Jump to content

THM325-4L


Bjones512

Recommended Posts

Good morning guys 

 

So i purchased a 1983 riviera last year was running and driving fine till last week, I was driving and the transmission just lost power, It won’t go into drive or reverse. 
I have fluid fluid in it 

Link to comment
Share on other sites

pfloro has a lot of experience with these units. Hopefully he'll see this and respond , since you don't yet have enough posts to access the private message function.

 

The 325, like a lot of things the bean counters got into, was just too light-duty for these cars. Even with the weenie engines most had. 

 

Good luck. Flimsy transmissions and not-ready-for-prime-time electronics notwithstanding, this generation (79-85) of the E-body were some of the nicest cars GM ever made.

Link to comment
Share on other sites

5 hours ago, rocketraider said:

pfloro has a lot of experience with these units. Hopefully he'll see this and respond

Thank you, Rockeraider...

 

********

1) Even though you can't drive you Riviera at the moment, warm up the fluid by letting the engine idle & give it a little throttle in Park. 

2) Check the fluid level with the engine running (standard GM Hydramatic procedure).  

3) Is the fluid level correct?

4) Does the fluid smell burnt?  The color should be fairly bright red.

5) Are you hearing any strange noises before you shift into Drive or Reverse?  Apply a little throttle to raise engine speed... Any strange noises heard?

6) Shift into Drive or Reverse.  What is the nature of the noise?  Do you feel anything (a little bump) to indicate that the clutches are applying...?

 

*****

 

I suspect that the internal hydraulic pump is not producing adequate pressure to "apply" the clutches for either forward or reverse operation.  Different clutches are used for "D" and "R" so the problem is upstream.  The engine's flexplate (at the back of the crankshaft) connects to the outer shell of the torque converter (the impeller or converter pump). Through an indexed hub, the converter shell drives the pump (inside the transmission, at the front)...  I don't think this is a converter problem.

 

Line pressure can be measured via a tap on the side of the unit. This is a very important first step. 

 

In any event, the 325-4L needs to come out, disassembled, and inspected.

 

Paul

 

 

Edited by pfloro (see edit history)
  • Thanks 1
Link to comment
Share on other sites

5 hours ago, Bjones512 said:

I have checked the fluid level with the car on and it’s full, when you put it in gear it dosent do anything, but once I shift it into park that’s when it makes a weird grinding, clacking noise  

Unfortunately, this sounds like a "hard part(s)" failure.  I'm leaning this way because of the symptoms and because it failed suddenly.  The pump output may be fine but a main internal drive component (hard part) may have failed.  The fact that noises are heard in "P" but not in "D" or "R" suggests that hydraulic pressure is being developed by the pump...

 

If you have the unit rebuilt, by all means have a Trans-Go Shift Kit  installed.  It will greatly improve the durability of the 325-4L without snapping your neck at every shift.  I had one I installed during the 1st rebuild of my '84 Toronado (77,000 miles) and at 200,000 miles, the shifts were still crisp.  That 1st rebuild was needed because the "intermediate" band (creates 2nd gear along with many hard parts) had burned up.  Those GM cloud soft shifts combined with the marginal design were responsible...

 

Granted, the 325-4L can't handle too much power. However, with a shift kit and a small Transmission Oil Cooler installed at the bottom right side in front of the A/C condenser, the 325-4L will provide good service.   You want to keep the OEM cooler (vertical in the right side tank of the radiator).  Plumb the auxiliary cooler in series with the radiator cooler and "before" it.  This way, in the winter, "cold" fluid won't be sent back to the transmission.

 

 

Paul

 

 

 

Edited by pfloro (see edit history)
  • Thanks 1
Link to comment
Share on other sites

Even those had an abnormally high failure rate and it took the aftermarket to get them reliable behind the turbo engine.

 

A good friend was a Zone service rep out of GM's Rockville MD Zone office in the 80s. His territory included the mountains of VA, WV and western PA. The factory couldn't understand that Zone's high warranty claims on the 1st gen metric overdrive automatics. Those mountains were eating them alive.

 

HydraMatic Division was on record saying they couldn't build a transmission that would hold up behind the Turbo Buicks. This from a Division that built transmissions that easily lived behind the torque of GM's family of big block engines.

 

They could have easily produced a transmission that would have taken anything the Turbo engines threw at it- if the bean counters had let them.🙄

Link to comment
Share on other sites

3 minutes ago, rocketraider said:

Even those had an abnormally high failure rate and it took the aftermarket to get them reliable behind the turbo engine.

 

A good friend was a Zone service rep out of GM's Rockville MD Zone office in the 80s. His territory included the mountains of VA, WV and western PA. The factory couldn't understand that Zone's high warranty claims on the 1st gen metric overdrive automatics. Those mountains were eating them alive.

 

HydraMatic Division was on record saying they couldn't build a transmission that would hold up behind the Turbo Buicks. This from a Division that built transmissions that easily lived behind the torque of GM's family of big block engines.

 

They could have easily produced a transmission that would have taken anything the Turbo engines threw at it- if the bean counters had let them.🙄

There's an article in an old Hot Rod magazine about Buick experimental engines. One engine was a turbo charged nailhead. Built it but GM didn't have a transmission that could handle the torque.

Link to comment
Share on other sites

  • 4 months later...

Clarification & Suggestions:

 

1) In the '79 - 85 "E" body cars (Eldorado, Seville, Riviera, & Toronado), the aluminum cased "transmission" was separate from the cast iron cased "differential".

        The differential (known as the Final Drive), can be unbolted from the 325-4L.  More modern transversely mounted transaxles have the differential integrated into the transmission.

2) In your situation, there is damage to the left side "Output Shaft Flange" (what I'm calling this broken part).  From the picture, it appears that the splined part of the shaft is sheered off.  

        The broken part is still inside the spider gear cage.  Can you provide a side view?

3) I suspect the shaft broke due the left tire being spun when the car was standing still.  When the tire grabbed, the load weakened the shaft and it finally snapped under your ownership.

        Of course, that part may have had a hidden weakness when it was manufactured.  However, that Final Drive may have other problems brewing...!

4) I don't think you'll find this this part as a separate item.  They have not been manufactured since sometime in 1985. 

5) Your best bet is to locate one of the front drive cars listed above and remove the entire differential (the pumpkin).  Be sure to take both Output Shaft Flanges (L+R).  I'm pretty sure

        these flanges simply slide into the internal spider gear cage (just like the axle shafts on rear drive vehicles). 

6) At the very least, you will have the remove the front cover from your Final Drive.  You may then be able to remove the broken splined part of the shaft.  If there is no other damage to your

        Final Drive, you can use the new part.  However, the seal on that side may have been damaged so it should be replaced. 

7) You may want to inspect the bone yard Final Drive, and swap the entire unit.  Keep in mind that although the majority of these Final Drives were of the 2.73:1 "Final Drive Ratio", some cars

       were ordered with the optional 2.93:1 (?) or 3.35:1 (?) ratios.  I'm pretty sure the turbocharged V6 Riviera will have the 3.35:1 ratio.

 

Keep us posted...

 

Paul

 

PS:  Final Drive picture below is NOT from a 325-4L transmission.

 

 

325-4L 01.jpg

325-4L 02.png

Edited by pfloro (see edit history)
  • Like 1
Link to comment
Share on other sites

1)  The new pictures indicate the the "axle shaft" has NOT broken.   This leads me to believe that something more serious has happened within the differential (carrier bearing failure?)

     I had both the "carrier" and "pinion" bearings replaced in my Toronado's Final Drive so I know what they look like.  They are beefy tapered roller bearings which support the

     carrier itself and the pinion shaft.

2)  Whether or not you are able and willing to remove & replace the entire Final Drive yourself, another Final Drive (from a bone yard) is in order.   This is in case more has been

      damaged beyond bearings (ring & pinion gears, etc).

3) You actually need a shop which repairs/rebuilds "rear ends" rather than a transmission only shop.  Your Final Drive is much more like a conventional rear end (sans axle "tubes") rather

      than a differential inside a modern transaxle.  If you source another Final Drive yourself and bring it to the shop, they are probably more willing to swap your broken unit for the "new" one.   

4) An old time shop (if you can find one) is going to be your best bet. 

 

Paul

Edited by pfloro (see edit history)
  • Like 1
  • Thanks 1
Link to comment
Share on other sites

To satisfy my interest and perhaps that of others, can you remove the front cover of the Final Drive and take pictures?

The car has to be towed to the shop anyway...

 

Crack the bottom first and let the stinky, heavy gear oil drain.  

 

It would be quite interesting to see what happened.  The picture taken from the side (drain plug showing) is scary.

The axle shaft is leaning downward and pulling on the bottom of the shaft seal.  A gap between the top of the shaft and seal is visible.

Something has really let go inside...

 

It appears that the driver's side of the carrier dropped downward when things went south.  My bet is on a carrier roller bearing failure on that side.

The alignment of the ring and pinion gear teeth would have severely changed and those gears might now be damaged.  

 

The attached picture shows what you should see if everything is OK.  The ring gear is bolted to the carrier (multiple bolts).  The four smaller "spider" gears are

inside the carrier. The pinion gear is is at the back of the ring gear. Under the two vertical side "caps" are the tapered roller bearings which support the carrier. 

In this rear drive unit, the external axle "tubes" are visible.  If your driver's side carrier bearing disintegrated, the carrier would no longer be supported on that

side and drop down.

 

This is why I feel the entire Final Drive should be replaced.   There were a decent number of '79 -'85 "E" bodies made so finding one in a bone yard 

shouldn't be that difficult.

 

Paul

 

 

Differential Internals 01A.jpg

Edited by pfloro (see edit history)
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...