeSunshine]

I have a '71 GMC Jimmy, 350/SM465/NP205/12-Bolt 3.73 posi/33x12.50x15 tires.
Except for the big tires, the drivetrain is Factory.
It's no Camaro, but it gets around OK.

[mongocanfly]

They're getting harder to find ,but you might look for a nv4500..I've got a couple of them and love the od...
but I'm thinking my next one will get a tr4050....mostly due to the rising prices and harder to find nv4500
My C30 has 4.10s and 31in tires...when it had the sm465, it was rpm screaming at highway mph..
The nv4500 od I swapped in made a huge difference..

[Accelo]

When they vent oil it's because the oil got hot enough to boil.
Yes, you will need to have it rebuilt.
I would confirm the transmission is a 1987 to 1992 Version.
If it's not I would find one as the newer versions solved a lot of the early teething problems.
(The GM manual, that covers the changes, is almost as thick as the GM rebuild manual)
Lots of upgrades!

We have all been spoiled by the low revving OD's. It is really difficult to go back.

Remember the SM465 is really a three speed as low doesn't count.
I never could figure the Low gear out from a marketing standpoint.
Maybe it made sense about 20 years before the 70's.
Cheers

[jfoley]

By the numbers on the tranny it is a 1986 model. I thought 1985's and above do not have to have the wiring hooked up for the look up?

[kwmech]

If it was blowing out the vent the trans is toast.

[Bigdav160]

Originally Posted by jfoley

I put this in the Blazer/Jimmy section but only got one response, so I thought I would try here.

Hello, I have three questions before I start buying parts and tearing things apart.

1. I have a 1972 blazer with a 700R4 and NP205. I love the OD, but not a huge fan of autos. The other day I overheated the tranny pulling a hill bad enough it started venting. Not sure why it overheated. It was pretty cool out, the blazer has 3:73 gears with 33" tires. Turns about 2500 rpm at 75 mph. Does not have a external tranny cooler. It is a 1986 model and not wired for lock up. It still shifts through all the gears but kind of slides into gear now not hard shifting like it once was. I set the TV cable using a pressure gauge and shift points were correct. I did change the fluid and it was pretty dark. Does this tranny need to be rebuilt? I have rebuilt 700r4s before, but I'm not an expert. I don't want it to fail in the middle of no where and leave me stranded.

2. I have a SM465 complete with pedals, bellhousing, ZBar etc. out of a '71 blazer. To swap this to the NP205, all I need is the adapter for the SM465 to bolt to the transfer case, the 27 spline to 10 spline coupler, and the tall tranny tunnel?

3. I know the 700R4 is longer that the TH350 the blazer came with. Will my drive shafts be the correct length with the SM465? The transfer case shifter is in its original location.

Thank you

The items in bold are all related. Lockup prevents the fluid from overheating. Once the fluid is scorched you need to flush it out. It has now lost it's lubrication properties.