hi all

when i romp the gas, the lever on my 90 six speed moves about 1/2" up...how much movement is considered normal?

the beam bolts are tight, motor mounts look obviously ok...(but will them replace anyway, PU mounts are on the way, my personal vote goes to tired stock motormounts...)


thank you

 

Have to agree, with only motor mounts and c-beam holding things in place, if one or the other is loose or worn then that's the only place that movement can originate from.

 

There is always going to be some movement no matter how new/tight your parts are.

1/2"seems too much

 

i'd definitely replace the motor mounts, but even though you've tightened the c beam, have the mounting holes in the (soft) aluminum of the c beam become oversized, elongated or egg shaped? also at the other end, I'd replace the batwing donuts with polyurethane.

 

BTW:

I get some movement (i cant feel it, however if I watch when I get on the gas and then abruptly let off, I can see the shift lever move up/down a little)

And this is with:

1. solid motor mounts from user churchkey
2. polyurethane batwing bushings
3. beam plates!

Im sure everything is tight.

Im guessing I have 1/8" of movement.

 

hi all

i wanted to change the mounts today...after closer inspection and removing the frame to mount bolts, with jacking up the engine...

no way to get them out.

i run headers, and they interfere a good bit with the mounts..

it seems, this will get a winter work..

btw, the stock mounts dont look bad or broken, they just seems to be really soft..

regards

 

hi all...

i know, it have been a good time ago, but i finally found time to change the rubber motormounts to Poly motormount

im really amazed, how these things are working, no, and i really mean no more vibrations than stock..i wonder myself, ...

the engine feels much more "defined" not so sloppy than before..

unfortunately, the shift lever still moves up and down around 3/8" when hitting the gas....

so, i have

Poly motormounts
Poly batwing bushings
C-Beam w/ Beam plates...

i think, thats all that can be done by the normal user

what comes to my mind next, is to install steel plates with a bushing in them on the c-Beam, so that the bolts dont ride in the aluminium but in a steel bushing..

i assume, the c-Beam is from factory not a very rigid construction...

let me know, what you think about!!

thank you

 

The c beams are what they are, and of course they could have been made more robust, but they weren't; so what's a C4 owner to do?

First, are the holes in your c beam egged out or oversized? Beam plates can only do so much. Your c beam may need replacement or repair.

I made my own beam plates, and I made them extra long so I could drill an extra hole and bolt the plates directly to the c beam so that now the beam plates and c beam were an unit and eliminated any possible "sliding" movement between the c beam and the beam plates. And I drilled the holes in the c beam plates very close in size to the mounting bolts, so IF there was any potential movement, the mounting bolts would hit the hard steel of the beam plate and not the soft aluminum of the C beam.

The limiting factor as far as c beam clamping force is the size of the fasteners used and the webbing structure on the tailshaft and differential nose.

Although I don't have the exact bolt sizes with me, I did find out that holes in the mounting webs were large enough to allow replacement of the stock metric bolts with slightly larger U.S. standard bolts; this eliminated another area of potential "slop". And increased the potential "clamping" force.

The simple truth is that the mounting web structure on the trans tailshaft housing and differential nose are not particulary robust. Continually tightening and retightening the mounting bolts will eventually cause them to deform. I took small sections of pipe, drilled them out slightly to accommodate the mounting bolts and placed them in the voids between the webs and then filled the voids with Devcon Steel, an steel impregnated epoxy designed for anchoring heavy machinery mounts. The pipe "bushings" eliminated another potential area of slop plus reinforced the mounting web structure eliminating any possible potential for deformation.

A last and often overlooked aspect, is that the factory used adhesive when mounting up the c beam. Many theories abound for this, elimination of potential squeeks, electrolosis issues, etc.; but I really believe it was an last ditch attempt to eliminate / reduce potential c beam movement;

My recommendation? use LIQUID NAILS; contractor grade.

good luck

 

mtwoolford,

thank you for your reply, i have found your name in this context, when i searched the forum...

the ultimate fix for the c-beam problem would be a self fabricated one, but with all the bends and angles, thats not that simple..

i get a good used one on tuesday for taking some measurements, then i will have some more insight, how possible a potential DIY Beam would be.

what i do next, i remove the c-beam from my car, and will look closely at the holes...what comes to my mind, is to open up the holes, make an steel plate with two "threaded" towers on them, and insert them tower down in the c-beam...also plan to make the plate as large as possible and screw and glue them on the beam. so, that would eliminate the need of nuts on top and even the "normal" beam plates, that i have now.
i will also look at the tailshaft housing, what comes here to my mind is to mill out the bores, insert sleeves of 7075 aluminium and weld them on the outsides, epoxy them on the inside of the webbing (like you did)

the tailshaft is easy to remove, so no problem here...
can also do this on the diff side, but i dont think i will insert sleeves here, its just too much work for now, and i álso doubt, that would help much

i *think* most of the movement comes out of the connection tailshaft-beam....

mtwoolford, did you notice improvement with the procedures you have done?

keep you posted!!

thank you

 

If you wanted to address the C beam itself as a separate issue, I don't think fabricating a complete new one would be necessary. Any shop with access to aluminum plate and a tig welder should be able to fabricate simple "doublers" or gussets and weld the onto the existing C beam; now that I think of it I'm kinda surprised someone doesn't offer aftermarket "reinforced" C beams

I like your plan to fabricate steel collars which slip down into the C beam itself....I like it a lot

My own evolution began when I removed the differential and batwing for installation of polyurethane mounting doughnuts. I noticed that the webbing on the nose of the differential where the c beam mounts, had begun to crack....so it was off to the welding shop for that repair. Then I noticed that the mounting holes in the c beam, especially at the transmission end were oversized and egg shaped...so I got a new c beam. Then I noticed that the oem holes in the c beam could accommodate slightly larger u.s. standard bolts. So I fabricated my own c beam plates, one difference being that I used angle iron instead of flat plate. I then fabricated the reinforcing bushings and mounted them in the webbing of the differential ....later, when I had the trans out for a clutch job, I did the same at the transmission tailshaft housing.

As far as the nuts on top of the beam plates, I considered welding captured nuts on top, but instead cut down two 6 sided sockets and welded them atop the beam plate, so now I have two "captured" nuts atop the beam plate which can transfer any force from any direction into the beam plate, but still can be replaced if necessary

Did I notice an improvement? well yes.

The shifter basically does not move and any movement, which is very little, is attributable to the engine torquing on the stock motor mounts. Even this can be addressed with inexpensive replacement motor mounts which are solid rubber...not hydraulically oil filled like the oem mounts.

I guess aftermarket solid mounts would eliminate even this. From my little research, I believe that in the beginning the idea was to produce a backbone structure ala a Lotus which would be a structural member ...but for whatever reason (Cost? Noise? Vibrations?) this was dumbed down with hydraulic motor mounts, rubber batwing bushings, etc.

So my next step...I'm not quite ready for solid motor mounts although some on this site speak highly of them...is to fabricate solid style mounts but with some polyurethane bushing in them, ala off road race / rally cars.

A last thought, if you can't eliminate the shifter rise ...and believe me you will...you can eliminate the "perception" of shifter rise by installing a shorter shifter..I installed a ZFdoc modified shifter that I am very pleased with...but that's another thread for another day. good luck

 

Sorry to bring up an old topic but watch the shifter rise in this c4. (Skip the first minute of intro)

 

Thats too much. When it goes up and down like that so much that it could yank off the under rubber boot, then somethings loose.

The first time i ever removed and reinstalled my c beam, i under estimated the torque required. In my case, i got so much movement it yanked off the inner rubber boot.

It was really noticeable, like in this car, when youd get on/off the gas. Thats where youd see all thhe rise/fall.

The c beam bolts need tightened a bit beyond what the fsm torques should be. Beam plates make this easier.

Be sure to check for ovalization of the c beam holes. Back in 02, i bought another c beam due to ovalizing the holes.

Mtwoolford's idea is real good! Ive thought about doing something similar, but he's thought this out better.

As i mentioned earlier, even with solid motor mounts, polyurethane batwing bushings, beam plates, and my bolts torqued as hard as i could, i still get about 1/8" up/down movement if i watch the shifter.

Though in the heat of the moment rowing thru gears i dont notice it

 

Once I replaced my clutch I had a noticeable amount of shifter movement so I went back and found to loose bolts. The c beam looked to be fine. Since I was there I made some C-beam plates to spread out the pressure surface and I have about 1\8 of rise. It hasn't gotten worse so I've just let it go. You have 7 feet of driveline, there's going to be some flex

 

Does it drive okay?

 

It has so far, I could tell that something was wrong when it was loose

 

Drive and enjoy then