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transmission mount

3K views 24 replies 8 participants last post by  Crosley 
#1 ·
I have been having an issue with trans mount. Typically the bolts get pulled out of the trans with the most severe being a broken tailshaft. Threaded inserts haven't helpe.

I thought up an idea and was wondering what you all think...see attached pictured.

Basically, wrap a shackle around the tailshaft and mount it to the trans crossmember using springs (maybe valve springs).

Add a rubber cushion betweeen the shackle and trans to prevent chafing, and udjust the preload with the bolt nuts on the bottom.

This is just a quick 5 minute sketch, so no scale has been utilized.

Any thoughts?
 

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#3 ·
Actually, I have been using the Lakewood brand, but the problem lies not in the mount itself breaking but rather in keeping the mount married to the trans...when I bang second the mounting bolts are being pulled from the transmission.

Right now the trans is chained to the crossmember until I can come up with a better solution.
 
#5 ·
KULTULZ said:
I am having trouble visualizing your setup. Can you show through photos? What kind of car is it?

Do you mean the capscrews are being pulled from the top of the actual mount?
As of today, my set-up is broke...no pictures.

The drawing that I attached was an idea that I thought of today. If you look at the picture, the trans housing would sit inside the u shaped metal loop. This loop would be bolted to the trans crossmember by spring loaded bolts...this way the loop could give a bit yet still take the strain off the mount. The inside of the loop would have a hard rubber lining that would sit against the trans housing to prevent chafing. I can see it in my head but I hope I explained it well enough.

The car is a 1985 Firebird with a TH-350.
 
#6 ·
Well ....there is a reason for everything.....you need to find the reason and fix it. Has the possibility of weak or bad motor mounts occured to you? That could be it and its throwing extra force to the rear thus over loading the trans mount thus pulling the bolts out. My suggestion would be to replace both motor mounts and the tranny mount with a good quality set of mounts.
 
#8 ·
The car is a 1985 Firebird with a TH-350.[/QUOTE]

Could be a clue here. The TH350 wasn't originally installed in your car. Does it have the stock rear axle torque arm set up which attached to the transmission? If so, how is it attached? To the transmission, crossmember, or what?

Bob
 
#9 ·
Henry Highrise said:
Well ....there is a reason for everything.....you need to find the reason and fix it. Has the possibility of weak or bad motor mounts occured to you? That could be it and its throwing extra force to the rear thus over loading the trans mount thus pulling the bolts out. My suggestion would be to replace both motor mounts and the tranny mount with a good quality set of mounts.
I have solid front mounts and the Lakewood trans mount.
 
#10 ·
#11 ·
bobscogin said:
The car is a 1985 Firebird with a TH-350.
Could be a clue here. The TH350 wasn't originally installed in your car. Does it have the stock rear axle torque arm set up which attached to the transmission? If so, how is it attached? To the transmission, crossmember, or what?

Bob[/QUOTE]

No, I ripped out the original suspension and installed a 4 link. I know what you are talking about with the torque arm, we used to snap off the trans tailshaft while running that setup. I learned that one a long time ago.
 
#12 ·
Lonestar said:
I have solid front mounts and the Lakewood trans mount.
If you are going to use solid engine mounts then you should also use a solid trans mount. Assuming that the Lakewood trans mount is not a solid mount, then the way you have it now allows the trans to "flex" in its mount while the engine can not flex causing a great increase in the forces at the trans mount.

Either mount the engine and the trans solid or mount them all in rubber.
 
#13 ·
Frisco said:
If you are going to use solid engine mounts then you should also use a solid trans mount. Assuming that the Lakewood trans mount is not a solid mount, then the way you have it now allows the trans to "flex" in its mount while the engine can not flex causing a great increase in the forces at the trans mount.

Either mount the engine and the trans solid or mount them all in rubber.
Exactly..... the way it is now...the engine mounts cannot flex so the tranny mount is getting all the force.
 
#14 ·
Henry Highrise said:
Exactly..... the way it is now...the engine mounts cannot flex so the tranny mount is getting all the force.
I have used solid mounts on the trans in the past with disastrous consequences. Typically the tailshafts are ripped off of the trans.

The best way that I have found so far is with my current setup, which I have used extensively over the years. One vehicle was a '73 Firebird loaded with a Kenne-Belle stroked Buick 455 (492 ci)...solid motor and rubber trans mounts were the only way I could keep the thing together.

We used a cable on another 3rd gen f-body in the same manner as my picture, only it did not have any give and coupled with the rubber motor mounts resulted in the trans being ripped off of the engine. It was quite a sight actually, left about 2" of the bell still bolted to the engine and the rest on the ground.

I do not seem to have any issues with launch, but the 1-2 shift gets me every time. My thought is that with this idea I can have a rigid mount with just enough give to absorb the shock.
 
#16 ·
johnsongrass1 said:
Have you thought about using a midplate and not using the rear trans mount at all?

Is your four link moving the axle forward enough to jam the driveshaft into the tranny and lifting the trans?

Is the body flexing enough to stress the joint?
I was just thinking of force from the drive shaft into the tranny also...that could very well be part of the problem......
 
#17 ·
johnsongrass1 said:
Have you thought about using a midplate and not using the rear trans mount at all?

Is your four link moving the axle forward enough to jam the driveshaft into the tranny and lifting the trans?

Is the body flexing enough to stress the joint?
There is no indication of either of these, I mounted one of those cheapo web / video cams under the car and recorded what was going on. Even though the recording was crappy I coudn't identify any issues.

I had thought about body flex, but I do have sub frame connectors and I do not see any indication of flex in all the normal areas (quarters, door jambs, etc..)
 
#21 ·
johnsongrass1 said:
What are your upper and lower links lengths?
I appreciate you all being helpful in trying to diagnose this issue, so I will post all my drawings / notes on the set-up. Considering that I recently got my drivers license back after almost 10 years I had plenty of time to play so there are a ton of notes. This will take me some time as my new wife has the house boxed up in storage right now while she is remodeling and painting it. If I missed something in the set-up and you guys spot it that would be great (although I must admit I hate being wrong).

On top of that I have a nasty head cold so I won't be going out to the shop to get actual measurements right now AND we are leaving tonight for a week down in Raleigh for Thanksgiving.

If memory serves me correctly, the uppers were appx. 24" and the lowers were appx. 32". Both do have 1" of adjustment available.

As far as installing motor plates, I do not want to do that as I do not plan on keeping this engine in the car forever. I intend on using this car for a variety of different engines, including a stroked Buick so using plates would severely complicate things. This vehicle needs to be a "universal" type set-up for this reason.

When I get back I will spend some time going through my notes and getting them in order so someone other than myself can understand them (I am horrible at documenting things).
 
#22 ·
Just to let you know that I'm back and will be compiling my paperwork and drawings as soon as possible. With the remodeling going on and the fact the wife wants it done by Christmas I don't know how soon it will be (there's a lot of notes, and the drawings are full scale so they will need to be scaled down), not to mention I have to dig them out of storage.

I went to move the car the other day and for some odd reason it won't go into gear now...haven't had a chance to look at it yet.

Will get some stuff posted asap.
 
#23 ·
Lonestar said:
Just to let you know that I'm back and will be compiling my paperwork and drawings as soon as possible. With the remodeling going on and the fact the wife wants it done by Christmas I don't know how soon it will be (there's a lot of notes, and the drawings are full scale so they will need to be scaled down), not to mention I have to dig them out of storage.

I went to move the car the other day and for some odd reason it won't go into gear now...haven't had a chance to look at it yet.

Will get some stuff posted asap.

Your wife wants remodel finished by Christmas? Did she specify a year?

:D
 
#24 ·
Crosley said:
Your wife wants remodel finished by Christmas? Did she specify a year?

:D
Put it this way, she almost has a degree in Architecture and she thinks she is a decendent of Frank Loyd Wright. I came home to walls literally torn out a couple of weeks ago.

I guess I was procrastinating too much so she thought she'd help me along.
 
#25 ·
Lonestar said:
Put it this way, she almost has a degree in Architecture and she thinks she is a decendent of Frank Loyd Wright. I came home to walls literally torn out a couple of weeks ago.

I guess I was procrastinating too much so she thought she'd help me along.

I got a PhD in procrastinating.

good luck,

post back when you can
 
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