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PostPosted: Sat Jun 17, 2017 9:28 pm 
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Joined: Wed Jul 29, 2015 12:30 pm
Posts: 21
Year and Trim: 1997 Pontiac Bonneville SE
I replaced my 87 Pontiac Bonneville SE's rotted #2 and #3 subframe bushings, and replaced its subframe. I went through the pain of doing this in order to pass all necessary safety inspections in my state,

I have a question, about rotted GM subframes, whose answer may motivate me to develop a solution to help the typical DIY mechanic (like myself), who has the same problem, by having their problem resolved quickly, at low cost.

Some background first: I seems that it would cost a typical non-DIY owner about $1000 to replace a rotted subframe and 4 bushings (#2 & #3) because the cost of a good used subframe is $300, 4 bushing kits is $200, and professional labor is about $500). Also, rotted subframes & bushings are a safety problem caused by faulty GM designs, and therefore replacement should be performed at no cost by having GM RECALL all cars having this problem. However, this is not the case, so it's now up to typical owners to pay the full cost of repair, or DIY mechanics to find a low-cost solution to their problem.

I have an idea for such a solution that I may be willing to develop, depending on its demand, which could cost a DIY mechanic only about $500 to only replace 4 bushings (#2 & #3), add a few more parts easily, and NOT NEED TO REPLACE OR EVEN REMOVE THE ENTIRE ROTTED SUBFRAME!

My question is:

1) How many GM cars, over all years and all makes and models, have a rotting subframe/bushing problem, (i.e. enough subframe/bushing rot for one, some or all of the #2 and #3 bushings to pop though their subframe)? These cars should be well enough to last for a few more years, at least, if their subframe problem is repaired.

Thank you in advance for your answers. I'll be checking this forum, from time-to-time, while I start by taking some subframe measurements and spend an hour or two to make preliminary drawings of my design idea.


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PostPosted: Sat Jun 17, 2017 10:18 pm 
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Joined: Tue May 27, 2008 8:53 am
Posts: 5179
Location: Las Cruces, NM
Year and Trim: 1993 Buick Park Avenue
1994 Buick Regal Custom
Fair warning, I live in the desert southwest, so I am probably the least qualified on this board when it comes to rust based issues.

However, I do have a few concerns.

I don't know what models are affected by the subframe issues specifically, but, let's say it's all 87-99 C/H bodies. Typically, a subframe issue is not the only issue on a car when it happens. Usually there is a fair amount of rust elsewhere, including the rockers, rear wheel wells, etc. I feel that corrosion at the subframe bolt points is as much of an issue as the subframe itself. Attrition is also taking its toll on these cars, whether it be failed LIM/UIM issues not caught in time that frag an engine, to transmission failures, rust is just another of the things working against these cars, that, at best, are 20 years old.

Also, the cars are a dime a dozen in my area. Likely the lack of corrosion plays a huge part in it, but I can easily pick up another one if mine decides driving is not all it's cracked up to be anymore.

I would be curious to see what you come up with, but you mentioned that it's $500 in parts as it is to fix it, which is the same $500 you are proposing as an alternate solution to a DIYer.

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1993 Buick Park Avenue - 197k - Some odds and ends done - Simply won't die
1994 Buick Regal - 78k - Bone stock - Always ready for a good kicking
1990 Oldsmobile 88 - Gone to a better place


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PostPosted: Wed Jun 21, 2017 9:49 am 
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Joined: Tue Aug 25, 2009 8:32 pm
Posts: 4134
Location: Dearborn, MI
Year and Trim: '93 SSEi
'05 STS-4
'97 Camaro
'97 LeSabre
I've been through this a few times now.

I too have seen that the rear mount points where the cage nuts as high risk of failure.

A full, proper repair of this rust issue involves cutting out the rotted frame corner as well. To do this you need an access hole inside the footwell another access hole in the wheel well so you can weld in a patch panel, and also weld in new weld nuts (which means ditching the metric hardware in favor of 1/2" bolts and weld nut). I don't have any pictures of this part.

The cheapest way you can do this job, and have a properly functioning bushing, is the way I did it on my '97.

Image

Image

The basic setup is the lower washer from the suburban (1/2 the cost of the H-body washer) although the H-body washer will work if yours can be re-used, a 3/4" stainless pipe nipple 2.5" unthreaded, a 1/2" stainless washer, and some 1/2" ID high pressure rubber hose to act as a bushing inside the pipe and keep the bolt centered. The bushings fit exactly the hole made by a 1-7/8" hole saw.

I got the bolts, pipe, washers from McMaster, the lower washer from GMpartsdirect and the bushings from ebay. All in I spent less than $200, and maybe 3 hours welding (you have to hang the subframe on the car so everything is centered properly before tacking everything in place). The benefit of this is the bushing kit comes with enough parts to do two vehicles. That's also a negative, if you only have one vehicle...

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'93 Pontiac Bonneville SSEi - Twincharged, manual, racecar! Build thread
'92 Pontiac Bonneville SSE
'97 Chevy Camaro - 3800, T5, T-tops, my DD
'05 Cadillac STS - V8, AWD, her DD
'97 Buick LeSabre - L67, her racecar
'89 Buick LeSabre Limited - winter DD
'87 Buick LeSabre T-type - future victim
'84 GMC Sierra Classic - Twin turbo 3800 project
'67 Buick LeSabre - future victim


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PostPosted: Wed Jun 21, 2017 9:36 pm 
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Joined: Wed Feb 11, 2015 8:34 pm
Posts: 163
Year and Trim: 1996 Buick Lesabre Custom - metallic dark cherry
I found just recently that certain cars are more difficult to determine if they have rot or will rot out... example, I just got rid of a 91 Cadillac Sedan DeVille... It took me months of hunting to find a clean one and heres how I was able to determine if a car has good subframe, these Cadillacs use the same subframe as the h bodies, which does lead to possibilities of V8 engine swaps to the 4.9 non Northstar, a very good motor in my opinion... But I digress.

Every clean one I found in my price range had horrible rust of variating degrees the subframe.... after looking at about a dozen I realized that the shock towers in the rear would get rust holes sooner than subframe and in finding a car would be about finding clean towers... I know this doesnt help people who already own cars with subframe problems, but this info should help while looking at a new car or while trying to find a good frame in the junkyard or on a parts car....

I ended up getting a perfect caddy with zero rust that had been lightly hit in front... I was worried about winter, salt as I bought the car in January and I did some research on oiling your car... I had seen it done with bar and chain oil before and it makes a mess however a new oil i found that comes in a spray.... Its called Fluid Film and it says you can apply a layer to a freshly clean car and it keeps salt from getting trapped against metal. I tried on the subframe mounts... washing a car underneath will wipe some off everytime so i kept adding some after every bath. Come summer my venerable spots are still spotless not a hit of rust and i can see some slight surface rust where I didnt put any...

There are places that will put this stuff on for you but do it yourself is far more cost effective. I do not like undercoating because water always slips between and hidden rust begins... oil repels water and can stay moving in hidden areas like rockers and door sills... hope this helps some people out there

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PostPosted: Wed Jun 21, 2017 9:36 pm 
Offline
SSEi Member
SSEi Member

Joined: Wed Feb 11, 2015 8:34 pm
Posts: 163
Year and Trim: 1996 Buick Lesabre Custom - metallic dark cherry
I found just recently that certain cars are more difficult to determine if they have rot or will rot out... example, I just got rid of a 91 Cadillac Sedan DeVille... It took me months of hunting to find a clean one and heres how I was able to determine if a car has good subframe, these Cadillacs use the same subframe as the h bodies, which does lead to possibilities of V8 engine swaps to the 4.9 non Northstar, a very good motor in my opinion... But I digress.

Every clean one I found in my price range had horrible rust of variating degrees the subframe.... after looking at about a dozen I realized that the shock towers in the rear would get rust holes sooner than subframe and in finding a car would be about finding clean towers... I know this doesnt help people who already own cars with subframe problems, but this info should help while looking at a new car or while trying to find a good frame in the junkyard or on a parts car....

I ended up getting a perfect caddy with zero rust that had been lightly hit in front... I was worried about winter, salt as I bought the car in January and I did some research on oiling your car... I had seen it done with bar and chain oil before and it makes a mess however a new oil i found that comes in a spray.... Its called Fluid Film and it says you can apply a layer to a freshly clean car and it keeps salt from getting trapped against metal. I tried on the subframe mounts... washing a car underneath will wipe some off everytime so i kept adding some after every bath. Come summer my venerable spots are still spotless not a hit of rust and i can see some slight surface rust where I didnt put any...

There are places that will put this stuff on for you but do it yourself is far more cost effective. I do not like undercoating because water always slips between and hidden rust begins... oil repels water and can stay moving in hidden areas like rockers and door sills... hope this helps some people out there

_________________
Roads... Where we're going, we don't need roads


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