Page 7-10 of the same manual gives the trouble diagnosis for leaks
especially the final drive to transmission leak. With so many final drives
lasting several hundred thousand miles, fluid contamination of it does not
seem to be a problem, nor does leaks from it to the tranny. However the
manual has missed one of the more obvious ones.
When working on the output shafts, some mechanics may not realize that the
final drive output shaft seal has a vent hole that ensures that pressure
does not build up in the final drive forcing fluids to places it should not
be. Some after market seals do not have this vent hole. Be careful!!!!
Install a seal without the vent hole and problems happen fast.
As for the failures of the transmissions, I have a strong opinion that fluid
contamination is not the culprit. Heat is. Remember for all practical
purposes you are using a transmission designed for a 5000 pound car in a
12,000 pound coach. When automatic trannys slip they produce heat. I would
wager that if everyone did the following they would eliminate 99% of their
problems.
1. Have their trannys tested at a reputable shop to ensure that pressures
etc are OK.
2. Add synthetic tranny fluid.
3. Disconnect the tranny lines from the radiator(remember the tranny can
also pick up heat from the radiator, overheat the engine and your could
overheat the tranny).
4. Install a good heavy duty tranny cooler such as the Perma-cool
PRM-12311(really beautiful unit with 500CFM fan) (available from Summitt
1-800-230-3030 for $139.95).
5. Install an inline tranny fluid filter kit with temperature gauge such as
Perma-cool PRM-10677, available from Summitt for $79.95
5. Install a tranny temperature gauge and monitor it.
6. Have a beer and relax.
The alternative? Worry about it until it fails.
I would also install syntehtics in the final drive.
Just what I am going to do as Arch would say.
>
>> Also found final drive fluid in the tranny so I pulled the final drive unit
>> this afternoon. Bearings seem to be worn as there was a lot of metal powder
>> in
>> the drive cover and around the pinion seal.
>
>Nelson et al,
> WARNING, FOLLOWING CONTAINS WILD SPECULATION, OR MAYBE A FLASH OF INSIGHT
>
> When I read the above message, I went running for my shop manuals. You
>see, for over 20 years I was in the foreign car repair business, and this
>brought back some things I should have remembered before. A few foreign cars
>(Subaru comes to mind) used a fore-aft engine driving an automatic FWD
>transaxle. Some (eg: Saab) even use a chain drive like the GMC. What I was
>concerned with was the connection from the transmission to the final drive,
>especially when the two use different kinds of fluid. Some cars (again, I
>think Subaru) just put two oil seals back-to-back between tranny and final
>drive to keep their respective fluids separated.
>
> The trouble with this design is that if one of the seals fails, the
>resulting leak will just pass through the other seal, as the oil comes to it
>backwards. It was very common on 1980s vintage Subarus to find the final
>drive overfull and leaking ATF, which caused accelerated wear of the final
>drive gears and bearings. Worse yet, occasionally final drive gear oil would
>find its way into the transmission. Automatic transmissions don't tolerate
>Extreme-Pressure gear oil very well. The stuff soaks into clutch discs,
>causing them to slip and eventually burn out. Even one-way roller and sprag
>cluthes may be made to slip by enough EP oil. The presence of gear oil was
>easily detected in the transmission by its strong sulfurous odor on the
>dipstick. Of course once a transmission was burned-out from slippage, the
>strong burnt-fluid/clutch odor might mask the gear oil smell, so no one would
>know the true cause...... And of course if someone used synthetic gear oill,
>it may not smell as strongly as dino-base gear oil. Hmmmm....????
>
> Now some later automatic transaxles, and some other makes, solved this
>problem by separating the two seals (ATF and gear oil) by just a millimeter or
>two, and drilling a drain hole to the outside. Now any leakage would go to
>the ground, where it might be noticed, instead into the wrong gearcase where
>it would wreak havoc. Looking at the pictures in my X-7525A manual (Section
>3-C, Fig. 1, A), the GMC's seals are back-to-back in a housing, and no weep
>hole is visible..... Can any transmission people confirm or deny this??? The
>pinion bearing/seal housing is part of the final drive assembly.
>
> My speculation is that this may explain some of the sudden transmission
>failures we see. Given the well-known problems with clogged final drive
>vents, gear oil could easily be forced into the transmission, ruining one or
>the other unit. (The transmission by contamination/slippage, the final drive
>by oil starvation.) Don't want to start another myth, but this idea really
>has me wondering....
>
> Given the placement of the trans/final drive seals in the pinion bearing
>holder, I'm not sure if a permanent fix is possible. I'd only suggest that
>everyone be alert for any gear oil smell in their ATF, check frequently for
>any sign of gain or loss of final drive oil, change ATF often, and replace
>those seals carefully if you ever separate the transmission and final drive.
>
> My .02. Comments anyone? Perhaps Jim Bounds can share some experience on
>this??
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
especially the final drive to transmission leak. With so many final drives
lasting several hundred thousand miles, fluid contamination of it does not
seem to be a problem, nor does leaks from it to the tranny. However the
manual has missed one of the more obvious ones.
When working on the output shafts, some mechanics may not realize that the
final drive output shaft seal has a vent hole that ensures that pressure
does not build up in the final drive forcing fluids to places it should not
be. Some after market seals do not have this vent hole. Be careful!!!!
Install a seal without the vent hole and problems happen fast.
As for the failures of the transmissions, I have a strong opinion that fluid
contamination is not the culprit. Heat is. Remember for all practical
purposes you are using a transmission designed for a 5000 pound car in a
12,000 pound coach. When automatic trannys slip they produce heat. I would
wager that if everyone did the following they would eliminate 99% of their
problems.
1. Have their trannys tested at a reputable shop to ensure that pressures
etc are OK.
2. Add synthetic tranny fluid.
3. Disconnect the tranny lines from the radiator(remember the tranny can
also pick up heat from the radiator, overheat the engine and your could
overheat the tranny).
4. Install a good heavy duty tranny cooler such as the Perma-cool
PRM-12311(really beautiful unit with 500CFM fan) (available from Summitt
1-800-230-3030 for $139.95).
5. Install an inline tranny fluid filter kit with temperature gauge such as
Perma-cool PRM-10677, available from Summitt for $79.95
5. Install a tranny temperature gauge and monitor it.
6. Have a beer and relax.
The alternative? Worry about it until it fails.
I would also install syntehtics in the final drive.
Just what I am going to do as Arch would say.
>
>> Also found final drive fluid in the tranny so I pulled the final drive unit
>> this afternoon. Bearings seem to be worn as there was a lot of metal powder
>> in
>> the drive cover and around the pinion seal.
>
>Nelson et al,
> WARNING, FOLLOWING CONTAINS WILD SPECULATION, OR MAYBE A FLASH OF INSIGHT
>
> When I read the above message, I went running for my shop manuals. You
>see, for over 20 years I was in the foreign car repair business, and this
>brought back some things I should have remembered before. A few foreign cars
>(Subaru comes to mind) used a fore-aft engine driving an automatic FWD
>transaxle. Some (eg: Saab) even use a chain drive like the GMC. What I was
>concerned with was the connection from the transmission to the final drive,
>especially when the two use different kinds of fluid. Some cars (again, I
>think Subaru) just put two oil seals back-to-back between tranny and final
>drive to keep their respective fluids separated.
>
> The trouble with this design is that if one of the seals fails, the
>resulting leak will just pass through the other seal, as the oil comes to it
>backwards. It was very common on 1980s vintage Subarus to find the final
>drive overfull and leaking ATF, which caused accelerated wear of the final
>drive gears and bearings. Worse yet, occasionally final drive gear oil would
>find its way into the transmission. Automatic transmissions don't tolerate
>Extreme-Pressure gear oil very well. The stuff soaks into clutch discs,
>causing them to slip and eventually burn out. Even one-way roller and sprag
>cluthes may be made to slip by enough EP oil. The presence of gear oil was
>easily detected in the transmission by its strong sulfurous odor on the
>dipstick. Of course once a transmission was burned-out from slippage, the
>strong burnt-fluid/clutch odor might mask the gear oil smell, so no one would
>know the true cause...... And of course if someone used synthetic gear oill,
>it may not smell as strongly as dino-base gear oil. Hmmmm....????
>
> Now some later automatic transaxles, and some other makes, solved this
>problem by separating the two seals (ATF and gear oil) by just a millimeter or
>two, and drilling a drain hole to the outside. Now any leakage would go to
>the ground, where it might be noticed, instead into the wrong gearcase where
>it would wreak havoc. Looking at the pictures in my X-7525A manual (Section
>3-C, Fig. 1, A), the GMC's seals are back-to-back in a housing, and no weep
>hole is visible..... Can any transmission people confirm or deny this??? The
>pinion bearing/seal housing is part of the final drive assembly.
>
> My speculation is that this may explain some of the sudden transmission
>failures we see. Given the well-known problems with clogged final drive
>vents, gear oil could easily be forced into the transmission, ruining one or
>the other unit. (The transmission by contamination/slippage, the final drive
>by oil starvation.) Don't want to start another myth, but this idea really
>has me wondering....
>
> Given the placement of the trans/final drive seals in the pinion bearing
>holder, I'm not sure if a permanent fix is possible. I'd only suggest that
>everyone be alert for any gear oil smell in their ATF, check frequently for
>any sign of gain or loss of final drive oil, change ATF often, and replace
>those seals carefully if you ever separate the transmission and final drive.
>
> My .02. Comments anyone? Perhaps Jim Bounds can share some experience on
>this??
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
>
Tom & Marg Warner
Vernon Center NY
1976 palmbeach
