WWU & Diff. Mounting to Transmission

[Daves]

What are the advantages and disadvantages of mounting the differential directly to the transmission as in the following photo?

I have seen the University of Texas at Arlington's differential, and it is also mounted to the transmission instead of the chassis.

It seems it would be easier to align the diff, but if one of the rear tires hits something (like a wall), will it jack up the whole engine, too?

http://dot.etec.wwu.edu/fsae/images/Drivetrain%20Test%20Fit%202_JPG.jpg

http://www.letu.edu/formula

Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[Daves]

What are the advantages and disadvantages of mounting the differential directly to the transmission as in the following photo?

I have seen the University of Texas at Arlington's differential, and it is also mounted to the transmission instead of the chassis.

It seems it would be easier to align the diff, but if one of the rear tires hits something (like a wall), will it jack up the whole engine, too?

http://dot.etec.wwu.edu/fsae/images/Drivetrain%20Test%20Fit%202_JPG.jpg

http://www.letu.edu/formula

Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[Travis Garrison]

Try not to hit walls.

Seriously, if you hit something hard enough to move your diff around you have a whole bunch of problems, engine mounts, and diff mounts aren't going to be that big of a deal when compared to replacing all of your suspension.

We mounted our diff that way primarily for ease of packaging, but also in hopes of making alignment a little easier...probably would have been better if we could have mounted 100% to the engine, then there wouldn't be alignment concerns due to chassis flex (probably not going to be an issue with our chassis, but I could see it being a problem for a light space frame).

Travis Garrison
WWU FSAE

[Daves]

Do you just drill and tap into the engine block? Also, how do you adjust the tension of your chain? Do your diff mounting brackets swivel a little?
How does mounting to the engine facilitate swapping engines quickly?

http://www.letu.edu/formula

Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[This message was edited by dave_s on December 11, 2003 at 04:03 PM.]

[Angry Joe]

Looks like there is a slotted mounting hole on top there...



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[Travis Garrison]

No drilling or taping, we use only the existing mounts found on any stock engine, slots and set screws are used for chain tensioning.

Our choice of mounting brackets had zero to do with engine swaping...and I don't think it really effects it one way or another...either way the diff would have to come off to really have the room you'd want to remove the engine.



Travis Garrison
WWU FSAE

[Denny Trimble]

Our diff mounts entirely to the engine, using the swingarm bolt holes in the case. The previous car mounted the diff to the rear box of the spaceframe, which deflected .125" or more under worst case loading. Sprocket wear isn't a problem now, probably because misalignment isn't happening. Our diff moves with our engine now http://fsae.com/groupee_common/emoticons/icon_smile.gif Oh, but we have a chain tensioner pulley that can be problematic. Workin' on the redesign of that right now...

University of Washington Formula SAE ('98, '99, '03, '04)

[Daves]

How high do you have to torque the top bolt to keep it from slipping? The bottom bolt appears to be in double-shear stress, as all of our bolts were last year. Is all the force on these bolts due to the weight of the differential assembly, or does the moving chain also add force?

http://www.letu.edu/formula

Formula Photos & Links (http://what3542.5u.com/dave/fsae/formula_photos.html)

[Travis Garrison]

The torque applied to those bolts is determined by the whomever has the wrench at the time...We are using lock washers to add some friction, but mainly rely on set screws (not shown in that picture) to keep everything in place.

...and yes there most definetly is some force being applied by the chain, think of it as having a tight and loose side...then look at the torque output from your transmission and you'll get the idea...


-Travis Garrison

[dancin stu]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Travis:
The torque applied to those bolts is determined by the whomever has the wrench at the time...We are using lock washers to add some friction
<HR></BLOCKQUOTE>

caution regarding lock washers, they actually reduce the clamping force on the nut/bolt arrangeemnt.

we are sponsored by loctite, part of the deal being we get guest lectures from their engineers. I'll try and obtain the graph showing different methods of clamping arrangements, but a lock washer provides lessforce than a nut bolt combo done up FT

[Travis Garrison]

I'd be interested in seeing that...

I never really thought about that...are you sure that applies to all metals? I can see it in steel, but in the aluminum it sure feels like its got more resitance to slipping, not to mention the lock washers actually dig into the aluminum significantly...

-addition- I should clarify also that the only time the additional frition of the lock washers is really usefull is during the assembly, when everything is only finger tight... -addition-

The other thing we have to consider with the current setup is that our engine was damaged before we got it and part of our repair involves aluminum threads on the left side of the swing arm mount, so we can't put a tremendous amount of torque on that bolt...

In either case we don't actually use those side bolts to resist movment, only to clamp the carrier up agains the "true" surface of the swing arm mount...We use adjustable stops (set screws) to actually fine tune alignment and resist movement.

Travis Garrison
WWU FSAE

[This message was edited by Travis on January 21, 2004 at 03:20 PM.]

[This message was edited by Travis on January 21, 2004 at 03:22 PM.]