Brake problem not holding - Competition Diesel.Com

97rada · 09-23-2017, 08:20 PM

My race truck is not holding on the brakes. It's a 94 with a hydroboost conversion, new napa power steering pump and I have swapped a known good booster in and still can't hold 25 psi well. When you pump up the brakes with the truck off it has great pedal. Start it and pedal doesn't kick back like it should. It also doesn't have nearly as strong of a pedal as I feel it should with the truck running. Kinda wanting to blame the 50 dollar napa pump. Anyone have any ideas?? I will say I havnt pulled the rear brakes apart yet to inspect but don't think that's the problem.

Redrider2911 · 09-24-2017, 01:35 AM

I was in this same situation when I trailered the truck to Seattle to race after changing the front brakes the week before. Felt like there was air in the line. Bled them 3 more times. Put a whole bottle of new fluid through it. No dice. Did some reading, grabbed a flat head screw driver and manually ratcheted over the rear adjusters through the little access hole. Went until I barely felt friction when rotating the tire with the rear end on the jack. Then backed off one click. Felt amazing ever since!

jasonc · 09-24-2017, 07:03 AM

I had a similar problem with mine, what fixed it was taking off the antilock valve or whatever it's called and found a coupler to just hook the lines direct. But I think I remember you saying you already did that. I also run a vacume booster, will hold 40psi no problem.

Red Sleeper · 09-24-2017, 10:33 AM

Before you throw another pump at it, why not pull the rear drums off and do an inspection?

97rada · 09-24-2017, 02:34 PM

Quote:

Originally Posted by Red Sleeper

Before you throw another pump at it, why not pull the rear drums off and do an inspection?

I plan to pull them apart this weekend and see what condition it's in. Just don't want to leave that as my only possibility when it needs to be loaded in the trailer ready to race after next weekend. I suppose that could very easily be the issue though.

zstroken · 09-24-2017, 03:34 PM

Also while you have them torn apart, I think you can buy a wheel cylinder from a chevrolet, believe those are the largest diameter available.

kxhonda · 09-24-2017, 05:20 PM

Quote:

Originally Posted by zstroken

Also while you have them torn apart, I think you can buy a wheel cylinder from a chevrolet, believe those are the largest diameter available.

Was just getting ready to say this. I have one ton chevy wheel cylinders in my dually and the difference is amazing. Definitely the way to go if you're not swapping to disc brake rear yet.

97rada · 09-24-2017, 05:45 PM

Quote:

Originally Posted by zstroken

Also while you have them torn apart, I think you can buy a wheel cylinder from a chevrolet, believe those are the largest diameter available.

Fits in a Dana 70?

97rada · 09-24-2017, 05:45 PM

Quote:

Originally Posted by kxhonda

Was just getting ready to say this. I have one ton chevy wheel cylinders in my dually and the difference is amazing. Definitely the way to go if you're not swapping to disc brake rear yet.

This is just to get me through the last 2 races it's getting discs this winter when I have more time.

f6jbob · 09-24-2017, 07:07 PM

3500 front calipers will swap right in place of the 2500 calipers (front). They have a larger diameter piston than the stock 2500 calipers. Every little bit helps. This should also apply if using stock parts on rear disc conversion. Little bit of research should tell if compatible.

97rada · 09-24-2017, 07:51 PM

Quote:

Originally Posted by f6jbob

3500 front calipers will swap right in place of the 2500 calipers (front). They have a larger diameter piston than the stock 2500 calipers. Every little bit helps. This should also apply if using stock parts on rear disc conversion. Little bit of research should tell if compatible.

Good info, I didn't know that one. My rear kit is going to be very generic and use mostly front end parts if I can. We shall see when the time comes.

Redrider2911 · 09-25-2017, 12:33 AM

Takes less than 5 minutes to adjust those drums through the access hole... I didn't care to take mine apart and inspect the pads as I will also be going disc soon.

jasonc · 09-25-2017, 05:49 AM

If you replace the rear wheel cylinders, tell them you want a set for a 1994 Chevy 3500 dually, that model is the larger diameter bore wheel cyl and a direct replacement.

jlbayes · 09-25-2017, 07:41 AM

Quote:

Originally Posted by f6jbob

3500 front calipers will swap right in place of the 2500 calipers (front). They have a larger diameter piston than the stock 2500 calipers. Every little bit helps. This should also apply if using stock parts on rear disc conversion. Little bit of research should tell if compatible.

If it has the 8800lb Dana 60 (which it does unless swapped) it will already have the larger bore calipers.

joefarmer · 09-25-2017, 10:50 AM

They could be glazed over as well. Ask Lyn about resurfacing the front pads/rotors.

*Big Blue24* · 09-25-2017, 11:15 AM

Rear wheel cylinder part number is 37337, these make a HUGE difference and will definitely let you hold more boost on the launch. They are cheap as well, like $8 to $12 per cylinder depending on brand name or supplier. I can hold 20 psi launch on the rear tires with a good firm stab on the brake pedal. Before it would start to push through the rear brakes on my 2wd around 7 psi boost. On a 4x4 truck with contribution from the front brakes, I'll bet 45 psi launch would be doable.

And to answer your question, these will fit both a Dana70 Dodge Rearend and Dana80 Dodge Rearend with no modification or changes period.

CorneliusRox · 09-25-2017, 12:29 PM

Definitely adjust the rear, but also make sure you've removed, or zip tied the height based proportional valve on the HR frame rail by the rear axle.

97rada · 09-25-2017, 03:17 PM

Thanks guys. I have a decent direction to go with now. For the record from the Master to the drops is all line I bent and flared. No oem components are left

*Chris Tobin* · 09-25-2017, 04:31 PM

Maybe it is just the mismatch between the size and weight of your left foot compared to your right foot!!! hahahaha

malibu795 · 09-25-2017, 06:07 PM

What fluids are you using?
PS
ATF
Or HYD

09-23-2017, 08:20 PM	#1
97rada Name: 97rada Title: Too Much Time Status: Not Here Join Date: Feb 2008 Member`s Gallery Posts: 5,410	Brake problem not holding My race truck is not holding on the brakes. It's a 94 with a hydroboost conversion, new napa power steering pump and I have swapped a known good booster in and still can't hold 25 psi well. When you pump up the brakes with the truck off it has great pedal. Start it and pedal doesn't kick back like it should. It also doesn't have nearly as strong of a pedal as I feel it should with the truck running. Kinda wanting to blame the 50 dollar napa pump. Anyone have any ideas?? I will say I havnt pulled the rear brakes apart yet to inspect but don't think that's the problem. __________________ Austin tow truck- 14-3500 with tuning toy truck -94 rclb auto- 5.2x with a lot left. Shooting for 4s Any intelligent fool can make things bigger and more complex...it takes a touch of genius- and alot of courage to move in the opposite direction.

09-24-2017, 01:35 AM	#2
Redrider2911 Name: Redrider2911 Title: Too Much Time Status: Not Here Join Date: Nov 2015 Location: Yakima, WA Member`s Gallery Posts: 780	I was in this same situation when I trailered the truck to Seattle to race after changing the front brakes the week before. Felt like there was air in the line. Bled them 3 more times. Put a whole bottle of new fluid through it. No dice. Did some reading, grabbed a flat head screw driver and manually ratcheted over the rear adjusters through the little access hole. Went until I barely felt friction when rotating the tire with the rear end on the jack. Then backed off one click. Felt amazing ever since! __________________ 49 Willys Pickup. 5600lb. 11.8sec @115mph 1/4. 12 valve. MegaSquirted 47RH. 3.54 posi rear. 35" tires. 64mm HE351ve, S475 (75/96/1.32), A/W Intercooler. AFC mods. 5x16s. 191 DVs, 180 pump. 23*. 85psi. Build Thread

09-24-2017, 10:33 AM	#4
Red Sleeper Name: Red Sleeper Title: Too Much Time Status: Not Here Join Date: Aug 2009 Location: Lone Star State Member`s Gallery Posts: 4,597	Before you throw another pump at it, why not pull the rear drums off and do an inspection? __________________ Nick J '14 Silverado LTZ 5.3 4wd '05 Cummins QCSB 4wd 48re '91 Cummins w350 5spd

09-24-2017, 03:34 PM	#6
zstroken Name: zstroken Title: For $$$ your name here Status: Not Here Join Date: Sep 2006 Location: Western Michigan(by the lake) Member`s Gallery Posts: 23,151	Also while you have them torn apart, I think you can buy a wheel cylinder from a chevrolet, believe those are the largest diameter available. __________________ 2008 4x4 Megacab, 68RFE 97 Dodge gone.... 24V P-Pump Mafia member #1(retired) Thanks to Mumau Diesel, Goerend Transmission, Northeast Diesel Service!

09-24-2017, 07:07 PM	#10
f6jbob Name: f6jbob Title: Too Much Time Status: Not Here Join Date: Apr 2006 Location: western Wi. Member`s Gallery Posts: 1,153	3500 front calipers will swap right in place of the 2500 calipers (front). They have a larger diameter piston than the stock 2500 calipers. Every little bit helps. This should also apply if using stock parts on rear disc conversion. Little bit of research should tell if compatible. __________________ 2006 RCSB Dodge Goerend tranny and converter, Stainless Diesel twins and exhaust manifold, B&B intake manifold, T&C Diesel CP3, rail and dual prv, Hellman intercooler, Porting by Joker Fabrication, Isspro Performax gauges, AirDog fuel pump. Supported by Pure Diesel Power, Garmons Diesel Performance, Blacks Diesel Performance and above vendors.

09-24-2017, 07:03 AM	#3
jasonc Name: jasonc Title: Too Much Time Status: Not Here Join Date: Nov 2009 Member`s Gallery Posts: 4,412	I had a similar problem with mine, what fixed it was taking off the antilock valve or whatever it's called and found a coupler to just hook the lines direct. But I think I remember you saying you already did that. I also run a vacume booster, will hold 40psi no problem.

09-25-2017, 12:33 AM	#12
Redrider2911 Name: Redrider2911 Title: Too Much Time Status: Not Here Join Date: Nov 2015 Location: Yakima, WA Member`s Gallery Posts: 780	Takes less than 5 minutes to adjust those drums through the access hole... I didn't care to take mine apart and inspect the pads as I will also be going disc soon. __________________ 49 Willys Pickup. 5600lb. 11.8sec @115mph 1/4. 12 valve. MegaSquirted 47RH. 3.54 posi rear. 35" tires. 64mm HE351ve, S475 (75/96/1.32), A/W Intercooler. AFC mods. 5x16s. 191 DVs, 180 pump. 23*. 85psi. Build Thread

09-25-2017, 05:49 AM	#13
jasonc Name: jasonc Title: Too Much Time Status: Not Here Join Date: Nov 2009 Member`s Gallery Posts: 4,412	If you replace the rear wheel cylinders, tell them you want a set for a 1994 Chevy 3500 dually, that model is the larger diameter bore wheel cyl and a direct replacement.

09-25-2017, 10:50 AM	#15
joefarmer Name: joefarmer Title: MR. Supreme Overlord Status: Not Here Join Date: Jul 2006 Location: ohio Member`s Gallery Posts: 6,137	They could be glazed over as well. Ask Lyn about resurfacing the front pads/rotors. __________________ brandon'); DROP TABLE Users;-- 1948 Dodge 1.5t 12v RH swap \| 99 F250 12v RE test rkt \| 11 X5 'no soup' \| 08 F250 CR RE swap \| 05 2500 CR 68 standalone firepunk.com

09-25-2017, 11:15 AM	#16
Big Blue24 Name: Big Blue24 Title: Comp Diesel Sponsor Status: Not Here Join Date: Jan 2008 Location: Cedar City, UT Member`s Gallery Posts: 6,310	Rear wheel cylinder part number is 37337, these make a HUGE difference and will definitely let you hold more boost on the launch. They are cheap as well, like $8 to $12 per cylinder depending on brand name or supplier. I can hold 20 psi launch on the rear tires with a good firm stab on the brake pedal. Before it would start to push through the rear brakes on my 2wd around 7 psi boost. On a 4x4 truck with contribution from the front brakes, I'll bet 45 psi launch would be doable. And to answer your question, these will fit both a Dana70 Dodge Rearend and Dana80 Dodge Rearend with no modification or changes period. __________________ 95' 2wd Junker Drag Truck 1502 HP Fuel-Only 12mm P7100 Pump SXE 472 over GTX55 116mm OEM 12v Block Last edited by Big Blue24; 09-25-2017 at 11:16 AM.

09-25-2017, 12:29 PM	#17
CorneliusRox Name: CorneliusRox Title: Seasoned Rookie Status: Not Here Join Date: Dec 2012 Location: Detroit, MI Member`s Gallery Posts: 4,154	Definitely adjust the rear, but also make sure you've removed, or zip tied the height based proportional valve on the HR frame rail by the rear axle. __________________ Corey - BSME '21 Tesla Model 3 Perf '22 DMax AT4 2500

09-25-2017, 03:17 PM	#18
97rada Name: 97rada Title: Too Much Time Status: Not Here Join Date: Feb 2008 Member`s Gallery Posts: 5,410	Thanks guys. I have a decent direction to go with now. For the record from the Master to the drops is all line I bent and flared. No oem components are left __________________ Austin tow truck- 14-3500 with tuning toy truck -94 rclb auto- 5.2x with a lot left. Shooting for 4s Any intelligent fool can make things bigger and more complex...it takes a touch of genius- and alot of courage to move in the opposite direction.

09-25-2017, 04:31 PM	#19
Chris Tobin Name: Chris Tobin Title: Too Much Time Status: Not Here Join Date: Jun 2008 Location: Dayton, TN Member`s Gallery Posts: 2,662	Maybe it is just the mismatch between the size and weight of your left foot compared to your right foot!!! hahahaha __________________ Chris Tobin Editor--Ultimate Diesel Builder's Guide Freelance Editor and Photographer Working with DIESEL WORLD, DIRT SPORTS, MUSCLE CAR POWER & STREET TRUCKS magazines tobinemail@aol.com I might be able to help get you in a mag. Custom poster size photos available. PM or email for info.