4BT swap questions.....

[CGarbee]

HHHMMMMM..........A crossmember should be a breeze and I like Kieth's solution for connecting the tranny to the case. The oil pan is a concern as I am doing all of this in my driveway, in the dirt, and I would really rather not have to mess with taking the pan off if I don't absolutely have to. The Frito-Lay van I found has an automatic, I would assume the TH400 but I haven't looked to be sure. I am still trying to come up with the cash to go buy the darned thing......Anyone interested in any of my stock parts let me know. Runs great, smokes a bit, probably valve seals.

Thanks, Mike

Hmm... Good question. I'll have to go look at my truck and check a few measurments... You might be able to rotate the exhuast on a rear dump turbo (what you find in a breadvan), routing the exhaust out the side and up a verticle stack (like on a M35 2.5 ton truck) and move the engine back far enough for the front edge of the sump on a rear sump Cummins 4BT to clear the differential with a 2" lift...

I know that it is possible to instal a 4BT into a M37 without knotching the oil pan using an engine with a turbo that is a mid-dump (low or high) in order to get the exhaust to clear the firewall by routing it out to the side instead of under the cab, but getting the parts may get pricey...

The engines found in the breadvans have the rear-low dump turbo that will limit how close you can put the engine to the firewall without trimming it for exhaust pipe clearance if you run the pipe down under the cab and out.

Of course, the above is moot if the TH400 is long enough that it becomes the limiting factor in how far back you can move the engine...

Knotching the oil pan isn't hard. Of course, you do have to tweak the oil pick up tube when you do (a tad more challenging) and relocate the drain plug (since it is on the corner that you have to remove to get the diff to clear)...

Removing the pan and looking at the bottom of the engine is also a great way to asses things on the bottom, especially if it is a takeout engine...

I did my first conversion in the dirt of the backyard, truck is going very strong nine years later...

Oh yes: to answer the other portion of your question... You are going to have to add some lift to the front even with the oil pan trim... I run 2" solid steel blocks welded to the axle (just makes the axle spring perch a bit taller) as do the folks running the old MARS Hercules conversions as are (I am very sure) the trucks that Charles at M-Series Rebuild is converting.

I know some folks have heartburn over having blocks in on the front axle and are doing spring work to avoid them, but I like the ride with one extra full length spring added to the pack combined with the blocks...

Good luck.

[slozukimc]

Hmm... Good question. I'll have to go look at my truck and check a few measurments... You might be able to rotate the exhuast on a rear dump turbo (what you find in a breadvan), routing the exhaust out the side and up a verticle stack (like on a M35 2.5 ton truck) and move the engine back far enough for the front edge of the sump on a rear sump Cummins 4BT to clear the differential with a 2" lift...

I know that it is possible to instal a 4BT into a M37 without knotching the oil pan using an engine with a turbo that is a mid-dump (low or high) in order to get the exhaust to clear the firewall by routing it out to the side instead of under the cab, but getting the parts may get pricey...

The engines found in the breadvans have the rear-low dump turbo that will limit how close you can put the engine to the firewall without trimming it for exhaust pipe clearance if you run the pipe down under the cab and out.

Of course, the above is moot if the TH400 is long enough that it becomes the limiting factor in how far back you can move the engine...

Knotching the oil pan isn't hard. Of course, you do have to tweak the oil pick up tube when you do (a tad more challenging) and relocate the drain plug (since it is on the corner that you have to remove to get the diff to clear)...

Removing the pan and looking at the bottom of the engine is also a great way to asses things on the bottom, especially if it is a takeout engine...

I did my first conversion in the dirt of the backyard, truck is going very strong nine years later...

Oh yes: to answer the other portion of your question... You are going to have to add some lift to the front even with the oil pan trim... I run 2" solid steel blocks welded to the axle (just makes the axle spring perch a bit taller) as do the folks running the old MARS Hercules conversions as are (I am very sure) the trucks that Charles at M-Series Rebuild is converting.

I know some folks have heartburn over having blocks in on the front axle and are doing spring work to avoid them, but I like the ride with one extra full length spring added to the pack combined with the blocks...

Good luck.

SOunds like I will likely be notching the oil pan. Can't be that hard really. Any pics I can look at to see how it should be done?

I see no issue with a 2 inch block on the front as long as it is welded solid to the perch in essence making a taller perch as that can't go anywhere and the extra leaf will compensate for any added spring wrap.

THis is really alot more than I originally intended for a swap but it will be well worth the while and probably the last work truck I will ever have to buy once it is finished.

Thanks again for all of the tips!!

Mike

[CGarbee]

SOunds like I will likely be notching the oil pan. Can't be that hard really. Any pics I can look at to see how it should be done?

I see no issue with a 2 inch block on the front as long as it is welded solid to the perch in essence making a taller perch as that can't go anywhere and the extra leaf will compensate for any added spring wrap.

THis is really alot more than I originally intended for a swap but it will be well worth the while and probably the last work truck I will ever have to buy once it is finished.

Thanks again for all of the tips!!

Mike

Photos of my oil pan on my computer waiting for me to finish up the page on my website that they will go on... Look for it in the next few days (I'll post a note when I put them up).

Your thinking is correct (IMHO) about the axle blocks...

[Charles Talbert]

Changes to our set up

SOunds like I will likely be notching the oil pan. Can't be that hard really. Any pics I can look at to see how it should be done?

I see no issue with a 2 inch block on the front as long as it is welded solid to the perch in essence making a taller perch as that can't go anywhere and the extra leaf will compensate for any added spring wrap.

THis is really alot more than I originally intended for a swap but it will be well worth the while and probably the last work truck I will ever have to buy once it is finished.

Thanks again for all of the tips!!

Mike

We stopped using 2" lift blocks on our conversions several years ago. I never did weld the blocks to the perch, that's running on the edge of destroying integrity in my opinion, it also limits your ability to do a perfect axle housing alignment. You are better off to center drill the blocks & fabricate 5/8" dowel pins so perfect alignment is possible. To accomplish this, center drill the block to a 9/16" bore all the way through, enlarge that bore to 5/8" on 1 side of the block to a depth of 1/2". The dowel bore on the spring perch center is 5/8". This way the block is center doweled to the perch & the center spring pack pin fits the centered 9/16" dowel bore on top of the block. This method is perfectly aligned & fool proof. We have gone to a 1" thick lift block with 2 leafs added to the spring packs. Depending on what the truck will be used for & the weight it will carry, we may use more than 2 additional leafs & no lift block. This method makes the power steering geometry better & much easier to work with. If you modify the oil pan, the pick up tube also has to be modified as it is routed on the right side of the pan where clearance issues come into play with the differential. Do a good job on the tube mod if you go this route, a failed pick up tube = a destroyed engine in most cases.

[slozukimc]

We stopped using 2" lift blocks on our conversions several years ago. I never did weld the blocks to the perch, that's running on the edge of destroying integrity in my opinion, it also limits your ability to do a perfect axle housing alignment. You are better off to center drill the blocks & fabricate 5/8" dowel pins so perfect alignment is possible. To accomplish this, center drill the block to a 9/16" bore all the way through, enlarge that bore to 5/8" on 1 side of the block to a depth of 1/2". The dowel bore on the spring perch center is 5/8". This way the block is center doweled to the perch & the center spring pack pin fits the centered 9/16" dowel bore on top of the block. This method is perfectly aligned & fool proof. We have gone to a 1" thick lift block with 2 leafs added to the spring packs. Depending on what the truck will be used for & the weight it will carry, we may use more than 2 additional leafs & no lift block. This method makes the power steering geometry better & much easier to work with. If you modify the oil pan, the pick up tube also has to be modified as it is routed on the right side of the pan where clearance issues come into play with the differential. Do a good job on the tube mod if you go this route, a failed pick up tube = a destroyed engine in most cases.

Charles,
I agree with you.....I would never use a block of any sort without a proper centering pin. I was just thinking it would be good to add the weld as well as the pin to prevent the possibility of the block ever moving in any direction. I will likely add the 2 leaves and 1 inch block as I really don't like blocks much either and an extra spring can't hurt with the added weight of the Cummins.
You say IF I go the route of notching the pan......Do I have a choice? I would prefer not to.

Thanks, Mike

[CGarbee]

Charles: Thanks for the update on your current method of clearancing the front end... I had remembered your trucks having the taller block in the past, but was not aware that you had changed things since the last time I crawled under one of your conversions. :)

My personal truck has the alignment pin in the 2" block just as you describe it...

I'm away from the home computer that has the correct photos on it (visiting with familly and friends for Thanksgiving), but I will update my website on Sunday night with photos of my trimmed pan.

Happy Thanksgiving.

[Chris Davis]

Overdrive...

Mike,

If you're going to use an automatic transmission, the TH400 could be swapped for a 700R4 giving you an overdrive. I'm in the process of making this same change over on our family Suburban.

From Wiki:

"The Hydramatic 700R4 was introduced in 1982 for use in Chevrolet/GMC vehicles.

The gearing for the 700 is (commonly rounded off to 3.06, 1.63, 1.00, 0.70, and 2.29):

First - 3.059
Second - 1.625
Third - 1.000
Fourth - 0.696
Reverse - 2.294

Initially, the 700R4 was not considered a strong transmission, since the torque of a 350 in³ V8 would lead to transmission failure. The original version of the transmission had a 27 spline input shaft - this was but one of many possible and common failure points with the early transmission. However, the design was continually refined and upgraded, and in 1987, the 700 was used behind a 350 small block V8 (from IROC-Z Camaros to pickup trucks).

From the engine/trans mating surface to the crossmember mount bolt is 22-1/2 inches (570 mm), and engine/trans surface to output shaft housing mating surface is 23-3/8 inches (594 mm) overall, with the tailshaft housing typically measuring 7-5/8 inches (194 mm)."

I understand the major upgrade was in 1987, so find a 1987 or newer 700R4 and you should have a reliable, bolt on, overdrive tranny. I paid a little over $500 for a freshly rebuilt one. Overall length looks like 31" with tail shaft. I don't know if that will fit without moving the transfer case, but it's worth checking.

Chris Davis
Centerville, UT
'45 WC-51

[Charles Talbert]

Engine tilt

Charles,
I agree with you.....I would never use a block of any sort without a proper centering pin. I was just thinking it would be good to add the weld as well as the pin to prevent the possibility of the block ever moving in any direction. I will likely add the 2 leaves and 1 inch block as I really don't like blocks much either and an extra spring can't hurt with the added weight of the Cummins.
You say IF I go the route of notching the pan......Do I have a choice? I would prefer not to.

Thanks, Mike

We have changed things in a number of ways since the 1st one to simplify & make our installations better & easier. There are 2 main reasons that I have chosen to stay away from welding on the axle tubes, #1 the heat will draw it in some way slightly, #2 it would be a chore to get the blocks off if someone wanted to go back original. We also use heavier than original spring u-bolts that can take extra torque, it holds everything in place very well. We have made every effort to make our set up as easy to undo as it is to do, this effort has included not having to undo modifications that were made so a diesel could be installed. I see no reason personally why I would ever want to convert back to original, but you wouldn't believe the people who inquire about the Cummins conversion who want to know if frame mods are required & if it could be easily converted back. We have strived to do it with that in mind for that reason. Tilting the engine such as to pull the pan away from the differential is an alternative to pan mods or at least holding mods to a minimum. We use a combination of tilt & pan mod in our set up. The tilt is designed into the engine mount brackets. Makes several issues come together better & holds necessary pan mods to a minimum. Not at all sure of your situation as using an automatic transmission may well limit the tilt angle you could use.

[slozukimc]

Mike,

If you're going to use an automatic transmission, the TH400 could be swapped for a 700R4 giving you an overdrive. I'm in the process of making this same change over on our family Suburban.

From Wiki:

"The Hydramatic 700R4 was introduced in 1982 for use in Chevrolet/GMC vehicles.

The gearing for the 700 is (commonly rounded off to 3.06, 1.63, 1.00, 0.70, and 2.29):

First - 3.059
Second - 1.625
Third - 1.000
Fourth - 0.696
Reverse - 2.294

Initially, the 700R4 was not considered a strong transmission, since the torque of a 350 in³ V8 would lead to transmission failure. The original version of the transmission had a 27 spline input shaft - this was but one of many possible and common failure points with the early transmission. However, the design was continually refined and upgraded, and in 1987, the 700 was used behind a 350 small block V8 (from IROC-Z Camaros to pickup trucks).

From the engine/trans mating surface to the crossmember mount bolt is 22-1/2 inches (570 mm), and engine/trans surface to output shaft housing mating surface is 23-3/8 inches (594 mm) overall, with the tailshaft housing typically measuring 7-5/8 inches (194 mm)."

I understand the major upgrade was in 1987, so find a 1987 or newer 700R4 and you should have a reliable, bolt on, overdrive tranny. I paid a little over $500 for a freshly rebuilt one. Overall length looks like 31" with tail shaft. I don't know if that will fit without moving the transfer case, but it's worth checking.

Chris Davis
Centerville, UT
'45 WC-51

I just can't believe an R4 would last long at all behind the Cummins. If the TH400 is questionable the R4 is certainly out.

Mike

[slozukimc]

Pics Link

I just can't believe an R4 would last long at all behind the Cummins. If the TH400 is questionable the R4 is certainly out.

Mike

Here are a few pics in this link of the ole girl......She's a young'n really bein a 68....

http://www.powerwagonadvertiser.com/...32&postcount=4

Mike

[Chris Davis]

'68 is young for an M37...

[QUOTE=slozukimc;30969]Here are a few pics in this link of the ole girl......She's a young'n really bein a 68....

Man, 1951 to 1968 is a pretty good production run!

I think mine was a '53.


Not to beat a dead horse on the 700R4, but the latter ones worked fine in the diesel powered suburbans... and that's a heavier vehicle. Granted the 6.2/6.5 GM motor isn't a Cummins, but the HP and torque numbers are about the same for that V8 as the 4 cylinder 4BT.

Builders are certifying the 700R's for over 400 hp / ft lbs Checkout:
http://www.bowtieoverdrives.com

I think you'll need some sort of overdrive... even with the 4.89 gearing. I know my 318 equipped truck turned around 3400 rpms to go 60mph with the stock 5.83 differential gearing. With the 4.89 gearing you'll get below 3000 rpm, but not by much.

It sounds like a fun project though. I liked my 318 V8 equipped M37, but I think the Cummins is really the way to go for a re-power.

Chris

[JimmieD]

Chris, that is one of the great pictures of all time and simply made my day!!! Thankyou!

Interesting the 6.2/6.5 GM only puts out the power of a stock 3.9 Cummins! Can I snicker in my cuff...?

I too believe the 700R4 might work okay in a lighter vehicle. One would certainly want a whole bunch of torque converter, read that as $$$$, but nonetheless the tranny should be able to handle it with a performance build and premium clutches, bands and valve body. I don't think they had enough converter or good enough clutches/bands in most of the 4BT/TH400 stepvans to transfer diesel torque to a rolling tugboat, therefore lots of tranny failures. Mine had a Pontiac TH400 but the vlave body's shifts were like a Buick or Cadillac: DON'T DISTURB THE PASSENGERS!!! That and even using it in a potential load application of 17,000 lbs GVWR there was NO TRANSMISSION COOLER! Are you guys kidding me? A B&M smart-cooler would really help. So would brains in the Engineering Dept.

Lastly, all speed calculations need to be made in light of a diesel's rpm max of 2,500 rpm's, unless the Bosch P/N 1 464 650 366 3,200 rpm governor spring is used. There's wilder springs available but this one usually gives very good results in 4BT and 6BT applications.

[slozukimc]

Chris, that is one of the great pictures of all time and simply made my day!!! Thankyou!

Interesting the 6.2/6.5 GM only puts out the power of a stock 3.9 Cummins! Can I snicker in my cuff...?

I too believe the 700R4 might work okay in a lighter vehicle. One would certainly want a whole bunch of torque converter, read that as $$$$, but nonetheless the tranny should be able to handle it with a performance build and premium clutches, bands and valve body. I don't think they had enough converter or good enough clutches/bands in most of the 4BT/TH400 stepvans to transfer diesel torque to a rolling tugboat, therefore lots of tranny failures. Mine had a Pontiac TH400 but the vlave body's shifts were like a Buick or Cadillac: DON'T DISTURB THE PASSENGERS!!! That and even using it in a potential load application of 17,000 lbs GVWR there was NO TRANSMISSION COOLER! Are you guys kidding me? A B&M smart-cooler would really help. So would brains in the Engineering Dept.

Lastly, all speed calculations need to be made in light of a diesel's rpm max of 2,500 rpm's, unless the Bosch P/N 1 464 650 366 3,200 rpm governor spring is used. There's wilder springs available but this one usually gives very good results in 4BT and 6BT applications.

Interesting info on the spring and RPM's.....Seems that would make one heck of a difference in the M37. I'll keep a note of that part number. I can see the TH400 holding up to the torque WITH a proper cooler and firm shifts, I still think the R4 would fail with the weight of the M37(5700 empty) pulling a trailer in overdrive. I have used R4's for towing befind 4.3V6's and every other Chebbie motor on up to a 454 and was never comfortable with leaving it in overdrive to tow a heavy load. Maybe a high dollar build would be OK but I am not willing to spend the money on an auto buildup when the same money could be spent on the NV4500. I have very limited funds(I know you all say not to do this if you can't afford it......I say neccessity is the mother of invention and I NEED an efficient all purpose truck so I will invent a way to get it done if need be.) and that is why I am leaning toward the WORKING TH400 already bolted to the 4BT. I have to look at it all when I get the Frito truck home so I can see if I can get away with tilting the engine to partially miss the diff without disturbing the function of the automatic....If not I will be looking for a 5 speed setup or an adapter to bolt to the SM420.
Put up another post last night....I have a centered rear diff here so I am now seriously looking at swapping in the NP205 as well.

Thanks again Guys,
Mike

[JimmieD]

It's my understanding that the SM465 bellhousing will bolt up directly to the adapter plate used with Cummins/GM TH400. Don't know about 420 but you can probably cross reference SM465/SM420 for fitment? Therefore stepvan's adapter plate might work fine.

There's a GM NV4500 and the bellhousing for it bolts directly to stepvan's Cummins adapter plate. Compared to the Dodge NV 4500 the GM NV4500 flywheel is smaller so only smaller sizes of clutch are available and the input shaft is smaller in diameter. Still, this would save a few bucks up front, but pricey indeed to swap to Dodge trans later!

It would not be as expensive or complicated to swap your installed TH400 for the GM NV4500 or SM465 once funds become available. Not saying it's a piece of cake but a bridge you can cross when you drive to it ha haha!

[slozukimc]

It's my understanding that the SM465 bellhousing will bolt up directly to the adapter plate used with Cummins/GM TH400. Don't know about 420 but you can probably cross reference SM465/SM420 for fitment? Therefore stepvan's adapter plate might work fine.

There's a GM NV4500 and the bellhousing for it bolts directly to stepvan's Cummins adapter plate. Compared to the Dodge NV 4500 the GM NV4500 flywheel is smaller so only smaller sizes of clutch are available and the input shaft is smaller in diameter. Still, this would save a few bucks up front, but pricey indeed to swap to Dodge trans later!

It would not be as expensive or complicated to swap your installed TH400 for the GM NV4500 or SM465 once funds become available. Not saying it's a piece of cake but a bridge you can cross when you drive to it ha haha!

WOW!! All this info in such a short time is something else!! Simply amazing!

Pretty much my thinking on driving to that bridge. I will make more upgrades later on if I have to and can afford to. I am also considering just driving the Frito van(after chopping off the back to make a ramp truck) and taking more time with getting the M37 ready for the swap. This will allow me time to collect all of the parts to do it right the first time.

Mike