Bolt #12

[rboltz]

By bolt #12, please refer to the drawing below. When I got my truck, bolt #12 was missing. “Not to worry”, I was told; it only holds the exhaust pipe bracket. My exhaust system was home made by the PO so no bracket was there. Well, when I finally installed the stock exhaust system this past summer, I ran a bolt up thru there to fasten the bracket. I did not put a bushing (#5), nut (#3 lower) or rubber damper (#10) in there as shown. What a difference in engine vibration! Before I put this bolt in, my engine would shake when pulling out or especially when backing up. Now, smooth as glass. However, if you look at the drawing, there is a nut, #3 (lower one), and a rubber bushing (#10) that makes bolt #12 a floating stud with its base attached to the frame plate. I did not do that as an all thread bolt was not available at the time. (The drawing doesn’t show the exhaust bracket under nut #3 upper). I believe they did it this way so the engine vibrations would not put stress on the first exhaust pipe or the manifold bolts. The first exhaust pipe rocks with the engine, so no stress on the pipe or manifold. Also, this bolt is necessary to dampen vibrations on the engine/transmission mounts. The pipe hangers would take care of any remaining variations further down the exhaust chain.

Questions;

What damage or problems could be created buy just running a bolt up there like I did?
Since the exhaust bracket is not shown, is there in reality another nut on bolt #12 to fasten the exhaust bracket? (Nut, bracket, nut)

[brute4c]

I dont think so...the exhaust bracket mounts on top of the trans bracket just below washer 4 and nut 3 at the top...I have a pic Tacoma sent me:

[rboltz]

I dont think so...the exhaust bracket mounts on top of the trans bracket just below washer 4 and nut 3 at the top...I have a pic Tacoma sent me:

Then I think the lower #3 nut is on one side of the transmission mount, the exhaust bracket on top and then the top #3 nut. Then the spacer #5 makes more sense. Otherwise, you can't get the exhaust bracket tight and the spacer prevents the transmission mount from compressing. Also, the rear mount can flex somewhat either side with bolt #12 on one side and bolt #15 on the other. Both have the rubber bushings under the bolt heads.

Without bolt #12, you can get a lot of engine rocking.

[brute4c]

It is actually stated in the -34 manual that:

CHAPTER 3
REPAIR OF ENGINE

3-1. General.
[skip down to subsection b]
b. Engine Supports. The engine is supported at the side by two rubber insulators attached to the frame side rail brackets. It is supported at the rear of the transmission by a rubber insulator attached to the engine rear support crossmember. A torque reaction support arm is attached at the rear of the transmission and bolted to the frame crossmember. The torque reaction arm relieves extreme torque loads from the rear transmission insulator when the vehicle is operating. An engine rear support crossmember is bolted to the frame side rail to enable it to be dropped when removing the transmission. Check the rubber insulators for separation and wear by jacking the power plant away from the frame near the supports, while observing the action of the insulators. Vibration cannot be effectively controlled by separated or worn insulators and they should be replaced if faulty.

I would say that completely verifies your position on the mount and bolts.