Hot Rod Forum banner
1 - 16 of 16 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
Hi all, looking for some advice on things to check on recent rebuild.
This is a 1984 700r4 I just rebuilt for my sons k20 it had a TH 400.
The problem is I have no gears what so ever.
I'm pretty sure the fluid level is full and it has 70psi pressure at idle. I believe the internal drums are turning because when I try to put it in park you can hear the parking paw dragging against the clog.
My first quest is when does the band engage and should this be happening when putting it in park.
Second question does anyone know when the band is engaged.
I suspect I have a servo pin length issue since I did not have the factory tool for setting the length. I went off end cap movement of about .090"
When air testing the band seemed to engage and release properly and hub would not turn when band was on and would turn when band was off.
Pretty sure TV cable is set correct too.
Any thought on things to check would be appreciated.

Thanks
 

·
Administrator
Joined
·
10,122 Posts
A K20 with a T-400 trans? You installed a 700r4 trans? DId you change the transfer case to fit the 700r4 trans output shaft? The T-400 has a 32 spline output shaft for the transfer case. The 700r4 has a smaller 27 spline output shaft.

The fact that the parking pawl is ratcheting when the shifter is placed into Park... tells me the output shaft of the 700r4 is spinning.
 

·
Registered
Joined
·
25 Posts
The two different size splines can feel as though they are engaged when they actually are not. Jack up the car safely , slightly set the parking brake to create drag, then have someone work the brakes and the shifter while you watch from u derneath to see what is slipping.
It took me two attempts to get my th700 working correctle because of overlooking (rookie) mismatcehd splines. Fluid level also was low after priming the system even though I checked it a couple times.
 

·
Registered
1979 Chevrolet Malibu 496-TH400-9" (cruiser). 1992 Chevrolet S10 355-700r4-7.625" (daily driver).
Joined
·
250 Posts
Second question does anyone know when the band is engaged.
I suspect I have a servo pin length issue since I did not have the factory tool for setting the length. I went off end cap movement of about .090"
When air testing the band seemed to engage and release properly and hub would not turn when band was on and would turn when band was off.
The band is engaged in 2nd and 4th gear. You do not have a servo pin length issue. The .090" movement is good. A lot people (even quite a few who own the tool) check it that way with the servo cover.
 

·
Registered
Joined
·
183 Posts
Still trying to figure out what would possess anyone from replacing a T400 with a 700R4? Yea the fourth gear thing but between all the expense for the swap, a T400 is simple to rebuild and so much heavier duty trans. Just my opinion, have fun with your project. .
 

·
1949 Ford Coupe RESURRECTION
Joined
·
1,050 Posts
So you spent a couple hundred to get a truck that will still get 7 mpg.
Lowering the rpm doesn’t always gaurentee better mileage.
At today's gas prices and what they are likely to be, (7 to 10 bucks) as long as the present folks who are now running the country, it's worth a try...
 

·
Registered
Joined
·
899 Posts
So you spent a couple hundred to get a truck that will still get 7 mpg.
Lowering the rpm doesn’t always gaurentee better mileage.
Yep. I've seen that first hand. When I built the TBI 350 for dad's '87 S-10 Blazer it had 3.42 gears in it. We picked up another rear axle with 2.73's in it. RPM's dropped, but the MPG didn't change a bit. Maybe 3.08's would have been better?
 

·
Registered
Joined
·
5,982 Posts
That wasn’t the point.
too many people assume reduced rpm means reduced fuel use. They spend a bucket full of cash and in a lot of cases their mileage remains the same.
 
1 - 16 of 16 Posts
Top