m135 underpowered

TURBO6X6 said:

Hi, I am a new member, not sure if your still looking at the mods for your truck. Anyway I have a 1955 M135, I got a 1991 GMC school bus with a 366BBC and an Allison 4spd automatic tranny. I transfered the engine, tranny, all the front end/dash wiring, power steering, power brake master cylinder, added propane tank and two turbo chargers. I now have about 450 lb-ft of torque and around 350 HP at 10lbs boost, according to turbo chart. I left the stock transferr case, and single speed also.. Anyway it works very well, i use it for hauling wood, water and landscaping stuff. I would like to convert the transferr case to a two speed but not sure how this is done. I have another same M135 and a 7.3lt powerstroke of which I want to install. The allison auto tranny and any engine will work, just would be nice to have low range in the tranfer case for those over weight had wood days...

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If you are going to do a two speed set up on the transfer case, you will have to do one of two things: (1) put an auxiliary gear box between the transmission and the transfer case that will give you the gearing options you are after. Or, (2) Find a way to put a typical type reverse cut ring and pinion in the front axle and put your two speed transfer case in.

If you are going to go through the trouble and expense, you are probably best to put something like a Gear Vendor Overdrive/Underdrive between the transmission and the transfer case as option (1) would imply. The reasoning is that many have searched for suitable gearing options on these axles with less than satisfactory results, and the transfer cases on these truck are uniquely setup to reverse the direction of the rotation of the front drive shaft to allow the ring and pinions to be interchanged between either rear differential or the front differential (in other words, all three axles have the same ring and pinion, not just the same ratios). Also, the transfer case also functions as a reduction box using a ratio of 1.16:1, unlike a normal 4x4 that uses a 1:1 ratio for high range.

JasonS said:

This is a 1930s technology engine. 2HP / cubic inch is very difficult and expensive. Anybody who says "it can be done with relative ease" is lying to you.

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Please research your comments before speaking or typing. You have been asked to do so several times throughout this forum.

And I believe I cited my source on the comment in which you replied. The GMC 302 has held (and may still hold) speed records on the salt flats in a Ford coupe.

Thanks Tplane, not sure I follow the axle explanation. I never new about the under drive thing, thanks for that. My transferr case is a single speed 1:1 ratio where the original tranny did the reduction. I replaced it with a normal tranny, auto 4spd. The transfer case is divorced from the tranny with a very short driveshaft. I heard there is a mod for this transfer case that would make it a two spd, with the pto shifter and gear somehow.. Pinion ratios are 6.1:1 I think..

TURBO6X6 said:

Thanks Tplane, not sure I follow the axle explanation. I never new about the under drive thing, thanks for that. My transferr case is a single speed 1:1 ratio where the original tranny did the reduction. I replaced it with a normal tranny, auto 4spd. The transfer case is divorced from the tranny with a very short driveshaft. I heard there is a mod for this transfer case that would make it a two spd, with the pto shifter and gear somehow.. Pinion ratios are 6.1:1 I think..

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Axle ratios should be 6.17:1. Transfer case should be 1.16:1. The original Hydro-Matic transmission should have had low rage on the right and high range on the left with reverse, "hilly," and "level" on either range and neutral at the top of the "half-H" (an "H" pattern with the top of the H cut off).

In most of your for wheel drives, the ring and pinion gears in the front axle are cut as almost a mirror image to the ring and pinion in the rear axle. What this does is allow the drive shafts to spin in the same direction (if you look from the rear axle to the front axle while it's in drive, both shafts are spinning in the same direction), but since the front pinion faces the rear pinion, they have to reverse the gears in the differential... If they didn't do this, the front tires would try to go backwards when the truck is in drive.

On the M135s and 211s, they reverse the rotation in the transfer case for the front drive shaft instead of the front axles. This saves money on tooling and parts because you can literally pull the gears out of your rear end and put them in the front axle. If you were top try the same thing on a modern for wheel drive, you'd end up with the front and rear tires pulling in opposite directions all the time... which is the same thing that will happen on your suede if you just swap in a modern divorced transfer case into it without doing something about the front gears.

This is why I suggested a gear box between the transmission and the transfer case... It retains the stock gear reversal.

However, if by two speed, you are referring to high and low range, you can have the modern transfer case in front of the deuce's case and achieve high and low range... But on the end, you just won't have anything connected to the front output of the modern case, and you still have an all wheel drive truck (front axle only engages when the rear tandems loose 6% traction.... Not sure how it detects this though)

Tplane37 said:

Please research your comments before speaking or typing. You have been asked to do so several times throughout this forum.

And I believe I cited my source on the comment in which you replied. The GMC 302 has held (and may still hold) speed records on the salt flats in a Ford coupe.

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I know of one 302 powered car which ran this fast and it blew the crank in the process. It takes a LOT of money to go this fast since you have to re-engineer the engine; you aren't exactly starting with a race engine. Nobody has been able to defeat poor engineering without spending lots of money and time. The 302 is based on the 270 which was released in 1939; ergo, it is 1930s technology. An objective comparison to something just 10 years newer than the GMC (ie. the Reo gold comet series) and you will realize just how archaic and "cost engineered" the GMC really is. Maybe, you need to put "relative ease" into a meaningful context; say compared to an LS1, BBC, SBC, 5.9 cummins, etc.

I have owned four or five 302s in my lifetime. One powered my daily driver in all weather for 5 years. How about you?

M135s are not underpowered. I think the op needed to rebuild his engine. Mine is 030 over and runs like a scalded dog. I run mine at 55 mph all the time, and it will flat tow another deuce at 45 mph.

NDT said:

M135s are not underpowered. I think the op needed to rebuild his engine. Mine is 030 over and runs like a scalded dog. I run mine at 55 mph all the time, and it will flat tow another deuce at 45 mph.

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I'd like to see this. I'm not calling you out or anything but when I had to flat tow an A2 with an A2 we averaged 37mph over a 13 hour (450 mile) trip. The fuel was probably bad I admit.

How about the 366 gas, if you already have the tranny

The 366 BBC I used in my truck works good, steel crank is stock, but originally I found in was still low on power when i was hauling, Of course I do not have low range any more, Sure would be nice. I think I should have installed a higher stall torque converter with the Allison, that is still on my list..By adding the turbochargers was like night and day for power, actually torque. Was well worth it, I think.