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Motor mounts and/or Tranny mounts Bad?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MudbogAD, Mar 28, 2002.

  1. MudbogAD

    MudbogAD 1/2 ton status

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    I have a 350, th350 and a 205 combo. If I look at my t-case shifter while accelerating it will move a good half to one inch to the right. If I hold the brake and give it gas it will do the same. It seems like it moves alot. My tranny mounts seemed to be a little loose, so I tightened them but it didn't really help. I'm wondering if my motor mounts are going bad. If you have the hood open and rev the engine it seems like it moves alot to the left, like an inch or maybe more. Is this normal?
    Thanks in advance.
     
  2. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    My shifter moves about the same when accelerating. Thats pretty normal as far as I'm concerned. Now about the motor, when you say it "moves" 1".....Do you mean the whole thing moves or kinda "slides" 1"? Or it just twists or "torques" 1"? If its actually sliding 1"...the you have waaaaay bad motor mounts. If its just twisting//tourquing, then thats normal.
     
  3. MudbogAD

    MudbogAD 1/2 ton status

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    It seems as if it is torquing (rotating) 1 inch. It doesn't slide. The t-case shifter has always moved when accelerating. I am beginning to think it is normal. Thanks for the reply
     
  4. bigmack

    bigmack 1/2 ton status

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    I have the same setup as you, this sounds so familiar. My truck was doing the same thing, I just found the problem Friday, the motor mount on the passengers side needs to be replaced, alot of the rubber is gone out of it. I also found that my adapter (the piece that mates the t-case to the transmission) is broken again. I assume the the bad motor mount is the cause for the broken adapter. This is the second adapter that I have broken, they are a pain in the ass to find used, you can get one from GM for around 300 bucks, I think I am going to try to fabricate a new way of supporting the thing.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Still hoping someone will step forward that can machine these adapters out of solid steel, or maybe even AL. At $300 a pop for stock cast ones, I'd pay easily 150-200 for a solid non-cast version that won't break.
     
  6. bigmack

    bigmack 1/2 ton status

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    I hear you, those cast adapters just don't hold up to my heavy foot I guess. I've been thinking about trying to fab something out of steel that would bolt to where the transmission mount bolts on (when using the transmission in a 2wd truck), put a couple of bends in it where it can be bolted to the frame. I don't know I'm just brainstorming trying to figure something out that would give the entire setup more support and stregnth.
     
  7. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    I thought about that as I broke a 350/205 adapter with new motor mounts (rubber) and new poly t-case mounts. I think the motor torqed in the motor mounts but couldn't twist down by the t-case and something had to give (especially with a transfer sled behind it). Before the machine shop closed that my father worked at, I was going to have him make one out of steel. He was going to and thought that a rigid mount like that with cast on one side (t-case) and aluminum on the other (350 or 700 in my case tranny) may make the tranny case the weak point. I would rather replace a couple hundred dollar adapter (I can get them around 2 bones) compared to a replacement housing/tranny. Just something to think about. Now I have a new adapter and poly motor and t-case mounts. Our first truck pull is this June. I will let you know how it holds **crosses fingers**.
    As far as the t-case shifter moving.....it will to some extent due to the motor and t-case being suspended in rubber (which is done to absorb shock loads and vibration). I don't know how much is "normal", but if the mounts look bad or are old, it probably would be a good idea to replace them. Once they are replaced look at how much the shifter moves and you can use that as a reference point for the future as they start to break down (and all rubber eventually will).
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    You poor, poor automatic transmission owner : )

    All kidding aside, I see where you are coming from. If there were steel adapters made I would go to poly at both the engine and the t-case, and even now won't consider only poly trans or motor mounts...both or neither.

    IMO power is supposed to get to the wheels, not be taken up by drivetrain movement.

    I understand that when you are exceeding rated capacity with enormous amounts of power and load, you are going to see some breakage, but until someone makes one of these adapters and tries them, we'll never know what the next weakest link is! : )
     
  9. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    True.....I just hate finding out the hard way, which is usually the ONLY way I find out /forums/images/icons/smile.gif.

    I do agree will all power should be hitting the ground and not absorbed by rubber mounts, especially when I'm pulling (That's why I'm now ALL poly). I guess from the factory, it was more of a case of longevity. In a solid system, each driveline part would absorb shock due to changing gears, accelerating/decelerating), wheelhop, etc. and would lead to fatigue (i.e. less component life, just ask racers), as well as transmit all vibration and shock to the driver's compartment. I for one would like to feel the shock as it tells me what is going on with my vehicle (kind of like an onboard computer in the seat of my pants /forums/images/icons/wink.gif), but Mr. and Mrs. Jones don't want to feel that so the auto manufacturers built in a smoother ride (hence rubber mounts).

    <blockquote><font class="small">In reply to:</font><hr>

    You poor, poor automatic transmission owner : )

    <hr></blockquote>
    /forums/images/icons/smile.gifI have so many people laugh at the pulls when they find out I run a "slush box", (90% run manuals, 100% of the Dodge boys as the diesels eat their autos), but I usually have the last laugh when we are done. All my trannys have been built from the ground up though (not stock, and by someone else as that is one skill I have not even come close to mastering) and I only lost one while going down the road due to an internal converter failure which then sent fine metal particles throughout the whole system (wasn't the tranny that let go). Granted I lose a little HP/Torque to the ground (nature of the auto vs. manual), but sometimes to much can cause the vehicle to lose traction especially at the end of the track. The auto tends to "auto"matically adjust a little better to the track conditions. Plus I have enough ponies to make up for any power lost through the "fluid pump".
    I do have do admit. There are times where I wish I had a manual, but there is more times I'm glad I have an auto (go figure.../forums/images/icons/crazy.gif)
    Pure strength and longevity=Manual as an auto it designed to fail (internal clutches) whereas a manuals clutch is external and easier to replace.
    Flexibility (at least for MY applications)=Auto. Once the truck becomes a pure toy (stop pulling) I might change to a manual, but if I do it will be an overdrive unit. $$$ I will do it right once and forget about it (other than dealing with a clutch replacement/flywheel resurfacing).
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd be willing to test a nice machined tranny adapter. I drive my truck everyday, so I could give it the longevity test. Someone just give me one lol.

    I think a lot of the "shock absorbing" nature of all of the components on GM vehicles of the time were to minimize passenger discomfort more than anything else. You look at Camaro's versus the passenger cars, (mid 80's) even with the same or similar rear suspension setup, the "higher performance" Camaro's received "harder" rubber bushings. Thats something the occupants will feel, but it also helps transfer power to the ground, and also helps the suspension actually work, instead of having rubber take up slack instead.

    My auto comment was solely about having to worry about the tranny case breaking. I'd like to see an SM465 crack from pure power. /forums/images/icons/smile.gif

    Manuals aren't for everyone, just as auto's aren't for everyone. End use is the single largest factor that someone needs to think about when deciding on one or the other.
     
  11. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    <blockquote><font class="small">In reply to:</font><hr>

    My auto comment was solely about having to worry about the tranny case breaking. I'd like to see an SM465 crack from pure power.

    <hr></blockquote>

    Wasn't thinking of it that way.....and you're right. I also wonder what the strength of the SM465 t-case to tranny adapter is compared to an auto (assuming both are the NP205 version). Just my curious mind at work again...**mad scientist look**

    But back to the original post. I think we agree he should replace the mounts (probably need it anyway), and go all new rubber or all poly (don't mix and match). Hope this all helps (after my sidetrack /forums/images/icons/blush.gif).
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    I think the major weak link of the adapter is the "feet" Most or all of the ones I've heard and seen have broken the little ears off where the bolts thread. To me, that indicates that the mount is moving enough to allow the adapter to move so much that the cast iron just cracks. If that is the weak link of the adapter (which I believe it to be) then all but the "shorty" adapters are inherently weak. The newer GM adapters may be a bit stronger, they are not cast hollow like mine is.

    I'd agree, and go one step further to say that if you have to replace all the mounts, go poly on all of it. They shouldn't need replacing again, and in the grand scheme of things, aren't that expensive.
     
  13. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Oddly enough mine broke above the feet, higher on the adapter (figures I would have to be the oddball, as with everything else on my friggin rig), but the other's I've seen have broken at or near the feet. As you say the new adapter I bought is different from the old one as it doesn't have the cavities cast into it. Maybe GM realized there was a problem.....
    I will try to post pics this weekend, but I still owe Steve some more pics of the 205 rebuild and some teardown and rebuild instructions first. Sorry Steve.
     
  14. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    adam i've seen the thing move, it's more than a half inch. i would get poly motor mounts if i were you.
     
  15. MudbogAD

    MudbogAD 1/2 ton status

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    Scott, I said half to one inch. I don't think I've ever seen it move more than that and I drive it every day. I do agree That I need new motor and tranny mounts sometime in the near future. Those are some interesting topics about the adaptor. I didn't know they broke. I guess I'm pretty lucky mine hasn't broke yet. When my dad drove the truck in the past he had u-joints snap, spider gears blow up, and a couple of trannys go. I think I'm pretty lucky the adaptor hasen't broke. That thing is very pricy. Thanks for all the help.
     
  16. 72THING

    72THING 1/2 ton status

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    I have broken my 465/205 adapter numerous times. It leaks like a sieve and now I'm in the market for another one. I considered having one made out of steel, but I think the next weak link would be the bellhousing. When I replace my adapter, I'm going with poly motor and t-case mounts. Right now they're all rubber and even though they're relatively new, they flex way too much. I'd rather put that extra force to the ground instead of in movement of the engine/tranny.

    Will
     
  17. bigmack

    bigmack 1/2 ton status

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    I must be the exception to the rule, the first one I broke split vertically between the t-case and transmission causing the t-case to fall down and rest on the skid plate, it was not broken at the feet. The one I have now is broken horizontally about one inch above the feet. These things are becoming a pain in the butt.
     
  18. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    <blockquote><font class="small">In reply to:</font><hr>

    The one I have now is broken horizontally about one inch above the feet AND I must be the exception to the rule

    <hr></blockquote>

    I think somebody may have said that the "feet" is where they break. Mine too broke like yours, horizontally a little over one inch above the feet. How long did yours last after replacing the first one? I never knew it was this big of a problem until recently.......design flaw????
     
  19. bigmack

    bigmack 1/2 ton status

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    Yeah, I think there may be a design flaw. This one lasted about 3 months before breaking. I had the truck for about a year before the first one broke. If I keep having this problem I will probably change my truck over to a 203 case. I don't want to do it, but if this keeps up something is gonna have to go.
     
  20. dyeager535

    dyeager535 1 ton status Premium Member

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    The stock "old" ones are hollow. The "new" solid GM ones are obviously not going to be able to crack as easily as the hollow ones, but at $2-300, I'd rather see someone make one out of steel, or AL if they think it will hold up.

    I'm not sure I'd be real worried about the bellhousing...obviously trucks put more stress on parts than cars, but even "fast" cars (10-11 second quarter miles) don't regularly rip the bellhousing. It does happen, but I think that depends on the individual vehicle/setup, not the transmission itself.

    It very well could be though, that our frames are just too damn flimsy, and the crossmember is twisting opposite directions when the truck flexes, (which may explain the cracks higher up in the adapter) in which case pretty much nothing will prevent breakage of SOME component.
     

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