1970 blazer 700r4/np208 conversion

[Jimman207]

Hello,
I assume this has been done before... And am looking for advice. I have a 70 blazer. I Just removed a rare 465/dana20 (leaking from everywhere and extremely heavy I might add) combo and picked up a 700r4/208 from an 89 suburban. I have the drive shafts as well as the cross member. It looks like the rear shaft is going to be short. The Dana 20 xmember is heavier but has a different drop/ bolt pattern. Wondering about angles as well. Also advice on 700r4 and the lockup. Thanks in advance.

 

[imiceman44]

Hello,
I assume this has been done before... And am looking for advice. I have a 70 blazer. I Just removed a rare 465/dana20 (leaking from everywhere and extremely heavy I might add) combo and picked up a 700r4/208 from an 89 suburban. I have the drive shafts as well as the cross member. It looks like the rear shaft is going to be short. The Dana 20 xmember is heavier but has a different drop/ bolt pattern. Wondering about angles as well. Also advice on 700r4 and the lockup. Thanks in advance.

If you want to use the crossmember from the 70 you can but you'll need the adapter from the earlier version of the 208.
I have one of those.
If you have the crossmember from the 89 you can use it and it should all bolt up.
The driveshafts will be different lengths and the rear will need a slip yoke.
As for lockup, you can use different setups.
My 84 diesel has it, I am trying to figure out what it has

 

[6872xtc]

The crossmember is going to move backwards some, which will require drilling new holes. I would suggest using the one from the '89 and then it should hold the transmission at the correct height without having to chase down other parts that may not be as easy to find as years ago.
We used an '89 crossmember under my son's '72 with a 241 case. It worked fine. Use the bolts and spacers from the '89 to hold the crossmember to the frame. They help keep the bolts tight. You may have to work on the exhaust due to the difference in the drop of the crossmember.
You can look into one of the lock up kits that are available or wire it with a vacuum switch from the early eighties factory installations, then power the circuit with a toggle switch. You can use a newer brake light switch to kick it out when you step on the pedal too, if you want.
What carburetor do you have? I really like the way that the TV cable kits from Bowtie Overdrives makes the transmission work, but the cable housing mounts aren't super sturdy. You should have mechanical throttle linkage so that you don't have to worry about using a kit with the throttle cable bracket.

 

[Jimman207]

OK,
so after more research looks like I got lucky with the 89 241 as it has the mechanical speedo output. I am running a sniper efi and I they make a bracket for it to attach the tv cable.
1. Is there a spacer(don't have) between the frame and the cross member for the (89) or just the spacer/bushing in the center(I have)? Do the bolts go to the top and bottom of the channel of the frame?
2.So in your 72 Blazer you didn't have any issues with the angle created by the slip joint of the rear driveshaft? I have been researching the SYE for the 241 and was hoping not to have to spend the time and money if it is not necessary. My goal is a daily commuter so my Blazer is not lifted.
3. I need the linkage to shift the Transfer case does anyone know if the linkage is the same for other years? There are no 89-91 Blazers or Suburbans at the local pick and pull.
Again I appreciate all the help. There is a ton of information searching in the forum archives, I just cant find some answers!

 

[imiceman44]

OK,
so after more research looks like I got lucky with the 89 241 as it has the mechanical speedo output. I am running a sniper efi and I they make a bracket for it to attach the tv cable.
1. Is there a spacer(don't have) between the frame and the cross member for the (89) or just the spacer/bushing in the center(I have)? Do the bolts go to the top and bottom of the channel of the frame?
2.So in your 72 Blazer you didn't have any issues with the angle created by the slip joint of the rear driveshaft? I have been researching the SYE for the 241 and was hoping not to have to spend the time and money if it is not necessary. My goal is a daily commuter so my Blazer is not lifted.
3. I need the linkage to shift the Transfer case does anyone know if the linkage is the same for other years? There are no 89-91 Blazers or Suburbans at the local pick and pull.
Again I appreciate all the help. There is a ton of information searching in the forum archives, I just cant find some answers!

I have a few shifter assemblies if you are looking for one

 

[6872xtc]

Well that is nice that you have the 241. I was wondering if you did with posting the year.

No spacer between the frame rail and crossmember. The '89 crossmember only bolts to the bottom flange of the frame rail, no brackets to tie to the upper flange.
I should clarify that my son has a '72 K10, and it isn't drivable yet due to ongoing body repairs. However, my '90 Jimmy used to have a 1.5" lift in the rear with the 700R4/241 combo and it was pretty good as far as not having driveshaft vibrations. It wasn't perfect, but I had swapped the rear axle into it, so I may have been off a little there. I would think that it wouldn't take much work to get yours dialed in.
The shifter for the 241 in the '89 was the same for the 208 trucks starting in '81. It bolts to the floor, so there may be a little playing with it to get things proper in yours. You can get a shifter out of a truck or blazer from '81 on up to the body change with the IFS trucks. I have saved a couple of them to experiment with in the '72, but nothing is done yet, so no help there yet. Having the proper space and contour to mount it may take a little planning and work. Or get creative and make one to look like the factory '70 unit.

 

[Jimman207]

So...
Installed 700/241 .. Almost. I am using the 89 crossmember and when jacking it into place the transfer case is hitting the body (can't go any higher) and I still need to go another almost 2 inches to get the crossmember up to the frame. Does anyone know where the center of the drive is supposed to be? What angle in relation to level it should be? Is it ok to just angle it down to fit and put spacers (2") between frame and crossmember?

 

[imiceman44]

So...
Installed 700/241View attachment 320604 .. Almost. I am using the 89 crossmember and when jacking it into place the transfer case is hitting the body (can't go any higher) and I still need to go another almost 2 inches to get the crossmember up to the frame. Does anyone know where the center of the drive is supposed to be? What angle in relation to level it should be? Is it ok to just angle it down to fit and put spacers (2") between frame and crossmember?

The biggest thing to look at is the fan against the radiator and shroud.
If the 2" drop doesn't make any problems there you'll be ok.
The front driveline might have to be modified if the angle becomes extreme if you have a lift.
I did a Chevy van 4x4 conversion and to clear the floor I had to drop the tcase 2" and everything was fine, the fan was not perfectly parallel to the radiator but didn't hit anything so I ran it

 

[6872xtc]

I forgot about that!
If I remember correctly, there is a tab set on the top of the case that we cut down on my son's truck. I believe that the tabs are for assembly of, and splitting the case halves. So we cut the top tabs down some, not completely off , just enough to be the same height as the top of the case. We then raised the floor up over it to gain the rest of the clearance. Not that you will want to do that, but maybe you can lessen the amount of drop that you need to do by trimming the tabs.

 

[Jimman207]

Ok new problem. Mounted the transfer case dropped 1.5". My only driveshaft shop in the area wants 450 for a custom rear shaft and 250 to lengthen my front. Not sure what options are available. Also oddly enough my rear driveshaft is 3" too long (86 blazer salvage) and a front is 3 inches short. (Measured at local salvage yard just havent bought it yet because I havent decided what to do.) I have read about moving the engine forward this seems like it would solve my odd problem. Also has anyone changed out the corporate 3R u joint for a conversion 1310?

 

[6872xtc]

If you don't have a lift in the suspension, I wouldn't consider moving the engine forward due to concerns about hitting the front differential into the oil pan in a bad moment. E.G: a large unforeseen dip in the road.

I don't see what is so custom about the rear shaft, take a stock one and cut it down to fit. They are straight tubed, I have several here, all straight with no steps to a different diameter.
A conversion joint should be fine, I know lots of them have been used in the past.

 

[Jimman207]

Slow progress. advice needed. Also information for the next builder.
Solving one problem seems to create another...
Moved engine forward 2 inches. Front and rear driveshafts solved. Exhaust will need to be re-routed around np241 so no added problem here. Installed 1 inch body lift for tcase clearance, which in turn required new body mount bushings- opens things up nicely underneath though. I also added a few body shims to help door alignment. (hope this doesn't bite me later when I put my top back on.) still plenty of room for radiator fan. Shift linkage finally adjusted properly.(although have not verified reverse and safety switch work- that may be a wiring job in itself to get to work even though I have correct wiring adapter). no problems with brake or power steering lines or fuel fill/vents. Oil pan not an issue as it is still far enough back for differential clearance. Installed transmission cooler lines and dipstick tube.
Installed tv cable and the mounting bracket which interferes with my rod style throttle linkage. Since the current linkage functions poorly as it was, Has anyone swapped a 73-87 pedal assembly in a 67-70 model and went to a cable style?
TCC lockup. lots of info out there that is conflicting. Here is my plan. 89 700r4. Pin A (front of tranny and outside) connected to +12 volt that provides power to the internal 4th gear pressure switch for normal operation. Pin D (rear of tranny and outside) connected to a dash mounted switch to provide +12v to bypass the internal 4th gear switch and manually provide lockup in 3rd or 4th gear.) other pins unused.

 

[diesel4me]

My '71 and '72 GM K5's and a '71 GMC K1500 all had throttle cables,not linkage--it is likely the pedal & cable from one of those 2 years would bolt up..though I have never tried it..