637 V8 gas engine

[BillT]

Originally Posted by POWERSTROKE

one had a Working '5th, from high 3rd you went to low 4th, low 5th, shifted the axle to hi, and 4th, then 5th in high.

That sounds like a Clark 5-Speed Trans. I had one in the '62 6500 and in my '67 7500. It liked it as I could go through 9 Gears and only have to downshift the Rear twice.

[65GMCKV4000]

It is a 62 4000 with a 305 V6, wide fenders and very large front end. Was a brush rig for the local fire department here where I live. Has 15K original miles. 1000 gal water tank with Wisconsin engine driven water pump. The truck was originally a 2 wheel drive, converted at the dealer to 4x4.
I also have a 65 KV4000 with wide fenders and the same front end and transfer case.

[LEWISMATKIN]

Originally Posted by BillT

The Crankshaft can't be that weak, lol.

The '71 9500 I used to drive had a 637 V-8 Gas with a 10-Speed Road Ranger behind it. I was the 2nd driver of the truck. The first driver was old school 5-Speed, 2-Speed and never learned to shift the RR properly. He did fine Up-Shifting, but never learned and probably never even wanted to learn how to Downshift a Non-Synchro Trans. I rode with him a few times and could not believe how he would lug the heck out of it, which we all know wreaks havoc on a Crankshaft. I would always joke saying that the Crankshaft is going to end up on the front seat someday.

Anyway, I left the company after about 3 years. Then one day saw the truck when it was about 15 years old, for sale as is by another owner. And guess where the Crankshaft was?

We would haul some heavy loads with it. Probably up to 48 or 50,000 on a 46,000 GVW truck. It's amazing how long that Crank actually lasted.

Very true, very true. However, I was speaking from a repair standpoint, not a longevity standpoint. Dad's shop replaced a number of crankshafts in the Toro-flows while a GMC dealer for Georgia Highway express. They would not had to have been replaced if they had been Tocco-hardened. I have seen only 1 637, and it was in a steel tilt cab. The other 637 I only know from speaking to the owner at the time. When I look at the repairability of an engine, I look for things such as the design flaws, like the type of hardening on these shafts. I can't for my life understand why these crankshafts (gas & T-F 637 and T-F 478's) weren't tocco hardened.

[LEWISMATKIN]

Originally Posted by BobBray

Yes, those were the Steel Tilts, not the Crackerbox aluminum tilt cabs.

Bob, the D-cab was the aluminum cab (crackerbox).

[LEWISMATKIN]

Originally Posted by 65GMCKV4000

Yes I think it is.

Road rangers of that era would more than likely been the RT-610 or RT-613 series transmission. These trannys are rated at 600 ft lbs of torque and were found behind many gas-engine trucks of all major brands of the day. This one looks like the RT600 series of Fuller transmission.

[2-Ton]

Anybody know where to get a fuel pump for one?
Mine went out a few years ago and I ended up covering the hole with a plate and mounted an electric one on the frame.

Napa books all said discontinued.

[POWERSTROKE]

Originally Posted by BillT

That sounds like a Clark 5-Speed Trans. I had one in the '62 6500 and in my '67 7500. It liked it as I could go through 9 Gears and only have to downshift the Rear twice.

Yes! I'm sure you are correct about them being a Clark. Dad took the Whole Darn Family sometimes, Mom rode Shotgun, my Sister and I traded between the sleeper bunk and sitting on the doghouse. The truck tended to jump out of 5th, and got "Tarp Strapped" into 5th so rolling hilly roads were driven like a roller coaster, just shifting the 2-speed.

Too bad GMC didn't Tocco harden the 478 & 637 crankshafts. International Harvester Tocco hardened crankshafts in the old Farmall H & M model farm tractors. Some just months away from 80 ( eighty ) years old are still running regularly with the original crankshaft. I've only ever seen ONE broken M crankshaft and heard of one other. Undersize main & rod bearings are NOT common in them.
Company I used to work for Nitrided lots of parts. Biggest advantage of Nitriding was the low temperature the process exposed the parts to, nitrided parts needed little if any finishing after nitriding. Depth of hardness was not real deep but deep enough. If crankshaft was reground nitriding would have to be redone.
Chrome plating crankshafts was common, but not used much anymore. On a stressed part like a crankshaft pealing the chrome off was a possibility. A plasma metal spray technique would be better, but enough heat is put into the crankshaft all the journals would have to be reground.

[BillT]

Originally Posted by LEWISMATKIN

Road rangers of that era would more than likely been the RT-610 or RT-613 series transmission. These trannys are rated at 600 ft lbs of torque and were found behind many gas-engine trucks of all major brands of the day.

Right, I believe the RR in my '71 9500 (J-Model, Conventional Cab btw) was an RT-610.

[bigblockv6]

Too bad GMC didn't Tocco harden the 478 & 637 crankshafts. International Harvester Tocco hardened crankshafts in the old Farmall H & M model farm tractors. Some just months away from 80 ( eighty ) years old are still running regularly with the original crankshaft. I've only ever seen ONE broken M crankshaft and heard of one other. Undersize main & rod bearings are NOT common in them.


I know GMC Tocco hardened 401 and 478 crankshafts back in the 60's, I have a factory shop manual that mentions it. In the 70's Tocco process was replaced with Tuftriding according to my factory parts manuals, they recommended after turning the cranks to have them Tuftrided, the posibility Diesel versions didn't have this process. When I had the crank turned on my 478 I told the machinist to have it tuftrided he told me that process was replace with Nitriding so that's what was done on my 478 crank

[2-Ton]

Really!
No answer to a good question, on where to find a part for a 637?
The 637 replaced the Twin Six.
And no one has any advice on how to find a new fuel pump?
Do you even know where it is mounted on the 637?