3spd manual trans crossmember-where is it?

[quick60]

Im under my truck working on parking brake cable today and Im laying there looking and thinking something just doesn't look right. Suddenly it hits me. There is no transmission crossmember!!!!!! The 3 speed manual is just hanging off the back of the 250 inline 6!!! Is this correct??? I cant find one on any of the parts suppliers so Im thinking it is correct. Any thoughts??

[geezer#99]

That is correct. No crossmember. Bell housing has mounts on it. The engineers deemed the tranny wasn't heavy enough and the bell is strong enough to support it.

[quick60]

Wow. Seems like a weak link.

Would it hurt to add one?

[SS Tim]

Can't see why you think it needs it. The same arangement works fine on C30/400/4-speed trucks with a 10,000gvw.

[Lattimer]

Mine is the same way. No rear crossmember. My truck has been upgraded to a 327 though. I'm putting a 4-speed in as soon as I get it back from being checked out, and I will install a custom rear crossmember with it. Already got the rear mount and the steel, just have to do some measuring and welding.

[SS Tim]

Just remember to remove the bell housing mounts/crossmember you really don't want to run a five point setup, three will do.

[Lattimer]

Originally Posted by SS Tim

Just remember to remove the bell housing mounts/crossmember you really don't want to run a five point setup, three will do.

Why do you say that?

[LockDoc]

-
with Tim. Too many mounts will put undo stress on your drive line components. No way you need more mounts with a stock three speed or four speed trans....

Just my 2 cents worth.

LockDoc

[Lattimer]

Originally Posted by LockDoc

-
with Tim. Too many mounts will put undo stress on your drive line components. No way you need more mounts with a stock three speed or four speed trans....

Just my 2 cents worth.

LockDoc

OK, so humor me here a little bit. I'm new to these trucks (owned mine a month tomorrow)----but I'm also a mechanical engineer and overly conservative on almost everything.

Right now I have a 4-point mount for the engine and trans combo. 2 normal motor mounts and 2 at the bellhousing. There is nothing supporting the transmission back of the bellhousing. The tailshaft is just hanging in empty space. The trans has a mount point for a rear center mounting pad.

I don't remember where I saw it, but I remember seeing a diagram showing 5 mounts for a manual trans in these trucks. It was probably in one of the online catalogs.


As I am looking at it, the overhung weight plus the torque being applied to the driveshaft during a hard acceleration certainly looks like it would put way too much stress on the bellhousing, and could allow the tailshaft to move to the side.

On my truck at least, there are holes where a crossmember could mount that look correct for the manual transmission location. I don't know if the trans is original to the truck or not. I know the truck was originally a 6-cyl 3OTT, and at some point it was converted to a 327 and 3 on the floor. I've been assuming based on the other half-a$$ed things the PO has done that there used to be a crossmember there and it was removed and never put back.

Now, if none of these trucks actually have a rear mount on the manual transmission......it makes my life easier and its a lot less fabrication I need to do. I'm out a few $$ on some steel and a mount I already bought, but oh well.


I realize this was very long.......but I do NOT want to break my truck any worse than it already was when I bought it.

[LockDoc]

Originally Posted by Lattimer

OK, so humor me here a little bit. I'm new to these trucks (owned mine a month tomorrow)----but I'm also a mechanical engineer and overly conservative on almost everything.

Right now I have a 4-point mount for the engine and trans combo. 2 normal motor mounts and 2 at the bellhousing. There is nothing supporting the transmission back of the bellhousing. The tailshaft is just hanging in empty space. The trans has a mount point for a rear center mounting pad.

I don't remember where I saw it, but I remember seeing a diagram showing 5 mounts for a manual trans in these trucks. It was probably in one of the online catalogs.


As I am looking at it, the overhung weight plus the torque being applied to the driveshaft during a hard acceleration certainly looks like it would put way too much stress on the bellhousing, and could allow the tailshaft to move to the side.

On my truck at least, there are holes where a crossmember could mount that look correct for the manual transmission location. I don't know if the trans is original to the truck or not. I know the truck was originally a 6-cyl 3OTT, and at some point it was converted to a 327 and 3 on the floor. I've been assuming based on the other half-a$$ed things the PO has done that there used to be a crossmember there and it was removed and never put back.

Now, if none of these trucks actually have a rear mount on the manual transmission......it makes my life easier and its a lot less fabrication I need to do. I'm out a few $$ on some steel and a mount I already bought, but oh well.


I realize this was very long.......but I do NOT want to break my truck any worse than it already was when I bought it.

If the bell housing to engine bolts and the transmission to bell housing bolts are torqued to factory specs and the rubber cushions on the four mounting locations are in good shape you will have no problems with the setup you have. Excessive movement of the engine and trans because these components are not serviced will lead to failure of drive line parts a lot quicker than the absence of a rear cross member. I put an aluminum S-10 5 speed overdrive trans in my '67 C-20 and it does not have a rear trans cross member. It is as you call it hanging out in thin air. I have had no problems with it in the two years it has been installed.

LockDoc

[SS Tim]

Originally Posted by Lattimer

...
I don't remember where I saw it, but I remember seeing a diagram showing 5 mounts for a manual trans in these trucks...

IIRC some of the medium duty trucks used a five point, but it was four on the trans. and a front single point engine mount at the balancer.

[geezer#99]

So true Tim. A 5 point system can crack the bellhousing.
Also Lattimer measure from the centre of the output shaft on your tranny that's in the truck now to a fixed spot on the underside of your cab. Make sure your new mount makes your new tranny sit at the same point. Your U-joints will last longer. Also measure from centre of output to each side of frame. Make your new one the same. Some drivelines sit offset to the passenger side.

[Lattimer]

Originally Posted by geezer#99

So true Tim. A 5 point system can crack the bellhousing.
Also Lattimer measure from the centre of the output shaft on your tranny that's in the truck now to a fixed spot on the underside of your cab. Make sure your new mount makes your new tranny sit at the same point. Your U-joints will last longer. Also measure from centre of output to each side of frame. Make your new one the same. Some drivelines sit offset to the passenger side.

Good to know. Thanks!

[SS Tim]

The auto. trans. application use a more conventional rear mount. This style is often used with engine and manual trans swaps. But removing the bellhousing crossmember is just taking strength out of the frame.

[Lattimer]

Originally Posted by SS Tim

The auto. trans. application use a more conventional rear mount. This style is often used with engine and manual trans swaps. But removing the bellhousing crossmember is just taking strength out of the frame.

I wouldn't remove the crossmember anyways. I would just remove the mounts.


But based on what you guys are saying I don't need to do anything.

[SS Tim]

Of course there is also the question as to where your current engine and trans. are positioned on the frame. Six cylinders are about 3 1/2" aft of the V-8 location from the factory. Most people just stick the engine in the sixes location. It will be good having a ME around to keep me honest. :-)

[Lattimer]

Originally Posted by SS Tim

Of course there is also the question as to where your current engine and trans. are positioned on the frame. Six cylinders are about 3 1/2" aft of the V-8 location from the factory. Most people just stick the engine in the sixes location. It will be good having a ME around to keep me honest. :-)

I can't see any evidence that the mounts were moved, so I presume the V-8 is sitting in the same spot as the 6.


Problem with being an ME is I second guess and extra analyze everything I do.

[unclesalty]

If thats a cast iron bellhousing like my sons 72 c10, 307-3ott, well thats a sturdy enough piece, it should be fine. You sure wouldnt want to drop it on your toe!

[quick60]

Can't see why you think it needs it. The same arangement works fine on C30/400/4-speed trucks with a 10,000gvw.
I dont necessarily think it needs it it just seems unnatural to me not to have one. Never owned a manual trans classic before always autos. and all autos. I have seen have a crossmember. I thought it was for controlling/counteracting the rotation in the driveline but I guess they are more for holding the transmission bacause the darn thing is so heavy.

BTW there is a mounting pad at the tailshaft of the transmission that looks like a crossmember would bolt up to. Why is the pad there if its not needed?

[geezer#99]

BTW there is a mounting pad at the tailshaft of the transmission that looks like a crossmember would bolt up to. Why is the pad there if its not needed?[/QUOTE]

The pad is there on your truck because that same tranny was used in car applications where they used a rear mount. Cheaper for the factory to build them all just one way.

[KQQL IT]

Fwiw my peterbilt has no trans x member. 2k ft lbs torque.
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[67c10rustbuket]

The first time I looked under my truck I was also in shock at the sight of nothing holding the tail of the trans up. Then I found this dang website with all the information I ever needed .
If your truck has been converted from an I6 3OTT to a V8 (any bell mounted manual trans) I would assume they located the engine on the I6 mounts. My reasoning is that the PO would have had to remove the frame rivets and relocate the bell x-member forward when using SBC motor mounts. In I6 configuration the rear most rivets are actually under the cab and a huge pain to remove. The SBC works fine in the I6 location other than making it a PITA to get to the distributor. In the stock SBC position the back side of the cylinder head would be approximately 6" from the firewall. positioning the engine in the I6 position may actually work in your favor as far as weight distribution goes.
All of these frames have several (4??) locations for a typical tailshaft trans mount crossmember and 2 hole locations for engine mounting. I have attached a pic where mine are in the forward position for an SBC. the I6 motor mount brackets would be mounted one hole back toward the firewall. There are 3 evenly spaced holes, the forward 2 for SBC/BBC and the rear position of I6.
You better watch out for Tim, he is one smart dude

[Lattimer]

Originally Posted by 67c10rustbuket

The first time I looked under my truck I was also in shock at the sight of nothing holding the tail of the trans up. Then I found this dang website with all the information I ever needed .
If your truck has been converted from an I6 3OTT to a V8 (any bell mounted manual trans) I would assume they located the engine on the I6 mounts. My reasoning is that the PO would have had to remove the frame rivets and relocate the bell x-member forward when using SBC motor mounts. In I6 configuration the rear most rivets are actually under the cab and a huge pain to remove. The SBC works fine in the I6 location other than making it a PITA to get to the distributor. In the stock SBC position the back side of the cylinder head would be approximately 6" from the firewall. positioning the engine in the I6 position may actually work in your favor as far as weight distribution goes.
All of these frames have several (4??) locations for a typical tailshaft trans mount crossmember and 2 hole locations for engine mounting. I have attached a pic where mine are in the forward position for an SBC. the I6 motor mount brackets would be mounted one hole back toward the firewall. There are 3 evenly spaced holes, the forward 2 for SBC/BBC and the rear position of I6.
You better watch out for Tim, he is one smart dude

Thanks! Mine is definitely in the I-6 position....the HEI only has about 1" clearance on the firewall. I had wondered why I seemed to have so much space between the water pump and the radiator compared to other photos I have seen.


Big thanks to everyone, especially the OP for bringing up the subject!

[MARKDTN]

Just FYI most class-8 trucks (18 wheeler) mount the engine to the frame with 4 point mounts and the transmission is just mounted to it with no support. If they do have a support, it is usually just a plate with some springs.

[burnin oil]

Originally Posted by MARKDTN

Just FYI most class-8 trucks (18 wheeler) mount the engine to the frame with 4 point mounts and the transmission is just mounted to it with no support. If they do have a support, it is usually just a plate with some springs.

I have seen a ton of Eatons with mounts. Top of the rear box has 2 5/8" studs that help support it from above. Then 2 mounts on the flywheel adapter and a mount on the front of the motor. It is pretty common to hang the trans of the rear with no adapter.