Flywheel Swap Advice

oldnotslow

Active member
I have a 3406B, 4MG engine with a brakesaver. This engine has an 8 1/2" bore flywheel. I want to install a 10" bore so I will have a greater selection of newer model clutches to install. The issue is the brakesaver engine does not have a ring gear on the flywheel. I have been unable to find a part number for a flywheel with a 10" bore for a brakesaver engine. If anyone has any advice on this swap please let me know. Last resort would be to machine the current flywheel out to 10", I guess. Thank you for any help.
 

Truck Shop

Well-known member
You haven't been on here for awhile I thought you fell off the planet. I have had standard flywheels and one brakesaver flywheel machined
for ten inch pilot before. Never had a problem. I just had the brakesaver cut to accept the disc diameter and to clear damper springs and
allow for wear. It didn't take the machinist very long to open it up and radius the sharp edges. Are you going to install a 208925-25 clutch?
That's about all I use anymore, easy peddle 2050 ft lb rating six paddle. Alot smoother engagement.

Truck Shop
 

oldnotslow

Active member
Machining the bore out is certainly an option. The turn around time on that around here could be 4-10 days. Was hoping to get a part nember to get one from CAT within a day. I plan to put in the 208925-20. Thanks for your response, glad to see your still here helping us mechanics in training.
 

Truck Shop

Well-known member
I suddenly remembered I had a Cat complete part number book at work. The later 5EK's also came with the brakesaver and you can swap that flywheel on to
your 4MG. All 5EK's had 10" openings in the flywheel. Try looking for part {#4P-4794 15.5 inch 7 spring clutch; brakesaver} Cat also lists #4W-6730 but it does
not list info about any clutch with that number.

Your hardly in training

Truck Shop
 

oldnotslow

Active member
Thank you so much! That is exactly what I was looking for. CAT has a 4P-4794 in Spokane. That will only keep me down 2 more days, or I can resurface my 8.5" bore and be finished tomorrow. Do you feel the upgrade to a 10" bore and the later designed clutch is worth the added cost $837 + shipping and wait time. I would like your opinion on how much benefit the conversion produces. I realize this is a matter of opinion but interested in feedback based on your experience. The cost and added downtime is not a deal breaker for me if I get a better truck. I do haul 105,500 most of the time and, a lot of hills and stop and start traffic. Thank you again for your help!
 

Truck Shop

Well-known member
When or if you call Pape' or Western States Cat make sure and ask for the diameter of pilot using that 4P-4794#.

I can tell you those 208925-20 or the 25 clutches are much easier on u-joints and rear ends and will last much longer. Most of it depends on how long you
plan on keeping that truck. All of our Coronado's that you see on I-5 are Series 60 Detroit's-550 HP 1850 torque-GVW 100'000 . I install the 2050 ft lb
because it's only $75.00 more and I like the clutch rated at least 200 ft lbs more than the engine will make at peak torque. I don't know how many
transmissions I have removed through the years for a rebuild or to replace the clutch. At my age I hate thinking about the next one. And having to replace
a clutch that takes a dump too soon is despair. :( So for me personally or a customer or the company trucks I like overkill when it comes to drive train
components.

Truck shop
 

oldnotslow

Active member
Apparently, the 4W-6730 is for an SAE #1 flywheel housing and the 4P-4794 is for both an SAE#1 housing and a 16" housing. Not sure what the difference in housings actually is. Also, you refer to the diameter of the pilot for the 4P-4794. What is that? Pilot bearing? I will need to have that also, if it is different than mine.
 

Truck Shop

Well-known member
The pilot is the opening or bore for the clutch. 10". I think the 4W-6730 is for stationary maybe.
The pilot bearing will be the same.

Truck Shop
 

oldnotslow

Active member
Ok. I think we have everything to put it together today. The 1850 clutch I have is easilt 300+ over the torque my engine is producing. I'm at around 460HP and I'm guessing 1500-1550 on the torque. I am really looking forward to driving the truck when it's done. I'll let you know how it goes. Thank you again for your knowledge and willingness to help.
 

oldnotslow

Active member
I am so glad I made the switch to the 10" bore flywheel and clutch. Makes driving the truck in traffic and starting on hills so much nicer. Much smoother engagement than the older clutch model. I would recommend spending the $800 for a larger bore flywheel to anyone still running an older truck like mine with the 8.5" bore.Thanks to Truck shop for his advise on this.
 
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