SuperTruck: Bell-Housing

by Ben N on August 12, 2014

Yesterday, I got to tinker with the transmissions some more for my diesel-electric hybrid truck project.

Not having actually DONE any transmission work before means that this is all pretty new to me. However, since I took the Mercedes transmission apart, it made working on the Chevy S-10’s T5 transmission that much easier.

Only four bolts held the bell on the T5. Frankly, it was as much work getting the odd steel exterior support rods off as it was to actually get the bell housing off. That really only needed to pull four outside bolts, and it was done.

T5, bell housing removedBoth bell housings

With the bell housings off both transmissions, it was much easier to compare and contrast the two. The bell from the T5 is larger and a simpler layout, with fewer bolt holes. The advantage of the bell from the Mercedes 4-speed is that it already matches the engine, including starter location and perfect alignment.

So, it seems like I’m down to two choices.
A) Use the T5 bell housing but use a custom plate directly on the engine for it to mount to, including a location for the starter and making sure everything is PERFECTLY centered, or
B) Use the Mercedes bell housing, which already accounts for alignment and the starter and make a small custom plate between the bell and the T5 transmission.

Right now, I’m leaning towards “B”. I managed to find a thread on DieselBombers where user “deck60” used a Mercedes diesel with the Mercedes bell housing custom fit to a T5 transmission in an S10. It’s always nice to find when somebody else is doing something similar. It gives me confidence where I would otherwise have no experience on the matter!

The down-side of using the Mercedes bell is that I will have to figure out how to cut into it to install a slave cylinder and likely somehow custom fit the fork that would match the T5.

I also measured the diameter of the tips of both transmission shafts and was surprised to find that they are both 15mm! That means that I SHOULD be able to use a stock pilot bearing, instead of fretting over finding an odd one or making something custom.

Replacing flywheel bolts

I also replaced the flywheel bolts. This OM616 engine was originally mated to an automatic transmission. The bolts to the torque converter are LONGER than those to the manual transmission flywheel. For testing, I simply used 6 of the old bolts, spaced out with oversized nuts. The bolts were long enough that if they were driven in all the way, they would go all the way through the crankshaft and hit the engine.

A friend of mine dropped off some diesel-related items a while back, including some assorted flywheel bolts. They were in fact the correct diameter and thread pitch. I managed to find enough short ones to fill all twelve holes, although four are different from the rest. I think that’s ok, as long as it’s balanced. I spaced them out symetrically. I was a bit surprised when I looked up flywheel bolts that they are $8 each, and the engine needs 12 of them. If this DOES work, I just saved myself $100.

I reinstalled the Mercedes bell housing on the engine. (Two mounting bolts go right through it to hold the starter in place.) With it in place, I set the Chevy’s T5 manual transmission nearby, and then lifted it into place. The transmission shaft slid almost all the way inside. Only the odd mis-match between the bell and the transmission kept it from going any farther.

I measured both the length of the shaft and the depth of the bell to the crankshaft, and found that I should only need a spacer of about 3/8″ to 1/2″. That should be just about perfect for the adapter plate. And FINALLY that’s something I have a bit of experience with too, as a similar piece was needed on the Electro-Metro to connect the electric motor to the transmission. (In fact, I should probably go visit Hot Rod Jim again for some more advice!)

Well, that’s it for now. Next, I’ll be looking for some advice that the Mercedes bell IS the way to go, and then start figuring out how to build that adapter plate!


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