Date: Wed, 3 Sep 1997 13:26:50 -0400 (EDT)
From: Mark Wallace
To: Big Jeep List
Subject: How To Rebuild your Automatic Transmission Part I.
Preliminary thoughts:
1. Automatic Transmissions have a lot of parts, and are not exactly
simple, If rebuilding a carburator or an engine represents a substantial
challenge for you you may be better of going to a non-AAMCO transmission
shop. On the other hand rebuilding an automatic transmission is definitely
within the realm of what a good ametuer mechanic can expect to do
correctly.
2. Cleanliness is of utmost importance. Any place where there is wind and
dust and dirt is probably unacceptable. I used the kitchen table after
coving it with first some plastic garbage bags and then some masking
paper. I had some newspaper down too.
3. More likely you will have to buy some tools, and it is not entirely
unlikely that those will be expensive tools. Of course keep in mind that
my taste in tools tends toward quality name brands, and that you'll
probably end up with at least a few new tools that you'll never know how
you did without. I tried to include tools used in the pictures whenever I
could.
4. You will need a good manual. I used a factory Jeep shop manual for the
81 model year. This particular manual actually has the same cover graphic
as the owners manual so it's a pretty cool relic too. I'm writing this how
to mainly so that anyone considering this undertaking can get a good idea
of what they are getting into from an ametuer's perspective.
5. I am not an expert on this subject. I rebuilt one transmission (a
Torqueflyte 727, but I'm sure the TH-400 is similar) and it made it across
the country without incident. Had it failed along the way I don't think
that I could have witten a workable how to.
With that in mind it's time to break out the tools and get dirty.
TRANSMISSION REMOVAL
1. Transmission Removal: There are a couple of ways to go about doing
this, and the various methods probably can be best chosen according to
what other work has to be done on the Jeep. Basically what I did was drop
the transfer case and remove it out the bottom, unbolt the engine mounts,
unbolt the transmission from the crossmember and then unbolt the
crossmember from the frame. I then pulled the engine and transmission as a
single unit following the transmission with a bucket to catch the fluid.
(With the stock tranny pan no matter what you are going to make a mess
with the tranny fluid) I then set the transmission on an overturned five
gallon bucket and divorced the engine and transmission. If you plan to
save your torque converter (more later) you want to try and hold it on the
transmission for the time being so that you don't beat up anything
important. After the transmission is out the entire transmission should be
set in a bucket with the tailshaft assembly pointed down to drain the
remainder of the transmission fluid out.
TORQUE CONVERTER REMOVAL
2. Torque Converter Removal: With the transmission divorced from the
engine pull the torque converter straight out. Set it someplace safe even
if you don't plan on re-using it as there will probably be a core charge
for the replacement torque converter.
TRANSMISSION PAN REMOVAL
3. Transmission Oil Pan Removal: With the transmission upside down, unbolt
the pan. The pan may need to be pried off. Note whether RTV has been used
to glue on the pan. (AAMCO did use RTV to glue on my pan, which is 100%
incorrect. Automatic transmission fluid will disolve RTV, so consequently
I found a substantial amount of RTV stuck to the transmission filter, and
floating around in the bottom of the pan.) Look for an excessive amount of
particulate matter. If there is a lot plan on replacing the torque
converter.
VALVE BODY REMOVAL
4. Valve Body: As soon as the pan is off you can see the valve body. This
is the hydraulic brain for the automatic transmission. It is full of
sliding valves, springs, and check balls. (If AAMCO rebuilt your
transmission last it is probably also full of particulate matter, which is
not correct. Judging from the dirt that I cleaned out of the valve body
I don't think AAMCO had ever even had it apart). Rebuilding the valve body
is fairly straight forward, but first it has to be removed from the
transmission. It is held on by a few bolts on each end and has the park
lock rod attached to the manual shift detent by an e-clip. you can remove
the whole valve body without removing the park lock rod from the valve
body and the park lock rod just slides out.
REBUILDING THE VALVE BODY
5. Rebuilding The Valve Body: This is no more complex that taking the
valve body apart, cleaning it carefully, and putting it back together,
except for one detail: The valve body for the 727 has 106 different parts
and they all look more or less the same. This is where the manual really
starts to help. What I did is I laid each part on the paper on my table,
drew a box around it, labeled what it was, and then proceeded to do the
next part. When I was cleaning the parts I made a new piece of paper so
that I did not have to set the clean parts back into the dirt that I had
just washed off. I cleaned the parts in a plastic dishwashing tub in paint
thinner, which is not the best solvent because it leaves a residue, but it
worked okay for me. Safety Clean, or brake cleaner would be better. It is
also important not to used either shop towels or paper products to clean
the valve budy (or any part of the transmission for that matter because
any lint left in mechanisms can cause problems later). When everything is
clean and dry reassemble the valve body in reverse order torquing
everything to proper spec. (You'll need a torque wrench that reads in
inch-lbs.)
MEASURE ENDPLAY
6. Rotating Assembly Endplay Measurement: Both the input shaft and output
shaft endplay need to be measured before the rotating mass is
disassembled. This is because a selective thrust washer is used to
determine endplay and it needs to be determined whether the selective
thrust washer needs to be replaced. (In my case The endplay was way out of
spec and by replacing the selective thrust washer with the thickest thrust
washer available I was just barely able to get it back into spec. Once
again this is something that AAMCO should not have screwed up) The manual
says to use a dial indicator, but I was able to use a straightedge and a
dial caliper. Once again the endplay spec is in the manual.
TAILSHAFT ASSEMBLY REMOVAL
7. Tailshaft Assembly Removal and Contents: On the rear of the
transmission there is a short (as in maybe about eight inches in length)
aluminum housing that adapts the transmission to the transfer case. It
also houses the park sprag, the governor, a ball bearing, a seal, and some
of the output shaft. Remove the six bolts that hold the tailshaft assembly
to the main case and slide the tailshaft assembly off. The ball bearing
should fall out, and the seal can be removed with a punch and a ball peen
hammer (or a seal pusher if you have one). The governor is a small valve
assembly that is held on the output shaft with a pin that goes through the
output shaft. The governor is bolted to the park sprag which rides on a
spline on the output shaft. Once this is all apart clean it and reassemble
it.
Mark Wallace
81 Wagoneer
Boston MA
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