4L80E & TH400 Tech.

[softballnrd27]

I made a mistake the 98 has just under 100,000 and I was also looking at a 03 unit with 80k and got the mileage mixed up. The 03 was sold before I could get to it.

[picklito]

Excellent thread. Helped me tune up my TH400 really nicely.

Now, how about a stock 2003 Yukon 2500XL with 8.1 and 4L85E. It has 116,000 miles, the trans "works" perfectly and there are no trouble codes... but it shifts so soft I can't stand it. It's a daily driver, so what would I do to just firm up the shifts? I'm about to go in for a filter change... can I just enlarge the feed holes a bit? I'm concerned the 3rd and 4th accumulator mod might be too harsh?

[clinebarger]

A Boost Valve & enlarging the feed holes will work, And....You are correct, Do not block Accumulators with a stock to 2800 stall converter.


For Non-Performance-Stock converter transmission orifice sizing, Do Not go bigger than a 50% "Area" increase over the Stock diameter! Shifts will get pretty rough if you do.

Stock 10% 20% 30% 40% 50%
0.040 0.042 0.044 0.046 0.047 0.049
0.045 0.047 0.049 0.051 0.053 0.055
0.050 0.052 0.055 0.057 0.059 0.061
0.055 0.058 0.060 0.063 0.065 0.067
0.060 0.063 0.066 0.068 0.071 0.073
0.065 0.068 0.071 0.074 0.077 0.080
0.070 0.073 0.077 0.080 0.083 0.086
0.075 0.079 0.082 0.086 0.089 0.092
0.080 0.084 0.088 0.091 0.095 0.098
0.085 0.089 0.093 0.097 0.101 0.104
0.090 0.094 0.099 0.103 0.106 0.110
0.095 0.100 0.104 0.108 0.112 0.116
0.100 0.105 0.110 0.114 0.118 0.122
0.105 0.110 0.115 0.120 0.124 0.129
0.110 0.115 0.120 0.125 0.130 0.135
0.115 0.121 0.126 0.131 0.136 0.141
0.120 0.126 0.131 0.137 0.142 0.147
0.125 0.131 0.137 0.143 0.148 0.153

**I have the chart spaced correctly in my reply, But the site will NOT take it without spacing it funny? I hope you can read it.....***

[picklito]

Originally Posted by clinebarger

A Boost Valve & enlarging the feed holes will work, And....You are correct, Do not block Accumulators with a stock to 2800 stall converter.


For Non-Performance-Stock converter transmission orifice sizing, Do Not go bigger than a 50% "Area" increase over the Stock diameter! Shifts will get pretty rough if you do.

Stock 10% 20% 30% 40% 50%
0.040 0.042 0.044 0.046 0.047 0.049
0.045 0.047 0.049 0.051 0.053 0.055
0.050 0.052 0.055 0.057 0.059 0.061
0.055 0.058 0.060 0.063 0.065 0.067
0.060 0.063 0.066 0.068 0.071 0.073
0.065 0.068 0.071 0.074 0.077 0.080
0.070 0.073 0.077 0.080 0.083 0.086
0.075 0.079 0.082 0.086 0.089 0.092
0.080 0.084 0.088 0.091 0.095 0.098
0.085 0.089 0.093 0.097 0.101 0.104
0.090 0.094 0.099 0.103 0.106 0.110
0.095 0.100 0.104 0.108 0.112 0.116
0.100 0.105 0.110 0.114 0.118 0.122
0.105 0.110 0.115 0.120 0.124 0.129
0.110 0.115 0.120 0.125 0.130 0.135
0.115 0.121 0.126 0.131 0.136 0.141
0.120 0.126 0.131 0.137 0.142 0.147
0.125 0.131 0.137 0.143 0.148 0.153

**I have the chart spaced correctly in my reply, But the site will NOT take it without spacing it funny? I hope you can read it.....***

Your chart came through well. Thanks. Some stock data if it's helpful:

2003 Yukon XL 2500 8.1/4L85E/4.1
1-2: .070"
2-3: .075"
3-4: .050"

The holes are so much smaller than I expected, I'm not quite sure what to do. Might just use your recommended .085/.093/.085.

[clinebarger]

Originally Posted by picklito

Is there a way to make the torque converter clutch engage more firmly?

A Sonnax TCC regulator valve with the (.300 OD spring) will firm up lock-up.
http://www.sonnax.com/parts/2025-tcc...1-instructions

Originally Posted by picklito

Your chart came through well. Thanks. Some stock data if it's helpful:

2003 Yukon XL 2500 8.1/4L85E/4.1
1-2: .070"
2-3: .075"
3-4: .050"

The holes are so much smaller than I expected, I'm not quite sure what to do. Might just use your recommended .085/.093/.085.

I don't know how you want the shift feel, "Feel" being very subjective!

Here are largest holes I would recommend. Your truck is pretty heavy & can absorb a lot of shift energy. And you seem to want the shifts to be noticeably firmer.
2nd: .093"
3rd: .101"
4th: .093"