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Old 08-31-2007, 07:42 PM
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Blowen front seal on 700R4

I was airing out the S10 today for the first time since getting it running. Looked into the rear view mirror and lots of blue smoke.

To make a long afternoon short, it appears the front seal has blown out and dumped all the trans fluid out. So it looks like it's not going to be able to handle all that line pressure. Or is there a way to hold the seal in better?

Line pressures at idle;
P=100
R=155
N=100
4=100
3=100
2=140
1=140

At 1500RPM w/TV cable pulled full out;
P=250
R=250
N=240
4=245
3=245
2=140
1=140

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Old 09-01-2007, 11:12 AM
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Quote:
Originally Posted by Overdriv
I was airing out the S10 today for the first time since getting it running. Looked into the rear view mirror and lots of blue smoke.

To make a long afternoon short, it appears the front seal has blown out and dumped all the trans fluid out. So it looks like it's not going to be able to handle all that line pressure. Or is there a way to hold the seal in better?

Line pressures at idle;
P=100
R=155
N=100
4=100
3=100
2=140
1=140

At 1500RPM w/TV cable pulled full out;
P=250
R=250
N=240
4=245
3=245
2=140
1=140


year , mileage , age of this trans 700r4?

Early 700r4 trans suffered with front converter hub seal blow out for several reasons.

Drain hole behind seal was small

Pump bushings were a bit loose or the converter hub a bit small... this allowed more fluid up against the back of the seal. Small drain hole did not allow enough oil to get out of there and the seal would blow out.

For a while there was even a special bushing made with a teflon seal ring in the babbit. Problem with this was the teflon would wear a groove in the converter hub area.

There are several items to address in this needed repair .

post back when you can.

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Old 09-01-2007, 01:12 PM
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Quote:
Originally Posted by Crosley
year , mileage , age of this trans 700r4?

Early 700r4 trans suffered with front converter hub seal blow out for several reasons.

Drain hole behind seal was small

Pump bushings were a bit loose or the converter hub a bit small... this allowed more fluid up against the back of the seal. Small drain hole did not allow enough oil to get out of there and the seal would blow out.

For a while there was even a special bushing made with a teflon seal ring in the babbit. Problem with this was the teflon would wear a groove in the converter hub area.

There are several items to address in this needed repair .

post back when you can.

This trans is out of a 1983 pickup with a diesel. Not many miles since the updates and overhaul. I have put in a lot of updated parts if you need a list, I can provide. It has the Bowtie Overdrive EZTV system in it and I emailed them with my pressures, they said they were correct for everything that has been done to it and their TV system.

I wonder if this being an older trans if the drainback hole is to small like you suggest. Can that be drilled out? To what size?

I also noticed after looking at a few transmissions on the internet that my trans mission does not have a seal retainer. It did not have one That I know of when I got it. I guess that is a very important part??

Do you think anything else has been damaged?

Thanks for the reply.
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Old 09-01-2007, 01:34 PM
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Quote:
Originally Posted by Overdriv
This trans is out of a 1983 pickup with a diesel. Not many miles since the updates and overhaul. I have put in a lot of updated parts if you need a list, I can provide. It has the Bowtie Overdrive EZTV system in it and I emailed them with my pressures, they said they were correct for everything that has been done to it and their TV system.

I wonder if this being an older trans if the drainback hole is to small like you suggest. Can that be drilled out? To what size?

I also noticed after looking at a few transmissions on the internet that my trans mission does not have a seal retainer. It did not have one That I know of when I got it. I guess that is a very important part??

Do you think anything else has been damaged?

Thanks for the reply.
yes , the drain back hole can be drilled out... 1/4 inch long drill bit from a Lowes or Home depot works. Also drill matching drain hole in the stator support (pump cover)

A fresh bushing & seal. Seal retainer is a band aid device IMHO , on the flip side I use them .

Check converter hub for wear.

You also need to check the pump bushing to see if it "walked" forward into the back of the seal. Early pump housings did not have a retaining lip machined into the bushing area to keep the bushing from walking forward.

A procedure to stake the bushing in place is easy to do... file notches on the inner edge of the bushing area. Then stake the spots of the bushing into the filed notches. Use of red locking chemical agent is suggested too.

Other damage could be many things IF the trans was run out of fluid.



stake the bushing:




drill hole - drain back :


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Last edited by Crosley; 09-01-2007 at 01:42 PM.
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Old 09-02-2007, 09:00 AM
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Crosley, thanks for the reply! We will have the trans out today, so will have a better understanding of what is going on in there.

Looking back on my notes during the rebuilding, it appears I did drill out the drain hole in the pump body, but no notes on the matching hole in the case?? We'll see.

I rebuilt this thing for my sons S10 hotrod in 2002, so memory of the details of the rebuild are gone. I'm lucky to remember my name some days.

I'm hoping it's just the fact that I didn't drill the drain in the case and I'm pretty sure I didn't use any adhesive on the bushing or the seal. Converter is new so hopefully the hub is the correct size.

Thanks again.
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Old 09-02-2007, 10:34 AM
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I use red loc-tite on the bushing and the seal.
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Old 09-02-2007, 04:03 PM
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Well, the 700 is out and we see the problem. I did not stake the pump bushing, and didn't use adhesive and the bushing walked out into the seal causing it to fail. That appears to be all the extent of the damage.

I have posted these pictures;
This shows the bushing as we found it after removing the seal.


Another view from inside of pump.


This hole is the same size as the drilled out drain from seal area, should it be bigger?


This is the mating hole in the pump cover that I did not drill out, I should correct?


Crosley, do you think I'd be better off getting a newer pump? This one seems to be doing well except for this???

Thanks for your time and expertise.
overdriv
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Old 09-02-2007, 05:15 PM
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drill the matching drain hole in the stator support ( pump cover).

Use a babbit type pump bushing. Babbit bushing is more forgiving.. teflon will flake off during the stake process... stake bushing in place , use the red locking agent too.

IF you get a late pump assembly there is a hole that needs to be plugged since the later units have a transfer tube for the aux v-body.

There are early designs of pumps and stator support covers. A mis-match of early & late designs can result in very low main line pressure.

I notice your stator support has a 3-4 clutch bleed hole in it. I suggest you plug that hole for better feed to the 3-4 clutch. GM eliminated this hole in later years.

In the photo is the hole I suggest to plug. Drive out the capsul check ball device & a 5/16 tap with thread this hole.... an allen head type plug will fit. Make sure the plug is below the surface. Run a file over the surface to correct any lifted metal from tapping.

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Old 09-02-2007, 07:43 PM
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Will do all you suggest.

What caused the bushing to move toward the seal? Should I replace that bushing, it hasn't many miles on it?

Is there a place online where I can buy individual parts & gaskets? I need a pump gasket and a bushing probably.

Thanks for the time and effort.
overdriv
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Old 09-15-2007, 10:32 PM
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Got the 700 back in and all is well. I want to recheck the line pressures to be sure everything is as before.

Crosley, what made the seal walk forward? High pressure or bad pump design, maybe both?
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Old 09-16-2007, 12:49 PM
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Quote:
Originally Posted by Overdriv
Got the 700 back in and all is well. I want to recheck the line pressures to be sure everything is as before.

Crosley, what made the seal walk forward? High pressure or bad pump design, maybe both?

usual cause is pressure / heat moves the bushing forward.

Gm changed the design so there is a small lip to stop the bushing from migrating forward into the seal.
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Old 09-26-2007, 05:03 PM
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Just wanted to update a bit. The 700R4 has survived several all out dashes through 4th gear under full throttle and seal and bushing seem to be staying put. Hope that is solved for good.

I'm very impressed with the 700R4. I've never had a trans shift as solid and operate as strong as this one feels. I don't know how long it's going to last but it's a hoot to drive. The clutchless manual trans guy haven't got anything on this one.

Thanks for your help on this Crosley, I appreciate it.
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